operation, maintenance, & management

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ManagementManagementManagementManagementManagementSystemsSystemsSystemsSystemsSystems

Operation, Maintenance,and Management

of Stormwater Management Systems

Produced by the:

Watershed Management Institute, Inc."Creating Practical Solutions for Complex Resource Challenges"

in cooperation with

Office of WaterU. S. Environmental Protection Agency

Washington D.C.

August 1997

This handbook was produced by the Watershed Management Institute in cooperationwith the United States Environmental Protection Agency, Office of Water, through

Cooperative Agreement CX823621-01-0. The contents do not necessarily reflect theviews or policies of the Environmental Protection Agency, nor does mention of tradenames or commercial products constitute endorsement or recommendation for use.

Produced by the Watershed Management Institute, Inc.

Principal Authors: Eric H. LivingstonEarl ShaverJoseph J. Skupien, P. E.

Contributing Author: Richard R. Horner, Ph. D.

Watershed Management InstituteP.O. Box 14

Ingleside, Maryland 21644Phone: 410/758-2731

Fax: 410/758-0386

Watershed Management Institute410 White Oak Drive

Crawfordville, Florida 32327Phone: 850/926-5310

Fax: 850/926-1534

Printed on recycled paper

ACKNOWLEDGMENTS

The preparation of this document was made possible through a Cooperative Agreement withthe U. S. Environmental Protection Agency (Assistance ID No. CX823621-01-0).

We would like to thank several individuals whose support and participation were essential to thecompletion of this handbook on the operation, maintenance, and management of stormwatermanagement systems. In particular, we want to extend our appreciation to Mr. Rod Frederick ofthe U. S. EPA for his support of this project, and especially to Mr. Robert Goo, our EPA ProjectOfficer, for his support and guidance in the preparation of this document. We also want to thankthe reviewers of the draft handbook who provided valuable comments which greatly improvedthe final document. Reviewers included:

Robert Goo, U.S. EPA, Washington D. C.Rod Frederick, U.S. EPA, Washington D. C.Dov Weitman, U.S. EPA, Washington D. C.Bill Swietlik, U.S. EPA, Washington D. C.Tom Davenport, U. S. EPA, Region 5, ChicagoRick Watson, Bellevue (WA) Utilities DepartmentBill Chamberlin, Orlando (FL) Stormwater UtilityDan DeWiest, Florida Department of Environmental Protection

We also want to thank the people who took time out from their busy schedule to respond to ourtelephone and mail requests, especially for information on the cost of operating, maintaining,and managing stormwater management systems. These individuals include Doug Harrison(Fresno Flood Control District), Paul Hoffman (Austin Public Works and Transportation Depart-ment), Scott Tucker and Mark Hunter (Urban Drainage and Flood Control District), Rick Watson(Bellevue Utilities Department), and Bill Chamberlin (Orlando Stormwater Utility).

We also want to acknowledge and thank the following:

The Delaware Department of Natural Resources and Environmental Control for allowingthe use of stormwater management system slides taken in Delaware.

The Florida Department of Environmental Protection for many of the slides taken in Florida.

Slides taken in Maryland were part of a personal collection, but were taken by a numberof individuals employed by the Maryland Department of the Environment.

Other slides were taken by the authors in numerous locations around the country andinternationally.

Finally, we want to acknowledge the 1989 Stormwater Management Facilities MaintenanceManual published by the New Jersey Department of Environmental Protection as one of theearliest efforts to address stormwater management facility maintenance in a coordinated andcomprehensive fashion. Many of the Manual's topics, definitions, recommendations, and evenmuch of its format, have been adapted for use in this handbook.

Operation, Maintenance, and Management of Stormwater Systems

Contents

CHAPTER 1: INTRODUCTION1. Why Is Stormwater System Operation, 1-1

Maintenance and Management Important2. Chapter Contents 1-23. Handbook BMP Terminology 1-4

3.1 Detention Practices 1-43.2 Infiltration (retention) Practices 1-53.3 Filtration Practices 1-53.4 Biofiltration Practices 1-6

CHAPTER 2: STORMWATER MANAGEMENT PRACTICES1. Overview 2-1

1.1 Intended Readers 2-12. Stormwater Management Program Considerations 2-1

2.1 Stormwater Program Components 2-12.2 Stormwater Program Evolution (Retrofitting) 2-22.3 Stormwater BMPs and New Development 2-6

3. Stormwater Pollutants and Reduction Mechanisms 2-104. Stormwater Management Practices (BMPs) 2-13

4.1 BMP Selection 2-154.2 BMP Fact Sheets 2-16

Infiltration Practices 2-17Infiltration Basins 2-23Infiltration Trenches 2-26Exfiltration Trenches 2-30Pervious Pavement 2-32Modular Pavement 2-38Detention Practices 2-41Dry Detention Basins 2-42Extended Dry Detention Basins 2-45Wet Detention Ponds 2-48Biofiltration Practices 2-54Constructed Wetlands 2-59Stormwater Filters 2-65

CHAPTER 3: PLANNING AND DESIGN CONSIDERATIONS1. Overview 3-1

1.1 Objectives 3-11.2 Intended Readers 3-2

2. Stormwater Management Practices and Components 3-22.1 Detention 3-22.2 Infiltration 3-3

i


ii

Contents2.3 Filtration 3-32.4 Biofiltration 3-3

3. The Responsibilities of the Facility Designer 3-34. BMP Design Considerations: Points to Ponder 3-7

4.1 Interested Parties 3-84.2 Operating Conditions 3-104.3 Design Methodologies 3-124.4 Facility Type 3-12

5. BMP Design Considerations: A Checklist 3-135.1 Safety 3-135.2 Performance 3-145.3 Constructability 3-145.4 Maintenance 3-155.5 Cost 3-165.6 Community Acceptance 3-16

6. Specific Maintenance Considerations 3-176.1 Maintainability 3-176.2 Accessibility 3-176.3 Durability 3-18

7. Suggested Design Review Techniques 3-187.1 Spend a Mental Year at the Facility 3-187.2 Who, What, When, Where, and How 3-19

8. Design Guidelines 3-209. Summary 3-2010. Design Guidelines for Detention Practices 3-21

10.1 Introduction 3-2110.2 Bottoms 3-2110.3 Dams, Embankments, and Side Slopes 3-2410.4 Principal Outlets 3-2510.5 Outflow System 3-2710.6 Inlets 3-2710.7 Emergency Outlets 3-2810.8 Low Flow Measures 3-2910.9 Vegetative Cover 3-3010.10Trash Racks 3-3110.11Access 3-3210.12Perimeters 3-34

11. Design Guidelines for Infiltration Practices 3-3511.1 Introduction 3-3511.2 Bottoms 3-3511.3 Dams, Embankments, and Side Slopes 3-3811.4 Inlets 3-3811.5 Emergency Outlets 3-39


Contents

11.6 Vegetative Cover 3-4011.7 Access 3-4111.8 Perimeters 3-42

12. Design Guidelines for Filtration and Biofiltration Practices 3-4312.1 Introduction 3-4312.2 Bottoms 3-4312.3 Dams, Embankments, and Side Slopes 3-4512.4 Principal Outlets 3-4612.5 Outflow Systems 3-4712.6 Inlets 3-4812.7 Emergency Outlets 3-4912.8 Vegetative Cover 3-4912.9 Trash Racks 3-5012.10Access 3-5112.11Perimeters 3-53

Appendix 3-1 Drawings of Typical Details of Some Important 3-54Stormwater System ComponentsFigure 3A Detention Basin Orifice and Weir Plates 3-55Figure 3B Detention Basin Trash Rack 3-56Figure 3C Infiltration System Underdrain 3-57Figure 3D Nonvegetated Infiltration Basin Bottom 3-58

CHAPTER 4: PROGRAMMATIC AND REGULATORY ASPECTS1. Overview 4-1

1.1 Intended Readers 4-22. Roles of Government 4-23. Federal Stormwater Programs 4-34. State Stormwater Management Programs 4-3

4.1 Program Guidance and Requirements 4-44.2 Stormwater Legislation 4-54.3 Stormwater Regulations 4-94.4 Example Language for State/Local Stormwater Rules 4-11

5. Local Stormwater Management Programs 4-116. Recommendations on Public vs. Private Maintenance 4-137. Examples of Maintenance Agreements 4-14

Appendix 4-1 Example Language That Should Be Contained 4-16in State, Regional, or Local Stormwater Rules

Appendix 4-2 Olympia, Wa. Residential Agreement to Maintain 4-31a Stormwater Management Facility

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Contents

Appendix 4-3 Olympia, Wa. Commercial/Industrial Agreement 4-35to Maintain a Stormwater Management Facility

Appendix 4-4 Alexandria, Va. Standard BMP Maintenance and 4-39Monitoring Agreement

Appendix 4-5 Recommended Maintenance of Stormwater 4-44Management Systems Included In FloridaNPDES Municipal Stormwater Permits

CHAPTER 5: MAINTENANCE CONSIDERATIONS FOR FACILITY OWNERS1. Overview 5-1

1.1 Objectives 5-11.2 Intended Readers 5-2

2. The Meaning of Stormwater Facility Ownership 5-22.1 Basic Stormwater Management Facility Operation 5-32.2 Stormwater Management Practices 5-42.3 Stormwater Facility Components 5-52.4 Operational Impacts of Facility Maintenance 5-52.5 Impacts of Facility Maintenance Neglect 5-7

3. Types of Facility Owners 5-94. Maintenance Program Development 5-10

4.1 Designate a Responsible Individual 5-104.2 Plan for Maintenance 5-114.3 Identify Costs and Allocate Resources 5-134.4 Create a Written Plan 5-144.5 Conduct Periodic Program Reviews 5-15

CHAPTER 6: CONSTRUCTION INSPECTION1. Overview 6-1

1.1 Intended Readers 6-22. Stormwater System Construction Impacts & Mitigation 6-3

2.1 Economic Impacts of Sedimentation 6-32.2 Environmental Impacts of Pollutant Discharge 6-4

3. Legal Authority for Inspection 6-54. Preconstruction Activities 6-6

4.1 Review of Approved Stormwater Plan 6-64.2 Preconstruction Site Meeting 6-7

5. Inspection Responsibilities During Construction 6-75.1 Routine Inspection Responsibilities 6-75.2 Progress Meetings 6-85.3 Final Inspections 6-9

6. Inspection Procedures 6-96.1 Have Necessary Inspection Equipment 6-10

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Contents

6.2 Check In at the Construction Trailer 6-106.3 Always Complete an Inspection Form 6-106.4 Walk the Site in a Consistent Manner 6-106.5 Wear Safety Equipment 6-11

7. Inspector Attitudes and Training 6-118. Individual BMP Inspection Considerations 6-13

8.1 Detention/Retention Systems 6-138.2 Constructed Wetlands 6-168.3 Infiltration Practices 6-208.4 Filtration Systems 6-318.5 Biofiltration Systems 6-34

9. Once Construction is Complete 6-3710. Recommendations for Inspector Training and 6-38

Certification Programs

Appendices - Construction Inspection Forms 6-396-1 Preconstruction Inspection Meeting Topics 6-406-2 General Site Inspection and Notice to Comply 6-436-3 Sediment/Stormwater Basin Construction Checklist 6-466-4 Sediment/Stormwater Pond Typical Sequence of 6-51

Construction6-5 Construction Checklist for Infiltration Practices: 6-556-5A Basins 6-566-5B Trenches 6-576-5C Dry Wells 6-586-5D Pervious Paving 6-596-5E Swales 6-606-6 Construction Checklist for Filtration Practices 6-616-7 Construction Checklist for Biofiltration Practices 6-63

CHAPTER 7: INSPECTION AND MAINTENANCE AFTER CONSTRUCTION1. Overview 7-1

1.1 Intended Readers 7-22. How Maintenance Can Reduce Downstream Impacts 7-2

2.1 Increased Discharge of Pollutants Downstream 7-22.2 Increased Risk of Downstream Flooding 7-32.3 Increased Downstream Channel Instability 7-32.4 Potential Loss of Life and Property 7-42.5 Aesthetic or Nuisance Problems 7-4

3. Importance of Checklists 7-53.1 Checklist for Inspectors 7-53.2 Checklist to Evaluate Stormwater System Function 7-5

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4. Highlighted Expected Operation, Maintenance, and 7-6Management Needs as a Function of Components

4.1 Detention/Retention Ponds 7-64.2 Infiltration Facilities 7-9

4.3 Filtration Facilities 7-104.4 Biofiltration Facilities 7-11

5. Inspection Frequency 7-126. Aesthetic and Functional Maintenance 7-13

6.1 Aesthetic Maintenance 7-136.2 Functional Maintenance 7-14

7. Training Needs 7-187.1 Mandatory vs. Voluntary Training 7-197.2 Components of an Inspector Training Program 7-197.3 Components of an Operator Training Program 7-20

8. Equipment and Resources Needed 7-219. Typical OMM Tools 7-2110. Importance of Tracking OMM 7-2311. Prioritizing Maintenance Tasks 7-2312. Safety Issues 7-24

12.1 Safety During Maintenance Inspections 7-2412.1 Safety During Actual Maintenance 7-26

13. Specific Maintenance Activity for Each Type of Facility 7-2613.1 Detention/Retention Ponds 7-2713.2 Infiltration Practices 7-3113.3 Filtration Practices 7-3513.4 Biofiltration Systems 7-39

14. General Discussion 7-41

Appendices - Operation, Maintenance, and Management Checklists7-1 OMM Inspection Checklist for Ponds 7-437-2A OMM Inspection Checklist for Infiltration Basins 7-487-2B OMM Inspection Checklist for Infiltration Trenches 7-507-2C OMM Inspection Checklist for Dry Wells 7-527-2D OMM Inspection Checklist for Pervious Pavement 7-537-2E OMM Inspection Checklist for Swales 7-547-3 OMM Inspection Checklist for Filtration Facilities 7-557-4 OMM Inspection Checklist for Biofiltration Practices 7-58

CHAPTER 8: COSTS AND FINANCING OF STORMWATER FACILITY OPERATION AND MAINTENANCE

1. Overview 8-11.1 Intended Readers 8-1


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Contents

2. Stormwater System Maintenance Costs 8-13. OMM Costs from Specific Stormwater Programs 8-2

3.1 Orlando, Florida 8-63.2 Fresno, California 8-63.3 Somerset County, New Jersey 8-63.4 Austin, Texas 8-93.5 Denver, Colorado 8-93.6 Bellevue, Washington 8-163.7 Kitsap County, Washington 8-18

4. Financing Stormwater System OMM 8-194.1 Public Financing of Stormwater OMM 8-20

CHAPTER 9: DISPOSAL OF STORMWATER SEDIMENTS1. Overview 9-1

1.1 Intended Readers 9-12. Potentially Applicable Laws and Regulations 9-1

2.1 Federal Laws and Regulations 9-22.2 State Laws and Regulations 9-3

3. Characteristics of Stormwater Sediments and Wastes 9-63.1 Contaminant Levels in Ultra-Urban BMP Sediments 9-13

4. Recommendations on Sediment Testing 9-144.1 Storm Facility Solids and Liquid Wastes 9-144.2 Sand Filter Medium and Accumulated Sediments 9-15

5. Recommendations on Disposal of Stormwater Sediments 9-155.1 Waste Collection Considerations 9-155.2 Disposal Methods 9-155.3 Decant Water Disposal 9-165.4 Sand Filter Waste Disposal Methods 9-17

CHAPTER 10. INFORMATION SOURCES 10-1

1. WHY IS STORMWATER SYSTEMOPERATION, MAINTENANCE, ANDMANAGEMENT IMPORTANT?

Over the last two decades, stormwater man-agement systems have evolved considerablyfrom their traditional roles as conveyance de-vices that are only intended to transport storm-water runoff safely and efficiently from one lo-cation to another. Such conveyance systemshave included bridges, culverts, ditches, andthe ubiquitous piped storm drain (sewer).However, in response to growing concernsover nonpoint source (NPS) pollution, flood-ing, and erosion, a new type of stormwatersystem has been created. This type not onlyconveys runoff, but also manages it by delib-erately modifying its flow rate, volume, and/orwater quality. These stormwater managementsystems rely upon practices such as infiltra-tion or retention areas, extended dry or wetdetention, sand filters, vegetated swales, andconstructed wetlands.

Whether designed for conveyance or man-agement, all stormwater systems requireproper design, construction, and mainte-nance to perform successfully. However,due to their more demanding duties and ob-jectives, today's multipurpose stormwaterpractices have proven themselves to be in-herently more complex than their more tradi-tional conveyance counterparts. Accordingly,they require a much greater level of effort bythose who design, construct, maintain, andoperate them.

This is particularly true for stormwater man-agement system maintenance and manage-ment. Maintenance has always been recog-nized as vital to the proper and prolonged per-

formance of all stormwater systems. How-ever, thorough and consistent maintenanceis particularly crucial to the successful per-formance of stormwater treatment prac-tices, an importance that carries over to theentire stormwater management program theysupport. Reasons for this increased impor-tance include:

As noted above, stormwater managementsystems are inherently more complex thantraditional runoff conveyances. Not only intheir function or operation, but also in thenumber and types of materials used to con-struct them. This may even include naturalmaterials such as aquatic vegetation andmicroorganisms. This increased complex-ity and variety demands a greater level ofmaintenance and management to assuresafe and effective operation.

Unlike drainage systems, many stormwaterpractices achieve their management goalsthrough impoundment or storage of runoffinstead of conveyance. This is accom-plished through the use of dams, berms,tanks, or chambers. To successfully im-pound water, either temporarily (for ex-ample, in a dry detention or infiltration ba-sin) or permanently (in a wet detention pondor constructed wetland), requires a greaterdegree of structural strength. Safely im-pounding stormwater requires more safe-guards to avoid the possibly catastrophicdownstream damage caused by structuralfailure and sudden release of the im-pounded water. These increased levels ofstrength and safety, which must be providedcontinually throughout the life of thestormwater management facility, demanda similarly higher level of maintenance.

1-1

Chapter 1Introduction


1-2

Stormwater conveyances and flood controlsystems typically are designed to transportor impound the runoff from a relatively rarestorm event, with a recurrence interval of25 to 100-years. As such, they may expe-rience maximum design conditions only afew times during their lifetime. However,stormwater management systems, par-ticularly those intended to treat runoff andreduce pollutants, typically are designed tocapture smaller, more frequent rainfall/run-off events (e.g., half inch storm; 2-yr, 1-hrstorm). Therefore, they may experiencemaximum design conditions severaltimes each year. This more frequent andrepetitive operation at their design limit cre-ates more stress, which again demandsgreater attention and commitment to propermaintenance and management.

Failure to perform adequate mainte-nance of stormwater management sys-tems not only leads to reductions in ex-pected or desired performance levels, butmay even create conditions that areworse than if the facility had not beenconstructed at all. For example, a ne-glected dam may fail and release im-pounded water onto downstream proper-ties, an eroding swale may be the sourceof excessive sediment, or a poorly managedconstructed wetland may create harmfullevels of nutrients or temperature.

Stormwater management has become an im-portant part of our efforts to achieve cleanwater and a safe environment. However, asseen above, neglect of stormwater manage-ment systems not only poses a threat to thoseliving downstream, but it can also underminethe entire stormwater management programthat led to their creation. The importance ofregular inspection and thorough stormwatersystem maintenance can not be understated.In fact, stormwater systems should noteven be constructed if the stormwaterprogram is not willing to make the neces-

sary commitments to assure that the sys-tems are properly maintained, managed,and operated.

The objective of this handbook is to help as-sure that necessary maintenance and man-agement of stormwater systems is performed.The handbook is aimed at a diverse audience- all of those individuals and groups which havebeen shown by both experience and researchto play an important role in a successful storm-water management system maintenanceprogram. This includes persons involved indeveloping and implementing stormwatermanagement programs, stormwater systemdesigners and builders, land developers andtheir consultants, stormwater system plan re-viewers and inspectors, stormwater systemowners and operators, public officials, and allcitizens.

2. CHAPTER CONTENTS

The handbook is divided into eight additionalchapters, each addressing an important as-pect of stormwater system operation andmaintenance:

Chapter 2 - Stormwater Management Prac-tices presents an overview of several dif-ferent types of commonly used stormwatermanagement practices. These include infil-tration or retention systems, wet and dry de-tention systems, constructed wetlands, veg-etated swales, and filtration systems such assand filters and biofiltration systems. For eachtype of practice, information is presented onits basic runoff quantity and quality controlmechanisms, pollutant removal potentials, siteand operating limitations, and operation andmaintenance obligations. This presentationof basic information is intended to improvethe understanding of the needs and limi-tations of each practice by those who de-sign, regulate, construct, own, operate, ormaintain them. All of these individuals play

CHAPTER 1 Introduction

1-3

a vital role in assuring proper maintenance andoperation of the practice.

Chapter 3 - Planning and Design Consid-erations is addressed directly tostormwater management system plannersand designers. Information is presentedwhich demonstrates how proper planningand design can help to both minimize andfacilitate system maintenance. The main-tenance problems that can result from inad-equate or inattentive planning or design arealso highlighted. Additionally, planning anddesign guidelines to help achieve minimummaintenance goals are presented for eachtype of stormwater management practice de-scribed in Chapter 2. This informationstresses the importance of simplicity, ac-cessibility, and durability in designingstormwater management systems.

Chapter 4 - Programmatic and RegulatoryAspects highlights the key role thatprogram implementers play in achievingproper levels of stormwater managementsystem maintenance and how their igno-rance or indifference can lead to mainte-nance neglect and facility failure. Properplanning, design, and construction all contrib-ute to a successful maintenance program.However, the key to success is ensuring thateach of these activities gets done, a role forwhich program implementation staff areuniquely suited. To achieve this goal, imple-mentation staff must become as involvedin the maintenance of stormwater manage-ment systems as they are with the plan-ning, design, and construction. Mainte-nance of stormwater systems can not simplybe left for others to resolve. Guidance forestablishing the proper institutional frame-work and standards is provided, includingessential program aspects such as manda-tory operation and maintenance plans, desig-nating responsible entities, operating permits,enforcement options, and maintenance de-fault contingency plans.

Chapter 5 - Owner, Operator, and User Con-siderations provides each of these indi-viduals and groups with important infor-mation regarding how their system works,why it is needed, and what maintenance itwill require. It also explains in clear termswhy it is in their best interest to provide thor-ough and consistent levels of system mainte-nance and how maintenance neglect on theirpart can lead to serious environmental, safety,and legal problems. The Chapter also pro-vides suggestions for establishing a success-ful maintenance program and will discuss theenvironmental, financial, aesthetic, and civicrewards for doing so.

Chapter 6 - Construction Inspection high-lights a vital but often overlooked aspectof successful stormwater managementsystem maintenance. It is the inspectors whomust complete the job started by the adminis-trators, planners, and designers, and whomust provide the owners, operators, andmaintainers with a sound, durable facility thatis worthy of their maintenance investment.The Chapter assists construction inspec-tors by providing detailed checklists ofimportant inspection items during eachstage of construction. It also emphasizesthe importance of system construction sched-uling, phasing, and coordination with other siteactivities and promotes close coordination andcommunication between inspectors, contrac-tors, owners, designers, and reviewers. Fi-nally, recommendations for establishing train-ing and certification programs for inspectorsare also provided, including a model programcurriculum.

Chapter 7 - Post-Construction Inspectionand Maintenance presents pertinent infor-mation to the final members of the overallmaintenance team - those responsible forinspecting, scheduling, and performing theactual maintenance and management ofstormwater management systems. ThisChapter seeks to address a deficiency in many


1-4

state and local stormwater management pro-grams. It provides detailed information to bothinspectors and owner/operators and empha-sizes the importance of both groups to the suc-cess of the overall stormwater managementprogram. Inspectors are provided withchecklists detailing a comprehensive sys-tem inspection program, including recom-mended inspection frequencies and a break-down of inspection practices by system com-ponent. Owner/operators are presentedwith descriptions of typical maintenancetasks, including recommended equipment,techniques, materials, and frequencies.Finally, information on developing a trainingand certification program for those who per-form system maintenance is also presented.

Chapter 8 - Maintenance Costs and Financ-ing discusses an aspect of stormwater man-agement system maintenance that is of inter-est to everyone from administrators to own-ers, and which is vital to the success of anystormwater management program. Summa-ries of expected or typical costs for vari-ous maintenance tasks, both regular andepisodic, are presented. Estimated costsof materials and equipment also are provided.In addition, various means of financing thesecosts are discussed, with examples of vari-ous institutional programs highlighted.

Chapter 9 - Disposal of Sediments presentsinformation on a new issue of concern thatemphasizes both the complex nature of storm-water management systems and the need fora comprehensive maintenance program.Sedimentation is one of the primary mecha-nisms for pollutant removal in manystormwater management systems. As a re-sult, the sediment collected in the facility maycontain heavy metals, hydrocarbons, greases,nutrients, and other pollutants depending uponthe character and use of the land draining tothe system. Depending upon their concen-trations and quantities, these pollutantsmay pose disposal problems for facility

owners, operators, and maintainers. Gen-eral recommendations for analyzing and prop-erly disposing of these sediments are pre-sented along with a discussion of potentialregulatory constraints.

As can be seen from the above review, storm-water management system maintenance is abroad and complex topic. It is hoped that thishandbook attracts an equally broad and di-verse group of readers. To assist readersfind the information they seek quickly, eachchapter in the handbook begins with a briefsummary of its contents, including thegoals of the Chapter and a list of its in-tended readers. This should allow the readerto quickly assess the contents of each Chap-ter and determine its applicability to his or herinterests or needs. To further guide the reader,major topics within each chapter are presentedunder their own descriptive headings.

3. HANDBOOK BMP TERMINOLOGY

The field of stormwater management hasgrown considerably in the past two decades.This growth has produced, among many ac-complishments, a long and sometimes con-flicting list of names for various stormwatermanagement practices. Unfortunately, thesenames can vary by state or region. This canconfuse or mislead the experienced practitio-ner, not to mention the new reader. There-fore, in order to minimize such confusion andmaximize the handbook’s effectiveness, thefollowing general definitions have beenadopted for use in the handbook:

3.1. Detention Practice:A stormwater management practice whichtemporarily impounds runoff and dischargesit through an outlet structure. Any additionaloutflow through infiltration or evaporation isnegligible and, therefore, not ordinarily con-

CHAPTER 1 Introduction

1-5

and chemical and biological processes to oc-cur, reducing stormwater pollutants. Duringand immediately after storms, runoff is tem-porarily stored above the permanent waterpool.

3.2. Infiltration (Retention) Practices:A stormwater management practice whichtemporarily impounds a specified amount ofrunoff (treatment volume), retains it on-site,and discharges it through percolation into theunderlying soil and by evapotranspiration. On-line practices typically will have outlet struc-tures to safely convey the flood control vol-ume, and emergency overflows from extremestorm events. Infiltration practices are ex-pected to be dry during non-rainfall periods.The retention practice tool box includes infil-tration basins and trenches, swales, perviouspavements, dry wells, and seepage pits.

3.3 Filtration Practices:A stormwater management system which fil-ters the runoff through a medium to removepollutants, especially particulate pollutants.

sidered in the facility’s design. Detention prac-tices may be either wet or dry. They oftenare divided into three categories:

A. Dry detention practices which detain run-off for a relatively short time (1 to 24 hours)and release it at a controlled rate until the sys-tem is once again dry.

B. Extended dry detention practices whichdetain runoff for a longer time (24 to 48 hours),thereby increasing sedimentation and pollut-ant removal before the runoff is released at acontrolled rate and the system is once againdry.

Extended Dry Detention System

C. Wet detention practices, or wet ponds,which have a permanent pool of water, detainand release runoff over five days or evenlonger, and allow sedimentation, flocculation,

Wet Detention System (Pond)

Infiltration Trench


1-6

Sand Filtration Facility

Filter systems usually are used in combina-tion with detention systems. Filter media in-clude mixtures of sand, peat, and compost.Filters can be either confined (in boxes, bags,etc.) or unconfined. They can be designedas sidebank or vertical systems, meaning thatthe water flow is sideways or downward, re-spectively.

3.4 Biofiltration Practices:A stormwater management system which in-corporates vegetative filtration, allowing run-off to slowly pass through the vegetation toreduce pollutants. In addition to vegetativefiltering, these systems may also promote theinfiltration of runoff, depending on soil condi-tions. The organic nature of the soils and sup-porting vegetation helps reduce the potentialfor ground water contamination. Biofiltrationpractices include swales, buffer strips, andbioretention areas.

Swale with a swale block.

••••• Persons involved in developing andimplementing stormwater managementprograms.

••••• Stormwater system designers andbuilders.

••••• Land developers and their consultants.

••••• Stormwater system plan reviewers andinspectors.

••••• Stormwater system owners or opera-tors.

••••• Public officials and citizens.

2. STORMWATER MANAGEMENTPROGRAM CONSIDERATIONS

Before discussing stormwater practices,stormwater management program consider-ations will be briefly reviewed. Successfulstormwater management requires morethan simply the use of runoff controltechniques. It also requires a stronginstitutional foundation. A key componentof this foundation is establishing effectivemechanisms to assure that stormwatersystems not only are designed and con-structed correctly, but that they also areinspected, maintained and operated properly.

2.1 Stormwater Program Components

This section briefly discusses the manycomponents of a successful stormwatermanagement program. No single frameworkfor a stormwater management program canbe recommended. Flexibility is needed to

Chapter 2Stormwater Management Practices

1. OVERVIEW

State and local governments have imple-mented a wide variety of programs to addressthe stormwater problems resulting fromchanges to land use. Traditionally, theseprograms have focused on the prevention orminimization of flooding to protect thehomes, buildings, property and lives of theircitizens. “Drainage” ordinances and pro-grams have been established in mostcommunities. Today, however, existingstormwater programs must evolve andbecome more comprehensive to addressstormwater management objectives whichextend beyond the traditional drainagefocus. Expanded program objectives nowinclude: erosion and sediment controlduring construction, water quality protec-tion, stormwater reuse, and open spaceand recreation.

The tools or management practices that areused to prevent and mitigate these stormwaterimpacts also need to evolve. This chapterwill review the stormwater managementpractices that are most commonly usedfor stormwater treatment. For eachpractice the pollutant removal mecha-nisms, expected performance, limitationson use, and operation, maintenance andmanagement needs will be discussed andsummarized. Additionally, for each practice,specific operation, maintenance, and man-agement recommendations will be made.

1.1. Intended Readers

This chapter is intended for all readers of thispublication. It's information will be useful to:

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2-2

establish or refine programs, based on anarea's existing legal authorities and institu-tional framework.

Experience has shown that no single entitycan do everything. Program implementa-tion typically will be shared by apartnership involving all appropriatelevels of government, together with thepublic sector and all citizens. Coopera-tion and coordination among all of thepartners involved in program implemen-tation are cornerstones of successfulprograms. It is especially important that theroles of each partner involved in programimplementation be clearly stated. This willhelp to avoid duplication and distributeprogram activities to the entity most suited forthe role. This is especially true for assuringthe long term performance of stormwatermanagement practices.

Experience also has shown that successfulstormwater management programs shareseveral common building blocks (WMI,1997). These involve the program's institu-tional framework, its technical foundations,and the many activities that are undertakenby the stormwater program (Figure 2-1).

2.2. Stormwater Program Evolution to Address Existing Development

Stormwater quality management programstypically must be phased in. They usuallymust be integrated with existing "drainage"programs to provide coordinated manage-ment of stormwater quantity and quality.Initial program efforts are aimed atpreventing and mitigating stormwaterproblems from new development, bothduring and after construction. Generally,these programs rely upon on-site planningand BMP implementation. Once all aspects,including inspections and operation/mainte-nance, of this new development program are

running smoothly, the program can beexpanded to correct stormwater problemscaused by existing development and landuses (retrofitting). Section 2.3 discussesimportant components of programs aimed atstormwater from new development.

Establishing a program to retrofit existingstormwater systems, however, presentsmany technical, institutional, financial,and cultural dilemmas. In many instances,the unavailability or high cost of land in urbanareas makes the use of conventional BMPsinfeasible. State laws and institutionalarrangements promote piecemeal, crisis-solving approaches aimed at managingstormwater within political boundaries — yetstormwater follows watershed boundaries.Retrofitting often is prohibitively expensive.With many local governments already shortof funds, the need for innovative, dedicatedstormwater funding sources, such asstormwater utility fees, cannot be overem-phasized. Finally, cultural change is neededto get citizens and businesses to embracenonstructural BMPs and to support thestormwater program.

Solving existing stormwater problems willrequire comprehensive, coordinated, creativeapproaches and technology. Essential ele-ments of a comprehensive, long-term effort toreduce pollutant loadings from existing landuses and older stormwater systems include:

A. Watershed Management

A watershed approach which integrates landuse planning with the development ofstormwater infrastructure is essential. Afterall, it is the intensification of land use andthe increase in impervious surfaceswithin a watershed that creates thestormwater and water resources manage-ment problems. Consequently, a “water-shed management team” effort is necessarywhich involves state, regional and local

CHAPTER 2 Stormwater Management Practices

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PROGRAM ACTIVITIESC

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Govt. RolesResponsibilities

PublicSupportStaffingFunding

LegalAuthority

Adopt stormwater utility ordinance/feesAdopt program laws/regulations

Integration with other federal, state and local programs

Watershed planningStormwater master planningLocal land use plan

Program evaluationCitizen surveysBldg. community surveysBMP monitoringWater body monitoring

Stormwater retrofittingWatershed goalTargeting/prioritizationCapital improvementsRegional BMPs

Compliance/enforcementStop work ordersFinesCivil or criminal

Education programsSchool curriculumGeneral publicElected officialsDesignersDevelopersBuildersInspectorsPractitioners

AdministrationLead agency?Separate agency?

StaffingEngineersInspectorsPlannersScientistsMaintenanceClerical

Stormwater system operation/maintenancePublic facilitiesPrivate facilitiesAdopt a pond program

Figure 2 -1. Cornerstones (the Big Cs), Building Blocks, and Activities of a Stormwater Management Program

InspectionsErosion/sediment controlsStormwater system constructionStormwater system operation

Plan review and approvalSite plansErosion control plansStormwater plans

Structural BMPsDesign criteriaResearch/performanceProper constructionProper operationMaintenance

Performance standardsPeak discharge rateVolumeTreatment

Nonstructural BMPsSite planningSource controlsStreet sweeping


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urban stormwater systems makes it essentialto carefully evaluate pollutant reductiongoals, allocation strategies, and BMPimplementation. States should establish apriority watershed program which leadsto development and implementation ofwatershed management plans. Implemen-tation of these long term (15-30 years) planswill be designed to protect or restore thebeneficial uses of priority, targeted waterbodies.

Within priority watersheds, sub-basins canbe targeted based on pollution sources,flooding, and water quality problems.Regional and local stormwater master plansare an essential component of the watershedplan. In these local plans, existing stormwatersystems can be targeted for modification toassure that citizens receive the greatestbenefit (pollutant load reduction, floodprotection) for the dollar. The upgrading ofolder systems also needs to be coordinatedwith other planned infrastructure improve-ments, such as road widenings, and withpark, recreation, and urban redevelopmentprojects .

D. Alternative Controls

Nonstructural BMPs and source controlsneed to be used extensively to reducestormwater pollution from already devel-oped areas. For example, street sweepersremove lots of litter, debris, and sedimentsfrom paved surfaces even if they can't collectthe smaller particles (<60 microns) whichcontain high concentrations of metals andother pollutants. Prohibiting and eliminatingthe discharge of wastewaters other thanstormwater into storm sewers and otherconveyances can also greatly reducepollutant loadings. These types of controlsare especially appropriate in downtownbusiness districts, where other BMPs usuallyare infeasible, and in certain industrialsituations.

governments, together with the private sectorand all citizens within a watershed.

B. Treatment Requirements for OlderSystems (Retrofitting)

Numerous problems inherent to a highlyurbanized area make it nearly impossibleto apply the same stormwater design andperformance standards that are applied tonew developments. Instead, a “watershedloading” concept should be considered.This "big picture" approach considers thebeneficial uses of the receiving waters,assesses the loadings from all pollutionsources, and establishes the maximumloadings of pollutants that can be assimilatedby those waters. A key element is setting a"stormwater pollutant load reduction goal" forexisting untreated stormwater discharges. Anecologically based goal should be estab-lished, such as increasing the area of seagrasses or restoring habitat for desiredaquatic species. It is important that theecologically-based goal is understood by thepublic and determined with broad communityparticipation.

Success in meeting the load reductiongoal will depend not only on the treatmentbenefits from retrofitting projects, butalso by assuring that the on-site systemsserving new development are con-structed, operated, and maintained prop-erly. Even with BMPs, post-developmentstormwater pollution loadings are still greaterthan pre-development levels. Minimizingstormwater pollutant loadings from newdevelopments is essential in assuring thesuccess of stormwater retrofitting programs.Otherwise, the desired watershed pollutantloadings will be exceeded and the community'sdesired ecological goals will not be achieved.

C. Selective Targeting

The extremely high cost of retrofitting older


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An excellent example is the stormwater utility- a dedicated source of revenue with feesbased on a site’s contribution to thestormwater problem.

F. Innovative BMPs

The infeasibility of using traditional BMPs toreduce stormwater pollutant loads in urbanareas requires creative and innovative BMPs.Regional stormwater systems, whichmanage stormwater from several devel-opments or an entire drainage basin, offermany advantages over the piecemealapproach that relies upon small, indi-vidual on-site systems. Regional systemscan use natural processes, such as extendeddetention and constructed wetlands, ormechanical processes, such as alum injection,

Storm drain stenciling.

Education programs for the public and forstormwater management professionalsalso are vital. Citizens, businesses, andpractitioners need to understand how theireveryday activities contribute to stormwaterpollution. For example, citizens should notdiscard leaves, grass clippings, used motoroil or other material into swales or stormsewers. Yet many people believe thatstorm "sewers" go to the wastewatertreatment plant and not to the nearestwater body. Getting youth and citizen groupsinvolved in storm sewer stenciling projects(Dump No Wastes, Drains to Lake) is anexcellent way of reducing dumping ofpotential pollutants into these conveyances.Equally important are comprehensive trainingand certification programs for those in theprivate and public sectors who design, review,construct, inspect, operate, or maintainstormwater management systems.

E. Funding

Even just to solve existing flooding problems,the national cost of improving stormwaterinfrastructure is gigantic. Yet, local govern-ments already are struggling financially.Traditional revenue sources such asproperty taxes cannot be relied upon topay for stormwater management. Alterna-tive funding sources are needed. Lake Jackson regional stormwater

system, Tallahassee, Florida.


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to reduce stormwater pollutants. Theyprovide economies of scale in construction,operation and maintenance. Regionalsystems are especially useful in managingstormwater from existing land uses. Theyneed to be a central part of any retrofittingprogram. They can also be used to providestormwater management for new develop-ment, but this requires excellent planning andan expenditure of funds by the localgovernment or a developer to build theregional system and then get repaid by thosewho use it. Regional systems are mostsuccessful when a watershed approach isused that fully integrates land use, stormwa-ter management, wetlands protection, parks,and recreation/open space.

Innovative practices which are not landintensive are urgently needed. Injectingchemical coagulating agents into stormsewers to enhance flocculation andsedimentation of stormwater pollutants isan example. This often may be a better BMPwhere land for traditional detention basins isunavailable or expensive. Several aluminjection systems have been installed inurban areas in Florida to help restorereceiving lakes. Concerns over potentialaluminum toxicity, however, must still beaddressed before this innovative BMP can befully endorsed.

2.3. Stormwater BMPs and NewDevelopment

This section will briefly discuss some keyissues of using BMPs to reduce thestormwater impacts associated with newdevelopment. These issues include thestormwater program's goals, the setting ofperformance standards, and the establish-ment of design criteria for specific BMPs.

2.3.1. Program Goals

The goals of a stormwater managementprogram must be clearly established upfront. Until recently, this was a relativelyeasy task since programs typically wereestablished only to control stormwater peakdischarge rates. This is why stormwatermanagement frequently is referred to as“drainage” -- the traditional focus is ondraining runoff away from developedproperty as quickly as possible.

A. Stormwater Quantity Goals

Today, even the goals of stormwater quantitymanagement are changing and broadening.Control of stormwater volume, not just peakdischarge rate, is being required in closedbasins and for discharges to estuaries. Peakdischarge rate control also is evolving - fromcontrol of a single frequency storm tomultiple frequency storms. It is becomingcommon to control the peak dischargefrom a 1 or 2-year storm to minimize theerosion of stream channels, in addition tocontrolling the peak discharges for 10-,25- and/or 100-year storms for floodcontrol. Some stormwater managemententities such as the Suwannee River WaterManagement District and the FloridaDepartment of Transportation are requiringcontrol of the “critical storm”. This stormcreates the biggest difference between pre-development and post-development peakdischarge rate and/or volume.

B. Stormwater Quality Goals

The increasing awareness of stormwaterquality problems by citizens and electedofficials, along with Federal Clean Water Actrequirements, is stimulating state and localgovernments to broaden the objectives oftheir stormwater programs. Today,stormwater management program goalsinclude consideration of stormwater


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quantity, stormwater quality, erosionprevention and sediment control, aes-thetic values, stormwater reuse, and evenopen space and recreational benefits.

Stormwater quality programs need to beimplemented within the framework of thefederal Clean Water Act. It establishes twotypes of regulatory approaches to controlpollutant discharges. Technology-basedeffluent limitations reflect the best controlsavailable, considering their technical andeconomic achievability. Water quality-based effluent limitations reflect the waterquality standards and allowable pollutantloadings set up by permit (U.S. EPA, 1994).

With respect to stormwater discharges, thelatter approach possibly can be developedand implemented through a comprehensivemonitoring approach. This not only involvestraditional water chemistry monitoring, butalso needs to includes sediment chemistry,and an assessment of physical habitat,stream bank erosion, biological communitystructure, and possibly even whole-effluenttoxicity. These techniques are moreappropriate than water column chemistry inassessing cumulative, intermittent stormwa-ter impacts.

However, implementing a water quality-based effluent limit permit program forstormwater discharges is nearly impossiblebecause of staffing and technical limitations.The many land use changes occurring in thiscountry create tens of thousands of newstormwater discharges each year. Site-specific analyses to establish water quality-based effluent limitations for so many newdischarges simply can't be done. Addition-ally, there is a sparsity of data on stormwatertoxicity and ecological impacts. Therefore,nearly all stormwater quality permittingprograms are technology-based.

In 1987, the EPA issued guidance on the

development of technology-based stormwa-ter programs and the role of water qualitycriteria. The guidance recognizes that BestManagement Practices (BMPs) are theprimary mechanism for achieving waterquality standards. BMPs are controltechniques used for a given set of siteconditions to achieve stormwater qualityand quantity enhancement at a minimumcost (Wanielista and Yousef, 1986). Theguidance also recommends that stateprograms should include the followingiterative process:

1. Design of BMPs based on site-specificconditions, technical, institutional andeconomic feasibility, and the water qualitystandards of the receiving waters.

2. Monitoring to ensure that practices arecorrectly designed and applied.

3. Monitoring to determine the effectivenessof BMPs in meeting water qualitystandards and the appropriateness ofwater quality criteria in reasonablyassuring protection of beneficial uses.

4. Adjustment of BMPs when water qualitystandards are not being protected to adesigned level, or evaluation and possibleadjustment of water quality standards.

The ultimate water quality goal of stormwatermanagement programs is to protect or restorethe beneficial uses of the receiving watersthrough the proper installation and operationof program-approved BMPs. If beneficialuses are not maintained or restored,additional BMPs need to be implementedand/or the design criteria for current BMPsshould be modified to improve theirperformance.

2.3.2. Program Performance Standards

Whether for BMPs serving new developmentor for retrofitting, a performance standardmust be established so that specific BMP


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design criteria can be developed. Theperformance standard establishes atechnology-based effluent limitation forstormwater treatment systems.

A. Stormwater Management Goals

Ideally, the basic goal for stormwater systemsserving new development is to assure thatthe post-development peak discharge rate,volume, timing and pollutant load does notexceed pre-development levels. However,this goal usually is unattainable because ourcurrent BMPs, either alone or in combination,can not achieve this level of treatment and/orvolume control, and because of the limitationsimposed by variations in site conditions. Thisnecessitates the establishment of perfor-mance standards that can be achievedthrough the implementation of BMPs.

B. Stormwater Treatment PerformanceStandards

The stormwater treatment programs inFlorida, Delaware, and Maryland haveestablished similar performance standardsfor stormwater systems serving new develop-ment. They require stormwater systems toachieve at least an 80% reduction in theannual average post-development pollut-ant loading of Total Suspended Solids(TSS) discharged to fishable/swimmablewaters. This performance standard corre-sponds to secondary treatment levels,thereby helping to create greater equitybetween intermittent stormwater dischargesand the treatment requirements for traditionalpoint sources such as domestic and industrialwastewater discharges. Florida’s programalso sets a 95% removal level for stormwaterdischarges to sensitive waters such aspotable supply waters, shellfish harvestingwaters, and Outstanding Florida Waters.

2.3.3. BMP Design Criteria Factors

Once the performance standard is estab-lished, design criteria then need to be set foreach of the various BMPs that are going tobe used for stormwater management. Thissection will briefly review some of thefactors that must be considered whensetting BMP design criteria. The primaryfactors influencing BMP removal efficiencyinclude rainfall characteristics; the volume ofstormwater that is detained, infiltrated, orreused ("treatment volume"); the time neededto recover the treatment volume; theprocesses used to capture, filter, orassimilate stormwater pollutants; whetherthe system is on-line or off-line; and siteconditions. By analyzing the factors below,an average annual pollutant removal effi-ciency can be calculated based on the annualmass of pollutants introduced and the annualmass removed.

A. Rainfall Characteristics

An analysis of long-term rainfall recordsneeds to be undertaken to determine thestatistical distribution of various rainfallcharacteristics such as storm intensity andduration, precipitation volume, number ofstorms, time between storms, etc. Unlikeflood control, which focuses on large,infrequent storms, effective stormwatertreatment generally relies on capturingand treating runoff from small, frequentevents that carry the majority of pollut-ants. For example, in Florida, nearly 90% ofa year’s storm events produce one inch ofrainfall or less, and 75% of the total annualvolume of rain falls in storms of one inch orless (Wanielista, 1977). Also, the averagetime between storms is an importantconsideration in designing stormwater man-agement practices (Wanielista et. al., 1991).


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B. "First Flush" Phenomenon

"First flush" describes the washing actionthat runoff may have on accumulatedpollutants in the watershed. In the earlystages of runoff, the land surfaces, especiallyimpervious surfaces like streets and parkingareas, are flushed clean by the stormwater.This can result in higher concentrations ofsome stormwater pollutants, especiallyparticulates, during the early part of the storm(Miller, 1985). However, the occurrence of"first flush" depends on many factors,including the pollutant, conveyance sys-tem, drainage area, percent impervious-ness, rainfall patterns, and location. Forexample, in the Pacific northwest, which hasfrequent, long duration, low volume storms,first flush is much less pronounced. Where atarget pollutant is associated with the firstflush phenomenon, only this early fraction ofthe total storm runoff volume must becaptured and treated to reach the desiredtreatment level.

C. Land Use Pollutant Loadings

Stormwater pollutant sources, concentrationpeaks, and decay functions vary from site tosite. Accordingly, the typical stormwaterpollutant loading from any particular typeof land use can vary greatly. Runoff from

residential lands have lower concentrationsand loadings of most pollutants whencompared to stormwater from commercialland uses or highways. Runoff from streetsand parking lots will have higher concentra-tions of heavy metals and other petroleumassociated pollutants. Consequently, settingdesign criteria for stormwater BMPs mustinclude evaluation of factors such as landuse, the pollutants on site, and thecharacteristics of the drainage basin, suchas the soil type, amount of imperviousness,type of stormwater conveyance system, andthe length and time of travel.

D. On-line vs. off-line BMPs

On-line BMPs capture all of the runofffrom a design storm, temporarily storing itbefore discharge. They primarily provideflood control benefits, with water qualitybenefits secondary. However, some on-lineBMPs, such as wet detention systems, can doan excellent job of achieving both objectives.

Off-line BMPs divert the runoff "treatmentvolume" for treatment and isolate it fromthe remaining fraction of runoff, whichmust still be managed for flood control. This

Example of first flush runofffrom a parking lot.


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helps to improve treatment efficiency, reduceBMP maintenance, and make maintenanceeasier.

E. BMP Efficiency and Cost Data

During the past 15 years, many investigationsof BMP effectiveness have been performed.Typical information generated often includesthe pollutant removal effectiveness of variousBMPs, and the costs of BMP construction andoperation. A review of Florida BMPinvestigations (Wanielista and Shannon,1977) revealed that the cost of treatmentincreases exponentially beyond “second-ary treatment” (i.e., removal of 80% of theannual load). Therefore, higher levels oftreatment are required in Florida only forstormwater discharges to the state's mostsensitive water bodies.

F. Site evaluation

The soil types, slopes, geology, water tableand other features of a site will greatlyinfluence which BMPs will be most effective.Sandy soils imply using infiltration practiceswhile natural low areas and high water tablesoffer opportunities for wet detention ponds orconstructed wetlands.

3. STORMWATER POLLUTANTS ANDREDUCTION MECHANISMS

The key to properly specifying, designing,and operating treatment practices is anawareness of the pollutants in stormwaterand an understanding of the biological,chemical, and physical mechanisms that canbe used to prevent them from proceeding intoreceiving waters. Table 2-1 lists the principalmechanisms that have potential to capture,hold, and transform the various classes ofpollutants in urban runoff. The most commonstormwater pollutants and ameliorationmechanisms are summarized below:

1. Sediment is solid material that originatesmostly from disintegrated rocks, eroded soil,or accumulated organic materials depositedon the land surface. The quantity,characteristics, and causes of the sedimentare influenced by many factors includingslope, slope length, soil characteristics, andland use, and traffic volume. Sedimentparticles vary greatly in size and density. Thesettleability of a particular sedimentparticle depends directly on it's size anddensity. Sediment size and density must bedetermined to know which BMPs are mostappropriate to remove the particles and tobuild into the stormwater managementsystem appropriate mechanisms to promotethe settling of these particles. Some soils,because of their silty, colloidal nature, canalmost never be settled once they get intosuspension. These soils may require the useof coagulating agents, such as alum or ferriccompounds, to remove them from the water.Of course, the most effective controlmethod for sedimentation is erosioncontrol--prevent the production of sedi-ment as much as possible.

2. Oxygen-demanding substances includenumerous organic materials that are decom-posed by microorganisms thereby creating aneed for oxygen. Consequently, a stormwa-ter system such as a detention pond mustinclude mechanisms to maintain high oxygenlevels and prevent the formation of anaerobicconditions. Oxygenation mechanisms can benatural (such as shallow depths, sufficientlength and width to induce wind mixing, andorientation to maximize the opportunities forwind mixing) or mechanical (such asaerators).

3. Heavy metals in highway runoff originatefrom the operation of motor vehicles,atmospheric deposition, and the degradationof highway materials. The most abundantheavy metals in stormwater are lead, zinc andcopper, which together account for about 90


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MECHANISM POLLUTANTS AFFECTED REMOVAL PROMOTED BY

Physical sedimentation Solids, BOD, pathogens,particulate COD, P, N,synthetic organics

Low turbulence, increasedresidence time

Filtration Same as sedimentation Fine dense herbaceousplants, constructed filters

Soil incorporation All Medium-fine texture

Chemical precipitation Dissolved P, metals High alkalinity

Adsorption Dissolved P, metals,synthetic organics

High soil Al, Fe, organics,circumneutral pH (around 7)

Ion exchange Dissolved metals High soil cation exchangecapacity

Oxidation COD, petroleumhydrocarbons, syntheticorganics

Aerobic conditions

Photolysis Same as oxidation High light

Volatilization Volatile petroleumhydrocarbons, syntheticorganics

High temperature and airmovement

Biological microbialdecomposition

BOD, COD, petroleumhydrocarbons, syntheticorganics

High plant surface area andsoil organics

Plant uptake andmetabolism

P, N, metals High plant surface area andactivity

Natural die-off Pathogens Plant excretions, saline water

Nitrification NH-3 Dissolved oxygen < 2 mg/l,low toxicants, temperature >5-7 C, circumneutral pH

Denitrification NO3 + NO2 Anaerobic, low toxicants,temperature > 15 C

TABLE 2-1. Summary of Stormwater Pollutant Removal Mechanisms


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percent of the dissolved heavy metals and 90-98 percent of the total metal concentrations(Harper, 1985). Except for copper, zinc,and cadmium, the majority of metals arepresent in particulate form. Consequently,very good removal efficiencies (60-95%) canbe obtained in properly designed stormwatermanagement practices.

To maximize heavy metal removal indetention designs, designers should providephysical configurations which encourage agradual reduction in flow velocity to promoteparticle sedimentation; maximize the flowlength from inlets to the discharge point;prevent short circuiting of flows andhydraulically dead zones; and includesuitable aquatic plants to promote uptake andremoval of dissolved metal species. To keepmetals bound to sediment, it is importantthat the sediment pH be kept near 7 andthat the sediments be aerobic. A decreasein pH and, to lesser extent, a reduction inredox potential, will cause metals to becomesoluble and release from the sediment(Harper, 1985). For this reason, it isimportant to monitor the accumulation ofsediment and decaying organic matter withindetention ponds since this can result inlowered pH and possible anaerobic condi-tions. Failure to properly remove sedimentscould cause release of accumulated metalsinto the underlying ground water or intosurface waters.

4. Nutrients, such as nitrogen andphosphorus, are common constituents ofstormwater. They stimulate the growth ofalgae and other aquatic plants, andcontribute to oxygen depletion as theseplants decompose. Excessive nutrientsaccelerate the natural process of eutrophica-tion in lakes and streams. Nutrients instormwater may be either dissolved orparticulate, with particulate forms slightlydominating (about 60%). Consequently, astormwater management system, especially

a wet detention system, must incorporateprovisions for settling to remove particulateforms of nutrients and include nutrientassimilation for dissolved forms. A littoralzone planted with suitable aquatic plantsshould be concentrated near the dischargepoint to provide nutrient assimilation.Biofiltration, swale conveyance, sedimentsumps, or a perimeter swale and berm systemcan be used to reduce particulate nutrients.

5. Increased temperature of stormwateroccurs because urban lands, especiallyimpervious surfaces, are heated on warmdays. Runoff stored in BMPs, especiallyshallow ponds, is also heated by the sunbetween storms. Proper selection of BMPs isthe best way to minimize adverse thermalimpacts from stormwater BMP discharges.Galli (1991) ranks the potential of BMPs toraise receiving water temperatures, fromleast to most serious, as: infiltration basins <extended detention wetlands < extended drydetention ponds < wet detention ponds.Other methods to lessen thermal impactsinclude using wetland plants, or trees to helpshade BMPs, especially pilot channels andoutfall channels for extended dry detentionponds. The use of exposed riprap or concretesurfaces for these channels also can beminimized. BMPs also can be oriented to takeadvantage of prevailing winds, promotingwater circulation and cooling.

6. Increased stormwater volume associ-ated with the increased imperviousnesswhich accompanies urbanization is nowbeing recognized as a major cause of waterbody degradation. The increased volume ofrunoff causes channels and streams to flow atbank full levels more frequently resulting instreambank and bed erosion, and loss ofhabitat. Additionally, the discharge of greatervolumes of runoff to estuaries has led todecreases in their salinity and shifts inbiological communities. Reducing stormwa-ter volume is not easy. Nonstructural BMPs to


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Addition of precipitating agents

Nitrogen control:Alternating aerobic and anaerobic conditionsLow levels of toxicantsCircumneutral pH (around 7)

Metals control:High soil organic contentHigh soil cation exchange capacityCircumneutral pH

Organics control:Aerobic conditionsHigh lightHigh soil organic contentLow levels of toxicantsCircumneutral pH

The degree of control that the treatmentsystem designer and operator can exert toinfluence the operation of these variousfeatures differs. Fortunately, at least three ofthe four features that promote all favorablemechanisms (possibly excluding the soil) areunder a high degree of control. The additionalfeatures that promote the more specificobjectives require more intervention (e.g.,developing some desired soil condition).

4. STORMWATER MANAGEMENTPRACTICES (BMPs)

The stormwater management tool boxcontains many tools that can help prevent orcorrect stormwater problems. The broaden-ing objectives of stormwater management isleading to the development of new tools andthe refinement of some of our existing tools.The goals of a stormwater program usuallywill play a major role in deciding which toolswill be selected and used.

Generally, the stormwater tool box can beseparated into two main drawers: nonstruc-tural controls and structural controls.

minimize imperviousness and reduce directlyconnected impervious area are the mosteffective. Structural BMPs which help toreduce stormwater volume include infiltrationsystems, many biofiltration systems, and wetdetention stormwater reuse systems.

Although not specifically listed in Table 2-1,treatment time is an important factor inthe functioning of all mechanisms. Theeffectiveness of settling a solid particle isdirectly related to the time provided tocomplete sedimentation at the characteristicsettling velocity of the particle. Time is alsoa crucial variable in determining the degreeto which chemical and biological mecha-nisms operate. Chemical reactions andbiologically mediated processes all proceedat characteristic rates, which must beimplicitly recognized to obtain their benefitsin treatment. For all of these reasons,water residence time is the most basicvariable for applying treatment practicetechnology effectively.

An alternative way of looking at theinformation presented in Table 2-1 is to groupfeatures that promote certain specificpollutant control objectives. The followinglist extracts those features for the mostcommon objectives:

Features That Help AchieveAll Objectives

Increasing hydraulic residence timeLow turbulenceFine, dense herbaceous plantsMedium-fine texture soil

Features That Help AchieveSpecific Objectives

Phosphorus control:High soil exchangeable aluminum and/or

iron content


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Generally, nonstructural controls are thosethat can help to prevent stormwater problems,while structural controls are used to mitigatestormwater problems. Until recently, moststormwater programs, because of their focuson flood control, have relied upon structuralcontrols.

Nonstructural controls often are somewhatdifficult to implement. Several of them requireconsideration and control of changes inproperty (i.e., growth management, land useplanning, zoning) - often very controversialtopics. Nonstructural controls also include“source controls”, which are used to limitthe types and amounts of potentialpollutants that get into runoff. Manysource controls involve modifying or control-ling certain aspects of human behavior suchas the use of fertilizers, pesticides orhousehold cleaners. Doing so may be verydifficult or highly controversial. However,source controls can be very effective,especially in highly urbanized areas, and lesscostly than structural controls. The dilemmafor stormwater managers is the effective-ness of nonstructural controls is not wellunderstood yet.

With respect to structural controls, broaden-ing of stormwater management goals oftenrequires reconsideration of the usual BMPdesign, less emphasis and use of certainpractices, changes in preferred alternatives,and greater emphasis on regular mainte-nance. For example:

• To improve pollutant removal, detentionpond design typically must be changed toincrease residence time, maximize lengthof flow through the pond, and includeshallow littoral zones planted withappropriate native wetland plants to helpremove dissolved nutrients and metals.

• Less emphasis is placed on use of drydetention, which is used widely for flood

control. However, dry detention systemsprovide very low pollutant removalbenefits because of very short detentiontimes, bottom discharge controls, andpaved channels.

• In many locations, local codes require theuse of street curbs and gutters with stormsewers to eliminate ponding of runoff,even for short periods of time. To promoteinfiltration, thereby decreasing runoffvolume and improving pollutant removal,many localities are eliminating thisrequirement and promoting the use ofroadside vegetated swales, especially inlow or medium density residential areas.

• There is increasing emphasis on the“BMP treatment train” concept, whereinseveral types of stormwater controlsare used together and integrated into acomprehensive stormwater manage-ment system. This is especially truewhere wet detention ponds are theprimary control but are being promoted asa visual and recreational amenity on aproject. To help prevent the wet pond fromturning into an algae-covered eyesore,swales can be used for conveyanceinstead of storm sewers, and vegetatedlittoral zones are added to assimilatenutrients. Increasingly, the use of small,off-line depressional storage areas isbeing integrated into site plans, usually aspart of the site’s required open space andlandscaping. These can not only reducepollutants but decrease the overall size


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and cost of downstream stormwatersystem components.

4.1. BMP Selection

Effective operation and minimum mainte-nance of a stormwater system begins withselection of the most appropriate BMP(s) forthe site. Factors which need to be evaluatedinclude:

A. Watershed Area

Infiltration, biofiltration, and filter BMPsgenerally are more suitable for smaller areas.Pond BMPs typically require a larger drainagearea to assure proper operation.

B. Area Required

Adequate area must be available at the site.Many BMPs are land intensive but some canbe installed underground, although thisincreases maintenance difficulties and costs.

C. Stormwater pollutants

Most BMPs are more effective at removingparticulate related pollutants. Some BMPs,primarily those with vegetative components,can also reduce dissolved constituents.

D. High Sediment Loading

Many BMPs are highly susceptible toclogging. Pretreatment (BMP TreatmentTrain) helps to increase effectiveness, reducemaintenance, and extend the life of BMPs.

E. Soil type

Soil permeability has a profound influence onBMP effectiveness, especially for infiltrationpractices. Also, silty and clayey soils that getinto stormwater are much harder to settle thansandy ones.

F. Slope

Steep slopes can restrict the use of severalBMPs, especially when water ponding or flowvelocity may cause instability or erosion.

G. Water Table Elevation

A crucial factor in the design of all BMPs iswater table elevation. Incorrectly estimatingthe seasonal high water table so it is too closeto the bottom can cause BMP failure,decrease effectiveness, and increase mainte-nance. This is especially true for infiltration ordry detention systems. Wet ponds need highwater tables to maintain their permanentpools.

H. Bedrock or Hardpan

Restrictive soil layers or rock can impededownward infiltration of runoff or makeexcavation for ponds impossible or expen-sive.

Solution pipe sinkhole in the bottomof an infiltration system.


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I. Karst Geology

Fractured limerock geology provides chan-nels for stormwater pollutants to migrate intothe ground water. Excavation or the hydraulichead of stored runoff may create sinkholes inthe bottom of BMPs creating a directdischarge to ground water.

J. Proximity to Foundations, Septic Tanks,and Wells

BMPs should not be located close to buildingfoundations, septic tanks, or drinking wells.Seepage problems or ground water pollutioncan result, especially from infiltration prac-tices.

K. Receiving Water

If the stormwater discharge will be to anestuary or other saline habitat, BMPs whichreduce stormwater volume need to beconsidered first. If the discharge is to a waterbody which supports a cold water fishery orbiological community, the potential thermalimpacts must be considered in the selectionof the most appropriate stormwater BMPs.

L. Water Availability

Water may be needed during the dry seasonto keep grass or other vegetation alive andcontinuing to function as a filtering media.

M. Side Effects and Ancillary Benefits

Potential for mosquito breeding or groundwater contamination need to be considered,as do opportunities for wildlife use andpassive recreation.

N. Public Acceptance

No stormwater system will be maintained ifthe property owner does not like or approveof its design or the types of BMP used.

4.2. BMP Fact Sheets

The remainder of this chapter consists of aseries of fact sheets on each of the majortypes of stormwater management practicesused to treat runoff. They are presented in thefollowing order:

• Infiltration Practices• Infiltration Basin• Infiltration Trench• Exfiltration Trench• Pervious Pavement• Modular Pavement

• Detention Practices• Dry Detention Basin• Extended Dry Detention Basin• Wet Detention Basin

• Biofiltration Practices• Constructed Wetlands• Filtration Practices

BMP Treatment Train. Runoff isrouted off the parking lot throughcurb cuts, into a swale whichconveys stormwater to a raisedinlet. A storm sewer transports therunoff to a wet detention pond, allin a landscaped setting. Remem-ber "BMP" does not stand for BigMuddy Pond!


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Description

A family of practices in which the "treat-ment volume" is infiltrated into the soilrather than discharged off-site. Infiltra-tion practices include basins, trenches,dry wells, pervious pavement, and, to a certain extent, swales, which will be considered abiofiltration practice in this handbook.

Purpose

Infiltration practices are used for two primary purposes: reducing the total volume of storm-water runoff, and reducing the stormwater pollutant loading discharged off-site.

Pollutant Removal Mechanisms

The primary "treatment" mechanism is the infiltration and evaporation of runoff. This reducesthe total volume of stormwater leaving the site, thereby reducing the total pollutant loading.Ancillary benefits of reducing stormwater volume include a decrease in stream channel ero-sion and loss of stream habitat.

Pollutant removal occurs as runoff passes through the soil profile and/or the vegetation rootmass. Pollutants are trapped, bound, or decomposed in the vegetation, its roots, and in thepore spaces between the soil particles, while runoff passes into the ground. Soils must havean appropriate infiltration rate, contain sufficient organic matter, and maintain aerobic condi-tions to minimize migration of pollutants into the ground water.

Expected Stormwater Quantity and Quality Performance

Infiltration BMPs are highly effective in reducing total stormwater volume. This helps toreduce peak discharge rates, downstream channel erosion, and downstream water eleva-tions. The infiltrated water also help to preserve stream base flow.

Stormwater treatment effectiveness depends primarily on whether the infiltration practice ison-line or off-line, and on the sizing criteria used to design the facility. When designed as off-line BMPs, infiltration practices remove 100% of the stormwater pollutant loading for all of therunoff which is infiltrated. Total annual pollutant load reduction depends on the volume ofannual runoff which is diverted into the BMP and infiltrated into the ground.

On-line infiltration systems will have lower treatment efficiencies than off-line systems.

InfiltrationPractices


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Expected annual average pollutant removal efficiencies of on-line systems are :

Total Suspended Solids 75% Total lead 50%Total Phosphorus 50% Total zinc 65%Total Nitrogen 40%, but highly variable Total copper 25%COD 40%

Limitations on Use

• Require porous soils, such as sands and gravels, to allow infiltration of runoff within de-sired time.

• Not suitable if soils have 30 percent or greater clay content or 40 percent or greater silt/clay content.

• Not suitable in areas with high water tables, shallow depth to highly impervious stratasuch as bedrock or clay soils.

• Not suitable on fill sites or steep slopes.• Risk of ground water contamination, especially in coarse sandy soils and karst geology.• May not be appropriate at sites where spills of hazardous materials may occur.

Operation, Maintenance, and Management Needs and Obligations

Operation

Infiltration practices all depend on theability of stormwater to pass through thevegetation and soil into the ground.Therefore, long term operation of thepractice depends on maintaining its per-meability.

The primary causes of infiltration systemfailure include:

• inadequate soil investigation,resultingin poorly designed systems that do notpercolate.

• inaccurate estimation of the soil infil-tration rate at the bottom of the pro-posed facility.

• premature use of facility before con-tributing area is stabilized.

• improper construction, resulting in soilcompaction or sedimentation.

• high sediment loadings or a lack ofmaintenance, leading to clogging.

Retention basin with soggy bottom because it doesn't infiltrate the runoff within the design time.


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Maintenance

The frequency and need for maintenance will depend primarily on the loading of particu-lates and whether pretreatment practices have been used. Maintenance activities willinclude:

• Removal of accumulated solids.• Mowing and removal of vegetation.• Vegetative stabilization of eroding sides or bottom.• Rototilling, disking, or aerating the bottom or bottom vegetation.• Clearing materials that have accumulated in the discharge structure.• Cleaning pretreatment BMPs (i.e., swales, sediment sumps) so they can continue

to protect the infiltration practice.

Management Needs and Obligations

• Inspect the facility semiannually (just before the wet season and at the end of it) andafter large storms. If there is still water in the BMP after 72 hours (or after 24-36hours for vegetated systems), it is time to clean it and restore its percolation capac-ity. Cleanout frequency will depend on whether the practice is on-line or off-line,vegetated or not vegetated, its design storage capacity, sediment loading, and useof pretreatment BMPs.

• Eroding sides or bottoms need to be revegetated as soon as possible.• Revegetate the contributing area where needed to stabilize and reduce generation

of particulates.

Recommendations to Assure Proper Operation, Maintenance and Performance

1. One of the most difficult aspects of designing infiltration practices, and the key to properoperation, is obtaining reliable information about the actual infiltration rate of the soilwhere the BMP will be constructed. To determine the infiltration rate, recommendationsinclude:• Use a conservative estimate and a safety factor.• Measure infiltration rates at the actual location where the BMP is to be sited.• Since soil characteristics, including infiltration rate, change with depth, it is crucial that

the measurements be made at the depth of the design elevation of the bottom of thepractice.

• Infiltration rates should be determined by mass balance field tests, if possible. If fieldtests are not possible, then infiltrometer tests should be used. Lab permeability testsare a third option. In either of these latter two tests, the design infiltration rate shouldbe half of the lowest measured rate.

2. To minimize the potential for ground water contamination, be sure that the bottom of theinfiltration practice is at least four feet above the seasonal high ground water elevation.Be sure to include consideration of ground water mounding.

3. Do not use infiltration practices for erosion and sediment control during construction.


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4. Do not place infiltration systems into operation until their contributing drainage area iscompletely stabilized.

5. Use pretreatment practices such as swale conveyances and sediment sumps to reducesediment loading and potential clogging.

6. Underground systems must include pretreatment BMPs and an observation well to alloweasy determination of whether runoff is percolating within the design time.

7. Include a maintenance access that lets O&M activities get done without moving heavyequipment onto the infiltration area.

8. Bedrock should be at least four feet beneath the bottom of the practice. In those parts ofthecountry with fractured bedrock or where limestone is at or near the land surface, spe-cial precautions must be taken to prevent ground water contamination. This is especiallytrue in "Karst Sensitive Areas" where sinkhole formation is prevalent. In these types ofareas, a site specific hydrogeological investigation needs to be undertaken including geo-logic borings wherever infiltration practices are proposed. Infiltration practices in theseareas should include several small off-site areas, swale conveyance for pretreatment, beas shallow as possible, be vegetated with permanent cover such as sodded grasses, andhave flat bottoms to keep the runoff spread out across the entire infiltration area.

Retention basin built in area of Karst geology.


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8. Construction Recommendations: To protect the natural infiltration rate and minimizepotential clogging, special precautions need to be taken during construction including:

• If possible, schedule construction so it does not occur during the rainy season and doesoccur during the vegetative growing season.

• Infiltration areas should be well marked in the field and heavy equipment and sedimentkept away from them.

• Construction should be overseen by someone who is trained and experienced in theinstallation of infiltration practices and who is knowledgeable about their purpose andoperation.

• The design team should inspect the exposed soil after excavation to confirm that soilconditions are as expected and are suitable. If they are not, work should stop and thesituation should be analyzed to determine whether or not design or construction changesare necessary to ensure success.

• If possible, build the facility without driving heavy equipment over the infiltration surfaceas this will compact the soil and reduce the infiltration rate. Any equipment driven on thesurface should have extra wide, low pressure tires.

• During construction, place excavated material at least 10-15 feet away from the infiltra-tion area.

Sediment from construction activities can quickly clog an infiltration basin.


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• Construction of the infiltration practice should not begin until after the site has been com-pletely stabilized. If this is not possible, then:

• Diversion berms should be placed around the perimeter of infiltration areas to divertrunoff and sediment away from them during the construction phase of a project.

• The facility should not be excavated to final grade until after the contributing drainagearea is stabilized. Leave one foot of native soil which can be removed in layers as itclogs while construction is occurring.

• Excavate infiltration areas using light equipment and construction procedures whichminimize compaction.

• After final grading, the infiltration surface area should be deeply tilled to provide a wellaerated, highly porous surface texture.

A retention basin which has been recently tilled tohelp restore its infiltration capabilities.


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Description

A surface area used to tempo-rarily store runoff for a selecteddesign storm or specified treat-ment volume. Storage volumeis recovered when the runoff per-colates into the soil orevapotranspires. Infiltration basins may be made by either excavating soil or by building anembankment.


• Percolation of runoff reducing stormwater volume discharged off-site.• Filtering and adsorption of pollutants by the vegetation, roots, and soil profile.

Advantages

• Can be integrated into a site's open space and landscaping helping to increaseaesthetics.

• Area can be used for ancillary purpose, such as recreation, between storms .• Surface systems are more easily inspected and maintained.

Disadvantages

Land needed for the basin can be expensive and prevents this area from being used forother development related purposes.


Operation

Successful operation depends on maintaining the percolation rate of the basin's floor andside slopes. To minimize the potential for ground water contamination, and to naturallyhelp maintain percolation rates, vegetation such as grasses should be planted and main-tained on the basin floor and side slopes.

Maintenance

Activities necessary to maintain the basin's function include:

Infiltration Basin


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• Removal of accumulated solids. Ideally, these are trapped in a pretreatment settlingforebay to minimize the need to disturb the basin's vegetation. In non-vegetatedbasins, sediments should be removed from the basin when its floor is dry and afterthe accumulated sediments have cracked and separated from the bottom. Hand rak-

ing and removal is recom-mended, if possible, to mini-mize compaction. In veg-etated basins, the grass of-ten will grow up throughsediment deposits unlessthey are extremely heavy.

• Mowing and removal ofvegetation. The use of lowgrowing grasses is recom-mended to minimize mowingfrequency.

• Fertilizers should only beused if absolutely neces-

sary.

• Vegetative stabilization oferoding sides or bottom.

• In vegetated basins, thegrassed floor should beaerated annually.

• Rototilling or disking thebottom in non-vegetatedbasins. Tilling is requiredperiodically (at least onceannually and perhapsmore often) to help re-store the natural infiltra-tion capacity. All accumu-lated sediment must be removed first. Light tractors with rotary tillers or disc harrowscan be used, followed by use of a levelling drag. After tilling, the basin floor should belevel, smooth, and free of ridges and furrows to ease future removal of sediments. Innorthern climates, the basin surface may be very porous in the spring due to the effectsof freeze and thaw. Infiltration capacity will diminish rapidly afterwards so tilling shouldbe scheduled for late spring or early summer to help restore percolation.

• Clearing materials that have accumulated in the discharge structure.

Infiltration systemvegetated with grass.

Unvegetated infiltrationsystem with sand bottom.


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Inspect semiannually and after large storms to assure proper percolation, prevent ero-sion, measure sediment accumulations, and assure proper vegetation growth. Signs thatthe basin is not infiltrating as designed include a "soggy" bottom, death of grass cover, orinvasion by cattails or other wetland type vegetation. A simple "staff gage" made from aone inch pipe driven into the ground can be used to measure sediment depths.

Recommendations to Assure Proper Operation, Maintenance, and Performance

1. See recommendations for "Infiltration Practices".

2. Use energy dissipation at inlet to minimize erosion.

3. Side slopes of at least 3:1 for safety, and for ease of mowing, although 4:1 is optimal.

4. Provide dedicated access to the basin bottom for maintenance vehicles.

5. Construction recommendations:

• Follow all of the construction recommendations under "Infiltration Practices".

• To maximize opportunities for infiltration, it is crucial that the basin's floor be evenlygraded with a zero slope. If the bottom is uneven, these low spots will remain underwater too long and may become chronically wet.

• Since some compaction will occur during excavation and construction, deeply till thebottom of the infiltration surface after final grading or excavation.

• Stabilize with vegetation within one week after construction. Vegetation not only helpsto prevent erosion, provide filtration and uptake stormwater pollutants, but the rootshelp to naturally maintain the soil's infiltration rate. The condition of the newly estab-lished vegetation should be checked several times during the first few months. Reme-dial actions such as reseeding, sodding, fertilization, or irrigation should be takenwhenever necessary.

Clogged infiltration basin.Standing water creates an

aesthetic and mosquitoproblem.


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Infiltration Trench

Description

A shallow excavated trench, usually two to ten feetdeep, backfilled with a coarse stone aggregate,allowing for temporary storage of runoff in thevoids between the aggregate material. Trenchescan be located on the surface or below the ground.Surface trenches receive sheet flow runoff directlyfrom adjacent area, usually after the runoff flowsover a grass buffer. Underground trenches receive runoff from storm sewers and musthave pretreatment inlets.


• Percolation of runoff reducing stormwater volume discharged off-site.• Filtering and adsorption of pollutants by the soil profile.

Advantages

• Require less land area than do surface basins.• One of the few BMPs that can be used when land area is limited and can be fit into

highway medians, site perimeters, and other unused areas of a site.

Disadvantages

• Difficult to monitor their continued performance, especially if observation wells arenot included.

• Can become clogged fairly easily and very difficult to unclog, especially under-ground trenches.


Operation

Successful operation depends on maintaining the percolation rate of the trench's sidesand bottom. The keys to assuring successful long term performance are accurate estima-tion of the percolation rate, proper construction, pretreatment, off-line design, and main-tenance accessibility.


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Maintenance

Activities necessary to maintain the trench's function include:

• Regular removal of accumulated solids from the pretreatment BMPs to preventthem from moving into the trench.

• Removing sediment buildup in the stone aggregate. This can involve monitoringand removal of sediments within the top foot of aggregate or allowing sediments topenetrate deeper into the trench necessitating removal and replacement of muchof the stone aggregate. The former option is preferred.


The observation well needs to be monitored periodically. For the first year after construc-tion, the well and pretreatment BMP should be monitored monthly after a storm during therainy season and quarterly in the dry season. A log book should be maintained by theresponsible maintenance entity and include information such as the date, water level,date of last rainfall, and calculation of the drawdown time. Once the trench's performancecharacteristics have been documented, the monitoring schedule can be reduced until theperformance data indicates a reduction in percolation rate.

Schematic of infiltration trenchwith observation well.


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1. Accurately estimating the trench's infiltration rate is crucial to successful operation.Whether infiltration primarily occurs through the trench bottom or sides will depend on theelevation of the water table and soil properties.

2. To minimize the potential for ground water contamination, the bottom of the trench shouldbe at least four feet above the seasonal high ground water elevation. Don't forget toinclude consideration of ground water mounding when setting the elevation of the trenchbottom.

3. Pretreatment is essential to minimize sediment and organic matter loading thereby reduc-ing the potential for the stone filled trench to become clogged.

4. A 4 or 6 inch diameter observation well with locking cap must be included to allow evalu-ation of performance and the infiltration rate over time.


• Follow all of the recommendations under "Infiltration Practices".

• Timing - The trench should not be constructed or placed into service until all of thecontributing drainage area is completely stabilized. If the trench is constructed prior todrainage area stabilization, then the trench should be covered with heavy plastic toprevent any inflow until stabilization is completed.

• Erosion and sediment control - Special care must be taken to prevent soil from gettinginto the trench between the aggregate and the geotextile fabric.

• Excavation - The trench should be excavated using a backhoe or trencher equippedwith tracks or oversized tires. Normal rubber tires should be avoided since they com-pact the subsoil and reduce infiltration capability. For the same reason, bulldozers orfront-end loaders should not be used unless they are equipped with extra-wide treads("low pressure treads"). Excavated materials should be kept at least 15 feet away fromthe trench to avoid backsliding and cave-ins.

• Geotextile fabric - Once the trench is excavated, the bottom and sides should be linedwith an appropriate geotextile fabric to prevent upward piping of underlying soils. Be-fore installing the fabric, inspect the bottom and side walls of the facility for any protrud-ing objects, like tree roots, that may puncture the filter fabric. Care should be taken inselecting the proper kind of fabric as available brands differ significantly in their perme-ability and strength. When cutting the fabric, be sure the length and width are sufficientto conform to the trench's dimensions and allow a 12 inch minimum top overlap. If morethan one roll of fabric is needed, the upstream roll should overlap at least 2 feet over thedownstream roll to provide a shingled effect.

• Unstable excavation sites - Vertically excavated walls may be difficult to maintain in


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areas where the soil moisture is high or where soft or cohesionless soils predominate.These conditions may require laying back the side slopes or using trench safety proce-dures. Trapezoidal excavation may result when laying back the side slopes creating aneed to carefully back fill the space between the filter fabric and the excavation sides.Natural soils should be placed in these spaces at the most convenient time duringconstruction to assure fabric conformity to the final side dimensions. Trenches overfour feet deep require shoring pursuant to OSHA regulations.

• Stone aggregate - Clean, washed stone aggregate should be placed in lifts and com-pacted with plate compactors. Soft stones such as limestone or bluestone aggregatesshould be avoided. A maximum loose lift thickness of 12 inches is recommended. Thecompaction process ensures fabric conformity to the excavation sides, thereby reducingpotential for soil piping, fabric clogging, and settling problems.

• Covering - Once the stone aggregate is placed, the filter fabric needs to be folded overit to form a minimum 12 inch longitudinal overlap. The desired fill soil or stone aggre-gate should be carefully placed atop the fabric so as to maintain the overlap.

• Operation - The trench shouldremain covered until all of thecontributing drainage area iscompletely stabilized.

InInfiltration trench coveredwith plastic, upon which

sediment has accumulated,to prevent sediment entry

during construction.


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Description

An infiltration trench in which therunoff (treatment volume) is storedin a perforated or slotted pipe, andpercolates out through the surrounding gravel envelope and filter fabric into the soil.


• Percolation of runoff reducing stormwater volume discharged off-site.• Filtering and adsorption of pollutants by the soil profile.

Advantages

Similar to infiltration trenches, except they can also be placed beneath paved surfacessuch as parking lots and streets.

Disadvantages

• Difficult to monitor their continued performance, requiring regular visual inspectionof the inside of the pipe to determine accumulation of sediments and other materi-als. Observation wells may not be as useful as for infiltration trenches.

• Can become clogged fairly easily, and they are very difficult and expensive to un-clog.


Operation

Successful operation depends on maintaining the percolation rate of the trench's sidesand bottom. The keys to assuring successful long term performance are accurate estima-tion of percolation rate, proper construction, pretreatment, off-line design, and mainte-nance accessibility.

Maintenance

Activities necessary to maintain the trench's function include:

• Regular removal of accumulated solids from the pretreatment BMPs to preventthem from moving into the trench.

ExfiltrationTrench


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• Implementation of source controls, such as street sweeping, landscaping practices,and other good housekeeping practices, which reduce the generation of sediments.

• Removing sediments and other organic matter that accumulates within the exfiltrationpipe.

• Pipes should be inspected quarterly for the first year to determine how quicklymaterials accumulate in them. Accumulated materials can be vacuumed out with avactor. High pressure cleaning of the holes or slots in the pipes can help to reduceclogging.

• Removing sediments which accumulate within the aggregate envelope, with pos-sible replacement of aggregate necessary if sediments aren't removed from thepipe.


The exfiltration system needs to be monitored periodically. For the first year after con-struction, the pipe should be monitored quarterly. The pretreatment BMP should be checkedmonthly during the rainy season and quarterly in the dry season. The observation well,included to monitor water levels in the surrounding gravel envelope, should be monitoredafter storms monthly during the rainy season and quarterly in the dry season. A log bookshould be maintained by the responsible maintenance entity and include informationsuch as the inspection date, date and amount of last rainfall, visual observations of thepretreatment BMP and pipe, water level, and calculation of the drawdown time. Once thetrench's performance characteristics have been documented, the monitoring schedulecan be reduced until the performance data indicates a reduction in percolation rate.


1. Follow all of the recommendations for "Infiltration Trenches".

2. When estimating the design exfiltration rate, Wanielista et. al. (1991) concluded:

••••• Permeability of the parent soil is not the limiting exfiltration rate.••••• The limiting exfiltration rate is set by the geotextile filter fabric not the soil.••••• A maximum rate of 0.5 inch/hour should be used if infiltration is assumed to occur

through both the sides and bottom of the trench.••••• A maximum rate of 1.0 inch/hour

should be used if infiltration isassumed to occur only through thetrench's sides.


• Follow all of the recommendationsfor "Infiltration Trenches".


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Pervious Pavement

Description

A pavement with traditional strengthcharacteristics but which allows rainfalland runoff to percolate through it ratherthan running off.

There are two types of pervious pavements - porous asphalt and pervious concrete. Porousasphalt consists of an open graded coarse aggregate held together by asphalt with sufficientinterconnected voids to provide a high rate of permeability. Pervious concrete is a discon-tinuous mixture of Portland cement, coarse aggregate, admixtures, and water which allow forpassage of runoff and air. Both types of pervious pavements omit most or all of the fineaggregate typically used in conventional pavements.


• Percolation of rainfall and runoff through the pavement into the underlying aggregatestorage reservoir and ultimately into the soil.

Advantages

• Reduces site imperviousness thereby reducing stormwater volume and peak dis-charge rate.

• Generally, ground water recharge rates are slightly higher under pervious pavementthan under natural conditions because vegetation is absent thereby reducing transpi-ration of soil water.

• Overall construction costs may be reduced because of the reduction or elimination ofstorm sewers, inlets, and traditional stormwater practices such as detention or reten-tion areas.

• Pervious pavements reduce hydroplaning and skidding by up to 15%.• Water puddles less on pervious pavement since it moves rapidly into the underlying

aggregate reservoir. Besides allowing people to walk through parking lots withoutgetting their feet wet, this also reduces headlight reflection off the surface and makespavement markings more visible.

Disadvantages

• The major disadvantage is the tendency for pervious pavement to clog. This canoccur as a result of improper batching, placement, finishing, and, most commonly, lackof maintenance. Once clogged, it is very difficult and expensive to rehabilitate, oftenrequiring complete replacement.


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• Another concern related to failure of pervious pavements is the lack of experiencemany pavement engineers and contractors have with these pavements. Proper de-sign, batching, pouring, and finishing are essential to the successful use of perviouspavements. Both porous asphalt and pervious concrete require a very high level ofworkmanship and special procedures to assure that they retain their porous qualities.

• Spills of gasoline or other potentially hazardous materials can lead to soil or groundwater contamination and may break down the asphalt binder to greater depths than inconventional pavements. Spills must be immediately vacuumed, followed by a jetwashing.

• In areas with long duration rainfalls, such as the Pacific Northwest, anaerobic condi-tions may develop in the underlying soils since the soils are unable to dry out betweenstorms. This can prevent aerobic bacteria from reducing organic pollutants. Addition-ally, the wet subgrade soils may not support the design load.


Operation

Successful operation depends on maintaining the permeability of the pavement surface.This begins with proper design and construction and is assured over time by proper main-tenance.

Improper batching at Florida Dept. of Environmental Protection parking lotnecessitated replacement of pervious concrete section.


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Maintenance

Activities necessary to maintain the performance of pervious pavements include:

• "Good housekeeping" practices by the users to minimize the production and trans-port of particulates onto the pervious pavement. This includes vegetative stabili-zation of adjacent areas which may erode and become a source of sediments.

• Routine maintenance to remove debris that is too coarse to be washed through thepavement.

• Regular vacuuming with avacuum street sweeper to re-move particulates that are fineenough to be carried into thepavement but too large to passthrough, thereby causing clog-ging of the void spaces. Thefrequency of vacuuming willdepend on factors such as theamount and type of traffic, andthe sources and loadings ofparticulates.

• High pressure jet hosing on anannual basis to "deep clean"the voids and help restore per-meability.

Management

• All pervious pavements shouldbe inspected several times inthe first few months after con-struction to assure that they areworking correctly and to makesure that they were installedproperly. Inspections should beconducted after storms tocheck for surface ponding that may indicate local or widespread clogging. Addi-tionally, the pavement should be checked for the first six months for raveling (dis-lodging of surface aggregate) or severe rutting.

• The surface should be visually inspected on a routine basis, especially after aprolonged storm event, for evidence of debris, ponding of water, oil dripping accu-mulations, clogging of pores, and other damage. Debris should be removed peri-odically to minimize accumulations. If ponding or clogging is noticed, then a main-

Pressure cleaning the FDEPpervious parking lot.


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tenance program needs to be implemented. First, a vacuum street sweeper shouldbe used. If ponding continues to persist, steam cleaning with a biodegradablecleaner should be performed, followed by vacuumsweeping.

• If pervious pavement continues to clog after vacuuming and steam cleaning, reha-bilitation or replacement of a section or all of the pavement may be needed. Cloggedpervious concrete pavements have been successfully restored by drilling holes,0.25 inch in diameter on one foot centers. Clogged porous asphalt sections havebeen similarly restored. If clogging continues, sections of pervious concrete canbe saw cut and removed. Six to twelve inches of subbase should be replaced withclean, coarse sand or crushed stone, then proof-rolled, followed by a new layer ofpervious concrete.


1. Only designers, engineers, and contractors experienced in the placement of perviouspavements should be used. Otherwise, the services of an experienced consultant shouldbe obtained.

2. Proper design is essential. The following steps should be taken to ensure proper design:

• Determine the suitability of the site for the use of pervious pavement. Examine thesoils, slopes, and projected use of the site including the expected traffic intensity.

• Sample and test the site's soils to determine their permeability and load carrying capac-ity. If permeability is marginal, ways to augment percolation (such as perforatedunderdrains) should be evaluated. Since pervious pavements distribute the loadsover a large area, uniformity of subgrade support, rather than strength, is the majorcriteria of a suitable subgrade. The presence of silts and clays that are highly com-pressible, lack cohesion, or expand when wet can create problems. These soil condi-tions must be analyzed individually for their support values and modified or replacedwhen necessary.

• In frost penetrates deeper than the thickness of the pavement and reservoir courses,and the subgrade soil has the potential for frost heaving, additional thickness must beadded to the reservoir base course to extend it below the frost line to allow for ad-equate drainage.

• Use specifications such as those of the Franklin Asphalt Research Laboratories orfound in the Portland Cement Pervious Pavement Manual to determine the appropri-ate thickness of the pervious pavement system, including its pavement course, filtercourse, and reservoir course. The thickness of the reservoir course will also dependon the desired storage volume.

• Prepare specifications for materials, product installation, testing, and maintenance.Consult literature from the Franklin Asphalt Research Laboratories or the PortlandCement Pervious Pavement Manual for example specifications.


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• To preclude premature clogging and/or failure of pervious pavements, they should notbe placed into service until the entire contributing surface drainage area has beencompletely stabilized.

• Clearly mark the planned area for per-vious pavement to prevent heavy equip-ment from compacting the underlyingsoils.

• Install diversions to keep runoff off thearea until the pervious pavement is inplace.

• Excavate the subgrade soil using equip-ment with tracks or oversized tires tominimize compaction.

• Once excavation is complete, the bot-tom and sides of the stone reservoirshould be lined with an appropriategeotextile filter fabric to prevent upwardpiping of underlying soils. Be sure thefabric is placed flush with at least a 2feet overlap between rolls. Note thatthe filter fabric is not used for perviousconcrete pavements.

• Clean, washed stone aggregate shouldbe placed in lifts and lightly compactedwith plate compactors.

• Porous Asphalt Surface Course - Before placement, be sure that the asphalt mix meetsthe desired specifications. Lay the asphalt in one lift directly over the aggregate basecourse but only when the air temperature is above 50o F and the laying temperature isbetween 230o and 260o F. Roll the asphalt when it is cool enough to withstand a ten-ton roller. One or two passes by the roller normally provides proper compaction.More rolling could cause reduction in the surface course porosity. After final rolling, alltraffic should be kept off the porous asphalt area for at least one day to allow properhardening.

• Pervious Portland Cement - Carefully follow the specifications and guidance set forthin the Portland Cement Pervious Pavement Manual. Before accepting the load, besure that it meets the desired specifications. To assure proper operation, it is crucialthat (1) the total water content in the mixture be within the desired narrow range; (2)the mixture is held within the truck for no more than 45 to 60 minutes depending on air

Unstabilized sides nextto pervious concrete


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temperature; (3) the mixture is visually inspected before placement to assure that theproper water-cement paste is uniform in consistency and adequately coating the ag-gregate surface; (4) the mixture should be discharged from the truck as rapidly andcontinuously as possible, and distributed on the prepared moist subgrade as evenlyas possible; (5) spreading, strike-off, and compaction should be performed as quicklyas possible; (6) a vibrating screed should be used to strike-off the mixture, with aninch of material along the base of the screed to provide uniform compaction; (7) com-paction, using a small plate vibrating or roller compactor on top of 3/4" plywood,should be done within 20 minutes after strike-off to minimize the potential for raveling;(8) moist curing is started within 20 minutes after placement. The concrete should besprayed with a light mist of water so as not to wash the cement paste off the aggre-gate. It is then covered with plastic sheets for 3 to 7 days.

• Be sure that the adjacent areas and all of the contributing drainage area is completelystabilized to minimize the generation of sediments that can enter the pervious pave-ment.

• Post signs to alert users that the area has pervious pavement and that vehicles withmuddy tires should not enter.

• Although snow and ice tends to melt more quickly on pervious pavement, it may still benecessary to apply deicing compounds. Do not use sand or ash because they maycause clogging of the pavement. Remember the potential for ground water pollution.


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ModularPavement

Description

Pavement consisting of strong structuralmaterials having regularly interspersedvoid areas which are filled with perviousmaterials such as sand, gravel, or sod. Generally used in low-volume traffic areas such asthe outer parts of a parking lots or in parking lots serving parks or recreational areas. Modu-lar pavement systems vary considerably in configuration. Categories include:

1. Poured-in-place Concrete Slabs - Steel reinforced concrete slabs covering largeareas are poured in place with void areas in between. Suitable for heavy loadsand has maximum resistance to movement caused by frost heave or settling.

2. Precast Concrete Grids - Concrete paving units incorporating void areas. Typesinclude lattice pavers, which generally are flat and grid-like in surface configura-tions, and castellated pavers, which show a higher percentage of grass surfaceand have a more complex surface configuration characterized by crenels andmerlons that are exposed when pervious materials are added.

3. Modular Unit Pavers - Small pavers in various shapes which may be clay bricks,granite sets, cast concrete, or even pervious concrete. These pavers are mono-lithic units which do not have void areas but provide pervious void spaces in thegaps between them.

4. GeoWeb - A geotextile material which is installed as a framework to provide struc-tural strength, then filled with sand, and sodded to provide a completely grassedparking area.


• Percolation of rainfall and runoff through the voids into the underlying permeablebase and then into the soil.

• Filtration of rainfall and runoff by the vegetation that can grow in the voids.

Advantages

• Reduces site imperviousness thereby reducing stormwater volume and peak dischargerate.

• Modular pavements reduce hydroplaning and skidding by up to 15%.• Water puddles less on modular pavement since it moves rapidly into the underlying

permeable base and soils.


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Disadvantages

• The major disadvantage is the tendency for modular pavement void spaces to clog,especially if not vegetated. Proper maintenance is essential to ensure long termperformance.

• Modular pavement may cost up to twice as much as conventional pavements. Someof the additional cost can be recovered by the decreased need for stormwater pipes,etc.

• Spills of gasoline or other potentially hazardous materials can lead to soil or groundwater contamination. Spills must be immediately vacuumed up with possible removaland replacement of underlying soils.

• In areas with long duration rainfalls, such as the Pacific Northwest, anaerobic condi-tions may develop in the underlying soils since the soils are unable to dry out betweenstorms. This can prevent aerobic bacteria from reducing organic pollutants. Addition-ally, the wet subgrade soils may not support the design load.

• Can present a safety hazard to some users (i.e. women in high heeled shoes.


Operation

Successful operation depends on maintaining the percolation rate of the void spaces andthe underlying base and soils. Keys to assuring long term performance are accurateestimation of the soil's percolation rate, proper construction, and regular maintenance.

Maintenance

Activities necessary to maintain the performance of modular pavements include:

• "Good housekeeping" practices by the users to minimize the production and trans-port of particulates onto the modular pavement. This includes vegetative stabiliza-tion of adjacent areas which may erode and become a source of sediments.

• Replacement of base and underlying soils if they become clogged and waterponding persists.

• When turf is incorporated into the installation, normal turf maintenance, will benecessary. However, mowing is seldom required in areas of frequent traffic andfertilizers and pesticides should be used sparingly since they may adversely affectconcrete products and ground water.

Management

All modular pavements should be inspected several times in the first few months afterconstruction to assure that they are working correctly and were installed properly. Inspec-tions should be conducted after storms to check for long duration surface ponding thatmay indicate local or widespread clogging.


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1. As with all infiltration practices, accurate estimation of the soil's percolation rate is essen-tial.

2. Be sure turf block parking is appropriate for the setting and the primary users.


• Install all modular pavements following manufacturer's specifications. The require-ment for skilled labor for laying modular pavement may be reduced if mechanicalvibrators are used for levelling uneven surfaces.

• To preclude premature clogging and/or failure, modular pavements should not be placedinto service until the entire contributing surface drainage area has been completelystabilized.

• Clearly mark the planned area for modular pavement to prevent heavy equipmentfrom compacting the underlying soils.

• Install diversions to keep runoff off the area until the modular pavement is in place.

• Excavate the subgrade soil using equipment with tracks or oversized tires to minimizecompaction.

• Be sure that the adjacent areas and all of the contributing drainage area is completelystabilized to minimize the generation of sediments that can enter the modular pavement

• Although snow and ice tends to melt more quickly on modular pavement, it may still benecessary to apply deicing compounds. Do not use sand or ash because they maycause clogging of the pavement. Remember the potential for ground water pollution.

Geoweb fabric being installedand filled with sand before sod

is added to create grass parking.Turf block parking lotunder construction.


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Detention Practices

Description

A family of practices which "detain" runoff,typically from a design storm, and then dis-charge it, usually at the pre-developmentpeak discharge rate. Detention practices can be classified as dry detention, extended drydetention, or wet detention systems.

Purpose

Traditionally, detention practices, especially dry detention, have been used only for floodprotection. They detain runoff and then discharge it at a specified rate supposedly reducingthe potential for downstream flooding by delaying the arrival of runoff from upper parts of awatershed. More recently, detention system designs have been modified to also reducestormwater pollutants. For example, dry detention systems have been modified to extend thedetention time of runoff thereby increasing pollutant settling. Wet detention systems havebeen modified to increase residence time and flow path, and to include shallow littoral zonesin which wetland plants grow.


The primary "treatment" mechanism of all detention systems is settling or sedimentation.However, the pollutant removal mechanisms vary depending on the type of detention system.They will be discussed in the following BMP Fact sheets on dry detention, extended drydetention, and wet detention systems.


All detention systems are highly effective in reducing peak discharge rates. Depending ontheir design and their location within a watershed, they also may be effective in reducingdownstream channel erosion and downstream water elevations and flooding.

Stormwater treatment effectiveness depends on the type of detention system. In general,they can be ranked, from least to most effective, in their ability to remove stormwater pollut-ants: dry detention, extended dry detention, wet detention. Unlike dry detention systems,wet detention provides mechanisms that promote the removal of dissolved stormwater pollut-ants, not just particulate pollutants.

Since each type of detention system is so different, aspects of their use, operation,maintenance, and management will be discussed separately in the following sectionson dry detention, extended dry detention, and wet detention.


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Description

An area used to detain stormwaterfor a relatively short period of time toreduce downstream peak dischargerates. The area should go dry be-tween storms. This is the traditionaltype of detention system used in "drainage" programs for many years to help provide floodprotection.


Settling or sedimentation of larger, heavier particles is the primary mechanism. In somesystems, limited infiltration may occur.

Advantages

Since these systems are dry between storms, the land area can be used for low intensitysecondary uses such as recreation or sports.

Disadvantages

• Very poor stormwater treatment effectiveness.• Often considered unattractive nuisances by residents.• Poorly designed or maintained systems which do not go dry may become breeding

areas for mosquitoes.


Dry detention systems generally provide good attenuation of peak discharge rates. How-ever, their pollutant removal effectiveness generally is very low, depending on detention time,flow path, and frequency of sediment removal. Sedimentation of larger particles is the pri-mary treatment in dry detention systems. Therefore, the small particles, to which the majorityof stormwater pollutants such as metals adhere, are discharged downstream. The ranges ofexpected pollutant removal in dry detention systems are:

• Total Suspended Solids 20 to 60 percent • Total lead 20 to 60 percent• Total Phosphorus 10 to 30 percent • Total Zinc 10 to 50 percent• Total Nitrogen 10 to 20 percent • Total copper 10 to 40 percent• COD 20 to 40 percent • Bacteria 20 to 40 percent

Dry DetentionBasin


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Limitations on Use

• Need fairly porous soils to assure that the bottom stays dry between storms.• Not suitable in areas with high water tables or shallow depth to bedrock.• Not suitable on fill sites or steep slopes.


Operation

Successful operation depends on maintaining the storage volume, the discharge rate,and, in many cases, the system's infiltration capability.

Maintenance

Activities necessary to maintain the functioning of a dry detention system include:

• Frequent removal of accumulated solids, debris, and litter from the detention area,especially from the low flow channel. Sediments should be removed when they aredry and have cracked, separating from the bottom and vegetation.

• Removal of debris from the control device, especially if it has a small orifice.

• Mowing and removal of vegetation. The use of low growing, native grasses isrecommended to minimize mowing frequency and the need for irrigation and fertil-izers, which should only be used when absolutely necessary.

• Vegetative stabilization of eroding sides or bottom.


Inspect monthly and after large storms to assure proper discharge, prevention of soggybottoms, assure healthy vegetative growth, and to monitor accumulation of sediments.

Recommendations to Assure Proper Operation, Maintenance, and Management

1. Provide a system to allow stormwater to bypass the facility. This will allow maintenance tobe done faster, and during the rainy season if needed.

2. Design the dry detention system as an "off-line" facility.

3. The seasonal high water table and bedrock should be at least four feet beneath the bot-tom of the system to minimize the potential for ground water contamination and to assurethat the bottom is dry.

4. Use a sediment forebay at all inflow points to trap sediments and allow for easy removal.


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5. The length of the basin should be at least three times the width (preferably five times),with the basin narrow at the inlet and wide at the outlet.

6. Side slopes should be at least 3:1 for safety and ease of mowing, although 4:1 slopes areoptimal.

6. The basin floor should be flat with a 2% slope toward the outlet.

7. Have an area on-site to hold sediments that are removed from the dry detention system.The area should be capable of holding the sediments removed during a two year period.Sizing of the disposal area should be based on the estimated annual sediment load trapped.

8. Provide dedicated access to the forebay and to all parts of the dry detention system formaintenance equipment and vehicles.

9. Construction Recommendations:

• If the system will rely on infiltration to some extent, then follow the recommendationsfor construction of infiltration practices.

• Make sure the embankment and discharge structure are installed properly, at thecorrect elevations, and with proper compaction.

• Make sure that anti-seep collars are installed properly.

South Florida dry detention system integrated into the site's landscaping.


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Description

A dry detention system with a discharge structure which is modified to extend the detentiontime of runoff, typically up to 24 to 48 hours. The modified discharge may also include sometype of filtering device (i.e., gravel or sand envelope) to improve the removal of particulatepollutants.

Extended dry detention systems may be designed as either on-line or off-line facilities. Theyalso may be designed as either a single-stage or two-stage basin. Single-stage basins nor-mally are used only for flood control and are not recommended for stormwater treatment. Atwo-stage basin detains runoff from small, frequent storms and the "first flush" from largerstorms in a lower second stage, with a normally dry upper stage for detention of larger stormsfor flood control. To improve stormwater treatment the second stage can be designed andmanaged as a shallow marsh.


• Settling or sedimentation, especially of larger, heavier particles, is the primary mecha-nism.

• Plant uptake and bacterial activity in two-stage systems with a shallow marsh.• In some systems, limited infiltration may occur.

Advantages

Since many of these systems are dry between storms, the land area can be used for lowintensity secondary uses such as recreation or sports.

Disadvantages

• Relatively low stormwater treatment effectiveness• May be less reliable in treating stormwater pollutants than other BMPs• Primarily remove particulate pollutants with little removal of dissolved pollutants.• Shallow depth can significantly warm the detained water, making use inappropriate

when discharge is to temperature sensitive receiving waters, such as a trout stream.• Often considered unattractive nuisances by residents.• Poorly designed or maintained systems which do not go dry may become breeding

areas for mosquitoes.• Discharge structure may clog easily, especially if a filtration system is used.• Relatively frequent removal of accumulated sediments is needed to prevent resuspen-

sion and discharge and to maximize treatment effectiveness.

Extended Dry Detention Basin


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Extended dry detention systems generally provide good attenuation of peak discharge ratesbut do not reduce runoff volume. Pollutant removal effectiveness generally is low but can beimproved by design considerations such as making the system off-line, increasing the "treat-ment volume", and increasing the detention time. The ranges of expected pollutant removalin extended dry detention systems are:


Limitations on Use

• Require fairly porous soils to assure that the bottom stays dry between storms.• Not suitable in areas with high water tables or shallow depth to bedrock.• Not suitable on fill sites or steep slopes.• Requires elevation differential between inlet and outlet.• May not be suitable if receiving water is temperature sensitive, such as a trout stream.


Operation

Successful operation depends on maintaining the storage volume, the discharge rate,and, in many cases, the system's infiltration capability.

Maintenance

Activities necessary to maintain the functioning of an extended dry detention system in-clude:

• Frequent removal of accumulated solids, debris, and litter from the detention area,especially the low flow channel if included. Sediments should be removed whenthey are dry and have cracked, separating from the bottom and vegetation.

• Removal of debris from the control device since it typically will have a small orifice.

• Mowing and removal of vegetation. The use of low growing, native grasses isrecommended to minimize mowing frequency and the need for irrigation and fertil-izers, which should only be used when absolutely necessary.

• Vegetative stabilization of eroding sides or bottom.

• Management of aquatic plants if portions of the basin have been designed as aconstructed wetland.


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Inspect monthly and after large storms to assure proper discharge, prevention of soggybottoms, assure healthy vegetative growth, and to monitor accumulation of sediments.


1. Include a system to allow stormwater to bypass the facility. This will allow maintenance tobe done faster, and during the rainy season if needed.

2. Design the extended dry detention system as an "off-line" facility.

3. The seasonal high water table and bedrock should be at least four feet beneath the bot-tom of the system to minimize the potential for ground water contamination and to assurethat the bottom stays dry.

4. Use a sediment forebay at all inflow points to trap sediments and allow for easy removal.

5. The length of the basin should be at least three times the width (preferably five times),with the basin narrow at the inlet and wide at the outlet.

6. Side slopes should be at least 3:1 for safety and ease of mowing, although 4:1 slopes areoptimal.

7. The basin floor should be flat with a 2% slope toward the outlet.

8. The discharge structure should incorporate mechanisms to promote filtering of stormwa-ter pollutants but minimize the potential for clogging. Experience in Austin (TX), Denver(CO), Washington, and Florida has found that a perforated riser pipe, wrapped in filterfabric and surrounded by gravel (1" to 3" stone), can greatly reduce the potential fororifice clogging. This design also increases the treatment effectiveness.

9. Have an area on-site to hold sediments that are removed. The area should be capable ofholding the sediments removed during a two year period. Sizing of the disposal areashould be based on the estimated annual sediment load trapped.

10.Provide dedicated access to the forebay and to all parts of the extended dry detentionsystem for maintenance equipment and vehicles.

11. Construction Recommendations:

• If the system will rely on infiltration to some extent, then follow the recommendationsfor construction of infiltration practices.

• Make sure the embankment and discharge structure are installed properly, at the cor-rect elevations, and with proper compaction.

• Make sure that anti-seep collars are installed properly.


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Description

A detention system with a permanent pool of water which is completely or partially displacedby stormwater from the contributing drainage area. Water is temporarily stored before graduallydischarging it, typically at the predevelopment peak discharge rate. A wet detention systemis essentially a small lake with rooted wetland vegetation in the littoral zone.


• Settling or sedimentation.• Chemical flocculation which occurs when heavier sediment particles overtake and

coalesce with smaller, lighter particles to form still larger particles.• Dissolved stormwater pollutants are reduced by a variety of biological processes in-

cluding filtering, adsorption onto bottom sediments, uptake by aquatic plants includingalgae, and metabolism by microorganisms inhabiting bottom sediments and aquaticplants.

••••• Removal of stormwater pollutants primarily occurs during the relatively longquiescent period between storms.

Advantages

• Relatively high level of flood control and stormwater treatment.• Can be used in areas with a high water table or poorly drained or percolating soils.• Excellent multiuse BMP which can provide ancillary benefits such as habitat, recre-

ational opportunities, high value aesthetics associated with "lake front" property, andserving as a source of fill dirt often needed in areas with high water tables or flattopography.

• Relatively low maintenance requirements.• Can be used as sediment trap or basin during construction phase of a project.

Disadvantages

• May provide limited flood storage in areas with high water tables.• Safety and aesthetic problems if the pond, especially the littoral zone and discharge

structure, is not maintained properly.• Fairly land intensive, often two to five percent of contributing area.• Wet season may not be coincident with plant growing season.• May be regulated as a "wetland".• May be an attractant for children creating potential safety and liability issues.• May become fecal and nutrient source because of attracted waterfowl.

Wet Detention Pond


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Wet detention systems provide very good flood control and stormwater treatment benefits.Only infiltration practices provide better management of stormwater quantity and quality. Thepermanent pool and wetland vegetation provide for a variety of pollutant removal mecha-nisms which are highly effective in removing both particulate and dissolved stormwater con-stituents. Treatment effectiveness of wet detention systems depends on a number of designfactors including the storage volume, detention time, permanent pool volume, volume ratio,depth of permanent pool, elevation of control structure in relation to seasonal high watertable elevation, pond geometry, size and location of littoral zone, type and density of littoralzone plants, and use of the "BMP Treatment Train" to incorporate pretreatment devices suchas sediment forebays and swale conveyances. The ranges of expected pollutant removal inwet detention systems are:


Limitations on Use

• Not suitable on fill sites or near steep slopes.• May need supplemental water supply to maintain permanent pool if not dug into the

ground water.• Minimum contributing drainage area of 8 to 10 acres is needed to maintain the perma-

nent pool.• Infeasible in very dense urban areas or areas with high land costs.• May not be suitable if receiving water is temperature sensitive, such as a trout stream.


Operation

Successful operation depends on good design, construction, and maintenance, espe-cially of the discharge structure and littoral zone vegetation.

Maintenance

Activities necessary to maintain the functioning of wet detention system can be brokendown into two categories: Routine and Corrective.

Specific routine maintenance activities include:

• Grass mowing and removal from side slopes and the embankment.• Removal of trees, brush, and animal burrows from the embankment.• Vegetative cover stabilization to prevent erosion of side slopes and the embankment.• Removal and disposal of trash and debris, especially from inlet or outlet structures.


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• Monitoring and periodic removal of nuisance species in the littoral zone.• Thinning and transplanting of thriving littoral zone plants as needed to maintain

good growth throughout the littoral zone.• Monitoring for mosquitoes and introduction of Gambusia or other natural predators

as needed.• Monitoring of sediment accumulations in forebays or in the pond bottom.• Monitoring of channel erosion in downstream conveyances.

Specific corrective maintenance activities include:

• Pond dewatering and removal of accumulated sediments. The frequency will de-pend on a variety of factors including use of pretreatment BMPs or forebays, con-tributing drainage area, land use, sediment loading, etc. Yousef et. al. (1992) deter-mined that the typical wet detention system in Florida needed sediment removalevery 10 to 15 years. A good rule of thumb is to remove sediments when 10 to 20%of the system's storage volume has been lost.

• Structural repairs to inlets, outlets, or discharge structure, including the emergencyspillway.

• Repairs to the dam, embankment, or slopes to prevent erosion or piping.• Repairs to fences, if applicable.


• Inspect monthly and after large storms to assure proper discharge, monitor accumula-tions of trash and debris, monitor sediment accumulations in forebays or inlets, deter-mine mowing or vegetation removal needs, and determine health of littoral zone veg-etation.

• Monitor pond sediment accumulations annually. This can be done by coring, installa-tion of a permanent measuring device such as a "yardstick", or even by mapping thepond bathymetry in larger ponds.


1. The design should include a bottom bleeddown device, and preferably a system thatallows stormwater to bypass the facility. This will allow easy pond dewatering and facili-tate maintenance.

2. Use the "BMP Treatment Train" concept such as swale conveyances and sediment fore-bays, especially if the wet pond is going to be promoted as an aesthetic amenity for thedevelopment.

3. To maximize removal of dissolved pollutants, pool storage hydraulic residence time shouldbe at least 2-3 weeks. This generally means that the pond will consume 3-7 percent ofthe contribution drainage area depending on factors such as impervious area, rainfallcharacteristics, water table elevation, etc.


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4. The system should include shallow areas (less than 3 feet deep) and deep areas (morethan 8 feet). The shallow areas should be used for the littoral zone which provide habitatfor aquatic wetland vegetation and serves as a shallow bench along the shore, helping tominimize the potential for drowning. Deep areas should make up 25-50 percent of thepond and be located near inflow points. The maximum depth should be limited to a levelthat minimizes the risk of thermal stratification. This helps to reduce short circuiting,maintain aerobic bottom waters and sediments, and minimize the potential for groundwater contamination.

5. The littoral zone should cover at least 30% of the pond's surface area and slope gently(6:1 or flatter) to a depth two feet below the control elevation. Ideally, the littoral zone andits emergent wetland vegetation should extend around the entire perimeter of the pondwith an expanded littoral zone at the outlet area. A wide variety of native plants, espe-cially those with attractive flowers, should be used as part of the "aquascaping" of thesystem, helping to increase aesthetics. Unfortunately, experience has shown that manyresidents will remove the beneficial aquatic plants adjacent to their lots because of con-cerns about snakes and other "swamp critters". This has led to the practice of concentrat-ing the littoral zone near inflows and at the outlet. A better alternative is to educateresidents about the values - environmental, safety, and aesthetics - of the littoral zoneplants.

6. Pond geometry has a very strong influence on the effectiveness of wet detention systems.Little or no pollutant removal occurs in dead storage areas where the inflow is bypassedwithout mixing. To avoid this problem, the effective length to width ratio should be at least3:1 and preferably 5:1. Additionally, the locations of inflows and the discharge structureshould minimize short circuiting and maximize the flow path.

7. Better performance can be expected by enlarging the surface area to gain volume asopposed to deepening the pond.

8. Proper design, construction, and maintenance of the discharge structure and the dam orembankment is critical, especially to minimize potential downstream damage from struc-tural failure. In particular, the designer should:

• Avoid potential piping of water along the outside of the outlet conduits by using drain-age seepage diaphragms, or by careful material selection and good compaction aroundthe conduit.

• Minimize the number of conduits through the embankment.• Ensure against leaky joints within the embankment.• Not use thin-walled conduit through the embankment without a protective exterior

encasement.• Provide a safety factor in outlet structure openings to account for debris collection.

Spillway and discharge structure entrances are natural locations for debris buildup.

9. Provide access to all parts of the system for equipment needed to conduct maintenance.The maintenance right-of-way should be at least 20 feet wide, as should any fence gates.


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Failure to properly construct the wet detention system, especially the embankment (dam)and discharge structure, can lead to failure possibly resulting in downstream flooding, prop-erty damage, and even personal injury. Experience has shown that problems in constructingwet detention systems primarily are associated with the following:

A. Contractor error

• Construction sequence or plans are not followed.• Concrete placement doesn't seal riser bottom.• Pipes are improperly placed or damaged while installed.• Separation of joints due to uneven settlement.• Connections are not water tight.

B. Improper use of soil materials.

• Overly pervious materials are used around pipes or in the dam resulting in pipingor failure.

• Top soil not spread or spread too thinly resulting in poor vegetative cover anderosion.

C. Principal spillway materials are not water tight.

• Connecting bands and gaskets are from different manufacturers or are too narrow.• Improper pipe placement - uneven grades, settlement, or poor alignment.• Water movement through connections from saturated zone.

D. Availability of specified materials.

• Rip rap sizes are unavailable.• Materials not present when needed to insure timely construction during critical

periods.


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To avoid the problems described above it is important to follow the construction sequence,especially if the wet detention system is used as a sediment basin during construction. Apotential construction sequence is:

1. Pre-construction meeting• Stress importance of proper construction sequencing and implementation.• Determine project phasing, especially of structures.

2. Install erosion and sediment controls.3. Clear and grub site.4. Strip and stock pile top soil5. Excavate and backfill the core trench.6. Install the principal spillway - pay special attention to compaction and installation of

anti-seep devices.7. Construct the dam and emergency spillway.8. Excavate pond.9. Spread top soil.10. Vegetatively stabilize all areas.11. If the wet detention system was used as a sediment basin, remove accumulated

sediments to restore required storage volume.12. Plant the littoral zone.

Wet detention pond at the Fl. Dept. of Environmental Protection office in Tallahassee.


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BiofiltrationPractices

Description

Biofiltration is a term used to describe the gener-ally simultaneous processes of filtration, infiltra-tion, adsorption, ion exchange, and biologicaluptake of pollutants from runoff as it flows througha vegetated stormwater management system.Biofiltration practices include vegetated swales,filter strips, and bioretention areas. Swales areconveyances where the flow passes through veg-etation at some specified depth. Filter strips arebroad surfaces which receive flow as a well dis-tributed thin sheet. Bioretention practices cap-ture sheet flow from impervious surfaces andtreats it by infiltration, filtration, plant uptake, and microbial processes as the runoff flowsthrough native forest or landscaped areas.

Purpose

Biofiltration practices are used primarily to reduce stormwater pollutants through natural veg-etative processes, but they can also reduce stormwater volume if infiltration occurs.


• Infiltration, ion exchange, and adsorption• Settling• Vegetative filtration and uptake• Microbial action• The degree to which the various pollutant removal mechanisms operate depends on

soil properties, condition and types of plants, depth, water velocity, slope, and resi-dence time.

Advantages

• Can be incorporated into a site's landscaping and open space areas.• Very effective at reducing oil, grease, and petroleum hydrocarbons.• Excellent use as part of the "BMP Treatment Train".• Can be aesthetically pleasing and enhance parking areas.


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Disadvantages

• Not useful by themselves for reducing stormwater quantity.• Successful operation depends mainly on proper construction and maintenance, which

requires effective inspection and enforcement efforts.• Except for swales, the treatment effectiveness of biofiltration practices is still largely

unknown.• Too little is known about the treatment benefits of various plant species to make

sound recommendations on the types of plants to use in biofiltration practices. Still,since filtering is the main function performed by the plants, the most important factor isa uniform, dense growth of fine grasses or herbaceous wetland plants.


Biofiltration practices, especially swales and filter strips, and bioretention practices generallyprovide minimum stormwater quantity benefits such as attenuation of peak discharge rates orrunoff volume. The extent of these benefits will depend largely on how much infiltration ofrunoff occurs.

Stormwater pollutant removal by biofiltration systems will vary depending on a wide variety ofdesign factors, especially the amount of infiltration and the hydraulic residence time. Ingeneral, biofiltration swales are very good at reducing particulate runoff pollutants such astotal suspended solids, turbidity, and the least soluble metals such as lead, iron, and zinc.Materials which adhere to grass surfaces, such as oil and grease and total petroleum hydro-carbons are also effectively removed. Removal of nutrients, especially nitrogen, and coliformsare often inconsistent, with best removals seen for bioavailable phosphorus. Some authori-ties believe that biofilters can achieve better nutrient reductions if vegetation is carefullymowed and removed before it dies and releases assimilated nutrients but this hypothesis isunproven. There is little information on the pollutant removal effectiveness of filter strips orbioretention areas.

The ranges of expected pollutant removal in biofiltration swales are:


Limitations on Use

• Can not be used where the contributing drainage area exceeds a few acres becauseof the excessive surface area needed to produce sufficient residence time. The maxi-mum drainage area depends on its specific characteristics (i.e., land use, % impervi-ousness, etc.).

• Should not be used for erosion and sediment control during construction nor wherethe post-development sediment loading will be high.

• Need fairly porous soils to promote infiltration.


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• Not suitable on steep slopes or where there is shallow depth to bedrock.• May be limited to areas where summer irrigation is feasible.• Generally not suitable in areas with high water tables, although "wet swales" with

wetland plants have worked well in Florida.


Operation

Successful operation depends on proper design, especially estimation of hydraulic resi-dence times and infiltration rates, proper construction and regular maintenance.

Maintenance

Activities necessary to maintain the functioning of biofiltration practices include:

• A key O&M need of biofilters is vegetation removal to maintain adequate hydraulicfunctioning. Biofilter turf grass height should not exceed 6 inches nor be less than2 inches. Excessively long grass can flatten when water flows over it, preventingsedimentation. Additionally, if not removed, decaying vegetation could releasecaptured nutrients and other pollutants.

• Frequent removal of accumulated solids, debris, and litter. Sediments should beremoved when they reach 20% of the design depth in any spot, cover or hinder thegrowth of vegetation, or otherwise interfere with operation. Maintenance workersshould give special attention to sediment accumulation in the upper portion ofswales after major storm events. Sediment and large debris should be removedfrom biofilters at least twice annually and more frequently, if needed.

• Vegetative stabilization of eroding sides or bottom, or of bare areas created whenremoving sediments. Fertilizer use should be minimized. Vegetation should bemaintained and replanted early enough in the growing season so that it is wellestablished before the rainy season or before the prime growing period ends.

• If swale blocks are used to promote infiltration or sedimentation, special attentionneeds to be paid to their maintenance. Sediments need to be carefully removedwithout damaging the swale block or its associated vegetation.

• If curb cuts are used as inflows to biofilters, sediments and vegetation growthsshould be removed from the curb cut when they begin to interfere with inflow.

• Roadside shoulder scraping and ditch cleaning should be based on hydraulic ne-cessity, not simply a timed schedule. When these operations are performed, onlythe amount of sediment to restore hydraulic capacity should be removed. Moreimportantly, the shoulder and swale should be revegetated immediately to mini-mize erosion and restore treatment effectiveness. Operations should be done inthe dry season.


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• Implement education programs for residents near biofiltration practices, such asresidents within subdivisions with swales, to teach them about their purpose, so-licit their help in maintenance, and minimize use of swales as debris or trash de-positories.


• Inspect semiannually and, when possible, after large storms to assure proper flow,vegetative growth, and to monitor accumulation of sediments, trash, and debris.

• Institutionally, a stormwater program which allows the use of biofiltration practicesmust have an inspection and enforcement program to assure that maintenanceoccurs. Public education programs also are highly recommended.


1. For dry systems, the seasonal high water table and bedrock should be at least four feetbeneath the bottom of the system to minimize the potential for ground water contamina-tion and to assure that the bottom is dry.

2. To provide proper flood control, biofilters must be combined with more traditional prac-tices such as detention. Biofilters can either be designed as on-line components of aBMP Treatment Train or as an off-line stormwater treatment component of the overallstormwater management system. Off-line systems are preferable because the detentionelement can meter flow into the biofilter up to the design storm intended to receive treat-ment and protect the biofilter from high flows.

3. The design of biofilters, especially swales and filter strips, will depend largely on therainfall, topographic, and land cover characteristics of the site. These will determine the"treatment volume" and greatly influence the location and use of biofilters, along withother design considerations such as their residence time. The specific length of a biofilterwill depend largely on the residence time and the associated length and width.

4. It is essential that flow through biofilter systems be uniform sheet flow (filter strips) or flowof minimal depth below the vegetation height (swales). This will maximize contact withthe vegetation and microbes which promote treatment. This requires a flat bottom tominimize any potential for channelized flow.

5. Use a flow-spreading device and/or energy dissipation device at the inlet to minimizeerosion and maximize uniform distribution of flow.

6. Maximum design velocity should not exceed 1.5 to 3.0 feet per second to prevent erosionand maximize treatment capability.

7. Slopes of biofilters should be between 2 and 4 percent. Underdrains may be needed ifslopes are less than 2 percent and a dry system is desired. Swale blocks should be usedwhen slopes exceed 4 percent.


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8. Water depth should be no greater than one half the height of the vegetation up to amaximum of 5 inches. Ideally, the water depth should not exceed 2 inches.

9. Biofilters should be situated along natural drainage routes and contours whenever fea-sible. Designers can reduce the risk of channelized flow and erosion by not forcing runoffto flow in unnatural directions.

10.Biofilter designers must investigate the climate and microclimate of the site in order tochoose optimal varieties of vegetation. Grasses are the superior choice of vegetationbecause they are resilient, provide abundant surface area, and can sprout through thindeposits of sand and sediment. Grasses that are stiffer, denser, and have greater leafsurface areas are preferable. If water tables are high, a "wet swale" should be designedusing appropriate wetland plants.

11. In regions that experience extended dry periods, selecting drought-tolerant plant speciesor constructing biofilters in locations where soils remain moist during dry periods canreduce irrigation needs.

12.Avoid heavy and prolonged shading of biofilters by adjusting placement relative to build-ings and trees.

13. Construction recommendations.

• Since most biofilters rely upon infiltration, follow construction recommendations for"Infiltration practices". The key is to minimize compaction of the soil and the resultingreduction of the infiltration rate of the soil.

• Do not place biofilters into operation until the contributing drainage area is completelystabilized.

• If possible, divert runoff during the period of vegetation establishment. If this is notpossible, sodding should be used whenever possible, especially if significant runoffcould occur before vegetation establishment. Other methods of minimizing erosion inflowing channels includes the use of "erosion mats" combined with seed.

Erosion matting is used toprevent erosion of biofiltrationswale during establishment of

its vegetative cover.


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ConstructedWetlands

Description

A runoff storage and treatment area con-structed in uplands which is vegetatedwith aquatic macrophyte plants nativeto the area. These systems attempt toincorporate properties of natural wet-lands such as shallow, sheet flowthrough dense, diverse assemblage ofwetland plants which also serve as habi-tat for microorganisms. There are nu-merous configurations for constructedwetlands. They range from shallowmarshes, to the littoral zones of wet de-tention systems, to a combination ex-tended detention and marsh system.

Purpose

Constructed wetlands are being used to remove stormwater pollutants through the naturalprocesses that occur within these ecosystems.


• Settling or sedimentation.• Adsorption to sediments, vegetation, or detritus• Filtration by plants.• Microbial uptake and/or transformations.• Uptake by wetland plants or algae.• Extended detention.• Removal of stormwater pollutants primarily occurs during the relatively long

quiescent period between storms.

Advantages

• Can be used in areas with high water table or poorly drained or percolating soils.• Can be used in areas with highly pervious soils if a liner is used to minimize infiltration.• Can remove dissolved pollutants.• Can be aesthetically pleasing and provide wildlife habitat.


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Disadvantages

• In many parts of the country, especially in the western states, wetland vegetation isdormant during the rainy season. However, since plant uptake is only a minor mecha-nism in removal of most pollutants, a standing crop of vegetation can still providefiltration and an area for surface removal processes.

• Provide limited flood storage and attenuation.• Shallow depth may significantly warm the detained water, making use inappropriate

when discharge is to temperature sensitive receiving waters, such as a trout stream.However, monitoring in Delaware shows that shallow, well vegetated systems havewater temperatures much lower than unvegetated systems.

• Fairly land intensive.• Possible mosquito problems associated with dense, emergent wetland vegetation.• May be regulated as a "wetland" unless continuously operated and maintained as a

treatment system.• Can become either a nutrient or fecal "source", depending on wildlife use and popula-

tions and vegetation management.


Constructed wetlands are used primarily to remove pollutants from runoff and typically arenot used by themselves to attenuate stormwater peak discharge rates or volumes. Con-structed wetlands should still be considered an experimental stormwater treatment BMP astoo little is known about their long-term treatment effectiveness or maintenance requirements.They have been used in numerous locations around the country with varying success. Treat-ment effectiveness will depend on a number of design considerations including the treatmentvolume, surface area to volume ratio, length and type of flow path, plant types and densities,plant growing season in relation to rainy season, deep water pools, and use of the BMPTreatment Train by incorporating pretreatment devices such as sediment forebays and swaleconveyances. The ranges of expected pollutant removal of constructed wetland systems are(median values for the relatively soluble pollutants like phosphorus, nitrogen, copper, andzinc are likely to be in the lower part of these ranges) :

•Total Suspended Solids 60 to 90 percent •Total lead 50 to 90 percent •Total Phosphorus 30 to 85 percent •Total Zinc 30 to 90 percent •Total Nitrogen 30 to 80 percent •Total copper 20 to 80 percent •COD 10 to 50 percent •Bacteria 20 to 80 percent

Limitations on Use• Not suitable on fill sites or near steep slopes.• May need supplemental water supply to maintain base flow if not dug into the ground

water.• Unless excavated into the water table, the minimum contributing drainage area needed

to maintain base flow will need to be determined. This will vary depending on rainfalland watershed characteristics.

• Overgrowth of aquatic plants can lead to reduced hydraulic capacity.• Infeasible in very dense urban areas or areas with high land costs.


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Operation

Successful operation depends on good design, construction, and maintenance, espe-cially of the sediment forebays, wetland vegetation, and the discharge structure.

Maintenance

Activities necessary to maintain the long term functioning of a constructed wetland sys-tem are still relatively unknown. As a minimum, the following actions will be needed:

• Grass mowing and removal from side slopes and the embankment.

• Removal of trees, brush, and animal burrows from the embankment.

• Vegetative cover stabilization to prevent erosion of side slopes and the embank-ment.

• Removal and disposal of trash and debris, especially from inlet or outlet structures.

• Monitoring and periodic removal of nuisance plant and animal species as specifiedin a written procedure prepared by a wetland scientist.

• Thinning and transplanting of thriving wetland plants as needed to maintain goodgrowth throughout the constructed wetland. Again, this should be done in accor-dance with a written procedure prepared by a wetland plant scientist.

• Monitoring for mosquitoes and introduction of Gambusia or other natural predatorsas needed.

• Monitoring and removal of sediment accumulations in forebays or within the con-structed wetland.


• Inspect quarterly and after large storms to assure proper discharge, monitor accu-mulations of trash and debris, monitor sediment accumulations in forebays or in-lets, determine mowing or vegetation removal needs, and determine health of wet-land vegetation.

• Closely monitor the wetland plant community, both during the growing season and,if needed, during the dry season, to assure healthy growth of desired plants. Re-move exotic or nuisance species as soon as they appear to limit their establish-ment and areal extent. Thin or transplant plants from areas where they are grow-ing densely and use them to further establishment or growth in areas with lessvigorous plant growth.


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• Monitor sediment accumulations in forebays semiannually. Sediments should beremoved when 25% of the storage volume of the forebay has been lost.


1. The design should include a bottom bleeddown device, and preferably a system thatallows stormwater to bypass the facility. This will allow easy dewatering of the wetlandand facilitate maintenance.

2. Use the "BMP Treatment Train" concept such as swale conveyances and sediment fore-bays to minimize sedimentation in the wetland. There are several rules of thumb forsizing and designing the sediment forebay. These should be reviewed and those whichare relevant to the conditions at the site should be followed. For example, Delaware'sstormwater program requires the forebay to be sized to hold 10% of the total basin vol-ume with a maximum depth of four feet.

3. Follow locally applicable design guidelines which take into account local rainfall condi-tions, hydrology, and plant characteristics. Specific design guidelines for constructedstormwater wetlands have been developed by several state stormwater management pro-grams including Maryland, Delaware, Florida, California, and Puget Sound. These de-sign guidelines can be used as a starting point for the development of state, regional, orlocally specific guidelines. It is important to keep the design simple and buildable withoutextensive supervision. Since the highest level of functioning for stormwater managementrequires some degree of structural complexity, however, designers and botanists shouldplan to be in the field to interpret the plans for construction staff.

4. Minimize short circuiting by maximizing the distance from the inlet to the outlet with aminimum length to width ratio of 3:1, preferably 5:1. Baffles, islands, and peninsulas canbe used to increase the flow path.

5. The designer needs a good understanding of the local hydrology at the site proposed fora constructed wetland. The ground water table should be at or near the surface, or soil oflow permeability should underlay the site. If excessive seepage is a concern, imperviousliners can be used. Liners can be geotextiles or 4 to 6 inches of silt loam, clay loam, ororganic muck. Experience has shown that most soils in Hydrologic Soil Groups B, C, andD will eventually seal themselves.

6. Soils must be suitable for wetland plant growth and for adsorption, especially if high re-moval levels of phosphorus or many metals are desired. Neutral soil pH (6 to 8) is best forsupporting microorganisms, insects, and other aquatic animals, and is also best for se-questering pollutants in the sediments. Soils with fairly high levels of aluminum or ironare best for adsorption. Medium to fine textured soils, such as loams and silt loams, areoptimal for establishing plants and capturing pollutants. A relatively high content of highlydecomposed organics ("muck") is favorable for plant and microorganism growth and theadsorption of metals and other organic pollutants.

7. Selection of the plants needs to be done by a wetland scientist. The selection will be


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based on climate, hydroperiod of the wetland, sensitivity to pollution, and aesthetic ap-peal. A well planned wetland will include a diverse mixture of floating, emergent, andsubmergent plants. The following guidelines for selection of wetland plants are offered:

• Base selections more on the prospects for successful establishment than on specificpollutant uptake capabilities. Plant uptake is a significant mechanism only for nutri-ents, which may be released upon the plants' death. Chemical and microbial pro-cesses remove more nutrients than plant uptake.

• Match the environmental requirements of plant selections to the conditions to be of-fered by the site. Consider especially the hydroperiod, light requirements, climate,sensitivity to probable pollutants, and aesthetic appeal. Also consider effects fromwind, waves, and water currents.

• Select species that are adapted to the broadest possible ranges of depth, frequency,and duration of inundation (hydroperiod). Careful selection is especially importantwhen runoff quantity control is an objective because water depths will be periodicallygreater than those that normally occur in natural wetlands.

• Select native species to ease establishment and minimize maintenance. Includesome plants that are strong colonizers but avoid exotic species and those native spe-cies that are aggressive invaders which crowd out more desirable species.

• Use a minimal number of species for each depth zone. Diversification will occur natu-rally. One planting recommendations is to use three species per depth zone.

• Select mostly perennial species.

• The establishment of herbaceous plants should precede that of woody species.

• Give priority to species that have been used successfully in constructed wetlands in thepast and to species that are commercially available. Use of plants propagated at wetlandplant nurseries will minimize pressure to remove plants from natural wetlands.

7. Experience has shown that wetland plants typically will establish themselves naturally in shal-low wet ponds, regardless of soil conditions. However, it has become increasingly clear thatplant communities develop best when soils harbor substantial vegetative roots, rhizomes, andseed banks. Hydric soils containing vegetative plant material are known as "wetland mulch."Use of this mulch greatly enhances plant community diversity and speeds establishment.However, the content of the mulch is unpredictable and donor sites are limited. A risk of usingwetland mulch is the possible presence of exotic, opportunistic species that will displace moredesirable natives. Therefore, use of mulch likely to harbor such species should be avoided.Potential sources of wetland soils include (a) spoils from maintenance of highway ditches,swales, and stormwater ponds; (b) spoils from dredging; and, (c) soils removed from naturalwetlands that are going to be filled under permit (although these soils are best used for miti-gating the loss). It is recommended that the upper 6 inches of donor soils be obtained at theend of the growing season, if possible.


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8. While wetland plants will establish themselves naturally in shallow wet ponds, experiencehas shown that constructed wetlands are best established by planting. This helps tominimize colonization by undesirable invader species. It is recommended that at leasthalf of the marsh area be planted at a constant density. The design guidelines for con-structed wetlands prepared by the state stormwater programs listed above can provide ageneral introduction to planting densities and strategies. Planting of wetland vegetationin stormwater systems, whether a constructed wetland or the littoral zone of a wet deten-tion system, can provide an excellent public education opportunity, especially for schoolchildren.

9. Construction recommendations

• Involve a wetland plant specialist in the system's design and construction.

• Implement good erosion and sediment controls to minimize sediment loading deliv-ered to the constructed wetland. If necessary, divert flows to a sediment basin or otherstormwater system during the construction phase until the contributing drainage areais stabilized.

• Schedule construction so that wetland plants can be planted during the growing sea-son, preferably the beginning of it.

• The landscaping plan should be finalized after the wetland has been constructed toconfirm soil, moisture, and inundation conditions.

• Order wetland plants from the nursery three to six months before the time planned forinstallation to ensure they will be available.

• Install control structures and embankment following wet detention guidelines.

• Grade the wetland to an interim elevation slightly deeper than desired final elevation.

• Add a 3 to 6 inch layer of soil amendments or wetland mulch, and spread out over theentire wetland area.

• Stabilize side slopes and allow the wetland to fill until the desired planting time.

• Once wetland plants are delivered to the site, be sure that they are frequently wateredand well-shaded to minimize plant loss.

• If necessary, drain the wetland to a depth that facilitates planting (3 to 12 inches).

• Remove plants from their containers and loosen up their root/soil ball before planting.

• A supplemental planting should be scheduled, typically at the beginning of the secondgrowing season, to reinforce plant establishment and obtain the desired plant cover-age and density.


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StormwaterFilters

Description

A family of stormwater treatment practices which typically consist of a storage BMP in con-junction with a filtering device. The most common filter media is sand, but filters have beenmade of peat/sand mixtures and even from leaf compost. Filters can be categorized aseither "unconfined" or "confined" systems. A side bank underdrain filter within a wet deten-tion system is an example of an unconfined filter - the sand/gravel filter media and underdrainpipes are built into the side banks of the wet pond. Alternatively, the filter media in a confinedfilter is contained within some type of structure, often a concrete vault. Examples includevertical volume recovery filters, the Austin sand filter, and the Delaware sand filter.

Purpose

Stormwater filters are used solely to remove certain pollutants, primarily particulates, fromrunoff. They must be used in combination with other BMPs to provide flood protection.


• Settling or sedimentation.• Filtration by sand or other filter media.• Microbial uptake and/or transformations.

Advantages

• Can be used in urban areas and on highly impervious sites.• Can be used at sites with high water tables but which have too small of a contributing

drainage area for use of wet detention systems.• May be very cost effective, especially the Delaware sand filter design where the con-

crete boxes are now being prefabricated in sections.

Disadvantages

• Very maintenance intensive. Filter media may need cleaning or even replacementseveral times a year, although this depends on a number of factors. However, thislevel of maintenance can be reduced by controlling erosion and otherwise restrictingsediment loadings.

• Provide limited flood storage and attenuation.


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Stormwater filter systems are used primarily to remove particulate pollutants from runoff andtypically are not used by themselves to attenuate stormwater peak discharge rates or vol-umes. Treatment effectiveness will depend on a number of design considerations includingthe treatment volume, whether the system is on-line or off-line, whether it is a confined orunconfined filter, the type of land use, and whether pretreatment is provided by use of theBMP Treatment Train. Studies of the effectiveness of stormwater filter systems have variedgreatly. In a study of a wet detention pond with an unconfined side bank filter, Harper andHerr (1993) concluded that most of the treatment occurred in the wet pond, with the filterenhancing removal of only total nitrogen, TSS, and total zinc. Field research in Austin, Texas(Chang et.al., 1990) indicates that their sedimentation/filtration systems remove 70 to 90% ofthe suspended solids, but only 20 to 85% of the metals, 20 to 40% of the nitrogen, and 50 to65% of the phosphorus. Two recent studies of the Delaware sand filter design (Horner, 1995and Bell, 1996) found these designs to be effective and fairly easy to maintain, at least forfilter systems. These filters removed 80 to 90% of the total suspended solids, 40 to 60% ofthe total nitrogen, 40 to 75% of the total phosphorus, and 30 to 90% of the total zinc. Theranges of expected pollutant removal of stormwater filter systems are:


Limitations on Use

• Not suitable on fill sites or near steep slopes.• Only use at sites with a full time maintenance entity.


Operation

Successful operation depends on good design, construction, and most importantly, onregular maintenance, especially of the filter media. With stormwater filters, the questionis not whether the filter will clog, but when.

Maintenance

Activities necessary to maintain the long term functioning of stormwater filtrations sys-tems include:

• Grass mowing and removal from side slopes and the embankment.

• Removal of trees, brush, and animal burrows from the embankment.

• Vegetative cover stabilization to prevent erosion of side slopes and the embankment.


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• Removal and disposal of trash and debris, especially from inlet or outlet structures.

• Removal of sediments and other materials that accumulate in pretreatment prac-tices, such as sediment traps or forebays.

• Periodic scraping and aeration of the filter media, with partial removal.

• Complete replacement of the filter media.


• Inspect monthly and after large storms to assure proper discharge, monitor accu-mulations of trash and debris, monitor sediment accumulations in forebays or in-lets, determine mowing or vegetation removal needs, and determine whether thefilter media is clogging.

• Closely monitor clogging of the filter media to determine when maintenance isneeded. There are two approaches to filter media maintenance. Most of the storm-water programs which have created design criteria for filters require eighteen inchesto two feet of filter media. This allows the filter to be periodically scraped to removean inch or two of filter media until only one foot is left. The coloration of the sandwill provide a good indication of what depth of removal is required. Then additionalfilter media is added to restore the original two feet of filter material. Alternatively,especially for unconfined filters, the filter media is completely replaced when thetime required to recover the stormwater treatment volume decreases to one-half ofthe design time.

• Monitor sediment accumulations in sediment traps or forebays semiannually. Sedi-ments should be removed when 25% of the storage volume has been lost.

• Since filters often are used on highly impervious sites with potentially high loadingof heavy metals and petroleum hydrocarbons, it is recommended that the filtermedia be analyzed periodically. This can help to prevent the accumulation ofthese materials in concentrations that may cause the filter media to be considereda hazardous waste. For example, Horner and Horner (1995) reported that withinseven months of use, the levels of total petroleum hydrocarbons in a DelawareSand Filter at a Seattle barge terminal exceeded Washington's Model Toxics Con-trol Act hazardous waste threshold of 200 mg/kg by two orders of magnitude.


1. Use the "BMP Treatment Train" concept such as swale conveyances and sediment fore-bays to minimize sedimentation loadings and reduce oils, greases, and other petroleumhydrocarbons. There are several rules of thumb for sizing and designing the sedimentforebay or the presettling basin/chamber for the Delaware Sand Filter (DSF). Theseshould be reviewed and those which are relevant to the conditions at the site should befollowed. For example, Alexandria's (VA) program recommends that the presettling basin/


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chamber for the DSF on highly impervious sites contain a minimum of 20% of the stormwatertreatment volume but that the entire volume be contained by this chamber on sites withpervious surfaces.

2. Use confined filters which are constructed as "off-line" stormwater treatment systems andwhich are designed to let stormwater bypass the filter during maintenance.

3. Carefully select the filter media to assure that it meets the specifications established bythe stormwater program. Neutral soil pH (6 to 8) is best for supporting microorganismsand is also best for sequestering pollutants in the sediments. Soils with fairly high levelsof aluminum or iron are best for adsorption and will help to increase removal of phospho-rus and some metals.

4. Balance the hydrologic efficiency of the filter media with its pollutant removal effective-ness. While coarse sands will pass stormwater quickly, few pollutants are removed.

5. Unconfined, mound filters which are sodded provide a relatively low maintenance filtersystem and provide higher levels of treatment than do sand filters without vegetation.


• For confined filters, do not allow inflow of runoff until construction on site is completedand all soil surfaces in the contributing drainage area are completely stabilized withvegetation.

• If detention ponds with unconfined sidebank filters are used for erosion and sedimentcontrol, the filter media should be completely replaced once construction is completedand all soil surfaces in the contributing drainage area are completely stabilized withvegetation.

• Side bank filters should contain clean out ports, spaced every 50 feet, to allowunderdrain pipes to be cleaned.


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• Filter media should be checked to assure that it meets all specifications, especiallygrain size and uniformity coefficient.

• Filter underdrain pipes should be carefully placed on a bed of gravel which has beencompacted properly, thereby reducing the potential for soil piping and settling prob-lems. Pipes must have proper slope as specified in the design plans.

• For the Delaware Sand Filter design, it is essential that:

• The top of the sand filter is completely level.• The inverts of the notches, orifices, or weirs dividing the sedimentation chamber

from the filter chamber are completely level.• If precast concrete lids are used, lifting rings or threaded sockets must be provided

to allow easy removal with lifting equipment which must be readily available tomaintenance crews.

• Where underdrains are used, the minimum slope of the pipe needs to be 0.5%.

Delaware sand filter being installed in Alexandria, Virginia.

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Chapter 3

Planning and Design Considerationspollution, such technical compliance is notenough.

Instead, the designer must also recognizehis or her unique responsibilities to thepeople who will inspect and maintain thefacility once construction is completed.For it is through such recognition that the de-signer can help ensure both the overall suc-cess of the community’s stormwater manage-ment program and the quality of life of thepeople that will live, work, or travel past thefacility they are creating. It is only by fulfillingthese larger design responsibilities that storm-water management will be able to achieve andsustain the public support and participation itneeds to effectively address the complex prob-lems demanded of it. A description of eachof these design responsibilities is pre-sented below, with particular emphasis onminimizing and facilitating stormwatermanagement facility maintenance. Sugges-tions for meeting these responsibilities arealso presented, including specific recommen-dations and design guidelines for varioustypes of stormwater management practices.

1.1. Objectives

To advance the handbook’s overall goal of ef-fective and efficient stormwater managementsystem operation, maintenance, and manage-ment, the objectives of this Chapter will be:

To describe maintenance needs and com-mon maintenance problems of varioustypes of stormwater management prac-tices, facilities, and systems.

design \di-zine\ vb 1: to conceive and plan out in the mind 2: to devise for a specific function or end 3: to conceive and draw the plans for - Merriam-Webster Dictionary

1. OVERVIEW

The above definition of the word “design” suc-cinctly describes both the scope and se-quence of activities typically undertaken bythe designer of a stormwater managementfacility. Having identified a stormwater prob-lem or need that can best be solved throughthe construction of a facility, the designer willthen select the most appropriate type, con-ceptualize its function and operation, and de-termine the specific characteristics necessaryfor the facility or practice to achieve its de-sired performance. Having completed this,the designer must then transform these char-acteristics into a physical entity. This is donethrough the development of detailed construc-tion plans and specifications, which are usedto construct the facility in the field.

Throughout the entire endeavor, the storm-water system designer must, of course, fulfillcertain technical responsibilities if the systemis to comply with the standards and require-ments of the community’s overall stormwatermanagement program. To do so, the designermust be familiar with these program require-ments as well as the technical data, equa-tions, and analytic techniques commonly usedto meet them. However, if stormwater man-agement is to grow beyond its traditional con-cerns for stormwater quantity to also addressstormwater quality and nonpoint source (NPS)


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To demonstrate the direct link betweenmany of these needs and problems andthe decisions and actions of facility plan-ners and designers.

To emphasize the ability of comprehensiveand enlightened planning, design, and re-view practices to minimize and facilitatestormwater management facility mainte-nance.

To illustrate the long-term cost-effective-ness of such practices during a facility’splanning, design, and review stages.

To encourage facility planners, designers,and reviewers to regard facility mainte-nance as equal in importance to a pro-posed facility’s hydrologic, hydraulic, struc-tural, biologic, and aesthetic aspects.

To present planning and design guidelinesfor specific types of stormwater manage-ment facilities and practices that minimizeand facilitate post-construction mainte-nance.


This chapter is intended primarily for the fol-lowing readers:

Stormwater management facility plan-ners and designers.

Project design and permit applicationreviewers and supervisors.

In addition, stormwater management facilityowners (both present and future) can gainvaluable insight into the planning and designprocess. This can help in the selection of acompetent designer of a proposed facility andin the development of an adequate project de-sign budget. Finally, construction managers,inspectors, and contractors can develop a

greater appreciation of the overall planningand design effort and the need to follow theresulting design plans and specifications asclosely as possible. Such understanding canalso promote a greater exchange of informa-tion and ideas between designers and con-structors, thereby enhancing the activities ofboth.

2. STORMWATER MANAGEMENTPRACTICES AND COMPONENTS

As noted in Chapter 2, the field of stormwatermanagement has grown considerably in thelast two decades. One of the less fortunateproducts of this growth has been a long andsometimes conflicting list of names for the fa-cilities (systems) and practices produced byplanners and designers. Therefore, to mini-mize confusion, increase effectiveness, andillustrate their different maintenance problemsand needs, the following definitions have beenadopted for use in this Chapter and through-out the entire handbook:

2.1. Detention Practice:A stormwater management facility that tem-porarily impounds runoff and discharges itthrough an outlet structure. Any additionaloutflow through infiltration or evaporation isnegligible and, therefore, not ordinarily con-sidered in the detention system’s design.Detention facilities may vary by the durationof time that they store runoff and, therefore,are further subdivided into the following threesubcategories:

A. Dry Detention Facilities detain runofffor a relatively short time (e.g., 2 to 6 hours)and, as such, are normally used for ero-sion and/or flood control purposes. In ad-dition, all detained runoff is released fol-lowing the storm event and the facility isnormally dry during inter-storm periods.

CHAPTER 3 Planning and Design Considerations

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B. Extended Dry Detention Facilitiesdetain runoff for much longer time periods(e.g., 18 to 48 hours) than dry detentionfacilities and, as such, also provide runoffquality benefits. Similar to dry detentionfacilities, they release all detained runoffthrough an outlet structure and are ex-pected to be dry during inter-storm peri-ods.

C. Wet Detention Facilities also releaserunoff through an outlet structure. How-ever, some runoff is retained permanentlyin a pool, pond, or lake during inter-stormperiods. This permanent pool providesgreater water quality benefits through in-creased sedimentation, flocculation, andbiological activity.

2.2. Infiltration Practice:A stormwater management system that tem-porarily impounds runoff and discharges itthrough infiltration through the surroundingsoil. Additional discharge may occur throughevapotranspiration. Similar to dry and ex-tended dry detention facilities, an infiltrationfacility is expected to completely drain and bedry during inter-storm periods. Typical infil-tration practices includes infiltration basins,swales, drywells, and seepage pits.

2.3. Filtration Practice:A stormwater management system that filtersrunoff through selected inorganic or relativelyinert media to remove pollutants. Since filtra-tion practices do not normally provide runoffquantity benefits, they are often used in com-bination with detention systems as pretreat-ment facilities. Typical filter media includesand, compost, gravel and other materials.

2.4. Biofiltration Practice:A stormwater management practice that fil-ters runoff through dense vegetation or otherorganic, biologically active media to remove

pollutants. The organic nature of the under-lying soils also promotes further pollutant re-moval as well as infiltration of runoff. Typicalbiofiltration practices include vegetatedswales, filter strips, and buffer areas.

To further organize the presentation andprovide thorough coverage of all facilitytypes, each facility or practice has beenbroken into one or more of the compo-nents described in Table 3-1. Due to theirdifferent physical or operating character-istics, it is important to note that somepractices will not have all of the compo-nents listed in the table. Additional infor-mation and photographs of the various typesof stormwater management practices are pre-sented in Chapter 2.

3. THE RESPONSIBILITIES OF THE FACILITY DESIGNER

As noted above, there are several levels ofresponsibility that the designer of a stormwa-ter management facility must fulfill. First andforemost, the designer is responsible forcomplying with the technical requirementsand standards of the overall stormwatermanagement program of which the facilitywill be a part. This will typically include achiev-ing the required level and range of peak out-flow control necessary to prevent or reducedownstream flooding, as well as the deten-tion times and pollutant load reductions nec-essary for stormwater quality enhancement.Additional technical requirements of thestormwater management program may in-clude emergency discharge capacity to insuredam or embankment safety and structural andgeotechnical standards to achieve stabilityand strength. Therefore, the facility designermust be familiar with the specific techni-cal requirements of the stormwater man-agement program as well as the theoreti-cal basis for and use of the various hydro-logic, hydraulic, structural, chemical, bio-


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COMPONENT DESCRIPTION

PRINCIPAL OUTLET Hydraulic structure that controls and conveys thefacility's outflow to the downstream conveyance orreceiving water.

EMERGENCY OUTLET Hydraulic structure or spillway that safely conveysemergency overflows from the facility. Includesapproach and exit channels.

DAM/EMBANKMENT Wall or structural fill that impounds runoff in the facilityabove the adjacent ground surface.

BOTTOM The lowest or deepest surface within the facility.

SIDE SLOPES Slopes at dams, embankments, spillways, and facilityperimeters constructed through excavation or filling.

TRASH RACK Device placed upstream of the principal outlet or drainto intercept trash and debris that would otherwiseblock it.

LOW FLOW SYSTEM Surface and/or subsurface measures that conveylow and dry weather inflows to the principal outletwithout storage.

INLETS Upstream surface and/or subsurface conveyancemeasures that discharge runoff into the facility.

OUTFLOW SYSTEMS Downstream surface and/or subsurfaceconveyances or water bodies which receive facilityoutflows from the principal outlet.

PERIMETER Area immediately adjacent to the facility.

ACCESS SYSTEMS Measures and devices that provide maintenancepersonnel and equipment access to various facilitycomponents.

VEGETATIVE COVER Vegetation planted on various facility components tostabilize their surface and/or provide stormwatertreatment.

TABLE 3 - 1.

Major Components of Stormwater Management Practices


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that must first be constructed and then main-tained. As such, it is vital that the facilitybe both simple and practical to build andmaintain. With regards to maintenance, astudy of 51 stormwater management facilitiesin New Jersey by the state’s Department ofEnvironmental Protection found that morethan half of the problems encountered bymaintenance personnel at the facilitiescould be linked to shortcomings in theplanning, design, and review process.These included:

a lack of adequate planning and de-sign standards,inadequate investigation and analysisof site conditions,poor understanding of facility functionand operational needs,inattentive review, and,at times, simply a failure by the de-signer and reviewer to recognize or re-member the facility’s post-constructionmaintenance needs.

According to the study, these shortcomingsand failures sometimes resulted in facilitymaintenance problems that “were virtuallyunsolvable without massive infusions of time,money, and hard work”.

logical, and geotechnical analyses typi-cally used to comply with them.

However, the responsible facility designer(and the government reviewer approving thedesign) should not only be familiar with thestormwater management program’s technicalrequirements, but also understand it’s overallintent or goals. The responsible designerand reviewer must recognize that theprogram’s technical requirements are onlythe means by which the program’s goalsare achieved. As such, a stormwater man-agement facility will contribute more towardsthose goals if its designer understands, forexample, not just what detention time an ex-tended detention basin should have, but whyit should even have one, why it should be acertain duration, and what will happen if itdoesn’t. Such understanding by designersand reviewers also produces facility designsthat are better able to achieve satisfactoryresults over a much wider range of real worldconditions than the limited few used in mostdesign processes.

In addition, due to the inherent complexitiesof stormwater quality and NPS pollution, thetechnical requirements of many stormwatermanagement programs are not defined as pre-cisely as the program’s goals. For example,it is much easier to specify a program goal of80 percent removal of suspended solids fromstormwater runoff than it is to specify the ex-act technical measures required to achieveit. However, this disparity between a storm-water program’s means and ends can be over-come to a great degree by the responsibledesigner who, aware of the disparity, is will-ing and able to look behind and beyond theprogram’s somewhat more limited technicalrequirements and produce designs that do abetter job of achieving the program’s goals.

Another design responsibility is based uponthe realization that the designer’s efforts willultimately result in an actual physical facility

Flat bottom in dry detention basinprevents complete emptying and complicates basin maintenance.


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Typical stormwater system operation, main-tenance, and management problems that canbe directly linked to poor planning and de-sign or to inattentive review include:

MAINTENANCE PROBLEM: Soggy, unstablebottom in dry detention basin which is difficultto mow.CAUSE: Bottom will not drain and dry com-pletely between rain events.SOURCE OF PROBLEM: Flat basin bottomspecified by designer.

MAINTENANCE PROBLEM: Mosquitobreeding in an infiltration basin.CAUSE: Persistent standing water in bottom.SOURCE OF PROBLEM: Basin bottom setbelow groundwater table due to designer over-sight.

MAINTENANCE PROBLEM: Inability to drainand desilt wet detention basin.CAUSE: Lack of low level drain.SOURCE OF PROBLEM: Low level drain notprovided due to designer oversight.

MAINTENANCE PROBLEM: Grass mowingalong basin side slopes is time consuming anddangerous.CAUSE: Excessively steep basin side slopes.SOURCE OF PROBLEM: Excessive sideslope specified by designer.

MAINTENANCE PROBLEM: Sediment anddebris removal from sand filter is time con-suming and difficult.CAUSE: Lack of access manhole from groundsurface to sediment chamber.SOURCE OF PROBLEM: Access manholenot provided due to designer oversight.

MAINTENANCE PROBLEM: Check forstanding water in dry detention basin by mos-quito control inspector is time consuming.CAUSE: Basin cannot be viewed from road-way or parking lot. Inspector must stop andexit vehicle and walk to basin to view.SOURCE OF PROBLEM: Basin located inremote part of site by designer. Access roadnot provided due to designer oversight.

MAINTENANCE PROBLEM: Continuing re-pairs of outlet structure and trash racks re-quired at detention basin.CAUSE: Structural failures due to debris load-ings and weather conditions.SOURCE OF PROBLEM: Inferior, nondurablematerials specified by designer.

As described above, poor facility designand/or inattentive review can adverselyeffect facility maintenance in several ways.These include hindering inspection andmaintenance activities through lack of

Highly visible and accessible facilitiescan be quickly inspected for mosquitoes

and other maintenance problems.

Less durable outlet structure materials, suchas cinder blocks, may save one-time construction costs but will increase

long-term maintenance costs.


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adequate access, increasing maintenanceefforts through adverse site conditions,and creating additional maintenanceneeds through the use of inadequate ma-terials. The result of any of these causes isincreased maintenance time, effort, and ex-pense and the increased potential for main-tenance neglect and facility malfunction oreven failure. These points have even greaterimpact when it is remembered that, unlike fa-cility design or construction, which are nor-mally completed in a matter of weeks, main-tenance must be performed for the life of thefacility. In addition, the increased potentialfor maintenance neglect and failure, which thedesigner or reviewer could have preventedwith a few extra hours of effort in the office,may remain a threat for years to come.

It must also be noted that maintenance per-sonnel are not the only people who will sufferthe long term effects of poor facility planning,design, and/or review. As noted above, a fa-cility design that first exists only on paper willultimately exist in or on the ground. Sincevirtually all stormwater management systemsare constructed as part of land developmentactivities, other structures such as homes, of-fices, stores, factories, warehouses and/orroads will normally be close by, along with thepeople that will live, work, or travel them.While the facility will only be required, onaverage, to function a few days a monthor year, these people must coexist with itevery day. If the system is poorly main-tained, these people may then be sub-jected to health threats from mosquitoes,rodents, and other vermin as well as ad-verse quality-of-life effects from odors orunsightly appearance. If these conditionsare due, even in part, to deficiencies in thesystem’s design (as demonstrated above),then the planner, designer, and reviewer mustshare the blame for their creation.

Finally, in the design of any stormwater man-agement facility or practice, cost must also

be an important factor. The responsible de-signer will not only appreciate this fact, butwill also be able to accurately determine andcompare the costs of the system and the ben-efits it provides in order to measure the itstrue cost effectiveness. To do so, the de-signer has a responsibility to fully under-stand both the combined cost of systemoperation and maintenance and the rela-tive benefits or cost savings that can begained from various design alternatives.For example, while the use aluminum trashracks or reinforced concrete structures (inplace of less durable materials) may increasethe client’s initial design and constructioncosts, these increases may be quickly offsetby reduced (and recurring) maintenancecosts. To accurately perform such analysesrequires, among other traits, a high degree ofobjectivity in order to ensure that the costsand benefits determined by the designer arebased upon reality and not the interests ordesires of his or her client, supervisor, or gov-ernment regulator.

4. BMP DESIGN CONSIDERATIONS:POINTS TO PONDER

From the above, it can be seen that the re-sponsible stormwater management sys-tem designer must not merely be con-cerned with the technical requirements ofa stormwater management program, butmust also strive to produce facilities withreasonable and affordable maintenanceneeds. The system must also be practical,safe, aesthetically pleasing, and relativelyeasy and inexpensive to build. The stormwa-ter facilities that result from such an effort willbecome assets to the community which theyserve and will promote the public interest andinvolvement necessary for overall stormwa-ter program success.

Faced with such a formidable list of require-ments, it can be seen that the responsible de-


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signer and reviewer must not only bring com-petent technical ability to the design process,but also an informed, open attitude and evena sense of mission or purpose. To help pro-mote such an attitude and more fully preparethem for the job ahead, the following pointsregarding stormwater management systemdesign, construction, and operation are of-fered:

4.1. Interested Parties

To produce a stormwater management facil-ity design good enough to earn an “Approved”stamp from a program reviewer (who is pre-sumably interested in assuring compliancewith the program’s regulations), a facility de-signer must identify with those interests andmake sure they are reflected on the construc-tion drawings. However, to further ensure thatthe facility will truly be an asset to the com-munity and will make a positive statementabout the value of stormwater management,the system designer must expand this list ofinterested parties to include the following:

The Client: Including the Client on a list ofparties having an interest in a facility’s de-sign should not come as a surprise. How-ever, a review of what those interests actuallyare can be enlightening. Therefore, the re-sponsible designer will not automatically as-sume to know their client’s interests (howeverobvious they may appear), but will instead fullydiscuss them with the client.

The prospect of having such a discussionshould then lead the responsible designer toask the following questions:

What should the client’s interests be?

Does the client fully understand thelong term operation and maintenancecosts which sometimes are the own-ers responsibility?

Does the client have a misinformed ormisguided attitude towards the goalsof stormwater management?

Is this attitude based upon a lack ofunderstanding or information?

In such cases, the responsible designercan, through education (and a touch of di-plomacy), both expand the client’s under-standing and improve their attitude to-wards stormwater management, therebyenhancing the designer’s own chances ofproducing a positive facility design. Thiswill also provide the designer with an excel-lent opportunity to educate the client aboutlong term system maintenance requirementsand costs which the client may not be awareof or fully appreciate.

The Reviewer: Similar to the Client, this indi-vidual is also an obvious choice for an “Inter-ested Party” list. However, once again, thefollowing questions may be raised: What arethe reviewer’s interests and what should theybe? Since a reviewer’s check of a BMP de-sign can sometimes stray from the program’stechnical standards into more subjective ar-eas (due, at times, to a lack of such stan-dards), it is often helpful to know what inter-ests the reviewer has in those areas. Arethose interests both in keeping with the goalsof the stormwater management program andwithin the program’s (and, therefore, thereviewer’s) jurisdiction?

Similar to the client, a facility designer mayencounter a reviewer who, through a lack ofknowledge or an abundance of incorrect in-formation, either misunderstands the impor-tance of system maintenance, or fails to ap-preciate the costs and effort required to do itproperly, or the consequences of neglectingit. Once again, the responsible facility de-signer can, through education and a com-petent, comprehensive design, expand theregulator’s knowledge, interests, and abil-


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ity, particularly in regard to BMP operation,maintenance, and management.

The Constructor: As noted earlier, one ofthe key responsibilities of a stormwater man-agement system designer is to transform thesystem from concept to reality by preparingdetailed plans and specifications of how itshould be built. It is then up to the construc-tor to finish the project by actually buildingthe facility from these plans and specifications.Therefore, the responsible designer appre-ciates the efforts of the constructor anddoes not see their own efforts as an inde-pendent exercise, but rather as an integralpart of a much larger process; a processwhich requires the participation of the con-structor and then, ultimately, the operator/maintainer.

As such, the responsible system designer willrecognize and respond to the constructor’s in-terests by producing a well-thought out de-sign that can be constructed as easily and sim-ply as possible. Since this may not alwaysbe possible, particularly when faced with com-plex structures, precise dimensions, or diffi-cult site conditions, the responsible de-signer will also take extra care to bring anydifficult or unusual aspects of the designto the constructor’s attention prior to thestart of construction and will even consultwith the constructor during the designphase to mutually devise the best con-struction technique, material, or sequence.

Under ideal circumstances, the facility de-signer will also continue their involvement inthe project throughout the construction phase.When contracts are agreed upon by the de-veloper and the designer, the contract shouldinclude input from the designer throughout theconstruction phase of project implementation.The designer should work with the construc-tor to correct mistakes, address oversights,and develop revised designs as necessary toovercome construction problems that were en-

countered in the field or that may becomemaintenance problems in the future. It is usu-ally very advantageous to the project for thedesigner(s) to be in the field to interpret thedesign at all critical points in the construction.This need is especially acute when the con-tractor does not have substantial experiencebuilding the precise type of project, or whenthere are any complex elements at all in thedesign.

The Maintainer: Once construction of thestormwater system has been completed, thedesigner’s involvement with the process (as-suming it lasted through construction) nor-mally ends. However, as described above,there are interested parties whose involve-ment with the facility is just about to start andwhose interests the designer must also con-sider. These are the maintenance personnelwho will be responsible for mowing the grass,removing the sediment, clearing the debris,managing the habitats, and performing thenecessary repairs at the facility for the rest ofits serviceable life. Similar to the constructor,the maintainer’s actions will be governed bywhat the designer creates on paper. How-ever, since construction has been completedand the designer has moved on to otherprojects, it will be considerably more difficultfor the maintainer to have deficiencies or over-sights in the design corrected.

As such, it is vital that the designer under-stand and address the interests of themaintainer before it is too late. As de-scribed in greater detail throughout this chap-ter, this can be accomplished by designing afacility that, optimally, requires a minimumamount of maintenance that can be performedas easily as possible.

The Resident: As described above, this in-terested party may also be the worker, com-muter, shopper, student, or local governmentofficial who will interact with the stormwatermanagement system on a regular basis once


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construction is completed and maintenancebegun. This interaction may be physical(through the sense of touch, sight, hearing,or smell) or psychological (as anyone who hasworried about their children’s safety or thevalue of their property will know).

In any case, these are the people who mostlikely have the strongest interest in seeing thata positive facility design is achieved. Theseare also the people who may soon be askedto participate in the community’s nonstructuralstormwater management programs by chang-ing some of their aesthetic values and lifestyles, and who will be paying for the facility’smaintenance through their drainage fees,owner association fees, rents, leases, or pur-chases. Therefore, the facility designer mustbe aware of their interests and incorporatethem into the design plans and specifications.

4.2. Operating Conditions

Just as there are a wide range of people withan interest, either direct or indirect, in the de-sign of a stormwater management system,there is also a wide range of conditions underwhich it must operate. However, just as thedesigner may fail to recognize all of thedesign’s interested parties, he or she may alsofail to consider all of the real world conditionsunder which the facility must operate. Instead,many designers focus solely on the designconditions necessary for official programapproval.

This is unfortunate, since these designconditions, which may receive all of thedesigner’s attention, will in reality onlyoccur during a small fraction of thesystem’s serviceable life. However, itsperformance during the remainder of itsexistence, while ignored by some design-ers, can largely determine both the amountand frequency of required maintenanceand the conditions under which it must be

performed. How the system “performs”under these non-design conditions mayalso largely determine the community’sopinion of it and the stormwater programit represents.

Therefore, it is important that the stormwatermanagement system designer be aware ofall the weather and other site conditions thatthe facility will be subject to, including:

Design Conditions: These are obviously thedesigner’s first concern and, as noted above,are normally established by the community’sstormwater management program. In thecase of runoff quantity control, these con-ditions usually include either a single orrange of relatively extreme storm events,the runoff from which must be stored andreleased at a predetermined rate. For ex-ample, New Jersey’s Stormwater Manage-ment Regulations require that the runoff froma proposed land development site for the 2,10, and 100-year storm events be controlledso that the peak rate of runoff after develop-ment for each storm does not exceed the peakrate that existed prior to development. TheSomerset County, New Jersey standards aremore strict, requiring a peak rate after devel-opment that is actually less than existing toaccount for development induced changes inrunoff volume and overall hydrograph shapeas well.

In the case of stormwater quality control,typical design conditions may include thetemporary storage and slow release of therunoff from a much smaller, more frequentstorm event in order to promote pollutantremoval through sedimentation. For ex-ample, New Jersey’s Stormwater Manage-ment Regulations require the temporary stor-age of runoff from a 1-year storm event, withrelease occurring over 18 to 36 hours depend-ing upon the character and intensity of theproposed development. Delaware'sstormwater program requires extended stor-


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age of the first inch of runoff from a proposedsite, with release occurring over 24 hours.Stormwater quality BMPs in Florida are de-signed to treat up to the first two inches ofrunoff, with release occurring between 24 and120 hours. In the Puget Sound Basin, the run-off volume or rate, depending on BMP type,from the 6-month, 24-hour "water quality de-sign storm" is the basis for sizing treatmentpractices.

Whatever exact design conditions thestormwater management program mayspecify, it is vital that the structural BMPfunction properly under them or the goalsof the program cannot be met.

Extreme Conditions: In addition to theprogram’s design conditions, which have beenselected with the goal of runoff quantity and/or quality in mind, the responsible system de-signer must also recognize that more extremestorms will also eventually occur. Therefore,due to the inherent dangers of storing run-off and the exceptionally large quantitiesof runoff that can be produced by theseextreme events, it is vital that the designeralso address the goal of safety by ensur-ing that the facility will also function prop-erly under such extreme conditions. Ex-treme conditions may be defined as eitherextreme weather or storm conditions whererainfall exceeds normal design values orwhere equipment or components fail structur-ally or operationally.

Addressing extreme conditions at a stormwa-ter management system will typically includethe provision of an emergency spillway orother auxiliary outflow device that will safelyconvey the extreme event runoff that exceedsthe capacity of the facility’s normal outflowstructure. It will also include protection of criti-cal portions of any embankment, dam, or dis-charge points that may be subject to scour orerosion from the high flow velocities gener-ated by this storm event. Protection of such

critical areas from damage will not only in-crease safety but reduce and even eliminatethe need for post-storm maintenance and re-pairs.

Consideration of extreme conditions isalso important when reviewing the acces-sibility of system components to mainte-nance personnel. For example, if a trashrack is blocked or damaged during a stormevent and is causing dangerous water levelsin a facility, will maintenance personnel beable to reach it safely? Will inspectors beable to reach the system itself during an ex-treme storm event to evaluate the potentialfor overtopping and failure? These questionscan only be answered satisfactorily if thefacility’s performance under such extremeconditions is thoroughly analyzed by the de-signer.

Dry Weather Conditions: While extremestorm conditions can be expected to occurperiodically, a common operating condition ata stormwater management system will be dryweather with various seasonal temperatures,winds, humidities, and periods of daylight.However, while dry weather may be the mostprevalent operating condition and the oneduring which most maintenance will be per-formed, it is also the one that is most frequentlyoverlooked by the system designer. As a re-sult, how the facility will look, smell, and evensound during the majority of its operating lifeis then left to chance. This can be particu-larly unfortunate for the system maintainerand, perhaps more critically, the resident,worker, or commuter who, knowing when tocome in out of the rain, will interact most of-ten with the BMP during dry weather condi-tions. This is especially true if the stormwa-ter system is a multipurpose dry practice. Asa result, the responsible BMP designer willnot only address design and extremestorm conditions, but will also make surethat the facility also performs satisfacto-rily when it isn’t raining at all.


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4.3. Design Methodologies

Prior to starting the actual design, the respon-sible stormwater management facility designerwill have an adequate understanding of thedesign methodologies that have been se-lected or required. These methodologies cancover such aspects as rainfall-runoff compu-tations, hydrograph routings, infiltration andground water movement, structural design,and geotechnical issues. In doing so, thedesigner’s understanding should include eachmethodology’s theoretical basis, assumptions,limitations, and applicability.

In addition, the responsible designer will alsohave an understanding of both the accuracyneeded to perform the design and the accu-racy of the method selected to do it. Fromthis information, the responsible designer willnot waste time producing unneeded accuracynor attempt to achieve a level of accuracy be-yond the limits of the method. In addition, theresponsible designer will understand the sen-sitivity of each of the method’s input variablesand will appropriately allocate his or her ef-forts, time, and resources in developing eachone.

Finally, the responsible designer will under-stand the applicability of each methodologyto the design of such maintenance-relateditems as bottom and side slopes, trash racks,erosion protection measures, low flow chan-nels, forebays, and outlet works.

4.4. Facility Type

The final point for a stormwater managementfacility designer to consider before or duringthe design process is the exact type of prac-tice to be used. There are typically a widerange of stormwater management practicesavailable for consideration, ranging from rela-tively simple vegetated filter strips and swalesto large wet ponds and constructed wetlands.

However, selection of the most appropri-ate type of facility may have a greater im-pact on maintenance effort than all otherfactors combined.

Selection of the most appropriate stormwaterBMP will depend upon a number of factors,including program requirements, facility loca-tion, site conditions, maintenance needs,safety, cost, and performance characteristics.Similar to that of selecting/determining facil-ity operating conditions, however, the facilitydesigner may often consider only a few ofthese factors, most notably program require-ments (keep the reviewer happy and get theapproval) and cost (keep the client happy,too). The responsible designer, however,will recognize the performance, construc-tion and maintenance needs, uncertain-ties, and risks inherent in each facility typeand will then select (or help influence theselection of) the most appropriate type ofsystem for the site or project. This pro-cess typically begins with the identification ofthe fundamental characteristics of each typeof stormwater management practice, alongwith the project’s physical, economic, social,and regulatory constraints. The process thenbecomes one of comparison and analysis,with the best match of site and facility foundby eliminating those options least suitable.

For example, a site with porous soils, lowground water table, and close proximity to resi-dences may not be best suited for a wet pondor constructed wetland, while the active rec-reational needs of the residents may benefitfrom an infiltration basin or dry, extended de-tention basin that can also serve as an ath-letic field. In addition, the maintenance needsof these two practices should be well withinthe homeowners’ abilities, while a constructedwetland may require expensive maintenanceexpertise far beyond both the homeowners’ability or budget. Recognizing that there arerarely perfect matches, comparisons andanalyzes such as this will help reduce the


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the wrong facility type, however, trans-forms a complex and demanding processinto an impossible one.

5. BMP DESIGN CONSIDERATIONS: A CHECKLIST

Having completed the BMP practice selectionprocess with idealism, and design contract stillintact, and armed with the necessary techni-cal and regulatory knowledge and economic,social, and maintenance sensitivity, the re-sponsible stormwater system designer is readyto begin the actual design process. Presentedbelow is a checklist of six key design con-siderations to help guide this effort, withparticular emphasis placed upon long termfacility maintenance. Ideally, these sixitems have or will become an integral partof the designer’s thought process and willautomatically be included in each designeffort. These items can also serve as guide-lines for reviewers responsible for the reviewand approval of specific system designs andcan even serve as goals for those developingnew stormwater management programs.

5.1. Safety

For many reasons, the safety of the stormwa-ter management system must be the primaryconcern of the designer. Due to its structuralnature and, in many instances, the fact that itwill impound water either permanently or tem-porarily, a stormwater facility will inherentlypose some degree of safety threat.

Those at risk will include people living, work-ing, or travelling downstream of the systemand whose safety and/or property will be jeop-ardized if the facility were to fail and releasestored runoff. Since this is a risk that has beencreated solely by the system, the designermust assure that the probability of such a fail-ure is acceptably small.

number of potential facility types, improvethe thoroughness and objectivity of theoverall selection process, and ideally pro-duce the optimum stormwater system, notonly from a performance or regulatory view-point, but from a maintenance viewpoint aswell. This process can even help identify in-herent weaknesses in or problems with theselected BMP or exceptional maintenancedemands. This will enable the responsiblefacility designer to devote additional time andeffort towards correcting or minimizing themduring the design phase.

To undertake such a selection process obvi-ously requires a stormwater designer who un-derstands the fundamental characteristics andneeds of each facility type and who can ob-jectively assess all of the pertinent site con-straints. Such a designer must also be will-ing and able to address the differing opinionsof other, less objective or informed parties (in-cluding the reviewer, client, or member of thepublic) in order to assure that the best prac-tice is ultimately selected. As noted through-out this chapter, achieving an optimumstormwater management facility design isa complex and demanding process whichmust incorporate numerous interests andrequirements. Starting the process with

Minimum maintenance performed atmaximum efficiency should be a goal of

every stormwater facility planner,designer, and reviewer.


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However, also at risk at the facility are main-tenance personnel, inspectors, mosquito con-trol personnel, and equipment operators, whomust work in and around it. Typical hazardsinclude deep water, excessively steep slopes,slippery or unstable footing, limited or unsafeaccess, and threats posed by insects and ani-mals. As noted above, the responsiblestormwater designer understands the im-portance of minimizing and facilitating fa-cility maintenance. Providing a safe work-ing environment for the system maintaineris one important way to do it.

Finally, those living, working, traveling, attend-ing school, or playing in the vicinity of a facil-ity may also be at risk, particularly if the sys-tem serves both as a stormwater managementand recreational facility. Once again, suchthings as standing water, steep slopes, un-stable footings, and insect and animal bitesmust be addressed by the designer in orderto avoid creating a system that is a detrimentto the community it is intended to serve. Fail-ure to do so will only alienate those membersof the community that are being asked to playa vital role in the community’s stormwatermanagement efforts.

5.2. Performance

Having made a strong commitment to safety,the designer must then consider facility per-formance. This will normally include achiev-ing the necessary stormwater detention times,flow velocities, settling rates, peak flow attenu-ation, and/or ground water recharge for therange of storm events to be managed. In ad-dition, again with a commitment to safety, thedesigner must also ensure that the systemperforms adequately under emergency con-ditions, most notably when the peak rate and/or volume of runoff flowing into the basin ex-ceeds the discharge capacity of the facility’sprincipal outlet. This will require the inclu-sion of emergency or auxiliary outlets in the

facility to safely convey this excessive inflowthrough the BMP without jeopardizing its struc-tural integrity.

In most instances, the performance standardsthat the system’s design must meet will bespecified in the stormwater managementprogram’s regulations. However, experiencehas shown that these performance standardsmay, at times, be vague, contradictory, or evenimpossible to meet. For example, many storm-water system designers have been confrontedwith a requirement to reduce both the peakrate and total runoff volume from a developed(or developing) watershed to predevelopedlevels. This has often led to much headscratching, for the solution will normally re-quire the use of an infiltration or recharge ba-sin which, due to site constraints, may eitherbe impossible to construct or impractical tooperate and maintain. Or the regulations mayrequire high sediment removal rates but pre-clude the use of low flow channels that cangreatly facilitate the sediment’s removal bymaintenance personnel. Faced with suchcircumstances, the responsible designerwill look beyond the written regulationsand investigate their origins and true in-tent with regulatory personnel. Direct in-clusion of these individuals in the designprocess will also help ensure more posi-tive overall results.

5.3. Constructability

Up until now, the designer’s efforts to achieveadequate facility safety and performance lev-els will be achieved only on paper or com-puter disk. However, since the ultimate goalof the design process is to actually createa stormwater management system, the de-signer must also give careful consider-ation to how it is to be constructed. Achiev-ing exceptional safety and performance char-acteristics in a system that cannot actually bebuilt solves nothing and wastes much. Achiev-


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ing required levels of safety and performancein a facility that can be constructed with rela-tive ease, using readily available materials,equipment, and skills is commendable. It notonly solves a specific stormwater manage-ment problem, but also helps to advance thecommunity’s overall stormwater managementprogram.

“Constructability” can be defined as ameasure of the effort required to constructa stormwater management system. A fa-cility that is highly “constructible” will use ma-terials that are readily available, relatively in-expensive, and do not require special ship-ping or handling measures. They will be bothdurable and easily modified in the field to meetspecific site conditions. Similarly, the con-struction techniques and equipment requiredto construct the system will also be relativelysimple, straight forward, and familiar to thepeople who will be performing and operatingthem.

In addition, construction plans and specifica-tions should be complete, clear, and concise.They should be well organized - with all ofthe necessary information regarding a spe-cific facility component or construction stageprovided on a single or adjoining sheets. Allnew or more difficult techniques, stages, orcomponents should be given extra attention,with ample instructions, notes, and details.

It is important to note that the above descrip-tion is not intended to discourage the use ofnew or innovative materials or constructiontechniques, nor to inhibit creativity in thestormwater system design process. In fact,innovation in design and construction isvital to the future growth of stormwatermanagement. Instead, the above descrip-tion of “constructability” is intended to reminddesigners that they must consider the con-struction aspects of the BMP in the designprocess and strike an optimum balance be-tween performance and safety requirements,

constructability, and innovation for each de-sign they undertake. In addition, the morewell-constructed a stormwater manage-ment facility is, the less overall mainte-nance and repair it will require.

5.4. Maintenance

Obviously, in a handbook on stormwatermanagement system operation and mainte-nance, the same recommendation, givenabove for constructability, must be repeatedfor facility maintenance. Similar to construc-tion, the degree of effort and expense requiredto adequately maintain a stormwater manage-ment system will help determine the overallsuccess of its design. A system with man-ageable maintenance needs can be expectedto remain in reasonably good condition andwill have a stronger chance to become andremain an asset to the surrounding commu-nity. On the other hand, a facility with exces-sive maintenance needs is more likely to beneglected and will quickly become a commu-nity liability. As such, BMP operation andmaintenance can directly effect the over-all success of the community’s stormwa-ter management program.

The stormwater designer can help determinea facility’s maintenance needs by consider-ing several aspects of that maintenance inthe design process. First, it is important thatthe system design include the use of durablematerials that are able to withstand the manyand varied physical conditions the facility willexperience over its lifetime. Secondly, suit-able access to key facility components andareas is vital if required maintenance levelsare to be achieved. This will include provi-sions for walkways, staging and disposal ar-eas, access hatches and gates, and safe,stable working areas. The frequency of main-tenance will have a large impact on both main-tenance cost and quality, and it is thedesigner’s responsibility to achieve an appro-


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priate level. Finally, the system designershould always strive to minimize the over-all amount of maintenance at the facilityand to make that amount as easy as prac-ticable to perform. A more detailed discus-sion of maintenance considerations duringsystem design is presented in the followingsection.

5.5. Cost

Inclusion of a stormwater managementsystem’s cost in a list of design considerationsshould not be surprising. However, onceagain, a review of the full costs associatedwith a facility may yield a few surprises thatmay increase designers’ understanding andencourage them to give system costs the fullconsideration they deserve. Where costs aresurprising, the designer should communi-cate with the local regulatory agency toensure that the costs are "real" and tomake the regulatory agency aware of theeconomic impacts of pertinent programrequirements.

The cost that will be most obvious to the de-signer will be the systems's construction cost.This can be readily estimated with reasonableaccuracy and will be the one most directlyborne by the designer’s client. As such, thiscost is the one that the designer will most of-ten focus on during the design process to theexclusion of all others.

In doing so, what other costs will be over-looked? One may be the designer’s own fee,which is part of the overall system cost butwhich has probably been excluded becauseit has already been determined. However, theamount of the designer’s fee will have a di-rect impact on the facility design, since it willdetermine the amount of effort and resourcesthe designer can/will use to produce it. Thelevel of effort expended during the system’sdesign can have a similarly direct effect on

the effort and cost of both construction andmaintenance. As such, it can be seen thatpaying a higher cost for a more compre-hensive facility design may ultimately re-sult in even greater cost savings to the cli-ent during subsequent project stages.

Therefore, while this is not a signal to facilitydesigners to raise their fees, it is meant toremind designers that their fee is part of theoverall system cost. It is their responsibilityto determine what level of design effort andcost represents the best investment for boththe client and the community.

Another portion of a system's total cost that isfrequently overlooked is the cost associatedwith its operation, maintenance, and manage-ment. While the annual cost is usually asmall percentage of the construction oreven the design cost, it must be remem-bered that, unlike construction or design,OMM costs are recurring and must be paidthroughout the life of the system. There-fore, while a maintenance cost savings mayappear to be insignificant on a per operationbasis and not worth the extra design or con-struction costs required to achieve it, valuemay be viewed quite differently when multi-plied by the numerous times the savings willbe realized. For example, an added invest-ment in design to produce a trash rack thatwill require less frequent cleaning or an addedinvestment during construction to reduce thefrequency of outlet structure repairs mayquickly yield a positive return in the form ofreduced maintenance costs. Similar conclu-sions can be reached for many other designand construction efforts, such as providingbetter access, using more durable materials,and selecting a BMP type that best suits siteconditions.

5.6. Community Acceptance

The final recommended design consideration


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once again involves those people who mayhave the greatest interest in the stormwatermanagement system: the community. Notcoincidentally, these same people will havethe greatest role in funding the facility’s main-tenance and will ultimately have the greatestrole in the various nonstructural programs in-tended to augment stormwater managementsystems in the future. To protect these inter-ests and encourage assumption of that role,it is up to the designer to help create a fa-cility that will be viewed as a communityasset rather than a liability.

As discussed above, this can be achieved onlyby considering the system's aesthetic value,preventing the creation of nuisances andsafety threats, minimizing and facilitating fa-cility maintenance, as well as achieving re-quired performance levels. It is only throughall of these factors that stormwater manage-ment will gain the understanding and cred-ibility it requires within the community.

6. SPECIFIC MAINTENANCECONSIDERATIONS

To further help stormwater management plan-ners, designers, and reviewers include sys-tem maintenance in their everyday thinking,three specific maintenance considerationshave been developed. These considerations,which were originally developed for the NewJersey Department of EnvironmentalProtection’s Stormwater Management Facil-ity Maintenance Manual, should ideally cometo mind whenever a stormwater managementpractice is pondered, planned, designed, orreviewed. The facility designer should pretendthat they must do the maintenance to see ifaccess and maintainability are provided.

6.1. Maintainability

Maintainability can be expressed in three

ways, all of which should be given equal im-portance by facility designers and reviewers:

Every effort should be made to mini-mize the amount and frequency ofregular maintenance at a stormwatermanagement system.Performance of the remaining mainte-nance tasks should be as easy to per-form as possible.All efforts should be made to eliminatethe need for emergency or extraordi-nary maintenance at the facility.

Recommended techniques for accomplishingthese goals, which can be used to both selectthe most appropriate type of BMP, as well asdesign and review it, are presented below.

6.2. Accessibility

According to many maintenance person-nel, the biggest problem they encounteris not the amount or frequency of mainte-nance they must perform, but the difficul-ties they have in simply reaching the loca-tion of the required maintenance work. Inorder for proper maintenance to be performed,the various components of the stormwatersystem and, indeed, the facility itself, must beaccessible to both maintenance personneland their equipment and materials. Physicalbarriers such as fences, curbs, steep slopes,and lack of adequate and stable walking,standing, climbing, and staging areas can se-riously hinder maintenance efforts and dras-tically increase maintenance difficulty, cost,time, and safety hazards. Amenities such asdepressed curbs, hand and safety rails, gates,access roads, hatches, and manholes will ex-pedite both inspection and maintenance ef-forts and help hold down costs and improveefficiency.

Important design considerations for compo-nents such as gates, hatches, manholes, trash


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racks, and other components that must belifted or moved during inspection or mainte-nance operations, include both the item'sweight and a secure place to put it when it’snot in its normal location. When weight be-comes excessive, mechanical aids such ashoists, lifts, and lifting hooks should be pro-vided. When fastening removable items liketrash racks, orifice and weir plates, and grat-ings, the use of noncorroding, removable, andreadily accessible fasteners will also helpgreatly.

Sometimes design considerations may con-flict. For example, in designing access roads,they must have the proper turning radius,slope, and wheel loading to allow cleaning ofa pond by heavy construction equipment. Theroad's storm drain covers, designed for thedesired wheel loading, may be too heavy tomove easily. Perhaps a different access waymay need to be provided.

Finally, legal barriers such as lack of ac-cess rights or inadequate maintenanceeasements can stop the best maintenanceefforts before they can even get started.This is especially pertinent to project review-ers, who normally have the authority to re-quire such legal aspects of the project.

6.3. Durability

The use of strong, durable, and noncor-roding materials, components, and fasten-ers can greatly expedite facility mainte-nance efforts. These include strong, light-weight metals such as aluminum for trashracks, orifice and weir plates, and accesshatches; reinforced concrete for outlet struc-tures and inlet headwalls; hardy, disease-re-sistant vegetation for bottoms, side slopes,and perimeters; and durable rock for gabionsand riprap linings. In most instances, theextra investment normally required for moredurable materials will pay off over time.

7. SUGGESTED DESIGN REVIEW TECHNIQUES

Throughout this chapter, the stormwater sys-tem designer has been encouraged to con-sider a wide range of interests, operating con-ditions, costs, and other responsibilitiesthroughout the design process. Presentedbelow are two recommended techniques tohelp accomplish it. They can either be usedas review techniques following completion ofa facility design or, ideally, be incorporatedinto the overall design process and used con-tinually during it.

7.1. Spend a Mental Year at the Facility

To use this technique, the stormwater de-signer or reviewer simply imagines condi-tions at the completed facility throughouta full year. This should not only include rainyand sunny weather, but also light rain show-ers (with little or nor runoff) and, where ap-propriate, both light and heavy snowfalls andfrozen ground conditions. Other site condi-tions may include late autumn, when treeshave lost their leaves and they have collectedat the facility bottom, and hot, dry weather ordrought, when the turf or other vegetation isstressed or killed. Finally, for safety purposes,the designer should also imagine what thesystem will be like at night.

As these conditions are visualized, the de-signer should also imagine how they mayaffect not only the operation of the sys-tem itself, but also the people that willmaintain it or otherwise interact with it. Willthe outlet structure’s trash rack be particularlyprone to clogging by fallen leaves, especiallyfrom the trees the designer just specified forthe facility’s bottom? Can falling and/or blow-ing snow completely fill the facility, leading theunsuspecting snow plower or pedestrian tothink that the grade is level? What about theice that will form on the surface of a pond or


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may prompt a revised design with a shorterlist.

When will maintenance need to be per-formed? Once a day? A week? A year?Remember, the recurring costs of systemmaintenance can be substantial. In addi-tion, can maintenance only be performedduring dry weather? If so, what happensduring two or three weeks of wet, rainyweather? What happens when repairs needto be made or debris removed during a ma-jor storm event? In terms of effort and pos-sible consequences, it is easier for the de-signer to find answers to these questionsnow, than for maintenance or emergencypersonnel to scramble for them later.

Where will maintenance have to be per-formed? Will the maintainer be able to getthere? Once there, will they have a stable,safe place to stand and work? In addition,where will such material as sediment, de-bris, and trash removed from the facility bedisposed of? Before answering that ques-tion, do you know how much there might beand what it might contain? Are there toxicor hazardous materials in the sediment ordebris? If so, is the place you originally in-tended to use for disposal still suitable?Once again, it is easier to address thesequestions now then when the dump truck isloaded and the engine’s running.

How will maintenance be performed?The simple instruction to remove the sedi-ment or harvest the vegetation can becomerather complicated if there hasn’t been anyprovisions made to allow equipment to getto the bottom of the facility or even into thesite. “Mowing the grass” can become “risk-ing your limbs” on long, steep slopes. Howwill you explain to your client why thestormwater management facility they haveinvested in has become a liability to them-selves and their community?

constructed wetland? Can someone fallthrough? Could that someone be a child takinga shortcut home or out looking for a place toskate? How will they be warned not to? Howwill they be rescued if they do anyway?

What about night conditions? Will the con-structed wetland next to the office parking lotthat’s so attractive during summer lunch hoursbecome a safety hazard to workers walking totheir cars in the winter’s darkness? Or will thatsame summer sun and a lack of rainfall pro-duce some of the wonderful aromas of anaero-bic decomposition?

At first, it may be exasperating to realize thatthe number of possible site conditions and cir-cumstances can be as numerous and varied asthe number of possible facilities types. But thenagain, that is the point of this exercise. It isintended to help the designer consider and de-sign for all possible conditions at the facility, notjust the 1 or 100-year storm event required bythe regulations. In doing so, the facility designerwill not only meet the letter of the regulations,but will raise the spirit of the entire stormwatermanagement program.

7.2. Who, What, When, Where, and How?

The second recommended review technique asystem designer may employ is to simply focuson one or more characteristic or function of thefacility and then ask (and attempt to answer)the above question. For example, let’s considerstormwater system operation and maintenanceand then ask:

Who will perform it? Does the stormwatersystem’s design require specialists or willsomeone with general maintenance equip-ment and training be able to do the job?

What needs to be maintained? Preparinga list of all facility components included in adesign that will need attention sooner or later


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Similar exercises can be performed with con-structors, inspectors, and residents as the ob-ject of inquiry. For example, where will the near-est residence be? How will the constructor buildthe emergency spillway? When will an inspec-tor need to visit to check for mosquitoes?

Similar to the “mental year” review tech-nique, the questions raised in this techniqueare intended to make the designer moreaware of all the possible impacts the facilitymay have and, further, to encourage the de-signer to address those impacts now, dur-ing the design phase, rather than leave themfor others, particularly maintenance personnel,to cope with later. Even if the designer cannotcompletely answer all of the questions, he orshe will be able to advise the others of any un-avoidable needs or problems that will be inher-ent in the facility and allow them time to ad-equately prepare.

8. DESIGN GUIDELINES

Presented on the following pages are tech-nical design guidelines that are intended tominimize and facilitate maintenance at de-tention, infiltration, filtration, and biofiltrationpractices. Separate guidelines are presentedfor each BMP type. In addition, the guidelinesare further divided into each facility’s major com-ponents for easier reading and reference use.Descriptions of typical maintenance problemsat various facility components have also beenincluded to further stimulate the reader’s effortsto produce BMP designs that require minimumlevels of maintenance effort. The technicalguidelines have been based upon similar guide-lines presented in the Stormwater ManagementFacilities Maintenance Manual prepared by theN.J. Department of Environmental Protection.

It is important to note that the guidelinesshould be used with all other hydrologic, hy-draulic, structural, geotechnical, biological,aesthetic, and legal requirements of the

stormwater management program govern-ing the design of a particular facility or prac-tice. As such, they are not meant to conflict orreplace these requirements but, instead, tocomplement and expand them. Finally, a re-sponsible designer understands that eachproject and facility site is unique and may re-quire special, additional, or more strict mea-sures.

9. SUMMARY

Stormwater management must still be consid-ered a relatively new endeavor, particularly ona nationwide basis. However, despite that sta-tus, it has been charged with the responsibilityof addressing some very complex environmen-tal problems. In order for stormwater manage-ment to grow to the level demanded by thischarge, the designers of stormwater manage-ment facilities must be willing to assume a de-gree of responsibility for that growth. BMP de-signers can fulfill that responsibility by pro-ducing facility designs that do not merelymeet official regulations and standards, buthelp inspire new, better, and more compre-hensive ones.

Facility designers must also incorporate a widerange of interests into the facility design, includ-ing those held by stormwater program regula-tors, contractors, maintainers, and those mem-bers of the community interacting with the facil-ity and paying for its long term maintenance.During the design process, the facility designermust not only consider the facility’s performance,but also the extent, frequency, difficulty, and costof facility maintenance. Finally, the BMP de-signer must always recognize the facility’s im-pacts both on the community around it and thestormwater management program the commu-nity has entrusted them with.


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10.1. INTRODUCTION

The following technical design guidelines areintended to help planners, designers, and re-viewers produce stormwater detention sys-tems that require minimum levels of mainte-nance. Typical detention practices include:

••••• Dry Detention Basins••••• Extended Dry Detention Basins••••• Wet Detention Basins or Ponds••••• Subsurface Detention Facilities

To help accomplish this minimum mainte-nance goal, the design guidelines have beendeveloped to:

1. Eliminate avoidable maintenanceinspections, tasks, and problems.

2. Minimize the long term amount ofregular facility maintenance.

3. Facilitate required maintenanceinspection and tasks.

4. Reduce the potential for extensive,expensive, and often difficult remedialor emergency maintenance efforts.

It is important to note that these designguidelines are intended to supplement allother applicable facility design standardsand requirements, including those pertain-ing to a facility’s hydrologic, hydraulic,structural, geotechnical, environmental,legal, and aesthetic aspects. As such, theyshould be used creatively with all otherapplicable standards and requirements toproduce stormwater detention systemsthat require optimum levels of mainte-nance performed with the least practicaleffort, time, and expense. Those involvedwith the planning, design, and review of spe-cific stormwater management systems must

10. DESIGN GUIDELINES FOR DETENTION PRACTICES

assume their share of the responsibilities fora system's performance, longevity, and safety.

To assist in their use, the technical designguidelines are presented separately for eachmajor facility component as listed in Table 3-1. Complete descriptions of each type of de-tention BMP are presented in Chapter 2.

Descriptions of typical maintenance prob-lems encountered at each facility compo-nent are also described. These descrip-tions, which have been based upon facil-ity inspections and interviews with main-tenance personnel, highlight the types ofmaintenance problems that the designguidelines are intended to prevent or mini-mize. They should serve to further stimulateplanners, designers, and reviewers to developadditional, improved, and/or site-specific de-signs.

10.2. BOTTOMS

A. Dry and Extended Detention DryFacilities

In a study performed by the N.J. Departmentof Environmental Protection, facility bottomswere the most likely location of chronic main-tenance problems at dry and extended drydetention facilities. Typical problems that im-pede or unnecessarily increase proper facil-ity maintenance include:

••••• Standing Water••••• Soggy Surfaces••••• Poor Grass Growth••••• Excessive Sedimentation••••• Limited Access

1. To promote complete emptying and pre-vent standing water or soggy surfaces, veg-etated bottoms should have a minimum slope


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of 2 percent and be graded to the outlet struc-ture or low flow channel.

2. To promote complete emptying and pre-vent standing water or soggy surfaces, thelowest point in the bottom should be at least4 feet above the seasonally high ground wa-ter level or bedrock unless adequate subsur-face drains are provided.

3. To provide adequate drying time, to avoiddelaying scheduled maintenance efforts, andto prevent mosquito breeding, the maximumstorage or ponding duration should not ex-ceed 24-48 hours, depending on thevegetation's tolerance to wetness.

4. To avoid delaying scheduled maintenanceefforts, topsoils and subsurface soils shouldbe sufficiently permeable to allow rapid infil-tration, evaporation, and evapotranspiration.

5. Subsurface drains connected to the prin-cipal outlet structure, low flow channel, orother discharge point are encouraged to pro-mote quick and thorough drying of the facilitybottom. In doing so, care should be taken toprevent stormwater inflow from inadvertentlybypassing the basin’s outlet controls. (SeeG. LOW FLOW MEASURES for additional de-tails.)

6. To minimize routine grass maintenancesuch as mowing and fertilizing, the use of na-tive grass varieties that are relatively slowgrowing and tolerant of poor soil conditionsare encouraged. Information on native grassvarieties and mixtures are available fromagencies such as the local Cooperative Ex-tension Service or Soil Conservation District.(See H. VEGETATIVE COVER for additionaldetails.)

7. To promote lasting growth, grasses andother vegetative covers should be compatiblewith the prevailing weather and soil conditionsand tolerant of periodic inundation and runoff

pollutants. (See H. VEGETATIVE COVER foradditional details.)

8. To facilitate removal efforts, sedimentationshould be promoted at localized, readily ac-cessible areas. Sediment traps or forebaysat inflow and outflow points should always beused. Those lined completely or partially withsmooth materials such as reinforced concretecan be more readily cleaned. For these rea-sons, the exclusive use of loose stone, riprap,and other irregular linings which requiremanual removal of weeds, sediment, and de-bris should be avoided wherever possible.

9. Wherever possible, sediment disposal andstorage areas should be provided adjacent tothe facility. These areas should optimally bedesigned to contain removed sediment, on along-term basis.

10. Suitable access for maintenance person-nel and equipment needs to be provided tothe facility bottom. (See J. ACCESS for de-tails.)

11. Construction plans and specificationsshould include provisions that minimize thepotential for localized settlement and subse-quent ponding. These provisions include

Forebays trap sediment and debrisbefore it enters the facility in areasthat can be more readily cleaned.


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1. In order to promote a healthy aquatic eco-system, the minimum permanent pool depthshould be 4 feet or greater. On the other hand,it should not be so deep as to allow thermalstratification to develop in the summer, withthe resultant likelihood of anaerobic conditionsdeveloping in the bottom stratum. Depthshould be limited to that at which small lakesin the vicinity stratify; 8 feet maximum is prob-ably a widely applicable limit.

2. Design of a wet detention system shouldinclude the determination of the proposedsite’s ability to adequately support a viablepermanent pool with an equally viable eco-system. The design should account for suchfactors as the required rate and quality of dryweather inflow, the quality of stormwater in-flow, seasonal and longer term variations inthe ground water table, and the effects of ex-pected sediment and other pollutant loadings.In the highly seasonal climates of the WestCoast, it may be appropriate to design for asemipermanent wet pool, which graduallydries in the summer.

3. The establishment of predacious native (ifpossible) fish species in the permanent poolwill help control mosquito breeding, but intro-duction of nonnatives or fish not already es-tablished in the area should be avoided.

4. Provisions to drain the permanent pool arenecessary for maintenance and safety. Agravity drain is the preferred method. If thisis not feasible, suitable pumps and both pri-mary and backup power sources should beprovided. To ensure that they are availablewhen needed, all pumps and backup powersources should be reserved for facility useonly. In residential communities, pumps mayonly be allowed to run during daytime hoursdue to noise. This needs to be consideredwhen determining times for the drainage tooccur.

proper surface and subsurface soil charac-teristics, compaction requirements, gradingequipment, and erosion control prior to theestablishment of permanent vegetative cover.

12. All nonvegetative linings which are bor-dered by grass should be designed to permitcomplete mowing along all edges.

13. At subsurface detention facilities, suit-able access, observation points and/or moni-toring wells should be provided to facilitateinspection and cleaning. (See J. ACCESSfor additional details.)

B. Wet Detention Facilities

While unseen, wet detention system bottomscollect sediment and other material at a muchfaster rate than their dry counterparts. Re-moval of this material can be difficult and ex-pensive. Other problems may arise in theaquatic ecosystem as well. Typical problemsthat impede or unnecessarily increase properfacility maintenance include:

Poor Water Quality Limited Access and Staging Areas Non-Permanent Pool Excessive Sedimentation

Access to all areas of the facility byboth personnel and equipment is vital

to successful maintenance.


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5. To promote complete emptying of the per-manent pool when necessary, the bottomshould have a minimum slope of 2 percentand be graded to the outlet drain or pump in-take.

6. Water quality, including suitable oxygenlevels, should be maintained through continu-ous recharge with fresh water from naturalsurface or subsurface sources. Alternatively,orienting the detention system to take advan-tage of prevailing winds can help to promoteaeration and circulation. Mechanical aera-tion should be relied upon only when abso-lutely necessary.

7. To facilitate removal efforts, sedimentationshould be promoted at localized, readily ac-cessible areas upstream of the permanentpool. The BMP Treatment Train is stronglyrecommended for wet detention systems, es-pecially if they are to be promoted as "lakes"and serve as an aesthetic and recreationalamenity for the development. Swale convey-ances and sediment traps or forebays at in-flows are encouraged. Those lined completelyor partially with smooth materials such as re-inforced concrete can be more readilycleaned. For these reasons, the exclusive useof loose stone, riprap, and other irregular lin-ings which require manual removal of weeds,sediment, and debris should be avoided wher-ever possible.

8. Wherever possible, sediment disposal andstorage areas should be provided adjacent tothe facility. These areas should optimally bedesigned to contain 5 years or more of re-moved sediment.

9. Suitable access for maintenance person-nel and equipment should be provided to thefacility bottom to allow proper use of equip-ment that is used by the maintainer. (See J.ACCESS for details.)

10.3. DAMS, EMBANKMENTS, AND SIDESLOPES

Typical problems that impede or unnecessar-ily increase proper maintenance include:

••••• Steep Slopes••••• Long, Continuous Slopes••••• Poor Grass Growth••••• Sloughing and Erosion

1. For safe movement of maintenance per-sonnel and safe operation of equipment, sideslopes greater that 5 feet in height should notbe steeper than 4 horizontal to 1 vertical. Sideslopes less that 5 feet high should not exceed3 horizontal to 1 vertical. Flatter side slopesare recommended wherever possible.

2. For safe movement of maintenance per-sonnel and safe operation of equipment, sideslopes steeper than 5 to 1 and higher than 15feet should be terraced at their midpoints. Theterrace should have a minimum width of 3 feetand should be graded at 2 percent or flattertowards the lower half of the slope.

3. Suitable access to and along side slopesshould be provided for maintenance person-nel and equipment. (See J. ACCESS for de-tails.)

Mild side slopes allow maintenancepersonnel to perform their jobs

quickly and safely.


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4. Topsoil and vegetative covers must be pro-tected from erosion caused by local runoff andthe slope’s steepness. Surface and subsur-face soil stabilization measures ornonvegetated linings should be used as nec-essary. In doing so, avoid the use of loosestones, riprap, and other irregular lining ma-terials which require hand removal of weedsand debris and may be a safety hazard tomaintenance personnel walking along or upthe slope.


6. The effects of rapid pool drawdown shouldbe checked to prevent side slope sloughing.

7. For safe movement of maintenance per-sonnel and safe operation of equipment,fences should not be constructed within 3 feetof either the top or toe of any side slope thatexceeds 5 horizontal to 1 vertical.

8. Below the permanent pool level at wet de-tention facilities, a 4-foot to 10-foot wide levelarea or safety ledge should be provided toprevent people or objects from sliding or fall-ing into deeper water. This area can be used

to create a vegetated littoral zone along theshoreline. The vegetated littoral zone pro-vides biological processing of dissolved pol-lutants, requires less regular maintenancethan a grass shoreline, and provides habitatfor predacious insects, fish, and birds whichcontrol mosquito breeding.

9. Durable linings such as gabions or riprapneed to be considered along wet detentionsystem shorelines prone to erosion due to ex-cessive wave action or ice movement. Suchlinings should extend sufficiently above andbelow the permanent water level to accountfor wave and ice run-up.

10.4. PRINCIPAL OUTLETS


••••• Structural Deterioration••••• Limited Access••••• Corroded Appurtenances••••• Vandalism••••• Excessive Debris Accumulation

1. For durability, principal outlet structuresshould be constructed of reinforced concretecontaining Type II cement and having a mini-mum specified 28-day compressive strength

Adequate distance should be providedbetween the top of a slope and adjacentstructures such as fences, walls, curbs,

or roadways.

Good shoreline erosion protection isvital for facility maintenance and safety.


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of 3,000 PSI. Concrete shall be designed inaccordance with all applicable codes and re-quirements.

2. For durability, all appurtenances, includ-ing access hatches, trash racks, gratings, rail-ings, orifice and weir plates, and fastenersshould be constructed of lightweight, noncor-roding materials. Material strengths shouldbe sufficient to withstand design loads with-out damage or failure.

3. Outlet orifice and weir plates should beconstructed from aluminum or other light-weight, noncorroding material. The platesshould be fastened to the structure with non-corroding, removable fasteners. A gasket ofneoprene or similar material should be placedbetween the plate and the structure wall. Theopening in the structure wall over which theplate is bolted should have at least twice thearea of the outlet orifice or weir to facilitatefield adjustments and future expansion. SeeFigure 3-A at the rear of this chapter for de-tails.

4. To facilitate access and movement by main-tenance personnel, principal outlet structuresshould have a minimum horizontal interior di-mension of 4 feet. (See J. ACCESS for addi-tional details.)

5. Vital parts of the principal outlet structureshould be readily and safely accessible tomaintenance personnel during both normaland emergency conditions. Gate valvesshould be able to be operated in the dry whenthe maximum design water level occurs. Tem-porary measures such as ladders are only ac-ceptable for emergency conditions as part ofan approved emergency action plan. (See J.ACCESS for additional details.)

6. To minimize both required maintenanceand the consequences of inadequate mainte-nance, principal outlets should avoid usingmoving or mechanized parts for outflow con-trol whenever possible.

7. To facilitate cleaning, outlet pipes shouldhave a minimum diameter of 15 inches. Thepipes should be constructed of durable mate-rials, such as reinforced concrete. To mini-mize potential leakage problems, the numberof outlet pipes should be kept to an absoluteminimum. More than one outlet pipe shouldbe used only where unavoidable. All outletpipes must be watertight under the maximumexpected head or pressure.

8. Grading and landscaping around principaloutlet structures should be designed to facili-tate mowing, trimming, debris removal, andother general maintenance tasks. Grassedslopes which require mowing should not ex-ceed 3 horizontal to 1 vertical. Vegetatedcover which does not require mowing ornonvegetated linings should be used wheresteeper slopes are necessary.

9. Stable areas that provide maintenancepersonnel with firm footing should be providedat the upstream face of principal outlet struc-tures at dry and extended dry facilities. Lin-ings such as reinforced concrete, gabions,and grouted riprap should be considered.

10. All nonvegetative linings which are bor-dered by grass should be designed to permit

Outlet structure gratings, trash racks,and other appurtenances should belightweight, durable, and removable.


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complete mowing along all edges.

11. Dry weather flow through a principal out-let structure should not interfere with routineinterior maintenance tasks. Benching, lowflow pipes and channels, drop structures, orsimilar measures should be used to conveylow flow into and through the structure.

12. Principal outlet structures should be de-signed to discourage vandalism and graffiti.The use of aesthetic type vegetation to coverwalls is encouraged.

10.5. OUTFLOW SYSTEMS


••••• Difficult to Clean••••• Erosion and Scour••••• Excessive Sedimentation••••• Displaced Lining

1. The outflow conveyance system down-stream of a detention system should have ad-equate capacity to accommodate its outflows.This will not only allow design outflows andwater surfaces to be attained, but will also helpachieve required drawdown and emptyingtimes.

2. Outflow velocities should be high enoughto prevent sedimentation and low enough toprevent erosion and scour.

3. Manholes, grates and other suitable ac-cess points should be provided for cleaningand inspection. (See J. ACCESS for addi-tional details.)

10.6. INLETS


••••• Difficult to Clean••••• Erosion and Scour••••• Excessive Sedimentation••••• Displaced Lining

1. The number of inlets to a detention systemshould be kept to a minimum. This will mini-mize the amount of required downstream lin-ing, forebays, and low flow channels. All in-flow pipes and culverts should terminate at aheadwall or flared end section with adequatecutoff walls. Inlet pipes or channels should beplaced on a minimum slope to prevent highentrance velocities. If high velocities can notbe avoided, the designer should consider rip-rap inlet protection to prevent erosion and baf-fling to slow flow and guard against short cir-cuiting to the outlet.

Inlets should be located to prevent or mini-mize flow short-circuiting. If inlets and outletscannot be spaced so that the flow path lengthis at least three, and preferably, five times theaverage width (dimension perpendicular tolength), the designer should attempt tolengthen the flow path by moving the inlet and/or outlet or using baffles to divert flow. An-other excellent impediment to short circuitingis dividing the system into two cells with flowrestricting to passing through a single pointbetween them.

Facility inlets must terminate with aheadwall or flared end section to

prevent scour and provide stability.


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2. Linings placed downstream of facility in-lets should accommodate design flows with-out erosion or scour. They should also facili-tate removal of sediment, trash, debris, andundesirable vegetation.

3. Forebays and other localized sediment anddebris traps should be placed immediatelydownstream of facility inlets. Where practi-cal, avoid loose stone, riprap, and other ir-regularly shaped linings which require handremoval sediment, trash, and debris. (See A.BOTTOMS for additional details.)

4. The BMP Treatment Train approach shouldbe used to minimize sediment entering the fa-cility. Street sweeping, offsite soil stabiliza-tion measures, and upstream sedimentationbasins, swales, and other source controlBMPs can significantly reduce the frequencyof required sediment and trash removal op-erations.

5. To facilitate cleaning, inflow pipes shouldbe a minimum diameter of 15 inches. Thepipes should be constructed of durable mate-rials, such as reinforced concrete, ductile iron,or PVC. Inlet pipes should not have trashracks placed on them at their outlets into thepond to prevent plugging of the inlet and wa-ter backing up into the site drainage system.

6. Grading and landscaping around facilityinlets should be designed to facilitate mow-ing, trimming, debris removal, and other gen-eral maintenance tasks. Grassed slopeswhich require mowing should not exceed 3horizontal to 1 vertical. Vegetated cover whichdoes not require mowing or nonvegetated lin-ings should be used where steeper slopes arenecessary.

7. Stable areas which provide maintenancepersonnel with firm footing should be providedat facility inlets. Linings such as reinforcedconcrete and gabions should be considered.

8. All nonvegetative linings which are bor-dered by native grass should be designed topermit complete mowing along all edges.

9. Dry weather flow from a facility inlet shouldnot interfere with routine maintenance tasks.Benching, low flow pipes and channels, dropstructures, or similar measures should be uti-lized to convey low flow from the inlet to theprincipal outlet.

10.7. EMERGENCY OUTLETS


Difficult to Clean Erosion and Scour Excessive Sedimentation Displaced Lining

1. Grass and other vegetative cover is en-couraged whenever flow velocities, soil sta-bility, and other design constraints permit.Surface and subsurface soil stabilization mea-sures should be used to increase allowableflow velocities and to reduce erosion andscour. [Note: Safe passage of emergencyoverflows and emergency spillway stabilitymust, however, receive first priority and mustnot be compromised by selection of emer-gency outlet lining.]

2. Where nonvegetative linings are required(see 1 above), loose stone, riprap, and otherirregular linings which require hand removalof trash, debris, and undesirable vegetationshould be avoided.


4. See B. DAMS, EMBANKMENTS, ANDSIDE SLOPES for information regardingemergency outlet side slopes.


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use of loose stone, riprap, and other materi-als with irregular surfaces which require handremoval of trash, debris, and undesirable veg-etation.

In addition, use of low flow channels must bebalanced with the need for pollutant removalin the facility. Therefore, low flow channelslined with nonvegetated lining should be usedin conjunction with pretreatment BMPs suchas inlet forebays and/or outlet structure wet-lands, or the channel's should include portionswith vegetated linings.

5. Low flow channel underdrains connectedto the principal outlet structure or other stabledownstream discharge point are recom-

Sediment and debris can be removedmore easily from low flow channelslined with concrete or other smooth,

durable material.

10.8. LOW FLOW MEASURES - DRY ANDEXTENDED DRY FACILITIES

Since low flow measures are typically one ofthe first facility components to receive sedi-ment, trash, and debris from incoming runoff,they usually require a high degree of mainte-nance Typical problems that impede or un-necessarily increase proper maintenance in-clude:

Erosion and Scour Difficult to Clean or Mow Settlement Excessive Sedimentation

However, while attempting to minimize lowflow channel maintenance, care should betaken to avoid reducing the system’s pollut-ant removal capabilities.

1. To ensure thorough drying of the facilitybottom, low flow channels should have suffi-cient capacity to convey the normal, dryweather discharges from the facility inlets tothe principal outlet structure without overtop-ping. The resultant channel size should alsoconsider the use of readily available liningmaterials or construction equipment.

2. Design velocities in low flow channelsshould be low enough to prevent erosion oflinings.

3. To simplify mowing and minimize trimming,grass-lined low flow channels are recom-mended whenever non-erosive velocities,smooth alignment, and thorough drying be-tween storm events can be achieved.

4. Where low flow channels withnonvegetative lining are required, the use ofgabions, concrete, grouted riprap, or otherdurable material with a relatively smooth sur-face is recommended to facilitate trash anddebris removal and simplify mowing and trim-ming of adjacent grassed areas. Avoid the


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mended to promote quick, thorough drying ofboth the low flow channel and facility bottom.

6. To prevent erosion and scour, bank fullvelocities in low flow channels lined withnonvegetative lining should not exceed themaximum permissible velocity in adjacentgrassed or vegetated areas. If non-erosivevelocities cannot be achieved, the liningshould be extended into the adjacent areas.When checking the bank-full velocities, theeffects of submergence by the principal out-let structure during passage of the bank-fullflow must be considered.

7. To ensure thorough drying of adjacentgrassed areas, low flow channels lined withconcrete, grouted riprap, and other rigid, im-pervious material should be designed with thetop of the lining at or below the elevation ofadjacent grassed areas. This will also assistmowing and trimming. To achieve this, con-sideration should be given to the potential forsettlement of both the impervious lining andadjacent areas and the effects of frost actionon the lining. Broken stone foundations andweep holes should be provided for all imper-vious lining. (See No. 8 below) In addition,the required depth and width of the low flowchannel must be remembered when prepar-ing the bottom grading plan.

8. Four inch diameter weep holes should beprovided in all rigid, impervious linings to re-duce hydrostatic pressure resulting from fluc-tuating groundwater levels. These weep holesshould be spaced a maximum of 12 feet oncenter or one for every 100 square feet of lin-ing, whichever is less. Weep holes must notbe directly connected to any low flow channelunderdrain pipe. Place geotextile filter fabricunder weepholes.

9. In subsurface facilities, dry weather inflowshould not interfere with routine inspection andmaintenance. Benching, underdrains, drop in-lets, and other measures should be utilized.

10.9. VEGETATIVE COVER


Excessive Sedimentation Erosion and Scour Difficult to Mow Poor Growth (traffic, compaction)

1. To minimize maintenance efforts, the useof existing, undisturbed site vegetation is en-couraged. To do so, the existing site topog-raphy must provide adequate storage volume.Where disturbance of existing vegetation can-not be avoided, replacement with low main-tenance, preferable native, vegetation withstrong resistance to disease and allelopathic(self-weeding) characteristics is encouraged.

In general and where appropriate, turf grassmay be easier to establish and maintain thanother types of ground cover vegetation. How-ever, pollutant removal efficiency will gener-ally be reduced. The use of native grass va-rieties that are relatively slow growing and tol-erant of poor soil conditions, crown vetch inthe East, will minimize routine maintenancetasks such as mowing and fertilizing.

The need for supplemental fertilizing can besubstantially reduced when the vegetativecover includes a percentage of nitrogen-fix-ing species, such as white clover and otherlegumes. In addition to minimizing mainte-nance costs, a reduction in required fertiliza-tion will also minimize the potential pollutioneffects of nutrients such as nitrogen and phos-phorus in the outflow.

3. To promote lasting growth, grasses andother vegetative covers should be compatiblewith the prevailing weather and soil conditionsand tolerant of periodic inundation and runoffpollutants.

4. To promote lasting growth, an adequate


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depth of suitable topsoil should be providedbelow all vegetative covers. A minimum thick-ness of 4-6 inches is recommended for turfgrasses.

5. Construction plans and specificationsshould include requirements for establishingall vegetative covers including requirementsfor reseeding or resodding as necessary.

6. At dry and extended dry detention systems,the effects of sediment removal from veg-etated surfaces should be considered in theselection of appropriate cover.

7. Additional information on vegetative cov-ers is available from such agencies as theNatural Resource Conservation Service, lo-cal Soil Conservation Districts, and CountyCooperative Extension Service offices. Con-sultation with these agencies during facilityplanning, design, and review is encouraged.

10.10. TRASH RACKS


Difficult to Clean Difficult to Remove Structural Failure Excessive Debris

1. Trash racks are intended to prevent trashand debris from blocking a facility outlet byintercepting it at an upstream point. There-fore, the need for a trash rack should be basedupon the relative sizes and shapes of boththe outlet opening and the anticipated debrisas well as the consequences of outlet clog-ging. Special consideration should be givento subsurface facilities.

2. For durability, all track rack components,including bars, hinges, fasteners, and clamps,should be constructed of lightweight, noncor-

roding material such as aluminum. The com-ponents should have sufficient design strengthto withstand anticipated heavy loads causedby facility outflows, debris, and, where nec-essary, maintenance personnel.

3. To facilitate cleaning, trash racks shouldbe comprised primarily of sloping bars, alignedlongitudinally (in the direction of flow). Per-pendicular bars, aligned transverse to the di-rection of flow, should be added for strengthand rigidity. These transverse bars shouldbe located below the top face of the longitudi-nal bars and, if possible, should be round insection. See Figure 3-B at the rear of thechapter for details.

4. To minimize the frequency of cleaning,trash rack bars should be spaced closeenough to collect debris which may block theoutlet orifice or weir but allow passage ofsmaller debris which will not. In general, lon-gitudinal bars should be spaced a distanceequal to 1/3 to 1/2 the diameter of the outletorifice or 1/3 or 1/2 the width or height (which-ever is less) of the outlet weir. Minimum andmaximum spacings of 1 inch and 6 inches oncenter, respectively, are recommended.Transverse bars should be spaced as neces-sary for strength and rigidity. See Figure 3-Bfor details.

Sloping trash rack bars aligned in thedirection of flow are more easilycleaned. Add transverse bars as

needed for stability.


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5. Trash racks should be sloped and hingedor attached with noncorroding, removable fas-teners to allow access to the outlet orifice orweir by maintenance personnel. Lightweighttrash racks are easier to lift, repair, and cleanbehind. See Figure 3-B for details.

6. Trash racks should be accessible for clean-ing when the system is dry (at dry and ex-tended dry facilities) or at normal or perma-nent pool levels (at wet facilities). In addi-tion, access should also be provided when thewater level is at the facility’s maximum de-sign water surface elevation. Stable areas ofadequate size should be provided around atrash rack to provide firm footing for mainte-nance personnel and equipment. Concretepads of other firm surfaces are recommended.

7. At wet detention systems, stable areas ofadequate size should be provided at all trashracks which protect permanent pool drains.Concrete pads or other firm surface is recom-mended.

10.11. ACCESS

Typical problems that impede or unnecessar-

ily increase proper maintenance include:

Inadequate or Unsafe Access to Fa-cility ComponentsHeavy or Inoperable Gratings andHatchesMultiple or Corroded LocksLack of Fence Gates

1. The stormwater facility must be readily ac-cessible from a street or other public right-of-way. Inspection and maintenance easements,connected to the street or right-of-way, shouldalso be provided around the entire facility. Theexact limits of the easements and right-of-wayshould be specified on the project plans andother appropriate property and legal docu-ments.

2. Field evaluations indicate that readily vis-ible detention systems receive more and bet-ter maintenance than those in less visible,more remote locations. This finding shouldbe kept in mind during overall site layout.Readily visible facilities can also be inspectedfaster and more easily by maintenance andmosquito control personnel.

3. Access roads and gates should be wideenough to allow passage of necessary main-tenance vehicles and equipment, includingtrucks, backhoes, grass mowers, and mos-quito control equipment. In general, a mini-mum right-of-way width of 15 feet and a mini-mum roadway width of 12 feet is recom-mended. Access gates should be sited to al-low vehicles to park off road for gate opening.

4. To facilitate entry, a curb cut should beprovided where an access road meets acurbed roadway.

5. To allow safe movement of maintenancevehicles, access ramps should be providedto the bottoms of all detention systems greaterthat 5 feet in depth. Vehicle access rampsshould not exceed 10 percent in grade.

Hinged, lightweight trash racks can bequickly lifted for cleaning and

inspection. Also note outlet orificeplate mounted to outlet structure wall

with removable anchor bolts.


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6. Access roads and ramps should be stableand suitably lined to prevent rutting and otherdamage by maintenance vehicles and equip-ment.

7. When backing-up is difficult or dangerous,turnaround areas should be provided at theend of all access roads.

8. To expedite overall maintenance efforts,vehicle and equipment staging areas shouldbe provided at or near each facility site.

9. A suitable number of gates should be pro-vided in all fences. The gates should be wideenough to allow passage of necessary equip-ment and personnel. They should be appro-priately located so that they can be fullyopened without interference by trees, parkedcars, existing or proposed grades, or otherobstructions. If it is necessary to lock a gate,it should be done with a noncorroding chainand padlock. This will permit the installationof additional padlocks on the chain (each pad-lock becomes a link in the chain), thereby al-lowing authorized access through the gate bymore than one person without the need formultiple keys.

10. Safe, suitable access for maintenancepersonnel and equipment should be providedto the exterior of each facility component. Indoing so, avoid remote component locations,steep slopes, unstable surfaces and linings,and narrow walkways.

11. Suitable access should be provided alongboth sides of a fence for mowing, trimming,and fence repair.

12. Safe, suitable access for maintenancepersonnel and equipment should be providedto the interior of the principal outlet. In doingso, avoid heavy hatches, gratings, and othercovers. Railings, grab rails, slip-resistantsteps, low flow channels, benchings, andhinged, lightweight access covers greatly fa-

cilitate interior maintenance. Sufficient inte-rior space should also be provided. A mini-mum horizontal dimension of 4 feet is recom-mended.

13. At subsurface detention systems, suit-able access, observation points, and moni-toring wells should be provided to allow in-spection and cleaning. Access should be pro-vided to all major components, particularly atinlets and the principal and emergency out-lets, and wherever sediment deposits are ex-pected. This will permit sediment and debrisremoval through high pressure water sprayand vacuum (e.g., Jet-Vac). All access pointsshould be at safe locations on the surfacewhich can be readily accessed, safely barri-caded, and clearly identified.

Confined space entry considerations must beconsidered including:

proper ventilationadequate opening for full protectiondevices, etc.

Successful facility maintenance demands adequate access for

personnel and equipment. Note bothwide access gate and concrete curbing

that keeps it accessible.


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10.12. PERIMETERS


Difficult to MowInadequate SizeToo Close To Adjacent Structures

1. Field evaluations indicate that readily vis-ible detention systems receive more and bet-ter maintenance than those in less visible,more remote locations. This finding shouldbe kept in mind during overall site layout.Readily visible facilities can also be inspectedfaster and more easily by maintenance andmosquito control personnel.

2. Fences, when required for safety or otherpurposes, should be located to minimize in-terference with grass mowing and trimming.Suitable access should be provided alongboth sides.

3. To allow safe movement of maintenancepersonnel; and equipment, fences should belocated at least 3 feet beyond the top and toeof any slope steeper than 5 horizontal to 1vertical.

4. Fences should be constructed of durable,vandal-resistant materials. Fences must meetall local code requirements.

5. To minimize the amount of required trim-ming, fences in grassed areas should be in-stalled, whenever practical, with a bottom railset high enough above finished grade to al-low mowing beneath it.

6. Grassed areas beyond the tops of deten-tion systems should have a minimum slope of2 percent to promote effective surface drain-age and thorough drying.

7. Perimeters should be planned and de-signed to discourage vandalism and dump-ing of trash and debris.

8. Facility perimeters should be large enoughto allow movement and operation of mainte-nance and mosquito control equipment. Aminimum perimeter width of 25 feet betweenthe facility and adjacent structures is recom-mended along at least one side of the facility.This portion of the perimeter should be readilyaccessible from a street or other public right-of-way.

Lack of accessprevents

maintenance.


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11. DESIGN GUIDELINES FOR INFILTRATION PRACTICES

with the planning, design, and review of spe-cific stormwater management systems mustassume their share of the responsibility for asystem's performance, longevity, and safety.

To assist in their use, the technical designguidelines are presented separately for eachmajor facility component as listed in Table 3-1. Complete descriptions of each type of in-filtration practice is presented in Chapter 2.

Descriptions of typical maintenance problemsencountered at each facility component arealso described. These descriptions, whichhave been based upon facility inspections andinterviews with maintenance personnel, high-light the types of maintenance problems thatthe design guidelines are intended to preventor minimize. They should serve to furtherstimulate planners, designers, and reviewersto develop additional, improved, and/or site-specific designs.

11.2. BOTTOMS

In a study performed by the N.J. Departmentof Environmental Protection, the bottoms ofinfiltration basins and swales were the mostlikely location of chronic maintenance prob-lems. Typical problems that impede or un-necessarily increase proper maintenance in-clude:

Standing Water Soggy Surfaces Poor Grass Growth Excessive Sedimentation Limited Access

1. The infiltration rate of the soil will deter-mine a site’s suitability as an infiltration sys-tem. In general, infiltration practices shouldonly be constructed in areas of Hydrologic Soil

11.1. INTRODUCTION

The following technical design guidelines areintended to help planners, designers, and re-viewers produce stormwater infiltration facili-ties that require minimum levels of mainte-nance. Typical infiltration practices include:

Infiltration BasinsInfiltration SwalesInfiltration TrenchDrywellsSeepage Pits

To help accomplish this minimum mainte-nance goal, the design guidelines have beendeveloped to:





It is important to note that these designguidelines are intended to supplement allother applicable facility design standardsand requirements, including those pertain-ing to a facility’s hydrologic, hydraulic,structural, geotechnical, environmental,legal, and aesthetic aspects. As such, theyshould be used creatively with all otherapplicable standards and requirements toproduce stormwater infiltration facilitiesthat require optimum levels of mainte-nance performed with the least practicaleffort, time, and expense. Those involved


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Group A or B as defined by the Natural Re-source Conservation Service. Borings, testpits, and other appropriate field tests shouldbe taken of the system’s surface and subsur-face soils. In subsurface facilities (e.g., drywells, seepage pits, infiltration trenches) whichare enveloped by geotextile or filter fabric, thelimiting infiltration rate of the facility may bedictated by the fabric instead of the surround-ing soil. See Chapter 2 for additional recom-mendations regarding the selection of appro-priate design infiltration rates for differenttypes of infiltration practices.

2. To provide adequate drying time, to avoiddelaying scheduled maintenance efforts, toavoid anaerobic conditions, and to preventmosquito breeding, the maximum storage orponding duration should not exceed 24-48hours, depending on the tolerance of thesystem's vegetation to wetness.

3. To promote complete infiltration and pre-vent standing water or soggy surfaces, thelowest point in the bottom of the facility shouldbe at least 4 feet above the seasonally highground water level or bedrock. Subsurfacedrains may be used to lower ground water lev-els and/or promote complete infiltration. (SeeNo. 4 below.) In determining the seasonallyhigh ground water level, the extent of poten-tial local ground water mounding due to theinfiltration of stormwater from the facility mustbe evaluated.

4. To promote complete infiltration and pre-vent standing water or soggy surfaces, bot-toms should have a minimum slope of 1 per-cent directed towards the center or other areaof the facility bottom. It is recommended thatbottoms be vegetated as the roots help tomaintain soil permeability and the vegetationhelps to minimize the potential for ground wa-ter contamination. A gabion-lined or stone-filled trench can be used to help promote in-filtration. This trench should be located at thelowest point in the bottom and extend to all

inlet points in order to direct small or dryweather inflows to the basin bottom. The el-evation of the trench bottom should be at least4 feet above the seasonally high ground wa-ter level or bedrock. See Figure 3-C at therear of the chapter for details.

5. To avoid delaying scheduled maintenanceefforts, topsoils should be sufficiently perme-able to allow thorough drying through evapo-ration and moisture uptake by vegetative cov-ers.

6. In order to prevent sloughing caused byoutflow seepage of infiltrated water, an infil-tration system should not be located on or neara steep slope. In general, a facility shouldnot be constructed where nearby slopes ex-ceed 15 percent. Appropriate geotechnicalanalyses should be conducted when neces-sary.

7. Sediment from construction operations canquickly clog soil pores of an infiltration sys-tem, often necessitating expensive mainte-nance work even before the facility is placedinto normal operation. Therefore, an infiltra-tion system should not be used for sedimentcontrol purposes during construction and, con-sequently, should not be constructed until theupstream drainage area is fully developed andadequately stabilized. If that is not feasible,the facility should not be excavated to it's fulldepth until all disturbed areas have been sta-bilized or protected. Thereafter, final exca-vation to finished grade should also includeremoval of all deposited sediment. Under nocircumstances should a subsurface infiltrationfacility (e.g., drywell, seepage pit, infiltrationtrench, etc.) be used for sediment control dur-ing construction.

8. During construction, heavy equipmentshould not be allowed on the facility bottom.Compaction of the natural subgrade can seri-ously impair the infiltration rate.


3-37

flow points should be used. Those lined com-pletely or partially with smooth materials suchas reinforced concrete can be more readilycleaned. For these reasons, the exclusive useof loose stone, riprap, and other irregular lin-ings which require manual removal of weeds,sediment, and debris should be avoided wher-ever possible.

13. Suitable access for maintenance person-nel and equipment should be provided to thefacility bottom. (See F. ACCESS for details.)


15. Temporary emergency measures such aspumps should be provided to drain standingwater from malfunctioning infiltration practices.

16. If feasible, alternative outlet measuresshould be designed to permanently convertan infiltration system to a detention facility ifnecessary due to loss of infiltration capacity.If practical, these alternative outlet measuresshould be included in the facility’s original con-struction.

17. At subsurface infiltration facilities, suit-able access, observation points, and/or moni-

9. As an alternative cover, a 12 inch layer offilter material, such as coarse sand, may beconsidered in the facility bottom. This layerof material can be cleaned of sediment or re-placed as necessary. Prior to the selection ofthis alternative material, such factors as aes-thetics, weed growth, and movement of main-tenance personnel and equipment about thebottom must be considered. See Figure 3-Dat the rear of the chapter for details.

10. To minimize routine grass maintenancesuch as mowing and fertilizing, the use of na-tive grass varieties that are relatively slowgrowing and tolerant of poor soil conditionsare encouraged. Information on these andother grass varieties and mixtures are avail-able from the local Cooperative Extension Ser-vice or Soil Conservation District. (See E.VEGETATIVE COVER for additional details.)

11. To promote lasting growth, grasses andother vegetative covers should be compatiblewith the prevailing weather and soil conditionsand tolerant of periodic inundation and harm-ful runoff pollutants. (See E. VEGETATIVECOVER for additional details.)

12. To facilitate removal efforts, sedimenta-tion should be promoted at localized, readilyaccessible areas. Swale conveyances andsediment traps or forebays at inflow and out-

Forebays trap sediment and debrisbefore it enters the facility in areas that

can be more readily cleaned.




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toring wells, should be provided to facilitateinspection and cleaning. (See F. ACCESSfor additional details.)

18. Wherever possible, sediment disposaland storage areas should be provided adja-cent to the facility. These areas should opti-mally be designed to contain 2 years or moreof removed sediment.



Steep SlopesLong SlopesPoor Grass GrowthSloughing and Erosion

1. For safe movement of maintenance per-sonnel and safe operation of equipment, sideslopes greater than 5 feet in height shouldnot be steeper than 4 horizontal to 1 vertical.Side slopes less than 5 feet high should notexceed 3 horizontal to 1 vertical. Flatter sideslopes are recommended wherever possible.

2. For safe movement of maintenance per-sonnel and safe operation of equipment, sideslopes steeper than 5 to 1 and higher than 15feet should be terraced at their midpoints. Theterrace should have a minimum width of 3 feetand should be graded at 2 percent towardsthe lower half of the slope.

3. Suitable access to and along side slopesshould be provided for maintenance person-nel and equipment. (See F. ACCESS for de-tails.)

4. Topsoil and vegetative covers must be pro-tected from erosion caused by local runoff andthe slope’s steepness. Surface and subsur-face soil stabilization measures or

nonvegetated linings should be used as nec-essary. In doing so, avoid the use of loosestones, riprap, and other irregular lining ma-terials which require hand removal of weedsand debris and may be a hazard to mainte-nance personnel walking on the slope.

5. All nonvegetative linings which are bor-dered by grass should be designed to permitcomplete mowing along all edges. The use ofherbicides is discouraged unless done bytrained applicators.

6. The effects of rapid pool drawdown shouldbe checked to prevent side slope sloughing.

7. For safe movement of maintenance per-sonnel and safe operation of equipment,fences should not be constructed within 3 feetof either the top or toe of any side slope thatexceeds 5 horizontal to 1 vertical.

11.4. INLETS


Difficult to CleanErosion and ScourExcessive SedimentationDisplaced Lining

Adequate distance should be providedbetween the top of a slope and

adjacent structures such as fences,walls, curbs, or roadways.


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1. The number of inlets to an infiltration sys-tem should be kept to a minimum. This willminimize the amount of required downstreamlining, forebays, and low flow channels. Allinflow pipes and culverts should terminate ata headwall or flared end section with adequatecutoff walls. Inlets should be located to pre-vent or minimize flow short-circuiting. How-ever, short circuiting is not an issue if the de-vice is fully retentive. It is an issue if it is aretention/detention situation.

2. Linings placed downstream of facility in-lets should accommodate design flows with-out erosion or scour. They should also facili-tate removal of sediment, trash, debris, andundesirable vegetation.

3. Forebays and other localized sediment anddebris traps should be placed immediatelydownstream of facility inlets. Where practi-cal, avoid loose stone, riprap, and other ir-regularly shaped linings which require handremoval sediment, trash, and debris. (See A.BOTTOMS for additional details.)

4. The BMP Treatment Train approach shouldbe used to minimize sediment entering the fa-cility should be considered. Street sweeping,offsite soil stabilization measures, andupsteam sedimentation basins, swales, and

other source control BMPs can significantlyreduce the frequency of required sedimentand trash removal operations.

5. To facilitate cleaning, inflow pipes shouldbe a minimum diameter of 15 inches. Thepipes should be constructed of durable mate-rials, such as reinforced concrete.











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Excessive SedimentationErosion and ScourDifficult to MowPoor Growth

1. To minimize maintenance efforts, the useof existing, undisturbed site vegetation is en-couraged. To do so, the existing site topog-raphy must provide adequate storage volume.Where disturbance of existing vegetation can-not be avoided, replacement with low mainte-nance, preferably native, vegetation withstrong resistance to disease and allelopathic(self-weeding) characteristics is encouraged.

In general and where appropriate, turf grassmay be easier to establish and maintain thanother types of ground cover vegetation. Theuse of grass varieties that are relatively slowgrowing and tolerant of poor soil conditionswill minimize routine maintenance tasks suchas mowing and fertilizing.

The need for supplemental fertilizing can besubstantially reduced when the vegetativecover includes a percentage of nitrogen-fix-ing species, such as white clover and otherlegumes. In addition to minimizing mainte-nance costs, a reduction in required fertiliza-tion will also minimize the potential pollutioneffects of nutrients such as nitrogen and phos-phorus in the outflow.

3. To promote lasting growth, grasses andother vegetative covers should be compatiblewith the prevailing weather and soil conditionsand tolerant of periodic inundation and runoffpollutants.

4. To promote lasting growth, an adequatedepth of suitable topsoil should be providedbelow all vegetative covers. A minimum thick-ness of 6 inches is recommended for turfgrasses.

5. Construction plans and specificationsshould include requirements for establishingall vegetative covers.

6. The effects of sediment removal from veg-etated surfaces should be considered in theselection of appropriate cover.

7. Additional information on vegetative cov-ers is available from such agencies as theNatural Resource Conservation Service, lo-cal Soil Conservation Districts, and CountyCooperative Extension Service offices. Con-sultation with these agencies during facilityplanning, design, and review is encouraged.


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11.7. ACCESS


Inadequate or Unsafe Access toFacility ComponentsHeavy or Inoperable Gratings andHatchesMultiple or Corroded LocksLack of Fence Gates

1. The facility must be readily accessible froma street or other public right-of-way. Inspec-tion and maintenance easements, connectedto the street or right-of-way, should also beprovided around the entire facility. The exactlimits of the easements and right-of-wayshould be specified on the project plans andother appropriate property and legal docu-ments and be of sufficient size to handle main-tenance equipment.

2. Field evaluations indicate that readily vis-ible infiltration practices receive more and bet-ter maintenance than those in less visible,more remote locations. This is especially truefor infiltration systems that are integrated intoa site's overall landscaping plan or where theyare used for recreation. These findingsshould be kept in mind during overall site lay-out. Readily visible facilities can also be in-spected faster and more easily by mainte-nance and mosquito control personnel.

3. Access roads and gates should be wideenough to allow passage of necessary main-tenance vehicles and equipment, includingtrucks, backhoes, grass mowers, and mos-quito control equipment. In general, a mini-mum right-of-way width of 15 feet and a mini-mum roadway width of 12 week is recom-mended.


5. To allow safe movement of maintenancevehicles, access ramps should be providedto the bottoms of all infiltration facilities greaterthat 5 feet in depth. Vehicle access rampsshould not exceed 10 percent in grade.




9. A suitable number of gates should be pro-vided in all fences. The gates should be wideenough to allow passage of necessary equip-ment and personnel. They should be appro-priately located so that they can be fullyopened without interference by trees, parkedcars, existing or proposed grades, or otherobstructions. If it is necessary to lock a gate,it should be done with a noncorroding chainand padlock. This will permit the installationof additional padlocks on the chain (each pad-lock becomes a link in the chain), thereby al-lowing authorized access through the gate by

Successful facility maintenance demandsadequate access for personnel and

equipment. Note wide access gate andconcrete curbing that keeps it accessible.


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more than one person without the need formultiple keys.

10. Safe, suitable access for maintenancepersonnel and equipment should be providedto the exterior of each facility components. Indoing so, avoid remote component locations,steep slopes, unstable surfaces and linings,and narrow walkways.


12. At subsurface infiltration facilities, suit-able access, observation points, and moni-toring wells should be provided to allow in-spection and cleaning. Access should be pro-vided to all major components, particularly atinlets and emergency outlets, and whereversediment deposits are expected. This willpermit sediment and debris removal throughhigh pressure water spray and vacuum (e.g.,Jet-Vac). All access points should be at safelocations on the surface which can be readilyaccessed, safely barricaded, and clearly iden-tified.

11.8. PERIMETERS



1. Field evaluations indicate that readily vis-ible and multipurpose infiltration practices re-ceive more and better maintenance than thosein less visible, more remote locations. Thisfinding should be kept in mind during overallsite layout. Readily visible facilities can alsobe inspected faster and more easily by main-tenance and mosquito control personnel.


3. To allow safe movement of maintenancepersonnel and equipment, fences should belocated at least 3 feet beyond the top and toeof any slope steeper than 5 horizontal to 1vertical.



6. Grassed areas beyond the tops of infiltra-tion systems should have a minimum slope of2 percent to promote effective surface drain-age and thorough drying.




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plicable facility design standards and require-ments, including those pertaining to a facility’shydrologic, hydraulic, structural, geotechnical,environmental, legal, and aesthetic aspects.As such, they should be used creatively withall other applicable standards and require-ments to produce filtration and biofiltrationsystems that require optimum levels of main-tenance performed with the least practical ef-fort, time, and expense. Those involved withthe planning, design, and review of specificstormwater management systems must as-sume their share of the responsibility for asystem's performance, longevity, and safety.

To assist in their use, the technical designguidelines are presented separately for eachmajor facility component as listed in Table 3-1. Complete descriptions of each type of fa-cility or practice is presented in Chapter 2.

Descriptions of typical maintenance problemsencountered at each facility component arealso described. These descriptions, whichhave been based upon facility inspections andinterviews with maintenance personnel, high-light the types of maintenance problems thatthe design guidelines are intended to preventor minimize. They should serve to furtherstimulate planners, designers, and reviewersto develop additional, improved, and/or site-specific designs.

12.2. BOTTOMS

Due to their wide variability, the bottoms offiltration and biofiltration practices may rangefrom the reinforced concrete bottom of a sub-surface sand filter to a wetland to the grass ina filter or buffer strip. Therefore, the directapplicability of the design guidelines pre-sented below will depend upon the type of fil-tration or biofiltration BMP under design. To

12. DESIGN GUIDELINES FOR FILTRATION ANDBIOFILTRATION PRACTICES

12.1 INTRODUCTION

The following technical design guidelines areintended to help planners, designers, and re-viewers produce stormwater filtration and bio-filtration facilities that require minimum levelsof maintenance. Typical practices include:

Sand FiltersPeat FiltersConstructed WetlandsWet and Dry SwalesVegetated Buffer Strips

In should be noted that, in many instances,filtration and biofiltration practices are oftenused in combination with or as an integral partof other types of stormwater management fa-cilities. For example, an extended dry deten-tion basin may include a constructed wetlandover all or portions of its bottom. In suchcases, the reader should also refer to the de-sign recommendations for those facilities pre-sented in this chapter.

To help accomplish the minimum maintenancegoal described above, the design guidelineshave been developed to:





It is important to note that the design guide-lines are intended to supplement all other ap-


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assist in their use, the following design guide-lines for bottoms will address both dry (e.g.,filter strip) and wet (e.g., constructed wet-lands) practices.

Typical problems that impede or unnecessar-ily increase proper facility maintenance in-clude:

Standing Water (in Dry Systems)Soggy Surfaces (in Dry Systems)Lack of Permanent Pool (in Wet Sys-tems)Poor Grass GrowthExcessive SedimentationLimited Access

1. To promote complete emptying and pre-vent standing water or soggy surfaces in drysystems, vegetated bottoms should have ad-equate bottom slope and be graded to theoutlet. In selecting a bottom, care must alsobe taken not to exceed the slopes requiredfor adequate pollutant removal. If a reason-able compromise cannot be achieved, anothertype of stormwater management practiceshould be considered.

2. To promote complete emptying and pre-vent standing water or soggy surfaces in dry-type facilities, the lowest point in the bottomshould be at least 4 feet above the season-ally high groundwater level or bedrock unlessadequate subsurface drains are provided.

3. To provide adequate drying time in drypractices, to avoid anaerobic conditions, toavoid delaying scheduled maintenance ef-forts, and to prevent mosquito breeding, themaximum wet or ponding duration should notexceed 24-48 hours, depending on the toler-ance of the vegetation to wetness.

4. To avoid delaying scheduled maintenanceefforts in dry facilities, topsoils and subsur-face soils should be sufficiently permeable toallow both rapid infiltration and evaporation.

5. In dry systems, subsurface drains con-nected to the principal outlet structure or otherdischarge point are encouraged to promotequick and thorough drying of the facility bot-tom. In doing so, care should be taken to pre-vent stormwater inflow from inadvertently by-passing the basin’s outlet controls.

6. To minimize routine grass maintenancesuch as mowing and fertilizing in dry systemssuch as filter and buffer strips, the use of na-tive grass varieties that are relatively slowgrowing and tolerant of poor soil conditionsare encouraged. Information on grass variet-ies and mixtures are available from agenciessuch as the local Cooperative Extension Ser-vice or Soil Conservation District. (See I.VEGETATIVE COVER for additional details.)

7. To promote lasting growth in dry systems,grasses and other vegetative covers shouldbe compatible with the prevailing weather andsoil conditions and tolerant of periodic inun-dation and runoff pollutants. (See I. VEGETA-TIVE COVER for additional details.)

8. To facilitate removal efforts, sedimentationshould be promoted at localized, readily ac-cessible areas. Sediment traps or forebaysat inflow and outflow points should always beused. Those lined completely or partially withsmooth materials such as reinforced concrete

Forebays trap sediment and debrisbefore it enters the facility in areasthat can be more readily cleaned.


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can be more readily cleaned. For these rea-sons, the exclusive use of loose stone, riprap,and other irregular linings which requiremanual removal of weeds, sediment, and de-bris should be avoided wherever possible.

9. Wherever possible, sediment disposal andstorage areas should be provided adjacent tothe facility. These areas should optimally bedesigned to contain 2 years or more of re-moved sediment.

10. Suitable access for maintenance person-nel and equipment should be provided to thefacility bottom. (See I. ACCESS for details.)

11. Construction plans and specificationsshould include provisions that minimize thepotential for localized settlement and subse-quent ponding. These provisions includeproper surface and subsurface soil charac-teristics, compaction requirements, gradingequipment, and erosion control prior to theestablishment or permanent vegetative cover.


13. At subsurface filtration facilities such assand filters, suitable access, observation

points, clean out ports, and/or monitoringwells should be provided to facilities inspec-tion and cleaning. (See I. ACCESS for addi-tional details.)

14. Design of a biofiltration facility such as aconstructed wetland should include the de-termination of the proposed site’s ability to ad-equately support a viable and desired eco-system. The design should account for suchfactors as the required rate and quality of dryweather inflow, the quality of stormwater in-flow, seasonal and longer term variations inthe ground water table, and the effects of ex-pected sediment and other pollutant loadings.

15. Provisions to drain the permanent pool ofwet systems (or the standing water chambersof a subsurface sand filter) are necessary formaintenance and safety. A gravity drain isthe preferred method. If this is not feasible,suitable pumps and both primary and backuppower sources should be provided. All pumpsand backup power sources should be re-served for facility use only.

16. To promote complete emptying of the per-manent pool when necessary, the bottomshould have an adequate slope graded to theoutlet drain or pump intake.



Steep SlopesLong, Continuous SlopesPoor Grass GrowthSloughing and Erosion

1. For safe movement of maintenance per-sonnel and safe operation of equipment, sideslopes greater that 5 feet in height should notbe steeper than 4 horizontal to 1 vertical. Side




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slopes less that 5 feet high should not exceed3 horizontal to 1 vertical. Flatter side slopesare recommended wherever possible.

2. Suitable access to and along side slopesshould be provided for maintenance person-nel and equipment. (See I. ACCESS for de-tails.)

3. Topsoil and vegetative covers must be pro-tected from erosion caused by local runoff andthe slope’s steepness. Surface and subsur-face soil stabilization measures ornonvegetated linings should be used as nec-essary. In doing so, avoid the use of loosestones, riprap, and other irregular lining ma-terials which require hand removal of weedsand debris and may be a safety hazard tomaintenance personnel walking along or upthe slope.


5. For safe movement of maintenance per-sonnel and safe operation of equipment,fenced should not be constructed within 3 feetof either the top or toe of any side slope thatexceeds 5 horizontal to 1 vertical.

12.4. PRINCIPAL OUTLETS


Structural DeteriorationLimited AccessCorroded AppurtenancesVandalismExcessive Debris Accumulation

1. For durability, principal outlet structuresshould be constructed of reinforced concretecontaining Type II cement and having a mini-mum specified 28-day compressive strengthof 3,000 PSI. Concrete shall be designed inaccordance with all applicable codes and re-quirements.

2. For durability, all appurtenances, includ-ing access hatches, trash racks, gratings, rail-ings, orifice and weir plates, and fastenersshould be constructed of lightweight, noncor-roding materials. Material strengths shouldbe sufficient to withstand design loads with-out damage or failure.

3. Outlet orifice and weir plates should beconstructed from aluminum or other light-weight, noncorroding material. The platesshould be fastened to the structure with non-corroding, removable fasteners. A gasket ofneoprene or similar material should be placedbetween the plate and the structure wall. Theopening in the structure wall over which theplate is bolted should have at least twice thearea of the outlet orifice or weir to facilitatefield adjustments and future expansion. SeeFigure 3-A at the rear of the chapter for de-tails.

4. To facilitate access and movement by main-tenance personnel, principal outlet structuresshould have a minimum horizontal interior di-mension of 4 feet. (See I. ACCESS for addi-tional details.)

Adequate distance should beprovided between the top of a slope

and adjacent structures such asfences, walls, curbs, and roadways.


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5. Vital parts of the principal outlet structureshould be readily and safely accessible tomaintenance personnel during both normaland emergency conditions. Temporary mea-sures such as ladders are only acceptable foremergency conditions such as part of an ap-proved emergency action plan. (See I. AC-CESS for additional details.)

6. To minimize both required maintenanceand the consequences of inadequate mainte-nance, principal outlets should avoid usingmoving or mechanized parts for outflow con-trol whenever possible.

7. To facilitate cleaning, outlet pipes shouldhave a minimum diameter of 15 inches. Thepipes should be constructed of durable mate-rials, such as reinforced concrete. To mini-mize potential leakage problems, the numberof outlet pipe should be kept to an absoluteminimum. More than one outlet pipe shouldbe used only where unavoidable. All outletpipes must be watertight under the maximumexpected head or pressure.

8. Constructed wetlands and some filter sys-tems often have a small orifices or a series ofsmall orifices as part of the outlet structure.These are used to slowly bleed down thestormwater treatment volume. Innovative de-signs are needed to minimize their potential

for clogging. Successful designs have in-cluded inverted siphons and half of a corru-gated metal pipe, filled with large gravel, andplaced in front of the orifices.

9. Grading and landscaping around princi-pal outlet structures should be designed tofacilitate mowing, trimming, debris removal,and other general maintenance tasks.Grassed slopes which require mowing shouldnot exceed 3 horizontal to 1 vertical. Veg-etated cover which does not require mowingor nonvegetated linings should be used wheresteeper slopes are necessary.

10. Stable areas that provide maintenancepersonnel with firm footing should be providedat the upstream face of principal outlet struc-tures at dry and extended dry facilities. Lin-ings such as reinforced concrete, gabions,and grouted riprap should be considered.


12. Dry weather flow through a principal out-let structure should not interfere with routineinterior maintenance tasks. Benching, lowflow pipes and channels, drop structures, orsimilar measures should be utilized to con-vey low flow into and through the structure.

13. Principal outlet structures should be de-signed to discourage vandalism and graffiti.

12.5. OUTFLOW SYSTEMS



Outlet structure gratings, trash racks,and other appurtenances should belightweight, durable, and removable.


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1. The outflow conveyance system down-stream of a filtration or biofiltration systemshould have adequate capacity to accommo-date its outflows. This will not only allow de-sign outflows and water surfaces to be at-tained, but will also help achieve requireddrawdown and emptying times.

2. Outflow velocities should be high enoughto prevent sedimentation and low enough toprevent erosion and scour.

3. Manholes, grates and other suitable ac-cess points should be provided for cleaningand inspection. (See I. ACCESS for additionaldetails.)

12.6. INLETS



1. The number of inlets to a filtration or biofiltra-tion system should be kept to a minimum. Thiswill minimize the amount of required downstreamlining, forebays, and low flow channels. All in-flow pipes and culverts should terminate at aheadwall or flared end section with adequatecutoff walls. Inlets should be located to preventor minimize flow short-circuiting.

2. Linings placed downstream of facility in-lets should accommodate design flows with-out erosion or scour. Flow spreaders will helpdistribute flow at a shallow depth more uni-formly over the facility bottom. They shouldalso facilitate removal of sediment, trash, de-bris, and undesirable vegetation.

3. Forebays and other localized sediment anddebris traps should be placed immediately

downstream of facility inlets. Where practi-cal, avoid loose stone, riprap, and other ir-regularly shaped linings which require handremoval sediment, trash, and debris. (See A.BOTTOMS for additional details.) Forebayoutlets can also be used to distribute inflowsmore uniformly over the facility bottom.

4. The BMP Treatment Train approach shouldbe used to minimize sediment, trash, andother debris from entering the system. Streetsweeping, offsite soil stabilization measures,and upsteam sedimentation basins, swales,and other source control BMPs can signifi-cantly reduce the frequency of required sedi-ment or debris removal operations.

5. To facilitate cleaning, inflow pipes shouldbe a minimum diameter of 15 inches. Thepipes should be constructed of durable mate-rials, such as reinforced concrete.





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3. All nonvegetative linings which are bor-dered by grass should be designed to permit

complete mowing along all edges.




Excessive SedimentationErosion and ScourDifficult to MowPoor Growth (traffic, compaction)Invasion by undesirable species

1. To minimize maintenance efforts, the useof existing, undisturbed site vegetation is en-couraged. To do so, the existing site topog-raphy must provide adequate storage volume.Where disturbance of existing vegetation can-not be avoided, replacement with low mainte-nance vegetation with strong resistance todisease and allelopathic (self-weeding) char-acteristics is encouraged.

For dry swales and vegetated buffers, turfgrass may be easier to establish and main-tain than other types of ground cover vegeta-tion. The use of native grass varieties thatare relatively slow growing and tolerant of poorsoil conditions will minimize routine mainte-nance tasks such as mowing and fertilizing.For constructed wetlands and wet swales,wetland aquatic plants are most appropriate.Specific recommendations regarding vegeta-tion is presented in Chapter 2.

The need for supplemental fertilizing can besubstantially reduced when the vegetativecover includes a percentage of nitrogen fix-ing species, such as white clover and otherlegumes. In addition to minimizing mainte-nance costs, a reduction in required fertiliza-tion will also minimize the potential pollution


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1. Trash racks are intended to prevent trashand debris from blocking a facility outlet byintercepting it at an upstream point. There-fore, the need for a trash rack should be basedupon the relative sizes and shapes of boththe outlet opening and the anticipated debrisas well as the consequences of outlet clog-ging. Special consideration should be givento subsurface facilities.

2. For durability, all trash rack components,including bars, hinges, fasteners, and clamps,should be constructed of lightweight, noncor-roding material such as aluminum. The com-ponents should have sufficient design strengthto withstand anticipated heavy loads causedby facility outflows, debris, and, where nec-essary, maintenance personnel.

3. To facilitate cleaning, trash racks shouldbe comprised primarily of sloping bars, alignedlongitudinally (in the direction of flow). Per-pendicular bars, aligned transverse to the di-rection of flow, should be added for strengthand rigidity. These transverse bars shouldbe located below the tope face of the longitu-dinal bars and, if possible, should be round insection. See Figure 3-B at the rear of theChapter for details.

4. To minimize the frequency of cleaning,trash rack bars should be spaced close

effects of nutrients such as nitrogen and phos-phorus in the outflow.

3. To promote lasting growth, grasses and othervegetative covers should be compatible with theprevailing weather and soil conditions and tol-erant of periodic inundation and runoff pollut-ants.

4. To promote lasting growth, an adequatedepth of suitable topsoil or wetland muck soilshould be provided below all vegetative cov-ers. A minimum thickness of 6 inches is rec-ommended for turf grasses.

5. Construction plans and specificationsshould include requirements for establishingall vegetative covers.

6. At both dry and wet systems, the effects ofsediment removal from vegetated surfacesshould be considered in the selection of ap-propriate cover.

7. Additional information on vegetative cov-ers is available from such agencies as theNatural Resource Conservation Service, lo-cal Soil Conservation Districts, and CountyCooperative Extension Service offices.Aquatic botanists should be consulted withrespect to selecting and planting vegetationin constructed wetlands and wet swales. Con-sultation with these agencies or profession-als during facility planning, design, and re-view is strongly encouraged.

12.9. TRASH RACKS


Difficult to CleanDifficult to RemoveStructural FailureExcessive Debris

Sloping trash rack bars aligned in thedirection of flow are more easilycleaned. Add transverse bars as

needed for stability.


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enough to collect debris which may block theoutlet orifice or weir but allow passage ofsmaller debris which will not. In general, lon-gitudinal bars should be spaced a distanceequal to 1/3 to 1/2 the diameter of the outletorifice or 1/3 or 1/2 the width or height (which-ever is less) of the outlet weir. Minimum andmaximum spacings of 1 inch and 6 inches oncenter, respectively, are recommended.Transverse bars should be spaced as neces-sary for strength and rigidity. See Figure 3-Bfor details.

5. Trash racks should be hinged or attachedwith noncorroding, removable fasteners to al-low access to the outlet orifice or weir by main-tenance personnel. Lightweight track racksare easier to lift, repair, and clean behind. SeeFigure 3-B at the rear of the chapter for de-tails.

6. Trash racks should be accessible for clean-ing when the facility is dry (at dry facilities) orat normal or permanent pool levels (at wetfacilities). In addition, access should also beprovided when the water level is at thesystem’s maximum design water surface el-evation. Stable areas of adequate size shouldbe provided around a trash rack to provide

firm footing for maintenance personnel andequipment. Concrete pads of other firm sur-faces are recommended.

7. At wet systems, stable areas of adequatesize should be provided at all trash rackswhich protect permanent pool drains. Con-crete pads or other firm surface is recom-mended.

12.10. ACCESS


Inadequate or Unsafe Access toFacility ComponentsHeavy or Inoperable Gratings andHatchesMultiple or Corroded LocksLack of Fence Gates

1. The facility must be readily accessible froma street or other public right-of-way. Inspec-tion and maintenance easements, connectedto the street or right-of-way, should also beprovided around the entire facility. The exactlimits of the easements and right-of-wayshould be specified on the project plans andother appropriate property and legal docu-ments.

2. Field evaluations indicate that readily vis-ible or multipurpose systems receive more andbetter maintenance than those in less visible,more remote locations. This finding shouldbe kept in mind during overall site layout.Readily visible facilities can also be inspectedfaster and more easily by maintenance andmosquito control personnel.

3. Access roads and gates should be wideenough to allow passage of necessary main-tenance vehicles and equipment, includingtrucks, backhoes, grass mowers, and mos-quito control equipment. In general, a mini-

Hinged, lightweight trash racks canbe quickly lifted for cleaning and

inspection. Also note outlet orificeplate mounted to outlet structurewall with removable anchor bolts.


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mum right-of-way width of 15 feet and a mini-mum roadway width of 12 week is recom-mended.


5. To allow safe movement of maintenancevehicles, access ramps should be providedto the bottoms of all surface facilities greaterthat 5 feet in depth. Vehicle access rampsshould not exceed 10 percent in grade.




9. A suitable number of gates should be pro-vided in all fences. The gates should be wideenough to allow passage of necessary equip-ment and personnel. They should be appro-priately located so that they can be fullyopened without interference by trees, parkedcars, existing or proposed grades, or otherobstructions. If it is necessary to lock a gate,it should be done with a noncorroding chainand padlock. This will permit the installationof additional padlocks on the chain (each pad-lock becomes a link in the chain), thereby al-lowing authorized access through the gate bymore than one person without the need formultiple keys.

10. Safe, suitable access for maintenancepersonnel and equipment should be providedto the exterior of each facility component. Indoing so, avoid remote component locations,

steep slopes, unstable surfaces and linings,and narrow walkways.


12. Safe, suitable access for maintenancepersonnel and equipment should be providedto the interior of the principal outlet. In doingso, avoid heavy hatches, gratings, and othercovers. Railings, grab rails, slip-resistantsteps, low flow channels, benchings, andhinged, lightweight access covers greatly fa-cilitate interior maintenance. Sufficient inte-rior space should also be provided. A mini-mum horizontal dimension of 4 feet is recom-mended.

13. At subsurface facilities, suitable access,observation points, and monitoring wellsshould be provided to allow inspection andcleaning. Access should be provided to allmajor components, particularly at inlets andthe principal and emergency outlets, andwherever sediment deposits are expected.This will permit sediment and debris removalthrough high pressure water spray andvacuum (e.g., Jet-Vac). All access pointsshould be at safe locations on the surfacewhich can be readily accessed, safely barri-

Adequate distance should be providedbetween the top of a slope and

adjacent structures such as fences,walls, curbs, and roadways.


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caded, and clearly identified.

12.11. PERIMETERS



1. Field evaluations indicate that readily vis-ible or multipurpose systems receive more andbetter maintenance than those in less visible,more remote locations. This finding shouldbe kept in mind during overall site layout.Readily visible facilities can also be inspectedfaster and more easily by maintenance andmosquito control personnel.


3. To allow safe movement of maintenancepersonnel; and equipment, fences should belocated at least 3 feet beyond the top and toeof any slope steeper than 5 horizontal to 1vertical.



6. Grassed areas beyond the tops of filtra-tion and biofiltration systems should have aminimum slope of 2 percent to promote effec-tive surface drainage and thorough drying.




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APPENDIX 3-1

DRAWINGS OF TYPICAL DETAILSOF SOME IMPORTANT

STORMWATER SYSTEM COMPONENTS

Figure 3A Detention Basin Orifice and Weir PlatesFigure 3B Detention Basin Trash RackFigure 3C Infiltration Basin UnderdrainFigure 3D Nonvegetated Infiltration Basin Bottom


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1. OVERVIEW

There are many important aspects ofstormwater management system mainte-nance. These include planning and designconsiderations, proper construction, inspec-tion, compliance, and funding. Equally impor-tant, though, are institutional or programmaticconsiderations. The institutional frameworkmust establish a legal basis to assure programmaintenance requirements are met. This mustinclude criteria establishing minimum stan-dards for stormwater system inspection andmaintenance - requirements that all ownersmust comply with to ensure the long term per-formance of their systems.

There are several program components whichmust operate cooperatively if maintenance ef-forts are to be effective. Initial requirementsmust include proper planning and design toassure that the stormwater management sys-tem, including each of its components, canbe effectively maintained and properly oper-ated. Stormwater program funding, which isbeyond the scope of this handbook, is essen-tial to assure proper design review, inspec-tion during construction, and regular inspec-tions of completed facilities. Funding alsomust be available for development of design,construction, and maintenance guidelines,and to actually perform needed maintenanceactivities. Educational programs are also im-portant. The importance of proper operation,maintenance, and management of stormwatersystems must be understood by designers,developers, contractors, the public, and own-ers of urban runoff controls. The stormwaterprogram's institutional framework must notonly create these important components, butassure that they are fully coordinated.

Chapter 4Programmatic and Regulatory Aspects

Constructed wetland serving aresidential community showing

good site stabilization.

4-1

Programmatic aspects of stormwater systemoperation and maintenance must include rec-ognition of the roles of the various levels ofgovernment involved in program implemen-tation (WMI, 1997). It is important that require-ments made at the various levels of govern-ment (federal, state, regional, local) becomplementary and not duplicative or conflict-ing. Stormwater system operation, main-tenance, and management must be ad-dressed by the urban runoff controlprogram whenever it requires the use ofBMPs. How explicitly or detailedstormwater system maintenance is ad-dressed varies, depending on the degreeof regulatory control exerted by each levelof program implementation.

This chapter will provide recommendations onhow stormwater programs can assure thatBMPs actually are maintained and operatedproperly. It will review the role of EPA, stategovernment, and local governments instormwater system operation and mainte-nance. Examples of successful institutional

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2. ROLES OF GOVERNMENT

Experience has shown that successfulstormwater management programs are builtupon a partnership among the different levelsof government involved in program implemen-tation (WMI, 1997). Until recently, stormwaterprograms were implemented by state and lo-cal governments using legal authorities estab-lished in state or local laws. However, in 1990,the EPA established federal stormwater per-mitting requirements under the NPDESprogram. These federal requirements havestimulated greater awareness of stormwaterproblems, the need for stormwater treatment,and the implementation of stormwater BMPs.

Whenever BMP implementation is re-quired, stormwater system operation andmaintenance requirements must be explic-itly stated and enforced. With at least threelevels of government often involved inprogram implementation, it is very impor-tant that program requirements be comple-mentary, not conflict, and not create du-plication. Stormwater maintenance con-siderations should be somewhat generalat the federal level, with state, regional, orlocal programs having progressively moredetailed program requirements. These re-quirements must then be implemented byindividual property owners or public enti-ties, with some type of compliance mecha-nism to assure that maintenance is actu-ally performed.

This hierarchical approach begins with gen-eral language that requires entities implement-ing urban runoff control programs to adoptmore specific requirements for the long termoperation, maintenance, and management ofstormwater management facilities. Impor-tantly, this allows the individual jurisdictionsto determine, through their existing programframework, how the requirements should beimplemented. Having minimum standardsis important, but the key to successful

approaches will be presented as will specificregulatory language on stormwater system op-eration and maintenance. The final subsec-tion of this chapter contains recommendationsrelating to public versus private maintenanceof completed stormwater management facili-ties.

The recommendations are based on themost effective approach to ensure the fu-ture maintenance of completed stormwa-ter management systems. The recommen-dations may appear idealistic, but they arebased on experiences by several success-ful state and local urban runoff control pro-grams around the country. They reflect themost optimal approach to stormwater man-agement system operation, maintenance, andmanagement which appears to be availableat this time.


Intended readers of this Chapter include:

• • • • • Persons involved in developing andimplementing stormwater managementprograms and their associated regulations.

• • • • • Elected and public officials who are re-sponsible for developing, promulgating, and/or interpreting stormwater management pro-grams and regulations.

• • • • • Stormwater system designers and build-ers who must assure that their systems com-ply with relevant regulations.

• • • • • Land developers, consultants, andstormwater facility owners who must receiveregulatory approval for their stormwater sys-tems.

CHAPTER 4 Programmatic and Regulatory Aspects

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implementation is providing flexibility to at-tain the standards within the institutionalframework of the stormwater program,whether at the state, regional, or local level.Since stormwater systems are an essentialpart of the local infrastructure, local govern-ments are the most appropriate level of gov-ernment to assure proper construction, inspec-tion, and maintenance of stormwater manage-ment facilities. At times, regional or water-shed-based entities may be involved in the dayto day implementation of stormwater manage-ment programs, including operation and main-tenance of stormwater systems. Except forhighway departments, state agencies usuallywill not be directly involved in stormwater sys-tem operation, maintenance, and manage-ment. Instead, they often will be responsiblefor establishing performance standards andBMP design criteria, reviewing plans or per-mitting BMPs, and they will have more of anoversight and technical guidance role. Simi-larly, except in those few states which are notdelegated NPDES stormwater permitting,EPA's role will be to set basic program goalsand requirements, and oversee implementa-tion by states.

3. FEDERAL STORMWATER PROGRAMS

Various federal programs (i.e., Sections 319and 402 of the Federal Clean Water Act, Sec-tion 6217 of the CZARA of 1990) may requirethe implementation of stormwater manage-ment programs by states, regional, or localgovernments, or stormwater BMPs by prop-erty owners. Consistent with the hierarchicalapproach discussed above, these programshave fairly general requirements forstormwater system operation and mainte-nance. For example, the NPDES stormwaterpermitting requirements for municipal sepa-rate storm sewer systems (MS4s) states "theapplicant must include a description of main-tenance activities and a maintenance sched-ule for structural controls to reduce pollution..."

Since the implementation of BMPs to treatstormwater is still a new concept, experiencehas shown that additional guidance on BMPoperation and maintenance is needed. Morespecific guidance and program require-ments should be adopted by state, re-gional, or local governments. For example,the stormwater staff at the Florida Departmentof Environmental Protection developed a tableof recommended BMP inspection frequenciesand maintenance activities (Appendix 4-5).EPA Region 4 is including this table in MS4permits issued to Florida local governments.The table is only guidance and is intended toserve as a starting point for local governmentsto develop and implement effective BMP in-spection and maintenance programs. Therecommendations in the table are not enforce-able permit conditions, simply guidance. Ad-ditional, more detailed BMP inspection, op-eration, and management language that couldbe included in state, regional, or local programrequirements is discussed in the next section.

4. STATE STORMWATER MANAGEMENTPROGRAMS

This section will discuss institutional aspectsof stormwater system maintenance in thosestates which have aggressively implementeda comprehensive statewide stormwater man-agement program. This is not the rule but theexception. Only five states currently havestatewide programs which require imple-mentation of stormwater BMPs by newdevelopments. In those states without acomprehensive program, or where state re-quirements are permissive, or where state leg-islation enables but does not require localimplementation, many of the requirements forlong term performance of stormwater systemswill be of interest to or implemented by localgovernments.

States may have a similar role to EPA in termsof overall program guidance, but they also

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have a greater capability to establish additionallegislative and regulatory requirements formaintaining stormwater systems than are pos-sible at the federal level. In some programs,the state is the permit issuing authority requir-ing the implementation of stormwater manage-ment facilities. In other programs, implemen-tation responsibilities are shared by the statewith regional or local governments.

This section will highlight several innova-tive approaches used around the countrywhich could be adopted as stormwatermanagement program components to sig-nificantly improve the long term perfor-mance of stormwater management sys-tems. It will also provide recommendedlanguage that should be included in statelaw and in stormwater regulations, whetherthey are implemented at the state, regional,or local level.

4.1. Program Guidance and Requirements

Several states have implemented stormwatermanagement programs to minimize floodingand the water quality impacts resulting fromstormwater discharges associated with newdevelopment. However, there is general rec-ognition by states that they alone cannoteffectively implement stormwater manage-ment programs at the state level. Most ofthese comprehensive statewide programshave, as their foundation, a "watershedmanagement team" approach. Implemen-tation involves a lead state agency alongwith some combination of regional, local,or watershed-based entities. Often the leadstate agency permits projects undertaken byfederal or state government and by the re-gional or local entities involved in programimplementation. Permitting of other projectsis done by the regional, local, or watershed-based entity to which the state has delegatedprogram implementation.

In these stormwater management programs,the roles of the various implementing enti-ties must be explicitly stated to avoid con-flicts and duplication. Accordingly, states,generally through legislation and regulation,establish the program's minimum goals andperformance standards, its administrative pro-cedures, and specify the minimum programcomponents that regional, local, or watershedentities must implement to be delegated theprogram's administration. The actual struc-ture of the implementing agency program de-pends on considerations such as the entity'sorganization, funding mechanism, and the pri-ority of the stormwater program.

States can, and should, be more specificthan federal agencies when establishingminimum stormwater management pro-gram standards. These standards must bedeveloped with the recognition of impacts thatthey will have on the resource needs of theregional, local, or watershed agency. If thestandards are absolutely necessary (as mostare), the state agency must provide assistance- financial, technical, and in securing politicalacceptance for the program at the local level.Program requirements must be directly relatedto effectiveness but also be realistic and in-clude some flexibility. Implementing agenciesmust be allowed to prioritize program com-ponents to fit their situation.

The stormwater program's institutionalframework, goals, and procedures need tobe established legislatively. Generalprogram requirements for stormwater sys-tem maintenance needs to be included inthis legislation. More explicit and detailedrequirements should be provided in theprogram's implementing regulations andguidance materials, such as its BMPmanual.


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4.2. State Stormwater Legislation

State legislation provides the legal authorityfor the stormwater program. If program imple-mentation can be delegated to regional or lo-cal governments, state law also provides thelegal backbone for these programs. In suchcases, the law also needs to establish crite-ria for delegation to assure that the programis implemented consistently statewide.

In general, the state stormwater legislationshould be relatively simple without lots ofdetails, especially with respect to the de-sign, construction, and maintenance ofstormwater systems. More explicit detailscan be established in the program's imple-menting regulations. The maintenance com-ponent of state legislation should provide abasic framework to assure that stormwatersystems are operated and maintained prop-erly. It must include compliance and enforce-ment mechanisms and procedures, includingpenalties. A section of the legislation shouldallow for regulations, and specify the programareas in which requirements can be set by therules.

Example legislative language might include:

The Department (the program's leadagency) shall develop regulations to spe-cifically guide program implementation.The regulations may include, but not belimited to, the following:

1. Criteria for local program implementa-tion or delegation.

2. Types of activities that require an ur-ban runoff control approval.

3. Waivers, exemptions, and variances.4. Plan approval and inspection fees

including construction or mainte-nanceperformance bonds.

5. Authority for a local stormwater utility.6. Specific design criteria.7. Permit application and approval pro-

cess.8. Operation permit requirements and

time frames.9. Development and implementation of

mandated educational programs re-lating to site inspection of active andcompleted stormwater managementsystems.

10.Requirements for any other educationalprograms.

11. Inspection requirements, includingcertification of inspectors.

12.Maintenance requirements onceconstruction has been completed.

13.Penalty provisions in the event ofnoncompliance with either design,construction, or operation ofstormwater management systems.

As can be seen from the italicized and boldedtext, maintenance aspects of program imple-mentation overlap with many other design andconstruction requirements.

Incorporating in the law the ability to adoptrules to establish maintenance require-ments allows for greater flexibility and forprogram evolution. It is important to re-member that the design, maintenance, andoperation of stormwater BMPs is a rela-tively young field. When changes need tobe made to enhance program or BMP ef-fectiveness, it is much easier to amendrules than legislation.

There are a several state laws and regulationswhich should be reviewed before developinglegislative language for a statewidestormwater management program. Theseinclude:

1. Delaware:• Chapter 40, title 7, Delaware Code,

Erosion and Sediment Control andStormwater Management Act;

• Sediment and Stormwater Regulations

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Contact:Delaware Department of Natural Re-sources and Environmental ControlDivision of Water Resources89 Kings HighwayDover, Delaware 19903

2. Florida:• Section 403.0891, Florida Statutes,

State, Regional, and Local StormwaterManagement Plans and Programs.Also, Section403.0893 - StormwaterUtilities and Section 403.0896 - Train-ing and assistance for stormwater per-sonnel.

• Section 62-40.432 (State Water Policy)Stormwater treatment performancestandards;

• Chapters 62-25 (FDEP stormwaterregulations) or 40C-42 (SJRWMDrules), Florida Administrative Code.

Contact:Florida Dept. of Environmental ProtectionNonpoint Source Mgmt. Section (MS3570)2600 Blair Stone RoadTallahassee, Florida 32399-2400

3. Maryland• Environmental Article, Title 4, Subtitle

1 - Sediment Control and Subtitle 2 -Stormwater Management.

• Code of Maryland Regulations 26

Contact:Maryland Department of the EnvironmentStormwater Management Program2500 Broening HighwayBaltimore, Maryland 21224

4. New Jersey• N.J.S.A. 40:55D-1, Stormwater Man-

agement Act.• N.J.A.C. 7:8 Stormwater Management

regulations.

Contact:N. J. Dept. of Environmental ProtectionStormwater Management Program401 East State StreetTrenton, New Jersey 08625

5. Washington• Chapter 90.70 Puget Sound Water

Quality Authority• Chapter 173-275, Washington Admin-

istrative Code (W.A.C.), StormwaterManagement in the Puget Sound Wa-tershed.

• Chapter 400-20, W.A.C. Puget SoundWater Quality Authority.

Contact:Washington Dept. of EcologyStormwater Management ProgramP.O. Box 47600Olympia, Washington 98504-7600

Recognize that the ideal program will con-tain a mixture of ideas and language fromother programs, in addition to original lan-guage necessary to address state specificconsiderations. No program is perfect.

Penalty provisions (Item 13 above) are criti-cal to ensuring the continued operation ofstormwater management facilities. A reviewof 32 stormwater management programs

Woody vegetation growing on a pond embankment because of a lack of mowing.


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around the country indicates the need for pen-alty provisions (WMI, 1997). Generally, pen-alty provisions will not be used very often.Clear statutory authority for them, however,helps to assure maintenance activities are ac-complished, especially when needed at siteswith reluctant owners.

There is a question of whether penaltiesshould be civil and/or criminal. There is agreat reluctance to use criminal penaltiesdue to the severity of the impact in theevent of a conviction. Consequently, themost commonly used penalty to ensurecompliance is a civil action. This generallyresults in some form of monetary penalty.Example statutory penalty language might bethe following:

"Any person who violates any rule, regu-lation, order, or condition imposed on anapproved plan or other provision of the Lawshall be fined not less than $_____ or morethan $_______ for each offense. Each daythat the violation continues shall constitutea separate offense."

The dollar amounts of penalties vary widelyaround the country. Representative levelsrange from $100 to $5,000.

Existing stormwater programs have foundthat the most effective compliance tool isa "stop work order". This administrativemechanism is particularly useful during theconstruction phase of development as it pre-vents any further work until the site's controlsare in compliance with the site plans or per-mit requirements. Example statutory languagefollows:

"The Department shall have the power toissue a cease and desist order to any per-son violating any provision of this Chapterby ordering such person to stop any sitework activity other than those actions nec-essary to achieve compliance with this law

or its implementing regulations."

Another widely used alternative to fines toassure maintenance and management ofstormwater systems is authority for thegovernment (state, regional, local) to per-form the maintenance and bill the owner.Example statutory language for this conceptis:

"If the owner or responsible maintenanceentity fail to maintain the stormwater man-agement system to acceptable standards,the (unit of government) shall issue a writ-ten notice specifying actions to be takenin order to bring the system into compli-ance with its approved design and perfor-mance. If these actions are not completedby the time specified in the written notice,the (unit of government) shall perform orcontract for this maintenance and bill theowner or maintenance entity for all costs.If the owner of maintenance entity fails topay the bill within 60 days, a tax lien forthe amount of the bill plus ten percent shallbe placed upon the property."

It is recommended that the operation andmaintenance violations be considered acivil offense, but that a criminal provisionalso be included for obvious deliberate vio-lations. Penalties are applied most commonlyfor poor erosion and sediment control at con-struction sites. They are less commonly im-posed for improper construction, mainte-nance, or operation of permanent stormwatermanagement facilities.

Where there is a significant maintenancerequirement that may be controversial, itshould be stated in law. The following threeexamples are provided for consideration byother stormwater management programs.

1. Florida Stormwater Operating Permit

Florida's stormwater program recom-

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mends that regional water managementdistricts and local governments issue re-newable operating permits for completedstormwater systems. These require anannual inspection and certification thatthe stormwater system is being main-tained and is performing as permitted.This is an excellent approach to ensurethat systems are regularly inspected andproperly maintained. The approach hasgeneral applicability to other stormwaterprograms and implementation can be tai-lored to a program's institutional frame-work.

The legislative framework for Florida'sstormwater program includes Section403.0891, Florida Statutes, which setsforth the stormwater responsibilities of theDepartment of Environmental Protection,the five regional water management dis-tricts, and local governments. The specificcriteria and implementation procedures forthe Operating Permit System are detailedin stormwater regulations, especially thoseof regional water management districts orlocal governments. For example, the Cityof Tallahassee's Environmental Manage-ment Ordinance includes Section 46, en-titled Stormwater Management Facility Op-erating Permit.

One reason this approach has strong meritis because eventual property owners (resi-dential owners especially) are seldomaware of their obligations to maintainstormwater management facilities. Re-quiring owners of stormwater systemsto have an Operating Permit helpsmake system owners aware that theyhave legal operation and maintenanceobligations. When the responsible legalmaintenance entity is a Property OwnersAssociation, the Operating Permit Systemhelps assure that the Association as-sesses the individual property owners fortheir portion of the costs incurred when

contracting for stormwater system main-tenance. The submittal by the responsiblemaintenance entity of the annual certifica-tion and of the information periodically re-quired to renew the Operating Permit alsohelps to reinforce continued awareness ofmaintenance obligations.

2. State of Washington Maintenance Bonds

Another option to assure maintenance ofcompleted stormwater management facili-ties, which may require specific legislativeauthority, is the posting of maintenancebonds. This is required by the State ofWashington as part of its Puget Soundprogram. This law requires land devel-opers to obtain a performance bond forstormwater management facility main-tenance. This helps assure that thestormwater management facility is con-structed satisfactorily and that there areno outstanding maintenance needs whichwould create an immediate hardship on theeventual property owners.

The legal foundation for requiring perfor-mance bonds is set forth in Washington'sStormwater Management Regulations forNew Development which are imposedwithin the Puget Sound watershed. Sec-tion WAC173-275-060(2)(g) states that"Performance bonding or other appropri-ate financial instruments shall be requiredfor all projects to ensure compliance withthese standards". Another section of theregulations requires a maintenance andoperation schedule be provided for all pro-posed stormwater management facilitiesand BMPs, along with the identification ofthe party responsible for maintenance andoperation.

3. Delaware'Certified Site InspectorProgram

Delaware's stormwater program includesa unique approach to site inspection that


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Although established in Delaware for im-proving construction practices, the conceptcould be modified to have a certificationprogram for those individuals, both publicand private, who are responsible for in-specting permanent stormwater manage-ment systems such as would be requiredby an Operating Permit System. Similareducation and certification programs alsocan be established for individuals who areactually responsible for conducting main-tenance activities. Florida's stormwaterprogram is implementing education pro-grams and voluntary certification in bothof the above areas.

4.3. Stormwater Regulations

Regulations are an integral component of ur-ban runoff control programs. Their develop-ment and implementation are subject to pub-lic review and comment, but they are not sub-ject to formal approval by the state legislativebody. As such, it is easier to enact and modifytechnical requirements that are needed forprogram implementation and evolution. Thisis very important in the relatively new field ofstormwater treatment where technologies andinstitutional approaches are rapidly changing.

With respect to stormwater facility main-tenance, requirements within the regula-tions will be significantly more detailedthan those specified in the stormwaterprogram's enabling legislation. At the lo-cal level, regulations usually are adopted asa local ordinance or law. However, they muststill include more detailed program require-ments such as those to assure long term main-tenance and operation of BMPs. Adoptionas a local law may make it more difficult toamend program requirements, especiallytechnical ones such as BMP design crite-ria. A better approach may be to includethem in a BMP Manual that is adopted inlaw by reference.

Partially clogged outlet at a detention basindue to not inspecting or maintaining

the facility.

requires site inspectors to be certifiedthrough a formal training program spon-sored by the State. Section 4013 of thestate's stormwater legislation (Chapter 40,Title 7) requires individual developers tosupply their own "certified" inspectors dur-ing construction to improve site implemen-tation of temporary erosion and sedimentcontrol and permanent stormwater man-agement facilities. The law also authorizesthe state stormwater agency to adopt regu-lations specifying when certified inspectorsare required and establishing the trainingcourse that they must attend and pass.

Section 12 of Delaware's Sediment andStormwater Regulations requires a cer-tified inspector on all projects disturb-ing over 50 acres and also allows thepermitting agency to require one on acase by case basis. Certified inspectorsare only required during the constructionphase of a project. This section of theregulations also set forth the curriculum forthe training course and specifies theinspector's responsibilities. The certifiedinspector documents site conditions, es-pecially of erosion and sediment controls,on a weekly basis and submits site evalu-ation forms to the contractor, developer,and appropriate permitting agency.

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A very important aspect of state programimplementation is the development of designcriteria and guidance. These are needed forprogram implementation and for individualstrategies and practices. When state pro-grams require local implementation or allowfor delegation to local governments, it is im-perative that guidance be provided on how toachieve state program goals and objectives.Typically, this detailed guidance is pro-vided in a BMP Design Manual.

The state program BMP Manual needs to pro-vide detailed design guidance, including spe-cifics on maintenance requirements and re-sponsibilities, for each practice endorsed orrequired. To assure use of, and compliancewith, the BMP Manual's requirements, statestormwater regulations (or local regula-tions, if applicable) should adopt it by ref-erence. The rules also need to include spe-cific statements requiring all stormwatersystems to be designed, constructed,maintained and operated in compliancewith the BMP Manual's requirements. Ex-plicit reference to a formally adopted BMPManual within state (or local) regulations es-tablishes a legal basis for implementation ofcomplex, technical information. It also allowsfor relatively easy revision of BMP design guid-ance as more information is gained about thedesign and performance of BMPs.

Standing water in a dry detention basincaused by a blocked outlet or bottom slopes

which are too flat.

Nearly all of the states that have implementedstormwater management programs have de-veloped a BMP Manual to provide the regu-lated public with explicit guidance. An ex-ample of a state required design manual usedto implement stormwater programs at the lo-cal level is the "Stormwater Management De-sign Manual for the Puget Sound Basin (TheTechnical Manual)", developed by the Wash-ington State Department of Ecology. Othersare referenced in Chapter 10.

Beside the traditional design considerationstypically contained in a BMP Manual, it or theprogram's regulations also need to includeother important needs related to the success-ful maintenance and operation of stormwaterfacilities. An example is the need to setaside areas where sediments removedfrom a stormwater management facility canbe placed. The single most expensive partof BMP maintenance is transportation ofremoved sediments to an appropriate dis-posal area. By setting aside an area on-site for sediment storage, maintenancecosts can be significantly reduced therebyincreasing the likelihood that the facilitywill actually be cleaned out when needed.

A detailed discussion of concerns associatedwith disposal of sediments removed fromstormwater management facilities, along withgeneral recommendations, can be found inChapter 9. The issue of sediment disposalmust be addressed in program implementa-tion, and needs to be considered during theinitial review of a proposed development orstormwater management facility. The rule lan-guage recommended in Appendix 4.2, estab-lishing the size of a set aside area, is appli-cable to facilities receiving expected pollutantloadings from residential lands or light com-mercial uses. Requirements for land uses withhigher pollutant loadings would need to beconsidered individually.


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4.4 Example Language That Should BeContained in State (or Local)Stormwater Management Regula-tions

Example language which should be consid-ered for inclusion in stormwater regulations ispresented in Appendix 4-1. Also included isa brief discussion of key issues, for four ma-jor BMP implementation areas, which need tobe addressed when developing a stormwaterregulation or law. Whether these requirementsare established in statewide regulations, orwithin regional or local government regula-tions, will depend on the stormwater program'simplementation framework.

5. LOCAL STORMWATER MANAGEMENTPROGRAMS

Most local governments have some type ofstormwater management program, such asflood protection, and provide stormwater in-frastructure. In those states without a com-prehensive stormwater managementprogram, the local stormwater law or regu-lations should include all of the recommen-dations included in the previous sectionof this chapter.

Even in those states with statewide stormwatermanagement programs, local governmentsusually have an important implementation role.Depending on the state program's framework,the local role may include design review andpermitting, inspections during or after con-struction, compliance, maintenance, or mas-ter planning. Since local governments typi-cally provide infrastructure such as thecommunity's master stormwater system,they have a more vested and direct inter-est than state or regional agencies in as-suring that all of the stormwater systemswithin the community are being maintainedand operating properly. This is not only tominimize potential flooding but also to limit the

local government's liability under Federal orstate environmental laws since the masterstormwater system almost always dischargesultimately to a water body. Additionally, if thelocal government has implemented astormwater utility, especially one with creditsfor on-site stormwater management, assuringperiodic inspections and proper maintenanceof privately owned stormwater systems is es-pecially important.

For the above reasons, along with the diffi-culty that state stormwater agencies have inobtaining sufficient staff to conduct regular in-spections of completed stormwater systems,it is strongly recommended that local gov-ernments implement a Stormwater Oper-ating Permit System. Possible language forinclusion in a local government stormwater or-dinance or regulation is:

Stormwater Operating Permits

1. Subsequent to the final inspection andsubmittal of the As-built Certificationand Record Drawings, no stormwatermanagement systems shall be useduntil a Stormwater Operating Permit ap-plication has been submitted, the re-quired application fee paid, and the ap-plication has been approved.

2. All permittees shall operate and main-tain the stormwater management sys-tem in a manner consistent with the au-thorized Operating Permit and any otherstate or local requirements.

3. The following information shall be re-quired in the Operating Permit applica-tion:

A. A property parcel map showing the loca-tions and tax parcel numbers of each par-cel for which an owner is required to ei-ther obtain an operating permit or main-tain membership in a Stormwater Facil-ity Property Owners Association.

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B. If the permit is to be issued to aStormwater Management Facility Prop-erty Owners Association, a copy of thearticles of incorporation and pertinentbylaws must be submitted, along witha list of the names, addresses, and tele-phone numbers of all Associationmembers and officers.

C. A narrative description of the stormwa-ter management facilities to be main-tained and operated.

D. A general location map which indicatesthe relative location in the watershed ,the property tax parcel numbers, andthe names and addresses of the cur-rent owners of all parcels on which thefacilities are located, the limits of thedrainage basin contributing to the fa-cilities, and the number of acres con-tributing runoff to each of the facilities.

E. Information regarding the operating ca-pacities of the facilities, demonstratingthat the capacities are not greater thanthose specified in the applicable per-mit for the facilities.

F. An operation and maintenance plan,including identification of an individual(including address and telephone num-ber) who shall be designated as the re-sponsible contact individual and whoshall be responsible for the day-to-dayoperation, maintenance, and manage-ment of the facility. The plan shallspecify operating procedures, possibleroutine intermittent and annual main-tenance, and all other activities requiredto ensure that the facility performs asdesigned and permitted. The plan mustalso include estimates of equipment re-quired, person hours and crew size,schedules, and an estimate of annualcosts. Most importantly, the plan mustclearly detail how funding and supervi-sion is to be provided.

4. Stormwater operating permits shall ex-pire three years after issuance or re-

newal. The permittee shall apply for apermit renewal at least three monthsprior to permit expiration.

5. The stormwater operating permit shallbe renewed when each of the followingconditions has been met:

A. Inspection by a local government or astate certified inspector that confirmsthat all components of the facility arein good working order, that the facilityis free of debris or excessive sedimentdeposits and is well stabilized, and thatthe facility is meeting or exceeding itsdesign performance criteria.

B. If the stormwater operating permit is be-ing renewed by an individual, the ap-plicant must submit updated recordsproviding the names and addresses ofcurrent property owners with cross-ref-erencing to the property parcel mapfiled with the original operating permitapplication.

C. If the stormwater operating permit is be-ing renewed by a Stormwater Manage-ment Facility Property Owners' Asso-ciation, the applicant shall provide acurrent list of the names, addresses,and telephone numbers of all Associa-tion members and officers, and submitany changes to the Association's by-laws (if any) along with a certificationof good standing from the (state agencyresponsible for corporations).

D. The applicant provides the name, ad-dress, and telephone number of the in-dividual responsible for day-to-day op-eration, maintenance, and manage-ment of the facility.

E. The applicant makes any repairs ormaintenance activities noted in the in-spection report.


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6. RECOMMENDATIONS ON PUBLICVERSUS PRIVATE MAINTENANCE OFCOMPLETED STORMWATERMANAGEMENT FACILITIES

Surveys conducted by several stormwatermanagement programs around the country in-dicate that stormwater systems often are notmaintained and operated properly. Maryland'sstormwater program has conducted a seriesof surveys on the maintenance of stormwaterpractices. The report "Maintenance ofStormwater Management Structures, A De-partmental Summary" (Md WRA, 1986) in-cluded the following conclusions:

1. Stormwater management facilities inMaryland, especially dry detention fa-cilities, are not particularly well main-tained. In fact, a majority of facilitieshave failed due to lack of routine main-tenance.

2. Public facilities are better maintainedthan private facilities.

3. Commercial/industrial facilities are lesslikely to be aesthetically unsatisfactory.

4. 45% of commercial/industrial facilitieswere completely satisfactory, com-pared to 24% of residential facilities.While there may be several reasons forthese results, an important one is thata very clear ownership exists for com-mercial/industrial facilities. The ownerfeels more responsibility for the facilityand is more likely to maintain it. This isnot the case for residential develop-ments, where a Homeowner's Associa-tion or the developer is responsible

5. Commercial/industrial facility ownersare more concerned about their image,including the appearance of theirgrounds, than residential facility own-ers, especially if the residential facility

owner is the developer.

The Maryland survey indicates that rely-ing on commercial and industrial propertyowners to properly maintain theirstormwater systems is probably appropri-ate. They generally either have staff dedi-cated to maintenance and landscaping activi-ties at their site who can be responsible forstormwater system maintenance, or they con-tract for such services. However, even theseowners need to be periodically checked bypublic inspectors or through submission ofcertifications such as required by OperatingPermits.

Assuring proper maintenance and opera-tion of residential stormwater systems ismuch more difficult. Typically, the mainte-nance of these systems is the responsibilityof a Property Owners Association. These en-tities seldom have the technical expertise toinspect or maintain their stormwater system,and they often lack the commitment to assesstheir members to raise the funds needed tocontract for maintenance. The implementa-tion of a Maintenance Agreement or an Op-erating Permit System can greatly increasecompliance by Property Owners Associa-tions. Implementation of education pro-grams, such as Hillsborough County's (FL)"Adopt - a - Pond" program, have alsoproven successful in getting maintenancedone.

Public ownership and responsibility appear tobe the best solution for assuring the long termmaintenance and operation of stormwater sys-tems serving residential developments. How-ever, local governments traditionally havebeen reluctant to accept ownership and re-sponsibility for maintenance of residential sys-tems. Reasons for this include the cost ofproviding maintenance, potential legal liabili-ties, and the fact that many stormwater sys-tems are part of a residential development'sopen space or landscaping areas with asso-

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ciated aesthetic concerns.

Overcoming these obstacles requires soundprogram administrative requirements for op-eration and maintenance and, most impor-tantly, an adequate program funding mecha-nism, such as a stormwater utility. Addition-ally, some local governments have requiredMaintenance Agreements between the resi-dential development and the local govern-ment. A key aspect of these Agreementsis the clear delineation of responsibilities.The local government accepts responsibil-ity for inspecting and maintaining thestormwater system's structural compo-nents, including the periodic removal of de-bris and accumulated sediments. However,aesthetic maintenance and pollution pre-vention still rests with the Property Own-ers Association.

7. EXAMPLES OF MAINTENANCEAGREEMENTS

There are several Maintenance Agreementswhich can be used as examples for other ju-risdictions initiating stormwater managementprograms. Three examples of MaintenanceAgreements worthy of consideration be-cause of their unique features are pre-sented in Appendices 4-2, 4-3 and 4-4.

The first two examples are from the City ofOlympia, Washington. "Residential Agree-ment to Maintain Stormwater ManagementFacilities and to Implement a Pollution Pre-vention Plan" is the first example (Appen-dix 4-2). This agreement is of interest for thefollowing reasons:

1. Maintenance responsibility for sedi-ment removal, managing vegetation inwet ponds, resetting orifice sizes andelevations on residential propertiesrests with the City.

2. The City clearly defines maintenanceresponsibilities of the residential prop-erty owners.

3. A pollution prevention plan that in-cludes source control of pollutants isformally included in the maintenanceagreement.

4. Authority for the City to be reimbursedfor maintenance activities undertakenby the City that are the responsibilityof the Homeowners Association but arenot performed.

5. Requires the submission to the City ofan annual report by the HomeownersAssociation. This helps theAssociation's members understandand demonstrate their commitment toundertake maintenance obligations.

6. The City obligates itself to an annualinspection of all stormwater facilities.

The second Maintenance Agreement ex-ample from the City of Olympia, Washing-ton program is a "Commercial, IndustrialAgreement to Maintain Urban StormwaterManagement Facilities and to Implement aPollution Prevention Plan" (Appendix 4-3).This Agreement is more typical and hasmore universal applicability in other juris-dictions. Maintenance responsibilityclearly rests with the property owner, withtechnical assistance provided by the City.This Agreement contains the following provi-sions:

1. A pollution prevention plan, includingsource control of pollutants, is formallyincluded in the maintenance agree-ment.

2. Authority for the City to be reimbursedfor maintenance activities undertakenby the City that are the responsibility


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of the property owner but are not per-formed.

3. Requires submission to the City of anannual report by the property owneragain helping the owner demonstratean awareness and commitment to com-plete maintenance obligations.

4. The City obligates itself to an annualinspection of all stormwater manage-ment facilities.

5. The City has implemented a stormwa-ter utility. One enforcement mechanismin this Agreement allows the City to re-voke stormwater utility rate credits forstormwater treatment if required main-tenance is not performed.

The third example Maintenance Agreementis entitled "Standard Maintenance andMonitoring Agreement for the City of Alex-andria, Virginia" (Appendix 4-4). ThisAgreement is especially interestingbecause of a component dealing with

"unconventional" stormwater manage-ment facilities. The City stresses new tech-nologies for stormwater management in "ul-tra urban" areas. This agreement obligates thelandowner to contribute the entire cost of awater quality monitoring program to assessthe performance of the unconventionalstormwater management practice before re-lease of the Final Site Plan. This requirementhelps the evolution of stormwater manage-ment facilities in situations where innovativepractices are necessary due to site con-straints. The Agreement contains the follow-ing provisions:

1. Grants permission to the City to enterthe property for inspection purposes.

2. Allows the City to do needed mainte-nance and assess the landowner forthe maintenance costs.

3. Allows the City to assess a monitoringfee for evaluating the performance ofinnovative stormwater management fa-cilities.

Good access and legal authority help assure that needed maintenance gets performed.

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APPENDIX 4-1

Example LanguageThat Should Be Containedin State, Regional, or Local

Stormwater Management Regulations


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This appendix contains a discussion of essential concepts needed in stormwater regulationsto effectively assure the proper design, construction, inspection, and operation and mainte-nance of stormwater management systems.

Several of the recommended sections might be more appropriately included in a BMPManual if the program has one. In this case, the regulations need to adopt the Manualby reference and require compliance with the Manual's criteria. These sections aredesignated by (BMP Manual) at the end of the recommendation.

The recommendations are divided into four major issue areas:• Design and review requirements• Construction requirements• Legal operation and maintenance

requirements• Maintenance inspection requirements

A. Design and Review Requirements for Stormwater Facilities and Plans

Design review requirements need to be considered from several different perspectives:

• Proper design and construction of the stormwater management system to ensure properperformance. Unfortunately, experience has shown that systems often are inappropri-ately designed for site conditions or are not constructed properly;

• Inclusion of long term maintenance and operation considerations in the design of thestormwater system. This helps assure that maintenance can be done relatively easily.This helps assure that systems will perform for a maximum time frame given their ex-pected design flows and pollutant loadings; and

• Institutional issues such as warranty requirements or review and approval of the legaloperation and maintenance entity along with its accompanying legal documents. Thisprovides the legal framework for subsequent inspection and maintenance by a specificentity, either public or private.

Recommended language includes:

1. Stormwater system design will include careful consideration of maintenance as anessential design element. All stormwater management systems and plans shall bedesigned in accordance with the _________ BMP Design Manual dated ______,withapproved supplements.

2. The applicant shall provide a legally dedicated easement with an access road to reten-tion, detention, and filtration facilities from a public right of way. The access road shallbe a minimum of 15 feet wide and suitable to allow heavy maintenance vehicles ac-cess to all points needed to maintain the facility.

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3. Stormwater management facilities serving residential developments and the accessroads serving these facilities shall be placed in separate tracts, owned in common bythe property owners served by the facility or by the development's Property OwnersAssociation.

4. Projects reviewed and approved for sediment control and permanent stormwater man-agement shall have a certified site inspector (may want to limit type of activity, e.g.,projects over 5 acres, etc.). The certified site inspector shall be responsible for thefollowing items:

A. Inspection of active construction siteson at least a weekly basis.

B. Submitting a completed inspection form which documents site conditions to thecontractor, developer, and permitting agency within five calendar days.

5. It shall be the responsibility of the permittee to maintain all erosion and sediment con-trol and permanent stormwater management facilities in good operating condition dur-ing the lifetime of the permit. The permittee shall clean and repair or replace all erosioncontrol practices as often as necessary to maintain their effectiveness and level ofperformance, or as directed by a certified inspector or by the permit authority. In addi-tion, the permittee shall be responsible for assuring that any practices damaged duringfloods, storms, or other adverse weather conditions are returned to normal operatingconditions within a defined time frame as determined by the certified inspector or per-mitting agency.

6. Land area adjacent to the stormwater management facility must be set aside for dis-posal of sediments removed from the facility when maintenance is performed. Theland set aside for facility maintenance shall be sized as follows: (only suggested siz-ing)

A. The set aside area shall accommodate at least 2% of the stormwater managementfacility volume to the elevation of the 2 year storm storage volume elevation,

B. The maximum depth of the set aside volume shall be one foot,C. The slope of the set aside area shall not exceed 5%, andD. The area and slope of the set aside area may be modified if an alternative area or

method of disposal is approved by the appropriate plan approval agency. (BMP Manual)

7. A clear statement of defined maintenance responsibility, an operation and mainte-nance schedule, and the specific parties responsible for maintenance shall be estab-lished during the plan review and approval process.

8. Prior to the issuance of any building or grading permit for which stormwater manage-ment is required, the responsible plan approval agency shall require the applicant or


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owner to execute an inspection and maintenance agreement binding on all subse-quent owners of land served by the private stormwater management facility. Suchagreement shall provide for access to the facility at reasonable times for regular in-spection by an inspection agency.

B. Construction Requirements for Stormwater Management Systems

Construction activities can have a significant negative impact on the short or long term perfor-mance of stormwater management facilities. Improper control of pollutants, especiallysediments, during site construction, or improper construction of the stormwater man-agement facility itself, can significantly reduce the expected performance and lifespanof the facility. Criteria and recommendations to address both of these situations areneeded to ensure long term performance.

1. Protection of Permanent Stormwater Management Facilities From Premature Failure CausedBy Pollutant Entry During Site Construction.

To a large extent, the treatment performance of stormwater management facilities dependson the available storage volume. In addition, several treatment practices rely upon the per-meability of surrounding soils or filter media. Consequently, excess sedimentation can sig-nificantly reduce treatment performance or prevent proper functioning of the facility.

The practical aspects of site control during construction are discussed in Chapter 6.However, ensuring effective site control during construction and protecting stormwatermanagement facilities from entry of construction site pollutants, especially sediments,also requires a strong legal foundation. Typically, the program's regulations adopt byreference its BMP Manual, and requires all plans and stormwater systems to be designed,constructed, operated, and maintained in accordance with the Manual's requirements. Theprogram's BMP Manual needs to include specific recommendations for each of the differentpractices, along with general statements meant to cover all stormwater management facili-ties.

The following recommendations are directed towards structural stormwater management prac-tices. However, it is extremely important to implement nonstructural, pollution preventionpractices on all projects with structural stormwater management practices. These nonstruc-tural controls serve as an overlay applicable to all types of structural stormwater managementpractices.

Recommended language includes:

Stormwater Detention Practices

Detention practices are often used for sediment trapping during construction. When theapproved erosion and sediment control plan uses a permanent detention facility for sedi-ment control, the following requirements should be included in the stormwater regulationsor in the BMP Design Manual:

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1. The detention facility shall be installed in compliance with all approved design require-ments and specifications. Special attention shall be paid to installation of the principalspillway cradle, anti-seep mechanisms (whether collars or diaphragm), core trench,compaction, and emergency spillway.

2. The principal outlet structure shall have a temporary structure attached to it whichprovides effective filtering of sediments prior to the release of runoff from the site. Thistemporary structure can either be a riser attachment surrounded by filter fabric andstone, or a horizontal pipe at the foot of the riser assembly which extends horizontallyon the detention facility bottom and is covered by filter fabric and stone. Other filteringvariations should be considered depending on their use, performance, and experiencewithin the stormwater program. (BMP Manual)

3. Sediment cleanout must be accomplished before the detention facility storage to thecrest of the principal spillway is reduced by 25% (may be more stringent depending onthe specific jurisdiction). (BMP Manual)

4. Removal of the temporary sediment control modifications to the outlet structure shallbe done only after the site has been vegetatively stabilized in accordance with theapproved erosion and sediment control plan and the detention system's design bottomelevations have been met. (BMP Manual)

5. Wetland plantings, where required, shall not be performed until final site stabilizationhas been accomplished. (BMP Manual)

Infiltration Practices

Infiltration facilities are extremely sensitive to clogging by construction generated sedi-ments. Therefore, stringent requirements are needed during construction to assure theirlong term performance once construction activities are completed. The following recom-mendations may be controversial. They need to be discussed thoroughly by theimplementing agency and with the regulated community to recognize difficulties inimplementation and gain support for their inclusion in the program.

1. Infiltration facilities should not be constructed or operated prior to overall site stabiliza-tion. (BMP Manual)

2. Infiltration facilities, other than dry wells and porous pavement, shall be off-line andhave pretreatment practices to reduce sediment loadings into the facility. Pretreat-ment can be provided by sediment sumps, biofiltration, extended detention ponding,or other means approved by the permitting agency. (BMP Manual)

3. Infiltration basin facilities shall not be used as sediment basins during construction.Sediment basins shall be constructed upstream of the infiltration basin and construc-tion runoff shall bypass the infiltration basin until site stabilization has been completed.(BMP Manual)


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4. To prevent soil compaction, areas to be used for infiltration facilities will be clearlymarked and construction equipment prevented from entering them. (BMP Manual)

Filtration Practices

Treatment in filtration practices is accomplished by passing runoff through a filter media.They often are used as a component of construction site sediment control. However,filters used for stormwater treatment need to have certain requirements placed upon themto better assure long term performance:

1. If used to filter sediments during construction, the filter media shall be completelyreplaced once the site is fully stabilized and before the filter is placed into operation forstormwater treatment. (BMP Manual)

2. If not used during construction for filtering sediments, runoff shall be diverted aroundthe filter and filter media shall not be placed in the facility until the contributing drain-age area has been stabilized. (BMP Manual)

3. Underdrain or outlet structures shall be protected from excess sediment entry. (BMPManual)

Biofiltration Practices

Biofiltration practices rely on vegetative fil-tering of stormwater runoff and, in manycases, infiltration. Their effective perfor-mance depends on their length, slope, soils,vegetative stand, and flow velocity. Assuch, activities which may adversely impacton any of the treatment mechanisms shouldbe addressed during construction.

1. If the biofiltration practice will rely uponinfiltration, then all recommendations forinfiltration facilities need to be followedfor biofiltration practices. (BMP Manual)

2. The facility shall be protected from ex-cess sedimentation which could retardor smother vegetation, or impair perco-lation. (BMP Manual)

3. Biofiltration facilities can be used as a component of an erosion and sediment controlplan, but primarily as a secondary sediment trapping facility. Examples include treat-ment of stormwater flows after discharge from a sediment trap, or sheet flow from a

Barrel/riser assembly installedupside down demonstrating a lack of

understanding by the contractor and lackof inspection oversight

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residential site into a biofiltration facility which, during the erosion and sediment controlphase, has stone check dams to reduce flow velocities. Before being placed intoservice for stormwater management, biofiltration facilities will be cleared of all accu-mulated sediments, excavated to the design depth, and vegetatively stabilized. (BMPManual)

4. Once the biofiltration practice has been shaped to final contours, it shall be sodded orerosion control matting or other practices shall be used to protect the soil and gradesuntil vegetation has become established to minimum density requirements. (BMPManual)

2. Ensuring Proper Construction of the Stormwater Management Facility

To help assure that stormwater systems are constructed properly, three essentialinstitutional components need to be included in the stormwater program: financialassurances, periodic inspections and as-built certifications. Recommended rule lan-guage includes:

Financial assurances

1. Prior to the issuance of any building or grading permit for which stormwater manage-ment facilities are required, the plan approval agency shall require the applicant orowner to submit a financial guarantee to ensure the initial function of the completedstormwater management facility. That guarantee shall be either a surety or cash bond,or irrevocable letter of credit. The amount of the guarantee shall be established by theplan approval agency but shall not be less than 50% (actual percentage can be deter-mined by individual state program) of theestimated construction cost of the storm-water management system.

Periodic inspections

The inspection entity, whether a public agency, state certified inspector, or site engineer,must have a visible presence during construction of stormwater management facilities.Inspections need to be made at specified stages of construction rather than at anassigned time frequency. Construction phasing may mean that a stormwater manage-ment facility may not be actively under construction for extensive time periods. Therefore,communication between contractor, consultant, and the inspection entity is critical. Thefollowing steps should be taken to assure inspections are conducted at the appropriatestages of construction:

1. The land developer shall notify the inspection entity before initiation of construction, atthe construction stages specified below, and upon project completion, when a finalinspection will be conducted to ensure compliance with the approved plan.

2. The land developer or contractor shall request an inspection at least 24 hours aheadof time. Inspectors will be required to approve work as it is completed at the critical


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stages of construction specified below for the different types of stormwater manage-ment facilities.

3. The approved stormwater management system plans shall be on the project site at alltimes during construction.

4. Site personnel shall be notified of any site inspection and receive a written report ofsite conditions. The report shall specify any corrections that are necessary to bring thesite and the stormwater management facility into compliance with approved plans.

5. All stormwater detention systems shall be inspected at the following stages of con-struction:

A. Upon completion of excavation to sub-foundation and, where required, installationof structural supports or reinforcement for structures, including, but not limited to:(1) Core trenches for structural embankments,(2) Inlet-outlet structures and anti-seep structures, watertight connectors on pipes,and(3) Trenches for enclosed storm drain facilities.

B. During placement of structural fill, concrete, and installation of piping and catchbasins;

C. During backfill of foundations and trenches;D. During embankment construction; andE. Upon completion of final grading and establishment of permanent vegetation.

6. Infiltration facilities shall be inspected at the following times:

A. When the area to be used for the infiltration facility has been staked out prior to itsconstruction;

B. During excavation to ensure minimal compaction and verify soil conditions;C. Upon completion of excavation and, if appropriate, before filling of the facility with

stone or other fill material; andD. Upon completion of facility construction, including complete establishment of veg-

etation, if appropriate.

7. Filtration facilities shall be inspected at the following times:

A. Upon completion of excavation;B. Upon completion of structural components, such as reinforcing bars, but prior to

any concrete pouring;C. For prefabricated units, during joining of prefabricated sections to ensure good

sealing between sections;D. After the facility has been filled with water to determine whether there is any leak-

age: andE. For sand filters which are part of a detention system, inspections shall occur as

specified for detention facilities and before and after placement of underdrain pipes,geotextile fabrics, and filter media.

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As-built Certifications and Record Drawings

1. Completed construction of the stormwater management system shall be documentedon an As-built Certification and Record Drawing, prepared and sealed by a construc-tion professional. Normally, this is the registered professional engineer who has su-pervised the construction of the stormwater system. These documents certify thatconstruction of the stormwater management system was done according to the ap-proved plan. Any variation from the approved plan must be noted.

2. Prior to requesting a final inspection, the permittee shall have a registered profes-sional engineer, or other qualified design professional (depending upon state or localrequirements), inspect the stormwater management system, submit a complete set ofdrawings, and certify on the plans that:

A. The stormwater management facilities were constructed in compliance with theapproved plans. The Record Drawings will show all pertinent constructed dimen-sions, elevations, shapes, and materials;

B. All variations in construction from the approved design plan shall be identified,including omissions to and additions from the approved plan;

C. If there are modifications from the approved plan, what changes or improvementsare required to bring the project into compliance with the approved plan; and

D. Any changes which might conflict with local, state, or federal regulations.

C. Legal Operation and Maintenance Requirements for Stormwater Systems

A very important element which must be considered during the design phase is determininghow to assure proper operation and maintenance of the stormwater system, both for the shortand long term. For the short term, it is recommended that there be a warranty periodduring which the original developer of the site is responsible for all maintenance andoperation. However, for the long term, a permanent operation and maintenance entitymust be identified which has appropriate legal authority to own, operate, maintain thestormwater system, and raise funds to complete maintenance when needed.

When there is one property owner, the maintenance responsibility is clearly defined. How-ever, a major concern arises when the owner or permittee involved in development andimplementation of site controls eventually sells all or part of the property. The newowners often will not be aware of permit requirements and will find that they have a perma-nent stormwater management facility on their property that they must inspect and maintain.This problem is especially compounded at residential developments, where there will be manydifferent property owners. Typically, a property owners association will be responsiblefor stormwater system operation and maintenance. Experience in urban runoff controlprograms around the country shows that, even with the best intentions, maintenanceof stormwater management facilities by these associations generally is not accom-plished (WMI, 1997).


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Example wording for both situations follows :

General Assurances

1. The owner or permittee shall assure that the stormwater management system is at alltimes properly operated, maintained, and managed in accordance with the require-ments of the permit and the approved stormwater pollution prevention plan.

2. Stormwater management facilities shall be maintained so that their performance isnot diminished or impaired. Failure to maintain stormwater facilities shall be consid-ered a permit violation and subject the responsible maintenance entity to any and allpenalties established by law or these regulations.

3. Stormwater management systems shall not be modified without specific approval ofthe permitting agency unless such modifications are part of an approved maintenanceschedule.

4. Stormwater management facilities shall be located on commonly owned property andnot located on one individual's property unless that individual accepts full maintenanceresponsibility for the facility. There shall be dedicated easements for access to allcomponents of the stormwater management system.

5. The owners, with a record interest in any non-public stormwater management facility,commercial, industrial, and other private practice, shall sign and record a covenantwhich runs with the land and binds the property on which the private stormwater man-agement facility is located to maintain the facility.

6. An operation and maintenance plan and schedule shall be provided to the owner orthe legal operation and maintenance entity.

7. The appropriate public inspection agency shall have authority to inspect private storm-water management facilities at any time to ensure compliance with maintenance sched-ules and requirements, and that the facilities are operating as designed and constructed.

Warranty Period

1. The permittee shall be responsible for all maintenance and proper operation ofstormwater facilities for a period of two years after completion of the overall project.The permittee shall satisfactorily maintain the facility and repair any failure within thistwo year period. Additionally, the permittee shall post and maintain a maintenancebond or other security acceptable to the permitting agency during this two year initialmaintenance period. The purpose of the maintenance bond is to cover the cost ofdesign defects or failures in workmanship of the facilities. The amount of the mainte-nance bond shall be ten percent of the construction cost of the stormwater manage-ment facilities.

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2. The permittee shall be responsible for proper operation and maintenance of thestormwater system. If the permittee is going to sell or otherwise divest its interest inthe permitted development or property, then a legal operation and maintenance entity,as specified below, shall be accept responsibility for the operation and maintenance ofthe stormwater system.

3. The permittee shall give the responsible maintenance entity copies of possible main-tenance inspection forms and other appropriate documentation to educate them abouttheir legal responsibilities of owning a stormwater management system.

4. The permittee shall provide a copy of an "as-built" plan of the stormwater manage-ment system to the responsible maintenance entity.

Legal Operation and Maintenance Entity

1. The following entities are acceptable for meeting the requirements necessary to en-sure that the stormwater management system will be operated and maintained in com-pliance with the requirements of these regulations:

A. Local governmental units including counties or municipalities, or special taxing dis-tricts.

B. State or federal agencies; orC. Duly constituted stormwater, water, communications, sewer, electrical, or other public

utilities.

2. The property owner or developer is normally not acceptable as a responsible entitywhen the property is intended to be subdivided. The property owner or developer shallbe acceptable in any of the fol lowing circumstances:

A. Written proof is furnished either by letter or resolution, that a governmental entity orsuch other acceptable entity as set forth in 1 above will accept the operation andmaintenance of the stormwater management system at a specified time in thefuture;

B. Proof of bonding or assurance of a similar nature is furnished in an amount suffi-cient to cover the cost of the operation and maintenance of the stormwater man-agement system;

C. The property is wholly owned by the permittee and ownership is intended to beretained. This would apply to a farm, corporate office, or single industrial facility, forexample; or

D. The ownership of the property is retained by the permittee and is either leased orrented to third parties such as in shopping centers or mobile home parks.

3. Profit or nonprofit corporations including homeowners associations, property ownersassociations, condominium owners associations or master associations shall be ac-ceptable only under certain conditions that ensure the corporation has the financial,legal and administrative capability to provide for the long term operation and mainte-nance of the stormwater management system.


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4. Entity requirements.

A. If a multimember association such as a homeowner, property owner, condominiumor master association is proposed, the owner or developer must submit Articles ofIncorporation for the association, and Declaration of Covenants and Restrictions,or such other organizational and operational documents which affirmatively assignauthority and responsibility for the operation or maintenance of the stormwatermanagement system.

B. The association shall have sufficient powers reflected in its organizational or op-erational documents to:

1. Operate and maintain the stormwater management system as permitted or ex-empted by the approval authority;

2. Establish rules and regulations;3. Assess members a fee for the cost system operation and maintenance and en-

force collection of such assessments;4. Contract for services to provide for operation and maintenance;5. Exist in perpetuity. The Articles of Incorporation must provide that if the association

is dissolved, the stormwater management system shall be transferred to and main-tained by an entity acceptable to the approval authority. Transfer of maintenanceresponsibility shall be effectuated prior to dissolution of the association;

6. Enforce the restrictions relating to the operation and maintenance of the stormwatermanagement system;

7. Provide that the portions of the Declarations which relate to the operation andmaintenance may be enforced by the approval authority in a proceeding at law or inequity; and

8. Require that amendments to the documents which alter the stormwater manage-ment system beyond maintaining it's original condition must receive approval agencyapproval before taking effect.

5. Phased Projects

A. If an operation and maintenance entity is proposed for a project which will be con-structed in phases, and subsequent phases will use the same stormwater manage-ment system as the initial phase or phases, the entity shall have the ability to ac-cept responsibility for the operation and maintenance of stormwater managementsystems for future phases of the project.

B. If the development scheme contemplates independent operation and maintenanceentities for different phases, and the stormwater system is integrated throughoutthe project, the entities either separately or collectively shall have the authority andresponsibility to operate and maintain the stormwater system for the entire project.That authority shall include cross easements for stormwater management and theability to enter and maintain the various facilities, should any sub-entity fail to main-tain a portion of the stormwater management system within the project.

In the event the legal operation and maintenance entity fails to maintain the stormwater man-agement system in good working condition, the permitting authority or local jurisdiction musthave the legal authority to enter the property, maintain the stormwater management system,

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assess the property owners, and be able to place a lien on the property if the owners do notpay the assessment. This may be necessary for safety reasons or it may be the only way toensure that the facility is maintained as constructed. There are several examples of legalmaintenance agreements provided at the end of this Chapter which offer wording regardingthis legal authority.

D. Maintenance Inspection Requirements for Stormwater Management Systems

To assure that the legal operation and maintenance entity is performing all required mainte-nance activities, periodic inspections and certifications are needed. Whether these inspec-tions are done by a public agency, such as the permitting authority, by a state certifiedinspector, or by a registered professional engineer, will depend upon the stormwaterprogram's institutional framework and staff resources. Unfortunately, due to a lack ofadequate funding, most public agencies will never have enough inspectors to regu-larly inspect completed stormwater management systems. To address this problem,Florida's program is implementing a certified inspector program and recommending that localgovernments implement renewable Operating Permits for stormwater systems.

A question that often arises is how frequently should stormwater management systems beinspected to assure proper performance. Often this is site-specific, depending on manyfactors such as the types of BMPs used, the pollutant loadings, the facility's size, the contrib-uting drainage area, and whether it is on-line or off-line. For example, while wet detentionsystems may only need annual inspections, BMPs such as oil/grit separators or sand filtersmay need monthly inspections. Chapter 6 provides recommendations on how often dif-ferent types of BMPs need inspecting. Additionally, Appendix 4-1 includes a tableprepared by the Florida Department of Environmental Protection that is included inNPDES municipal stormwater permits.

Recommended rule inspection language follows:

General Inspection Requirements

1. The permittee or responsible maintenance entity shall conduct regular inspections ofall components of the stormwater management. The person conducting the inspectionshall complete and retain a stormwater management facility inspection form after eachinspection.

2. At least once each year, the permittee or responsible maintenance entity shall arrangefor an inspection of their stormwater management system by either a public agencyinspector or a private inspector.

3. Inspection reports (detailed in Chapter 7) shall be maintained by the responsible in-spection agency. The inspection reports shall include the following items:

A. Date of inspectionB. Name of the inspector


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C. The condition of:(1) vegetation,(2) fences,(3) spillways,(4) embankments,(5) reservoir area,(6) outlet channels,(7) underground drainage,(8) Filter media,(9) sediment load, or(10) other items

D. If maintenance activities are needed, the recommendations for maintenance andan expected time for completion of the needed maintenance activities will be notedon the form.

4. The permitting (or inspection) agency shall implement procedures to ensure that defi-ciencies indicated by inspections are rectified in a timely manner. These shall include:

A. Notification of the responsible maintenance entity of deficiencies and needed main-tenance activities, including a time frame for repairs;

B. After the maintenance activities have been completed, the inspector will be notifiedso that the facilities can be reinspected. The inspector will complete a new inspec-tion form, noting whether all recommended maintenance activities have been com-pleted and if any other actions are needed to assure proper operation of the facility.

C. Effective enforcement procedures or procedures to refer projects to the appropri-ate legal entity if repairs are not undertaken or are not done properly.

5. Copies of all stormwater management facility "As-Built" Plans shall be provided to theappropriate maintenance inspection agency and to the legal maintenance entity re-sponsible for performing maintenance.

6. All public agency or private inspectors of permanent stormwater management facilitiesshall attend and pass a Departmental course on stormwater system maintenance. Inaddition, individuals responsible for maintenance of completed stormwater manage-ment facilities shall also be required to attend this stormwater management mainte-nance course. The course shall include discussion of at least the following topics:

A. Context of the course.B. Aspects of law and regulation.C. Soils information including texture, limitations, erodibility, and classification.D. Stormwater management facilities and the importance of their proper function and

performance.E. Inspection and problem documentation.F. Proper approach to actual maintenance including erosion and sediment control

during maintenance.G. Disposal of materials removed from the practice.H. Submission of an activity completion form.

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Public Agency Inspections

1. The responsible public inspection agency shall conduct inspections of all stormwatermanagement systems at least once per year. More frequent inspections will be con-ducted after an unusually high runoff event or for stormwater systems with a higherpotential to fail such as filters or oil and grit separators.

Private Inspections

1. If there is no responsible public inspection agency, the legal maintenance entity shallprovide for period inspections of their stormwater management system by either aregistered professional engineer or a state certified inspector.

2. Inspections shall be conducted at least once per year, with more frequent inspectionsafter an unusually high rainfall or for stormwater systems such as filters or oil and gritseparators.

3. The inspector shall provide the legal maintenance entity with a copy of all inspectionreports and send one to the permitting or responsible inspection agency.

4. The legal maintenance entity shall complete all maintenance activities and repairs rec-ommended in the inspector's report within the time frame specified and request theinspector to reinspect the stormwater system following completion of all maintenanceactivities.


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APPENDIX 4-2

Residential Agreement to MaintainStormwater Management Facilities

and to Implement a Pollution Prevention Plan

Olympia, Washington

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Drainage Design and Erosion Control Manual for Olympia, Washington

Residential Agreement to MaintainStormwater Management Facilities and to Implement

a Pollution Prevention Plan

The upkeep and maintenance of stormwater management facilities and the implementationof pollution prevention best management practices is essential to the protection of aquaticresources. All property owners are expected to conduct business in a manner that promotesresource protection. This Agreement contains specific provisions with respect to maintenanceof stormwater management facilities and use of pollution prevention practices.

LEGAL DESCRIPTION

Whereas, the ____________ have constructed improvements, including but not limited tobuildings, pavement, and stormwater management facilities on the property described above.In order to further the goals of the Jurisdiction to ensure the protection and enhancement ofaquatic resources, the Jurisdiction and the ______________ hereby enter into this Agree-ment. The responsibilities of each party to this Agreement are identified below.

________________________ SHALL

1. Implement the stormwater management facility maintenance program included herein asAttachment "A". (maintenance checklist similar to that developed in Chapter 7)

2. Implement the pollution prevention plan included herein as Attachment "B". (homeownerresponsibilities such as disposal of household wastes, lawn care, etc.)

3. Maintain a record (in the form of a log book) of steps taken to implement the programsreferenced in (1) and (2) above. The log book shall be available for inspection by appoint-ment at _____________________________. The log book shall catalog any action taken,who took the action, when it was taken, how it was done, and any problems encounteredor follow-on actions recommended. Maintenance items ("problems") listed in Attachment"A" shall be inspected as specified in the attached instructions or more often if necessary.The ___________ are encouraged to photocopy the individual checklists in Attachment"A" and use them to complete its inspections. These completed checklists would then, incombination, comprise the logbook.

4. Submit an annual report to the Jurisdiction regarding implementation of the programsreferenced in (1) and (2) above. The report must be submitted on or before ______, 199_and each calendar year and shall contain, at a minimum, the following items:

A. Name, address, and telephone number of the businesses, the persons, or firmsresponsible for plan implementation, and the persons completing the report.

B. Time period covered by the report.C. A chronological summary of activities conducted to implement the programs refer-

enced in (1) and (2) above. A photocopy of the applicable sections of the logbook,


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with any additional explanations needed, shall normally suffice. For any activitiesconducted by paid parties, include a copy of the invoice for services.

D. An outline of planned activities for the next year.

THE JURISDICTION SHALL:

1. Execute the following periodic major maintenance on the subdivision's stormwater man-agement facilities: sediment removal from facilities, managing vegetation in wet ponds,resetting orifice sizes and elevations, and adding baffles.

2. Maintain all stormwater management facility elements in the public rights-of-way, such ascatch basins, oil-water separators, and pipes.

3. Provide technical assistance to the _______________ in support of its operation andmaintenance activities conducted pursuant to its maintenance and source control pro-grams. Said assistance shall be provided upon request and as Jurisdictions time andresources permit.

4. Review the annual report and conduct a minimum of one (1) site visit per year to discussperformance and problems with the _____________.

5. Review the agreement with the _______________ and modify it as necessary at leastonce every three (3) years.

REMEDIES

1. If the Jurisdiction determines that maintenance or repair work is required to be done tothe stormwater management facilities located in the subdivision, the Jurisdiction shallgive the ____________ notice of the specific maintenance and/or repair required. TheJurisdiction shall set a reasonable time in which such work is to be completed by thepersons who were given notice. If the above required maintenance and/or repair is notcompleted within the time set by the Jurisdiction, written notice will be sent to the_____________ stating the Jurisdiction's intention to perform such maintenance and billthe _____________ for all incurred expenses.

2. If, at any time, the Jurisdiction determines that the existing facility creates any imminentthreat to public health or welfare, the Jurisdiction may take immediate measures to rem-edy said threat. No notice to the persons listed in Remedies (1), above, shall be requiredunder such circumstances. All other ______________ responsibilities shall remain ineffect.

3. The ________________ grant unrestricted authority to the Jurisdiction for access to anyand all stormwater management facilities for the purpose of performing maintenance orrepair as may become necessary under Remedies (1) and/or (2).

4. The _________________ shall assume responsibility for the cost of maintenance andrepairs to the stormwater management facilities, except for those maintenance actions

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explicitly assumed by the Jurisdiction in the preceding section. Such responsibility shallinclude reimbursement to the Jurisdiction within 90 days of the receipt of the invoice forany such work performed. Overdue payments will require payment of interest at the cur-rent legal rate for liquidated judgements. If legal action ensues, any costs or fees incurredby the Jurisdiction will be borne by the parties responsible for said reimbursements.

This Agreement is intended to protect the value and desirability of the real property describedabove and to benefit all the citizens of the Jurisdiction. It shall run with the land and be bindingon all parties having or acquiring any right, title, or interest, or any part thereof, of real propertyin the subdivision. They shall inure to the benefit of each present or future successor ininterest of said property or any part thereof or interest therein, and to the benefit of all citizensof the Jurisdiction.

Agreed to and signed by:

Owner Date

STATE OF WASHINGTON, COUNTY OF THURSTON

On this day and year, the above personally appeared before me and provided photo identi-fication, and who executed the foregoing instrument and acknowledge that they signed thesame as their free and voluntary act and deed for the uses and purposes therein men-tioned.

Given under my hand and official seal this _____ day of _____________, 199__

Notary Public in and for the State ofWashington, residing in _________________My commission expires _________________

Dated in Olympia, Washington, this _______ day of _____________, 199__


On this day and year, personally appearing before me, and , who executed the foregoing instrument and acknowledge the

said instrument to be the free and voluntary act and deed of said Municipal Corporation forthe uses and purposes therein mentioned and on oath states he is authorized to executesaid instrument.





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APPENDIX 4-3

Commercial, Industrial Agreementto Maintain

Stormwater Management Facilities and to

ImplementA Pollution Prevention Plan

Olympia, Washington

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Drainage Design and Erosion Control Manual for Olympia, Washington

Commercial, Industrial Agreement to MaintainStormwater Management Facilities and to Implement

A Pollution Prevention Plan

The upkeep and maintenance of stormwater management facilities and the implementationof pollution prevention plans is essential to the protection of aquatic resources. All propertyowners are expected to conduct business in a manner that promotes resource protection.This Agreement contains specific provisions with respect to maintenance of stormwater man-agement facilities and use of pollution prevention practices.

LEGAL DESCRIPTION:

Whereas, Business Name, has constructed improvements, including but not limited to, build-ings, pavement, and stormwater management facilities on the property described above. Inorder to further the goals of the Jurisdiction to ensure the protection and enhancement ofJurisdiction's aquatic resources, the Jurisdiction and Business Name hereby enter into thisAgreement. The responsibilities of each party to this Agreement are identified below.

BUSINESS NAME SHALL:

1. Implement the stormwater management facility maintenance program included herein asAttachment "A". (maintenance checklist similar to that developed in Chapter 7)

2. Implement the pollution prevention plan included herein as Attachment "B". (parking lotmaintenance, covering outdoor storage areas, etc.)

3. Maintain a record (in the form of a logbook) of steps taken to implement the programsreferenced in (1) and (2) above. The logbook shall be available for inspection by Jurisdic-tion staff at __________________ during normal business hours. The logbook shallcatalog the action taken, who took it, when the action was done, how it was done, andany problems encountered or follow-on actions recommended. Maintenance items ("prob-lems") listed in Attachment "A" shall be inspected on a monthly or more frequent basis asnecessary. Business Name is encouraged to photocopy the individual checklists in At-tachment "A" and use them to complete its monthly inspections. These completed check-lists would then, in combination, comprise the monthly logbook.

4. Submit an annual report to the Jurisdiction regarding implementation of the programsreferenced in (1) and (2) above. The report must be submitted on or before ________ ofeach calendar year and shall contain, at a minimum, the following items:

A. Name, address, and telephone number of the business, the person, or the firm re-sponsible for plan implementation, and the person completing the report.

B. Time period covered by the report.C. A chronological summary of activities conducted to implement the program refer-

enced in (1) and (2) above. A photocopy of the applicable sections of the logbook,


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with any additional explanation needed, shall normally suffice. For any activities con-ducted by paid parties not affiliated with Business Name include a copy of the invoicefor services.

D. An outline of planned activities for the next year.

THE JURISDICTION SHALL:

1. Provide technical assistance to Business Name in support of its operation and mainte-nance activities conducted pursuant to its maintenance and pollution prevention controlprograms. Said assistance shall be provided upon request, and as Jurisdiction time andresources permit, at no charge to Business Name.

2. Review the annual report and conduct a minimum of one (1) site visit per year to discussperformance and problems with Business Name.

3. Review this agreement with Business Name and modify it as necessary at least onceevery three (3) years.

REMEDIES

1. If the jurisdiction determines that maintenance or repair work is required to be done to thestormwater management facility existing on the Business Name property, the Jurisdictionshall give the owner of the property within which the facility is located, and the person oragent in control of said property, notice of the specific maintenance and/or repair re-quired. The Jurisdiction shall set a reasonable time in which such work is to be completedby the persons who were given notice. If the above required maintenance and/or repair isnot completed within the time set by the Jurisdiction, written notice will be sent to thepersons who were given notice stating the Jurisdiction's intention to perform such main-tenance and bill the owner for all incurred expenses. The Jurisdiction may also revokestormwater runoff utility rate credits for the quality component or invoke surcharges to thequantity component of the Business Name bill if required maintenance is not performed.

2. If at any time the Jurisdiction determines that the existing facility creates any imminentthreat to public health or welfare, the Jurisdiction may take immediate measures to rem-edy said threat. No notice to the persons, listed in (1) above, shall be required under suchcircumstances.

3. The owner grants unrestricted authority to the Jurisdiction for access to any and all storm-water management facility features for the purpose of performing maintenance or repairas may become necessary under Remedies (1) and (2).

4. The persons, listed in (1) above, shall assume all responsibility for the cost of any main-tenance and for repairs to the stormwater management facility. Such responsibility shallinclude reimbursement to the Jurisdiction within 30 days of the receipt of the invoice forany such work performed. Overdue payments will require payment of interest at the cur-rent legal rate for liquidated judgments. If legal action ensues, any costs or fees incurredby the Jurisdiction will be borne by the parties responsible for said reimbursements.

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5. The owner hereby grants to the Jurisdiction a lien against the above-described propertyin an amount equal to the cost incurred by the Jurisdiction to perform the maintenance orrepair work described herein.

This Agreement is intended to protect the value and desirability of the real property describedabove and to benefit all the citizens of the Jurisdiction. It shall run with the land and be bindingon all parties having or acquiring from Business Name or their successors any right, title, orinterest in the property or any part thereof, as well as their title, or interest in the property orany part thereof, as well as their heirs, successors, and assigns. They shall inure to thebenefit of each present or future successor in interest of said property or any part thereof, orinterest therein, and to the benefit of all citizens of the Jurisdiction.

Agreed to and signed by:

Owner Date


On this day and year, the above personally appeared before me and provided photo identi-fication, and who executed the foregoing instrument and acknowledge that they signed thesame as their free and voluntary act and deed for the uses and purposes therein men-tioned.





On this day and year, personally appearing before me, and , who executed the foregoing instrument and acknowledge the

said instrument to be the free and voluntary act and deed of said Municipal Corporation forthe uses and purposes therein mentioned and on oath states he is authorized to executesaid instrument.





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APPENDIX 4-4

Standard Maintenance and Monitoring Agreement

BMP Facilities Maintenance/Monitoring Agreement

City of Alexandria, Virginia

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City of Alexandria, Virginia

Standard Maintenance and Monitoring AgreementBMP Facilities Maintenance/Monitoring Agreement

THIS AGREEMENT, made and entered into this __________ day of ____________, 19__,by and between __________________________________, herein called the "Landowner"and the City of Alexandria, Virginia (the "City")

WITNESSETH

WHEREAS the Landowner is the owner of certain real property described _________________as acquired by deed in the land records of the City of Alexandria, Virginia, Deed Book _______at Page __________, hereinafter called the "Property".

WHEREAS, the Landowner is proceeding to build on and develop the property; and

WHEREAS, Plan of Development/Site Plan/Subdivision Plan __________________, herein-after called the "Plan" which is expressly made a part hereof, as approved or to be approvedby the City, provides for detention on-site treatment of stormwater runoff within the confinesof the property; and

WHEREAS, the City and the Landowner, its successors and assigns agree that the health,safety, and welfare of the residents of the City of Alexandria, Virginia, require that on-sitestormwater management facilities be constructed and maintained on the property; and

WHEREAS, the City requires that on-site stormwater management facilities as shown on thePlan be constructed and adequately maintained by the Landowner, its successors and as-signs.

NOW, THEREFORE, in consideration of the foregoing premises, the mutual covenants con-tained herein, and the following terms and conditions, the parties hereto agree as follows:

1. The on-site stormwater management facilities shall be constructed by the Landowner,its successors and assigns, in accordance with the plans and specifications identifiedin the plans.

2. The Landowner, its successors and assigns, shall maintain the stormwater manage-ment facilities in good working condition, acceptable to the City, so that they are per-forming their design functions.

3. The Landowner, its successors and assigns, hereby grants permission to the City, itsauthorized agents and employees, to enter upon the property, and to inspect the storm-water management facilities whenever the City deems necessary. The purpose of theinspection is to assure safe and proper functioning of the facilities. The inspectionshall cover the entire facilities, berms, outlet structures, pond areas, access roads, etc.


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When deficiencies are noted, the City shall give the Landowner, its successors andassigns, copies of the inspection report with findings and evaluations.

4. In the event the Landowner, its successors and assigns, fails to maintain thestormwater management facilities in good working condition acceptable to the City,the City may enter upon the Property and take whatever steps it deems necessaryto maintain said stormwater management facilities and to charge the costs of therepairs to the Landowner, its successors and assigns. This provision shall not beconstrued to allow the City of Alexandria to erect any structure of a permanentnature on the land of the Landowner, outside of an easement belonging to the City.It is expressly understood and agreed that the City is under no obligation to maintainor repair said facilities, and in no event shall this Agreement be construed to imposeany such obligation on the City.

5. The Landowner, its successors and assigns, will perform maintenance in accor-dance with the maintenance schedule for the stormwater management facilitiesincluding sediment removal as outlined on the approved plans and the followingspecific requirements:

For extended dry detention facilities, wet ponds, or infiltration facilities, insert thefollowing:

Maintenance of the (Insert type of facility) shall conform to the maintenance require-ments contained in the Northern Virginia BMP Handbook published by the NorthernVirginia Planning District Commission.

For unconventional BMPs for which design criteria is provided in the Design Manual,insert the following:

Maintenance of the (insert type of facility) shall conform to the maintenance require-ments contained in Chapter 2 of the Alexandria Supplement to the Northern VirginiaBMP Handbook.

For unconventional BMP's not detailed in Chapter 2 of this manual and for experi-mental BMP's, insert specific maintenance requirements as approved by the Direc-tor of Transportation and Environmental Services prior to release of the Final SitePlan.

6. In the event the City, pursuant to this Agreement, performs work of any nature, orexpends any funds in performance of said work for labor, use of equipment, sup-plies, materials, and the like on account of the Landowner's or its successors' andassigns, shall reimburse the City upon demand, within ______ days of receiptthereof for all costs incurred by the City hereunder. If not paid within such ______day period, the City shall have a lien against the property in the amount of suchcosts, plus interest at the Judgment Rate, and may enforce same in the same man-ner as a lien for real property taxes may be enforced.

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7. The Landowner, its successors and assigns, shall indemnify and hold harmless theCity and its agents and employees for any and all damages, accidents, casualties,occurrences or claims which might arise or be asserted against the City for the con-struction, presence, existence or maintenance of the stormwater management facili-ties by the Landowner, its successors and assigns.

In the event a claim is asserted against the City, its agents or employees, the City shallpromptly notify the Landowners, their successors and assigns, and they shall defend,at their own expense, any suit based on such claim. If any judgment or claims againstthe City, its agents or employees shall be allowed, the Landowner, its successors andassigns shall pay all costs and expenses in connection therewith.

The following additional paragraph shall be added for all agreements covering non-conventional or experimental BMP's.

8. The Landowner, its successors and assigns, hereby grants permission to the City, itsauthorized agents and employees, and to the Northern Virginia Planning District Com-mission, its authorized agents, employees and consultants, to enter upon the property,and to install, operate and maintain equipment to monitor the flow rate and pollutantcontent of the input flow, the effluent, and at intermediate points in the BMP. TheLandowner further agrees to design and construct the facility to provide access formonitoring. The Landowner further agrees to a contribution of (as established duringthe Site Plan approval process ______ in the case of experimental BMP's) the entirecost of the monitoring program, payable prior to the release of the Final Site Plan,towards the cost of the monitoring program.

8. or 9. This Agreement shall be recorded among the land records of the City of Alexan-dria, Virginia, and shall constitute a covenant running with the land and/or equitableservitude, and shall be binding on the Landowner, its administrators, executors, as-signs, heirs and any other successors in interests.

WITNESS the following signatures and seals:

(Landowner) (Seal)

By:

Type Name

Type Name


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ATTEST:____________________________________________

STATE OF _________________

CITY OF _________________

I, _____________________________, a Notary Public in and for the City and State afore-said, whose commission expires on the _______ day of _______________, 19___, dohereby certify that ____________________________ whose name(s) is/are signed to theforegoing Agreement bearing date of the _______ day of ____________, 19___, hasacknowledged the same before me in my said City and State.

GIVEN UNDER MY HAND THIS ______ day of __________________, 19___.

NOTARY PUBLIC

WITNESS the following signatures and seals:

Director, Department of T & ES (Seal)

By:

Type Name

Type Name

ATTEST:____________________________________________

STATE OF _________________

CITY OF _________________

I, _____________________________, a Notary Public in and for the City and State afore-said, whose commission expires on the _______ day of _______________, 19___, dohereby certify that ____________________________ whose name(s) is/are signed to theforegoing Agreement bearing date of the _______ day of ____________, 19___, hasacknowledged the same before me in my said City and State.

GIVEN UNDER MY HAND THIS ______ day of __________________, 19___.

NOTARY PUBLIC

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APPENDIX 4-5

RECOMMENDED MAINTENANCEOF

STORMWATER MANAGEMENT SYSTEMS

EXAMPLE OF LANGUAGEINCLUDED IN

STORMWATER NPDES MS4 PERMITSISSUED IN FLORIDA

1. OVERVIEW

Of all the individuals, groups, and agen-cies that influence or participate in themaintenance of a stormwater managementfacility, the facility’s owner has by far themost powerful and direct role. The owner’smaintenance action (or inaction) not only af-fects the facility itself, but also strongly influ-ences the actions (or reactions) of others.However, facility maintenance is only one ofmany activities and responsibilities vying forthe owner’s attention. As a result, facility main-tenance is sometimes overlooked, neglected,or abused by the owner. Furthermore, as thecomplexity of a facility’s ownership increasesfrom a single to multiple and even corporateownership, or ownership is conveyed over timeto a series of new owners, the potential foroversight, neglect, or abuse also increases.This can lead not only to a failure to achieveexpected or required facility performance lev-els, but can also threaten peoples’ health,safety, property, and their water bodies.

Perhaps the power and influence of stormwa-ter management facility owners can best besummarized in the following observations. Attheir best, stormwater facility owners canform the solid foundation of a successfulstormwater management program, provid-ing leadership to regulators and programmanagers, motivation to facility planners,designers, and maintainers, and securityto fellow community members. Con-versely, at their worst, facility owners,through neglect and disinterest, can mis-lead, discourage, and threaten these very

same people, thereby undermining thestormwater management program and fos-tering mistrust and cynicism of its goalsand importance.

1.1. Objectives

To advance the Handbook’s overall goal of ef-fective and efficient facility maintenance andto avoid the grave consequences describedabove, the objectives of this Chapter will be:

To explain the full meaning of stormwatermanagement facility ownership.

To educate stormwater facility ownersabout the purpose, goals, and operationof stormwater management systems.

To present an overview of the mechani-cal, hydrologic, and biological processesby which stormwater facilities fulfill theirpurpose.

To describe the potential hazards inher-ent in stormwater management systemsby virtue of these characteristics and thepotential liabilities inherent in facility own-ership.

To demonstrate to facility owners the im-portance of responsible maintenance inminimizing and managing these hazardsand liabilities.

To define the scope and content of a re-sponsible facility maintenance program.

Chapter 5Maintenance Considerations For

Facility Owners

5-1


5-2

To assist and encourage facility owners inestablishing and conducting maintenanceprograms.

1.2 Intended Readers

Intended readers of this Chapter include:

Single, multiple, and corporate ownersof both onsite and remote site facilities. Thisincludes present facility owners as well asthose who may or will become owners in thefuture.

Public officials who are responsible fordeveloping, promulgating, and/or operatingstormwater management programs and over-seeing facility performance, maintenance, andsafety. These officials will find valuable insightsinto the duties, demands, and liabilities of fa-cility ownership that should be useful in creat-ing more effective and successful programs.

Facility planners and designers whoshould also view stormwater managementfacilities through the eyes and budget of theirowners, an experience that should motivatethem to include the minimization and ease ofmaintenance as a primary design goal.

2. THE MEANING OF STORMWATERMANAGEMENT FACILITY OWNER-SHIP

Perhaps the best way to begin a discussionof such a philosophical topic would be to de-scribe how and why someone, some group,or some organization becomes the owner ofa stormwater management facility. This canbest be described by explaining how and whystormwater facilities have come to be part ofan owner’s property or project in the first place.Next, a discussion of basic facility operationand components will help explain why storm-water facility maintenance is both necessary

and important to the owner. Finally, this dis-cussion will also explain how these mainte-nance needs and priorities may vary depend-ing the type of facility and how the owner mustidentify and respond to the particular needsand priories of their own facility.

The productive use of land for agriculture, in-dustry, commercial enterprise, recreation, andgovernance has been a cornerstone of civili-zation since ancient times. As populationsgrew and social needs and interests ex-panded, the development of land for thesepurposes also grew. In many ways, the mod-ern land developer, redeveloper, or owner issatisfying many of the same societal needsfor housing, employment, and material goodsas explorers, traders, and pioneers have donein past centuries.

Since the middle of this century, however,many of the adverse impacts of land develop-ment and land use change have come intoclearer focus. Two of the most pervasive arethe effects they have on the quantity and qual-ity of stormwater runoff. As land is convertedfrom a natural, undisturbed condition to a man-made one, a process which usually includesthe elimination of indigenous vegetative cover,the regrading of the land surface, the additionof buildings, roadways, and other impervioussurfaces, and the installation of more efficientstormwater drainage systems, the quantityand velocity of runoff that will flow from a par-cel of land onto downstream properties andwaterways can increase by several hundredpercent. These increases can create new, andseverely aggravate existing, flooding and ero-sion problems on these downstream areas.In addition, by introducing into the runoff theby-products of the new land use, including theemissions and drippings from vehicles, indus-trial processes, power generation and wastedisposal, and the solid and liquid wastes gen-erated by the land’s inhabitants and users, therunoff’s chemical and biological quality can bedramatically reduced.

CHAPTER 5 Maintenance Considerations for Facility Owners

5-3

The rewards and penalties for developing andchanging land use has presented society witha dilemma. While society's growth needs can-not be ignored, neither can the harm causedby our attempts to meet those needs throughcontinued land development and redevelop-ment. How can this dilemma be resolved?

One possible method or technique is the cre-ation and use of stormwater managementpractices, which are physical devices or fa-cilities designed and constructed as part ofthe land development process to address theadverse runoff quantity and quality impacts de-scribed above. While there are several typesof stormwater management facilities (seeChapter 1 - Introduction for definitions of theprimary facility types contained in the Hand-book), most facilities accomplish their storm-water management goals through a few fun-damental processes. These processes werediscussed briefly in Section 3 of Chapter 2 -Stormwater Pollutants and ReductionMechanisms and are further described be-low.

2.1. Basic Stormwater ManagementFacility Operation

As noted above, the adverse impacts of landdevelopment or redevelopment can be an in-crease in the rate, volume, and speed of therunoff from the development site during astorm event. In order to prevent these in-creases from creating or aggravating floodingor erosion problems downstream, all or a por-tion of the site’s runoff can be conveyed to astormwater management facility. During pe-riods of excessive runoff (that could causedownstream problems if it had not been con-structed), the stormwater management facil-ity will temporarily store this excess runoffwithin its storage area while, at the same time,discharging only a portion of the runoff throughits outlet structure at a nonharmful rate.

This rate, which is sometimes established bythe government agency having jurisdictionover the land development, may be equal tothe rate of runoff that flowed from the site priorto its development. In other instances, par-ticularly where there are known flooding orerosion problems downstream or where de-tailed engineering analyses of the downstreamwaterways or the entire watershed have beenperformed, the outflow rate considered orspecified to be “nonharmful” may at times beeven less than the predeveloped rate. Nev-ertheless, the outflow rate can be seen to bea function of both the size of the facility’s stor-age volume and the hydraulic characteristicsof its outlet structure. Thus, the size andcharacteristics of storage volume and out-let structure will, in turn, be dependentupon the amount of excessive runoff cre-ated by the development or, in other words,the difference in the runoff amounts from thesite under predevelopment and post-develop-ment conditions. This is one reason why somedevelopment projects will require large storm-water management facilities occupying con-siderable amounts of land, while others willbe able to accomplish the same stormwatermanagement goals with less extensive facili-ties occupying much smaller areas.

In order to prevent or at least mitigate someof the harmful runoff quality impacts of the landdevelopment project, stormwater manage-ment systems may employ a variety of tech-niques to either remove some of the harmfulpollutants from the runoff or to treat or con-vert them to less harmful forms. Many of thepollutants will settle to the bottom of thefacility by gravity if the runoff is left in thefacility’s storage area for a long enoughtime. This requires careful discharge ofthe runoff from the storage area in orderto prevent short-circuiting of the pollutantsthrough the storage area or resuspensionof the pollutants from the bottom after theyhave settled. Other removal techniques in-clude passing the runoff through filtering me-


5-4

dia such as sand, peat, or dense vegetationthat removes certain pollutants by blockingtheir passage. Other practices use vegeta-tion to actually absorb some of the runoff andpollutants into the plants through their rootsystems, where they are stored or convertedby the plants’ biological processes. Finally,some stormwater management facilities willenhance the natural removal and/or conver-sion processes described above through thecontrolled addition of chemicals or the use ofmechanical treatment devices.

2.2. Stormwater Management Practices

As noted above, the characteristics of boththe site and the downstream waterways canaffect the required storage volume and landarea of a stormwater management facility.However, facilities may vary in several otherways, including the location and nature of thestorage area and the characteristics and be-havior of the facility’s outlet. All of these varia-tions will create different maintenance de-mands that the facility owner must respondto. A review of these variations should helpowners to better identify, understand, and re-spond to the maintenance demands of theirown facilities.

For example, the storage areas of most storm-water management systems are locatedabove the ground surface, where they can bereadily inspected and accessed by mainte-nance personnel and equipment. However,due to site constraints, some stormwater fa-cilities are located below ground in tanks orchambers, where access and mobility is muchmore restricted. In addition, some facilitiesmay only detain incoming runoff during andimmediately after a storm event, while othersmay retain some water permanently, creatinga lake or pond that is present under both wetand dry weather conditions. As defined inChapter 1 - Introduction and described indetail in Chapter 2 - Stormwater Manage-

ment Practices, such facilities are designatedas either dry or wet detention practices,depending upon whether they are normally dryor wet during nonrainfall periods.

Detention practices, whether wet or dry,discharge their runoff onto downstream ar-eas through an outflow structure, whichmay include orifices, weirs, pipes, and chan-nels. However, stormwater facilities definedin Chapter 1 as infiltration (or retention)practices may not have formal outlet struc-tures. Instead, they discharge their runoffthrough the soil which surrounds the bottomand/or sides of the facility’s storage area.

As noted above, there are several differenttechniques by which runoff pollutant loadingsare reduced by a stormwater managementfacility. These include settlement by gravityin detention practices and a combination ofsettling, evapotranspiration, and percolationthrough the ground in infiltration practices.Other facilities defined in Chapter 1 as filtra-tion practices force runoff to flow throughbeds of sand, peat, or even compost to re-move pollutants, while facilities defined asbiofiltration practices use dense stands ofvegetation or other organic media. Finally,it is important to note that many stormwatermanagement facilities have the physical andoperating characteristics of several differentpractices, particularly with regards to storm-water pollutant removal, and therefore can-not easily be categorized. Additionally, manystormwater systems may include a com-bination or series of facilities or practices.

A final characterization is important. Sincethe runoff quantity impacts of land develop-ment or redevelopment (i.e., volume, rate,and/or velocity) have been recognized for amuch longer period of time than the runoffquality impacts, many older stormwater man-agement facilities were designed and con-structed to only address these quantity im-pacts. In recent years, however, the runoff


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quality impacts of land development/redevel-opment have gained considerable attentionand, in some instances, even priority over thequantity concerns, resulting in the use of fa-cilities for runoff quality control only. There-fore, it becomes necessary at times to des-ignate whether the type of facility underconsideration is intended for runoff quan-tity or quality control purposes. This willbe done in the Handbook by adding eitherword to the facility type (e.g., a “quantitydetention facility” or “quality infiltrationfacility”). When neither word is added, thereader can assume that the facility is intendedto address both stormwater management im-pacts. Finally, facility types such as filtrationor biofiltration facilities are only intended toaddress runoff quality impacts and, therefore,no additional description is necessary. De-tailed information regarding the variousstormwater management practices includedin this manual is presented in Chapter 2.

2.3. Stormwater Facility Components

Just as different stormwater management fa-cilities may employ different storage, outflow,and pollutant control mechanisms, there aredifferent functions assigned to each area orcomponent of a facility. To help facility own-ers better understand the characteristicsand operation of their own facilities,thereby enhancing their ability to identifyand respond to their unique maintenancerequirements, a description of the majorcomponents of most stormwater manage-ment practices is presented in Table 5-1.As discussed below, each of the componentsdescribed in the table not only have differentfunctions, characteristics, and locations withina stormwater management facility but, by vir-tue of these attributes, also have differentmaintenance needs and priorities.

In reviewing the table, it is important to notethat not all facility types have all compo-

nents. For example, since an infiltration fa-cility discharges its outflow through the sur-rounding soil, it will may not have a principaloutlet structure, especially if it is an off-linefacility. Similarly, a vegetated swale or filterstrip, which controls runoff quality by filteringrunoff at shallow depths through dense veg-etation, will not normally have a principal out-let structure, dam, or trash racks. In addition,since some stormwater management systemsdisplay the characteristics of many facilitytypes, the list of components presented in thetable should not be considered exhaustive. Fi-nally, the component descriptions have beendeveloped specifically for this Handbook. Assuch, different or additional descriptions maybe used in other publications.

2.4. Operational Impacts on FacilityMaintenance

It should be apparent by now that stormwatermanagement facilities achieve their assignedstormwater management goals through a widevariety of means and techniques and, as such,each may consist of a similarly wide variety ofcomponents and characteristics. It is also im-portant for facility owners to recognize that,due to these facts, each type of facility hasits own unique maintenance demands andpriorities. For example, an infiltration facil-ity, which will discharge its runoff through thesurrounding ground, will require more frequentremoval of sediment and small debris than adry detention facility, whose outlet structurewill allow a much greater portion of the incom-ing sediment and small debris to pass through.This is also true of a wet detention facility,where a greater amount of sediment and de-bris will be captured and retained in the per-manent pool than the normally dry bottom ofthe detention facility.

Further comparisons will also be useful. Forexample, while both infiltration and wet de-tention facilities will capture and retain a


5-6

COMPONENT DESCRIPTION

PRINCIPAL OUTLET Hydraulic structure that controls and conveys thefacility's outflow to the downstream conveyance orreceiving water.

EMERGENCY OUTLET Hydraulic structure or spillway that safely conveysemergency overflows from the facility. Includesapproach and exit channels.

DAM/EMBANKMENT Wall or structural fill that impounds runoff in the facilityabove the adjacent ground surface.

BOTTOM The lowest or deepest surface within the facility.

SIDE SLOPES Slopes at dams, embankments, spillways, and facilityperimeters constructed through excavation or filling.

TRASH RACK Device placed upstream of the principal outlet or drainto intercept trash and debris that would otherwiseblock it.

LOW FLOW SYSTEM Surface and/or subsurface measures that conveylow and dry weather inflows to the principal outletwithout storage.

INLETS Upstream surface and/or subsurface conveyancemeasures that discharge runoff into the facility.

OUTFLOW SYSTEMS Downstream surface and/or subsurfaceconveyances or water bodies which receive facilityoutflows from the principal outlet.

PERIMETER Area immediately adjacent to the facility.

ACCESS SYSTEMS Measures and devices that provide maintenancepersonnel and equipment access to various facilitycomponents.

VEGETATIVE COVER Vegetation planted on various facility components tostabilize their surfaces and/or provide stormwatertreatment.

BYPASS SYSTEM A system which allows a facility owner to temporarilybypass the stormwater facility to allow a maintenanceactivity to occur in the "dry".

Table 5.1.

Major Components of Stormwater Management Practices


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greater portion of the inflow’s sediment anddebris than a dry detention facility, the pres-ence of the wet basin’s permanent pool willnormally make it much more difficult, time-consuming, and expensive to remove sedi-ments than the normally dry bottom in the in-filtration facility. In addition, the removal ofsediments from a properly constructed wet de-tention pond typically is only needed every 10to 15 years, while an infiltration facility oftenrequires annual removal. Finally, it can beseen that since a stormwater facility intendedto address both runoff quantity and quality im-pacts will, by its nature and operation, cap-ture and retain more sediment than a quan-tity-only facility, it will also require more fre-quent sediment removal efforts.

In addition to the varying maintenance needsof different stormwater management facilities,it can also be seen that different facility com-ponents will also impose different mainte-nance demands on the facility owner. Forexample, trash racks, low flow channels, andadjacent areas of the bottom will collect moresediment and debris than emergency spill-ways, side slopes, dams, and other compo-nents and will, therefore, require more frequentand thorough cleaning. Conversely, the struc-tural integrity of dams, embankments, emer-gency spillways, and outlet structures are, rela-tively speaking, more vital to the safety of thefacility and downstream areas and, therefore,will warrant more thorough inspection andmore immediate repair than low flow channels,perimeters, or bottoms.

It is important that stormwater manage-ment facility owners understand these dis-tinctions and comparisons, for it is throughsuch understanding that owners can moreeffectively and economically allocate theirmaintenance resources and meet theirmaintenance responsibilities. This is par-ticularly true where such resources are lim-ited due to economic, personnel, or equipmentconstraints. It is also true for potential facility

owners such as land developers, home buy-ers, and commercial or industrial leasees, whomust plan and budget for facility maintenanceas part of their overall operations. Failure todo so can be disastrous, as described in thefollowing section.

2.5. The Impacts of Facility MaintenanceNeglect

When the maintenance of a stormwatermanagement facility is neglected, the im-mediate impacts can quickly escalate intoserious health and safety problems. Imme-diate impacts typically include a decline in thefacility’s appearance, which can adverselyimpact the overall aesthetic character of thesurrounding area. Such impacts may be se-vere to some owners, particularly if the area’sappearance is vital to its economic or socialvitality. Examples of such instances includeoffice sites, shopping malls, and commercialbuildings that need to attract and keep ten-ants and customers, and residential neighbor-hoods that want to sustain both their qualityof life and high property values.

Other impacts from initial maintenance neglectcan include the creation of nuisances at thefacility, including odors, mosquitoes, and habi-tats for mice, rats, and other vermin. All ofthese can once again adversely impact thesite’s aesthetic character, and potentially ad-versely impact on site property values. Theywill also reduce the quality of life and may cre-ate health and safety threats to workers or resi-dents in the immediate area.

If the neglect continues, the facility’s ability toperform its intended functions will begin to beimpaired. This can have several serious andescalating impacts. For example, if the facil-ity is intended to provide stormwater treatment,a reduction in this treatment can result in eco-logical damage to downstream water bodies.If the facility has been required as part of a


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site discharge permit or land developmentapproval, these impacts may also have seri-ous legal consequences. If the facility is in-tended to prevent excess runoff from leavingthe site, downstream flooding or erosion mayoccur. This will not only physically threatendownstream property owners but will poseserious legal and liability problems for theneglectful facility owner.

Finally, the maintenance neglect can reachsuch a level that dams and embankmentsbegin to weaken and structures become un-stable. At this point, the facility has become adirect threat to the health and safety of thepeople that live or work both at and down-stream of the facility. This is particularly trueif the facility impounds a significant amount ofwater which can suddenly be released with-out warning and with disastrous effects ondownstream properties.

As shown above, many of the adverse ef-fects of facility maintenance neglect willbe felt by someone other than the facility’sowner. This is unfortunate since, as describedabove, these are the people that the facilitywas built to protect. As such, it can be seenthat any harm caused to these people or theirproperty due to facility maintenance neglectcan be the strong basis for a negligence law-suit against the owner, particularly if it can bedemonstrated that the owner willingly ne-glected the facility’s maintenance despite theknowledge that such neglect could be harm-ful. Such a lawsuit may be further strength-ened by the fact that the owner derives most,if not all, of the benefits provided by the facil-ity, and not the downstream residents or own-ers that are threatened by the neglect or mal-function.

The exact extent of an owner’s liability fordamages arising from facility maintenanceneglect will vary from state to state and willdepend, in part, upon the exact type of facilityin question. In general, however, two legal

concepts may by applied, particularly if thefacility impounds a body of water and is le-gally considered to be a dam. Under the le-gal concept of negligence, the degree of careexercised by the owner would be a factor indetermining the owner’s liability for any dam-ages that might have occurred due to facilityfailure. Under the legal concept of strict liabil-ity, however, the facility owner would be heldliable for any damages that occurred due tofacility failure regardless of the cause of thatfailure. In either case, it can be easily seenthat stormwater management facility own-ership involves a significant degree of le-gal responsibility for regular and thoroughfacility maintenance and operation.

In addition to the adverse physical and legalimpacts of maintenance neglect, the neglectedfacility that fails to meet outflow quality orquantity requirements or safety standards mayplace its owner in violation of local, state, orfederal discharge regulations. Such violationsmay subject the owner to fines, sanctions, and/or the loss of operating or occupancy permits.They will also undermine the stormwater man-agement programs upon which the regulationsare based and reduce the overall effective-ness and credibility of local, state, and fed-eral stormwater management programs.Chronic and widespread neglect can eventhreaten the existence of such programs. Assuch, it can be seen that the facility owneralso has a civic responsibility to conducta regular and thorough stormwater facilitymaintenance program.

Finally, neglect of a stormwater facility’s main-tenance can have severe economic impactsfor its owner over and above any fines, legaljudgements, settlements, and attorney fees.This is due to the fact that the cost to per-form facility maintenance on a regular ba-sis can be several times less than a one-time cost to restore a long-neglected facil-ity to normal or required condition. Forexample, a program of grass mowing and


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sediment and debris removal performed regu-larly at a dry detention facility may only re-quire a few man-hours per month using onlylawnmowers, shovels, and wheelbarrows. Onthe other hand, if such activities where ne-glected for a protracted period of time, theeffort to restore the facility to its normal condi-tion can require considerably more effort,money, and equipment.

In summary, there are many legal, eco-nomic, civic, and ethical impacts that awaitthe owner of a neglected stormwater facil-ity. These impacts should be sufficient rea-son for all owners to establish and conduct aregular and thorough facility maintenance pro-gram. Details about such a program and theresources that will be required to develop oneare presented below.

3. TYPES OF FACILITY OWNERS

It can be seen from the above that there aremany different types of stormwater manage-ment facilities controlling the quantity and/orquality of stormwater runoff. As such, it is notsurprising that there are many different typesof facility owners. Since each type of ownerwill have somewhat different operating pro-cedures, resources, organizational structures,and legal standing and authority, each typewill have to take somewhat different steps todevelop and conduct a stormwater manage-ment facility maintenance program. There-fore, it will be helpful to review the basic cat-egories and types of facility owners.

The three basic categories of facility own-ers include private, public, and joint pub-lic-private ownership. Private owners in-clude individuals, partnerships, corporations,and cooperative associations. Public ownersinclude municipalities, counties, states, au-thorities, utilities, and federal agencies. Jointownership may exist in certain instances, par-ticularly where one party owns the facility (in-

cluding the land it is located on) and the sec-ond party is responsible for its maintenance.Such arrangements are common betweenmunicipal or county governments, which areresponsible for the maintenance of a facility,and residential, commercial, or industrial siteowners who own the property on which thefacility is located.

In the case of private ownership, it can be seenthat the resources, organizational structure,and legal standing of a private individual willbe considerably different from a corporation.For example, the individual can be held per-sonally responsible for the maintenance of afacility and personally liable if damage occursto offsite property or third parties due to main-tenance neglect. A corporation may only beliable for the assets of the corporation, therebyprotecting the individual shareholders. An in-dividual owner can also be expected to bemore directly involved in the actual mainte-nance activities, be more readily engaged inevaluating program performance, to act morequickly to remedy problems, and more flex-ible in addressing changes in operating pro-cedures. However, the individual can also beexpected to have fewer resources to performfacility maintenance at their disposal and lessability to raise additional capital to finance fa-cility maintenance or repairs.

Similarly, a municipal government may bemore directly involved in facility maintenanceactivities than its state or federal counterpartsand have greater flexibility to address changesand problems. However, the municipality mayonce again have less overall resources at itsdisposal. All levels of public ownership canbe expected to have less options for financ-ing than private owners and will not be able toaddress changes in maintenance costs aseasily or quickly. Public bidding and purchas-ing laws and annual budget cycles may fur-ther limit a public owner’s financing and oper-ating options.


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The overall operating experience and capa-bilities of the owner will also directly effect theirability to adequately perform facility mainte-nance. For example, a municipal or countygovernment whose public works departmentregularly maintains open spaces, recreationalfacilities, and structures will be better preparedto develop and conduct a facility maintenanceprogram than a homeowners association or acommercial building owner. Perhaps theowner best suited to perform facility mainte-nance is the stormwater utility or authoritywhich has been established for stormwatermanagement purposes and vested with itsown financing capabilities.

Finally, studies and experience have shownthat while all types of owners may neglectfacility maintenance, the likelihood of suchneglect increases with the size and com-plexity of the ownership organization. Thisis due, in part, to the more vague, diffuse, andeven fractured designation of maintenance re-sponsibility within the larger organization, theability of the organization to monitor the per-formance of its members, and its ability toquickly respond to problems and adopt newprocedures where necessary.

In summary, a successful maintenanceprogram will require the facility’s owner tohave some level of organizational and man-agement skills, legal counsel, financial re-sources, emergency response capabilities,maintenance equipment and personnel,and a basic understanding of facility op-eration and associated government regu-lations. In developing and then conducting asuccessful facility maintenance program, it isimportant for the owner to objectively identifyand evaluate their strengths and weaknessesin these areas. This will enable the owner torealistically determine what program compo-nents they can best perform and which oneswill be better performed by contractors or con-sultants. It will also help potential owners toevaluate the implications of facility ownership

prior to assuming ownership responsibilities,so that appropriate prior arrangements can bemade or ownership can either be shared withanother party or avoided entirely.

4. MAINTENANCE PROGRAMDEVELOPMENT

While the details of a maintenance programfor a specific stormwater management facilitywill be somewhat unique, there are generalsteps that most if not all facility owners canfollow. Details of each are presented below.In many instances, additional information re-garding specific aspects of each step can befound in other sections of this manual. Whenthis is so, the specific section will be noted.

4.1. Designate a Responsible Individual

As noted above, the potential for facility main-tenance neglect typically increases with thesize and complexity of the organization that isresponsible for the maintenance. Therefore,a key step in developing a successful fa-cility maintenance program is to designatea key individual within that organization tobe personally responsible for theprogram’s overall performance. It is notnecessary for this person to actually partici-pate in the various maintenance tasks, al-though a working knowledge of these tasksbased upon personal experience is certainlypreferable. The responsible individual must,however, have some direct role in managingand supervising the maintenance activities.The selection of this individual should bebased upon several factors. Since the indi-vidual owner is the simplest ownership orga-nization possible, the choice of who that indi-vidual should be is obvious. However, as thesize of the ownership organization increases,the choice may not be so obvious and eachof the selection factors warrants careful con-sideration and evaluation by the owner.


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The choice of responsible individual shouldbe a function of the person’s experience, ex-pertise, and position of responsibility within theorganization. Typically, this position shouldbe low enough to allow the person to have asignificant degree of direct, personal involve-ment with the overall maintenance program,particularly its personnel and the various tasksthey perform and equipment they use. How-ever, the position must be high enough withinthe organization that the responsible individualhas the authority to effectively manage theprogram and can command the attention ofpeople higher up when necessary, particularlyin regard to program funding.

Since the responsible individual will, indeed,be held personally responsible within the own-ership organization for facility maintenance,they must be granted sufficient authority overpersonnel, procedures, and expenditures toachieve the success they’re held accountablefor. Optimally, this includes the authority toidentify tasks, establish relevant policies andprocedures, hire, fire, and assign personnel,delegate authority, and establish priorities.

The responsible individual should also havea basic understanding of stormwater manage-ment facility function, operation, and construc-tion as well as an understanding and appre-ciation for the physical, social, regulatory, andlegal implications of facility ownership andmaintenance. This understanding should alsoextend to knowing when outside technical,physical, or legal assistance is needed to fill agap in organization’s in-house expertise orability.

Finally, since the responsible individual willoften be acting as a liaison between such di-verse groups as maintenance personnel, up-per management, residents, customers, gov-ernment regulators, and contractors, goodcommunication skills will also prove highlyvaluable.

4.2. Plan for Maintenance

A successful facility maintenance programdoes not happen by chance. Instead, a re-sponsible facility owner will plan and bud-get for maintenance, not merely performit. Such planning should obviously be per-formed as far in advance as possible of actu-ally beginning the maintenance work, a rec-ommendation that should not be lost on thosepotential or pending facility owners who arelooking to develop or purchase a site with astormwater management facility. Such plan-ning should include several program aspects:

1. Identify Facility Characteristics andMaintenance Needs - As detailedabove, each type of stormwater man-agement facility has some physical,functional, and operating characteris-tics that are unique and, as such, eachwill have certain distinct maintenanceneeds. For example, a wet detentionbasin or pond intended to provide bothrunoff quantity and quality control willhave largely different maintenanceneeds than a subsurface sand filter in-tended to provide only runoff qualitycontrol. The basic understanding ofstormwater management facilities ad-vocated earlier in this chapter will servean owner well at this stage of the main-tenance planning process.

This identification process can be-gin with a list of all types of onsitefacilities that the owner will be re-sponsible for maintaining. Basedupon each type, the basic operatingcharacteristics and maintenance needscan then be determined. If possible,particularly for new facilities, the ownershould consult with both the facility’sdesigner and constructor to help iden-tify these characteristics and needs.For new facilities, the owner shouldmake sure that the designer will include


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maintenance as one of their primarydesign considerations. Further infor-mation regarding the design aspects offacility maintenance can be found inChapters 2 and 3 of this Handbook.

2. Identify Regulatory and Legal Re-quirements - In many instances, thestormwater management facility willhave been designed and constructedto meet regulatory constraints placedupon the development and/or use ofthe property. These regulations mayhave been in the form of an approvingresolution from a local or county plan-ning board or an actual facility operat-ing permit issued by a regional, state,or federal agency. In many jurisdic-tions, the owner will have been requiredto sign a maintenance agreement withthe approving authority guaranteeingadequate facility maintenance andgranting that authority certain inspec-tion rights. In order to be both thor-ough and efficient, the maintenanceplanning process should identify allrelevant requirements in such ap-provals, agreements, and permits,which should then be evaluated fortheir impacts on facility mainte-nance. Further information regardingthe regulatory and administrative as-pects of facility maintenance can befound in Chapter 4. While written pri-marily for regulators and administra-tors, this chapter can provide ownerswith valuable insight into this importantaspect of facility maintenance.

In addition to regulatory require-ments, the owner should also reviewthe legal implications of facility own-ership, particularly in regard to fa-cility maintenance and the legal im-pacts of its neglect. This should in-clude both the legal impacts of violat-ing agreements, permits, and other

regulatory controls as well any physi-cal harm caused to onsite workers, resi-dents, customers, tenants, and/ordownstream individuals and entities. Inmany instances, such a review not onlyhelps to define the tasks and resourcesnecessary for the maintenanceprogram but also serves as a strongincentive for conducting it successfully.

3. Define Maintenance Tasks, Person-nel, and Equipment - Once the physi-cal, operational, and legal needs aredetermined, the actual maintenancetasks and their associated personneland equipment needs can be defined.Such tasks may range from simplegrass mowing and periodic debris re-moval, to sediment testing and re-moval, to aquatic plant habitat and wild-life management. Details of the vari-ous maintenance tasks required at dif-ferent types of stormwater facilities canbe found in Chapter 7.

In addition to direct maintenancetasks, the need for periodic inspec-tions of the facility should be in-cluded in the planning process.Since the exact success or frequencyof an individual maintenance task can-not be determined prior to its execu-tion, it will be necessary to inspect thefacility periodically to assess whetherthe selected procedures and their fre-quency are adequate. Even when theyare, facility operating conditions can stillvary considerably over a time periodand the maintenance program will beconstantly subjected to dynamic forces.As a result, the inspection programmust continue throughout the facility’slife if the program is to remain both ef-fective and efficient. Details of a com-prehensive maintenance inspectionprogram are also presented in Chap-ter 7.


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4. Establish Schedules - Since success-ful facility maintenance is an ongoingprocess, schedules must also be es-tablished. These include such obviousitems as the frequency of the variousmaintenance tasks identified in Step 3above. Since conditions at the facilitymay vary greatly over the year, theneed to periodically change the typeand frequency of maintenance tasksshould not be overlooked. Facility in-spection schedules must also be es-tablished. In addition, all regulatoryreporting schedules required as part ofan operating permit or other approvalcondition must also be determined.Some facilities may also require a for-mal inspection by a licensed engineeror other professional on an annual orbiannual basis.

Finally, funding availability will normallybe affected by budgetary cycles or ac-counting periods. As such, it will benecessary to determine how fre-quently different expenditures willbe required so that they can bescheduled and coordinated withtheir associated funding process ormechanism. Such expenditures mayrange from daily or weekly expensesfor fuel and material to monthly invoicesfrom outside contractors to annualequipment upgrades. Provisionsshould also be made for funding emer-gency repairs and for such typically in-frequent and/or irregular tasks as ponddesilting. In addition, the frequency ofany regulatory costs such as inspec-tion fees or permit renewal fees shouldalso determined.

5. Establish Record Keeping Proce-dures - Due to the nature of stormwa-ter management facilities in generaland the specific tasks necessary fortheir maintenance, a record of past

maintenance efforts and the resultsof past inspections can greatly as-sist the continued effectiveness ofthe maintenance program. For ex-ample, such records can be used toidentify chronic maintenance problemsthat can be addressed more effectivelythrough a new piece of equipment orchange in procedure. They will alsobe extremely useful at budget prepa-ration time when past costs need to bejustified and new ones need to esti-mated and funded. Finally, compre-hensive maintenance and inspectionrecords may prove invaluable if theowner and/or the maintenance programis challenged legally by a plaintiff orregulatory agency.

4.3. Identify Costs and AllocateResources

Prior to this step, which may be consideredthe most important step of any facility mainte-nance program, the necessary maintenancetasks and their associated equipment, person-nel, and frequency should have been deter-mined along with the facility’s regulatory andlegal obligations. Based upon this informa-tion, the costs of these various items and theoverall cost of the maintenance programshould be estimated. Once determined, thesource(s) of the necessary funding must beidentified and secured.

The importance of identifying costs andfunding sources in a facility maintenanceprogram cannot be overestimated. In mostinstances, experience has shown that themaintenance of a stormwater managementfacility does not, in general, require extraordi-nary levels of effort or expertise on the part ofthe maintenance personnel, nor specializedor exceptionally sophisticated equipment toassist them. As such, these are usually notthe predominant factors associated with the


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failure or ineffectiveness of a facility mainte-nance program. Instead, such results aremore likely to be simply a lack of adequateprogram funding, which can occur due to alack of prior planning by the owner. In sum-mary, adequate and stable funding is, inmost instances, the most important key tomaintenance program success.

4.4. Create a Written Plan

Once the maintenance program and itsfunding have been developed, it is impor-tant that it be formalized in a written docu-ment. The exact format or level of sophisti-cation of the document are not as importantas the actual existence of the document inwritten form. In written form, it will be mucheasier to 1) understand and appreciate theoverall scope of the program and all its fac-ets, which can be particularly helpful for fund-ing, budgeting, and regulatory purposes; 2)establish a coordinated and effective imple-mentation plan of all those facets; 3) estab-lish performance goals that people, especiallythe designated responsible individual, will beheld accountable for; 4) conduct periodic pro-gram reviews (see Section 4.5 below); 5) de-scribe and justify the scope and intent of theprogram in case of legal challenge.

The written plan should include:

1. The name of the current responsibleindividual.

2. The names and/or positions of the vari-ous maintenance staff members and,if helpful, an organization chart.

3. A list of all facilities maintained by theprogram along with their location, type,and other pertinent details.

4. A list and description of each of the iden-tified maintenance and inspection tasks.

5. Lists of all required and available equip-ment and material.

6. All regular inspection and maintenanceschedules.

7. Copies of the pertinent sections of allregulations, permits, approvals, andagreements.

8. Copies of maintenance and inspectionlogs.

9. An "as constructed" plan of the facility.

The written plan should also include or refer-ence other pertinent facility information suchas design computations, construction and as-built plans, emergency action plans (whererequired or developed). A list of off-hour tele-phone or pager numbers of key maintenancepersonnel should also be included in case ofemergencies. See Chapter 7 - Inspectionand Maintenance after ConstructionCompletion for more information.

There should be at least two identical copiesof the maintenance plan. The owner of thefacility must have one of the plans while theagency responsible for stormwater programimplementation or maintenance inspectionsshould have the other. If a third entity assumesmaintenance responsibility on behalf of theowner, that entity must also have a copy.

The maintenance plans should be locatedwhere they can be referred to as the needarises. The public agency should have a per-manent file system where all maintenanceplans reside and are available for public re-view. The owner's plan should be placed withother important property information, and re-viewed at least on an annual basis to ensurethat the plan is in good condition and accu-rately reflects ongoing efforts.


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4.5. Conduct Periodic Program Reviews

As noted above, both a stormwater manage-ment facility, and the program established tomaintain it, will be subjected to constantlychanging forces and factors. With the facility,these will include variable climatic and rainfallconditions, development and maturation ofvegetation, wear and impacts on structuresand linings, and even vandalism. With theprogram, these will include changes in per-sonnel, cost increases due to inflation, newor revised regulatory programs and permitconditions, new equipment, material, or main-tenance techniques, or internal managementor ownership changes. As such, a success-ful facility maintenance program must in-clude a regular process of review andevaluation.

Such reviews can begin with the effectivenessand efficiency of the various maintenancetasks, including an evaluation of personnel ex-pertise and experience and equipment per-formance. The program’s ability to meet main-tenance and reporting schedules should alsobe reviewed. Costs should also be trackedand evaluated to determine if rising trends canbe reversed or cost savings can be realized.In this instance, such a review may best beheld prior to the start of the organization’sbudgetary cycle.

A comprehensive program review will revisitpast problems to determine what their causewas and how they might be prevented or cor-rected more effectively and/or efficiently. Thismay include an assessment of how thefacility’s design and/or construction may becausing the problem and how changes tothese procedures may eliminate similar prob-lems at future facilities.

In conducting the program review, it may alsobe productive to evaluate whether an internalmaintenance program may be more effectivelyor efficiently performed by outside contractors.

Conversely, services presently provided bysuch contractors should be compared withthose that could be provided by in-house per-sonnel and/or equipment. Finally, the legalenvironment and regulatory conditions un-der which the program must function shouldbe periodically reviewed to identify neces-sary or helpful changes to reduce legal ex-posure or to comply with new regulations,laws, or permit conditions.

Chapter 6Construction Inspection

1. OVERVIEW

Plan design and review, construction inspec-tion, maintenance inspections, and owner/op-erator understanding of obligations are essen-tial components of successful implementationand long term performance of stormwater fa-cilities. A breakdown in any of these areas willcause premature failure of the BMP. The bestdesign plan has no value if the facility is notconstructed according to the design. Construc-tion inspection determines, to a very largeextent, the frequency that subsequentmaintenance is needed on a given facility.The use of poor quality materials for construc-tion, and poor construction in general, can ne-gate all of the time and effort expended duringthe design phase.

Stormwater facilities are constructed by indi-viduals having a wide range of experience intheir construction. Individuals with little experi-ence constructing BMPs need assistance inknowing what to look for and what componentsare essential for quality control of construction.Even individuals having significant experiencein BMP construction often need assistance dueto changes in site conditions upon which thedesign was based, or where a modification tothe design would improve facility constructionand maintenance. The most important indi-vidual in these situations is the construction in-spector.

The construction inspector interacts with the sitecontractor and the plan approval agency. Theinspector is vital in assuring proper construc-tion and links the overall process from designthrough construction. The contractor is indepen-dently retained by the site developer and gen-erally has no input into the actual design of the

stormwater facility. He is hired for constructionand must review the approved plans and speci-fications and determine the best constructionmethod to fit the site and approved plans. It isnot his role to question design assumptions orrecognize that an approved plan will not neces-sarily result in the best approach to site man-agement from a stormwater managementstandpoint. The construction inspector,through his interaction with the plan ap-proval agency and experience instormwater management, assumes thatrole.

Problems associated with poor stormwaterBMP construction range from minor to major.Minor problems can include partial clogging ofinfiltration practices, premature maintenanceneeds related to sediment removal, replace-ment of a system component such as riprap,mosquito breeding, slope erosion, or standingwater in a facility not designed to have it. Majorproblems could necessitate replacement of theentire facility, structural repairs, or safety con-cerns. It is easier and more cost effective tobuild a stormwater facility right the first timethan to have to remobilize constructionequipment to repair the facility on a prema-ture basis. In addition, the quality of reconstruc-tion often means that the level of expectationsmust be reduced from the initial design as-sumptions. For example, an infiltration basin,prematurely clogged with fine sediments, willprobably never achieve design infiltration ratesdue to the presence of an increased level offine particles in the bottom and sides, even withexcavation of the finer sediments. Proper con-struction of stormwater facilities will have a sig-nificant beneficial impact on future maintenancecosts.

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Construction inspection can be broken downinto several components which together providefor effective implementation of stormwater fa-cilities. The inspection components include:

a clearly defined legal authority,preconstruction activities,inspection during construction,construction site inspectionprocedures, andshort term post-construction inspectionresponsibility to determine stormwaterfacility bond release approval.

Quality of construction affects more than the longterm stormwater management system perfor-mance. Facility construction can also have adirect impact on receiving systems, especiallywhen problems are encountered during theirconstruction. Proper inspection is needed toreduce downstream impacts of the constructionprocess itself. The last section of this chapteris devoted to discussing ways to reduce pollut-ant discharge, primarily of sediments, impactson receiving systems.

It should be recognized that the discussion pro-vided in this chapter and elsewhere is devotedto general activities which are associated withurban runoff control. Where a specialized ac-tivity exists, such as control of industrial runoff ,then individual consideration of the types andquantities of pollutants expected and their po-tential adverse impacts on the stormwater BMPmust be done.


In attempting to achieve a "minimum mainte-nance" stormwater system, construction in-spection is often one aspect of a project thatdoes not receive the attention it deserves fromowners, project managers, and government of-ficials. With that thought and the objectives dis-cussed above in mind, those who will benefitmost from this Chapter include:

••••• Project and Construction Managers,who should view construction inspection asa vital quality control measure that is in thebest interests of all those concerned withthe creation of a stormwater managementsystem.

••••• Construction Inspectors, who shouldclearly understand their project responsi-bilities and the specific tasks that are criti-cal to achieving the intended design.

••••• Contractors, who should realize that properconstruction inspection will help avoid con-struction problems and delays and assureboth quality workmanship and rapidcompletion.

••••• Code officials, who should fully understandthe important role they must play in achiev-ing a high quality, minimum maintenancestormwater facility.

Additionally, several other readers can benefitfrom this Chapter including:

••••• Planners, Designers, and Project Re-viewers, who should be aware of the valueof proper construction inspection while pre-paring or reviewing construction plans,specifications, and other contract docu-ments.

••••• Project Managers, whose responsibilitiesinclude providing assurance that the projectwill be constructed to the best possible stan-dards.

••••• Stormwater System Owners, who shouldrealize that it is in their long term interest tocreate the highest quality facility and therebyavoid unnecessarily high OMM costs in thefuture.

CHAPTER 6 Construction Inspection

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2. STORMWATER SYSTEM CONSTRUC-TION IMPACTS AND MITIGATION

The impacts associated with construction ofstormwater management systems are verysimilar to those occurring from general site con-struction activities. A major difference is thaterosion and subsequent sedimentation fromgeneral construction may not result in all sedi-ment leaving a site. Sediment may travel for adistance down a slope and then deposit itselfin an area that promotes sedimentation of thesuspended particles. Construction of stormwa-ter management systems, especially ponds,generally occur in low areas of a constructionsite. Wet ponds often are located in a ravineor incised area adjacent to a perennial streamwhere the delivery of sediments is unbufferedby downstream areas of deposition. In addi-tion, stormwater management system construc-tion occurs where concentrated flow of runofffrom upstream drainage areas accelerates theuplift and transport process of soils and sedi-ments generated by the dam construction.

The proximity of the stormwater system con-struction to major stream systems and definedfloodplains typically results in delivery of thesediments into environmentally sensitive areas.Also, high stream flow may inundate the facil-ity construction area causing scour and exces-sive sedimentation. It is important for an in-spector to realize the sensitive nature of con-struction impacts of stormwater facilities. Theyare placed on sites to reduce environmentalimpacts, but their construction may have a sig-nificant impact if good site control is not pro-vided. During an inspection, the inspectormust carefully consider the potential im-pact of stormwater system construction ondownstream sensitive areas.

The impacts of sedimentation off-site and down-stream can be classified into two categories ofimpacts: Economic and Environmental.

2.1. Economic Impacts of SedimentationDuring Stormwater ManagementPond Construction

The displacement and transport of sedimentsinto stream systems will create negative im-pacts from several perspectives. The most tra-ditional and clearly understood economic im-pacts are those resulting from sedimentationto navigable waters, especially in estuaries,and to increases in the risk of flooding. Be-cause of sedimentation, dredging of channelsand boat docking areas is needed more fre-quently, thereby increasing the cost of mainte-nance dredging and sediment disposal.

Flooding and out-of-channel storm flow mayincrease due to sediment deposition withinchannels and floodplain areas. Maintenanceis a significant responsibility where flood con-trol channels have been constructed previously.In these situations, flood protection is providedthrough channel storage and conveyance.Sedimentation of the channel reduces its’cross-sectional area, and its ability to providethe desired level of flood protection. Anotherflood related impact occurs when nontidal wet-lands are smothered. The wetlands vegetation,due to its dense growth, serves as a buffer dur-ing runoff events, providing flood storage andretarding flood flows. This reduces velocitiesof stormflow and helps provide additional floodprotection to downstream areas.

Economic impacts are incurred in associationwith impaired function of culverts and pipesdownstream from construction activities. Theseconveyance systems rely on the cross-sectionalarea of the pipe or culvert to convey the designstorm flow. Sedimentation of culverts or pipesreduces their storm flow conveyance capacity.This may lead to increased road flooding, in-creased flooding on properties upstream of theroad crossing, or increased risk of floodingdownstream if the road embankment fails dueto water pressure or scour.


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ery of the stream system to occur.

TABLE 6-1. POLLUTANTS GENERATEDBY CONSTRUCTIONMOTOR VEHICLES

Pollutant Automotive Source

Asbestos clutch plates, brake liningsCopper thrust bearings, bushing,

and brake liningChromium metal plating, rocker arms,

crankshafts, rings, brakelinings

Lead leaded gasoline, motor oil,transmission babbitt metalbearings

Nickel brake liningsPhosphorus motor oil additiveZinc motor oil and tiresGrease and spills and leaks of oil and hydrocarbons lubricants, antifreeze and

hydraulic fluidsRubber tire wear

Beside the environmental impacts to streamecosystems, other environmental impacts areassociated with wetland loss and degradation.Wetlands provide significant water storage andpollution removal. Filling wetlands, as a resultof construction sedimentation, reduces theirability to store floodwaters and remove pollut-ants. Wetlands also provide habitat for wild-life. As wetlands are filled by sediments, itshabitat is destroyed and its wildlife value is re-duced.

It is also important to note that there are othersecondary, but lesser understood, impacts as-sociated with toxics carried by stormwater.These potentially can disrupt the food chain.Uptake of toxic substances by micro- andmacro-organisms can lead to bioaccumulationand biomagnification as the toxic substancesare ingested by higher organisms in the food

Another economic impact of sedimentation isrelated to the loss of biological resource pro-ductivity. Shellfish beds and fish eggs aresmothered by sediment. Also, fish can't seefood which also affects the resource. A signifi-cant commercial or sporting industry can beand has been reduced by sedimentation.

2.2. Environmental Impacts of PollutantDischarge During Construction

In addition to strict economic impacts, storm-water system construction can cause environ-mental impacts. From a water quality perspec-tive, there are a many pollutants that may begenerated at a stormwater system constructionsite. The first and most obvious pollutant is sedi-ment. Many other types of pollutants adhere tosediment and get transported downstream.Toxic metals are inert by nature, and many bindstrongly to sediments. Control of sediment will,to some degree, control the migration of otherpollutants.

Other types of construction generated pollut-ants are present on stormwater managementfacility construction sites. These pollutants areassociated with motor vehicle equipment op-eration and commonly include the constituentslisted in Table 6-1. They accumulate on construc-tion sites and can migrate downstream caus-ing impacts to aquatic resources. These otherpollutants include organics and inorganics, nu-trients, construction debris, pesticides and her-bicides, and bacteria.

The health of a stream ecosystem dependslargely on its benthic community. Sedimentsmothers aquatic organisms, upon which largerspecies feed. Thus, the loss of the benthicorganisms reduces the stream's capability tosustain larger organisms. Experience hasshown that the single largest, long term impacton a stream ecosystem results from excessivedownstream sedimentation during site devel-opment. It may take years for a partial recov-


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chain. Little is known about the actual pro-cesses and levels of impact associated withstormwater toxics, although shellfish beds havebeen closed to harvesting. Additional work isneeded in this area to more accurately deter-mine their impacts.

3. LEGAL AUTHORITY FOR INSPECTIONS

Stormwater management construction inspec-tors must have adequate legal authority, fromstate or local laws or regulations, to inspect andenforce the program's construction require-ments. Outlined below is an example of legalauthority for construction inspections adaptedfrom the Prince George's (MD) Department ofEnvironmental Resources Stormwater Manage-ment Design Manual:

1. Inspectors must conduct inspections andfile reports for periodic inspections, asnecessary, during construction of storm-water facilities to assure compliancewith the approved plans.

2. Inspectors are authorized to furnish thepermittee or agent the results of the in-spection in a timely manner after thecompletion of each required inspection.

3. Inspectors are authorized to issue a Cor-rection Order to the permittee or agentwhen any portion of the work does notcomply with the approved plans.

4. Inspectors are authorized to issue a No-tice of Violation in accordance withguidelines as a result of unsatisfactorywork or progress.

5. They are authorized to issue Stop WorkOrders as the result of unsafe conditions,working without a permit, unsatisfactorywork, progress, or other noncompliance.

6. Inspectors are authorized to issue a Civil

Citation as a result of unsafe conditions,noncompliance with a Stop Work Order,unsatisfactory work, progress or othernoncompliance.

7. Inspectors are authorized to perform afinal inspection upon the completion ofthe stormwater facility to determine if thecompleted work is constructed in accor-dance with the approved stormwaterdesign plan, approved "as-built" planand certified by the permittee's regis-tered professional engineer.

8. Inspectors are authorized to inspect thestormwater facility at a specified post-construction time to determine releaseof the maintenance performance bond.

The authority to accomplish these functionsshould be provided in law, ordinance, or reso-lution. This provides the inspection programwith the necessary "teeth" to ensure that storm-water systems are constructed in accordancewith the approved plan. A variety of enforce-ment options should be available, as one op-tion may be more effective than another in aparticular situation. It is also important that theenforcement aspect of program implementationbe progressive. The intent should be that minorenforcement actions are generally attemptedfirst, with more serious action being reservedfor those situations where there is a knowingand willful violation. There must be an abilityand willingness to take aggressive action whenit is required.

Having the legal authority to take enforcementactions does not necessarily mean that they willbe taken. Too many programs have excellentlegal authority for enforcement actions, but staffare seldom allowed to take actions necessaryto improve site implementation of stormwatercontrols. This is especially a problem when in-spections necessitate additional expendituresto correct problem areas, or where necessarysite controls have not been constructed. This


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especially is a problem for erosion and sedi-ment control practices, but is also a serious con-cern for the construction of permanentstormwater facilities.

The stormwater program must make a com-mitment to allow its staff to conduct siteinspections and take necessary enforce-ment action when it is needed. This is not tosuggest that enforcement action can be takenwhenever desired - only that it is available asan option to assure compliance. Senior agencystaff must be briefed when a particularly aggres-sive action is intended, but day-to-day enforce-ment actions must be endorsed by the appro-priate jurisdiction to ensure continuity ofprogram implementation and to ensure thatstormwater facilities are given the best oppor-tunity to perform to design standards for thelongest possible time.

4. PRECONSTRUCTION ACTIVITIES

An approved stormwater management permitmay be transferred to the responsible inspec-tion agency for construction inspection. The in-spector has two primary functions at this stageof project implementation - review of the ap-proved plan, and a preconstruction site meet-ing.

4.1. Review of Approved StormwaterManagement System Plan

The construction inspector should review the ap-proved stormwater management plan to be-come familiar with the requirements placedupon the land developer. This review should in-clude the following items:

A. The overall site development proposaland site conditions,

B. Location of the stormwater managementfacility, erosion and sediment control

plan, and site grading plan,

C. Location of storm drain system,

D. Dimensions, as specified, are shown onapproved plans,

E. Potential problem areas with construc-tion that may require special attention,

F. Any special approval conditions,

G. Specifications for construction materials,

H. Shop drawings, where needed,

I. Sequence of construction (may be a re-quirement of plan approval or submit-ted by contractor prior to work initia-tion), and

J. Any easements or site areas having re-strictions placed upon them such as well-head protection areas or natural wet-lands.

It is important that the inspector completelyunderstand all aspects of the approvedstormwater control plan, especially its struc-tural practices and their components. Ifthere are any questions, the inspectorshould contact the plan review and approvalagency and receive answers to any con-cerns or questions. If the construction inspec-tor is unsure of any aspect of the construction,it can almost be a certainty that the contractorwill also have misunderstandings. Communi-cation between the plan review agency and con-struction inspector is essential so that each canunderstand the perspective of the other.

One helpful approach is to have the plan re-view individual highlight on the plans erosionand sediment control and stormwater manage-ment BMPs or make special notes to empha-size these items to the inspector. If this cannotbe done, the inspector should highlight them.


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This helps to assure they have a high visibilityduring future inspections. It also highlights themfrom other special notes that tend to be on con-struction drawings.

Shop drawings should be submitted for allstormwater management system components.Shop drawings should include methods of con-struction, as well as detailed specifications ofthe materials. Problems can be avoided if po-tential areas of ambiguity are resolved beforefacility construction. A situation which shouldbe avoided is an on-site confrontation betweenthe inspector and contractor over some mate-rial specification that was not considered be-fore construction. Having shop drawings avail-able for the preconstruction meeting helps re-duce potential areas of disagreement. Often acontractor's bid to do work is based on the costof materials that the contractor commonly uses.Changes to these commonly used materialsmay increase project costs and cause problemsbetween the land developer and the contractor.By resolving potential conflict areas beforeconstruction, the quality of construction canbe enhanced and potential conflicts re-duced.

4.2. Preconstruction Site Meeting

It is important to meet with the owner, contrac-tor, project engineer, and any other site relatedinspectors to establish a dialogue and line ofcommunication. Other individuals having rolesin the stormwater facility construction alsoshould be included, especially subcontractorsand utility companies. Preconstruction meet-ings also let the owner and contractor knowwhat aspects of the stormwater system con-struction are in need of the most attention. Thismeeting also establishes the inspectionagency's importance and priority on properconstruction. Items which should be discussedat the preconstruction meeting include:

A. Telephone numbers (during and after

work) of the different individuals in theevent of the need to communicate.

B. Recognition that the approved plansmust be on site whenever there is con-struction.

C. The project's overall purpose and ob-jective.

D. Specific areas where stormwater facil-ity details need to be emphasized orwhich require special attention.

E. Construction sequences, schedules,and timetables.

F. A chain of command in the event thatfield modification or changes needs tobe made.

A detailed list of recommended preconstruc-tion meeting topics is summarized in Appen-dix 6-1 at the end of this chapter.

5. INSPECTION RESPONSIBILITIESDURING CONSTRUCTION

There are a number of specific responsibilitiesthe inspector must assume during construction.These can be broken down into two areas:routine inspection responsibilities and activity-specific inspections.

5.1. Routine Inspection Responsibilities

Routine inspections are important to gauge theprogress of site development and to assessthe quality of construction. These inspectionshelp ensure that the developer/contractoris aware of the inspector's periodic pres-ence onsite. Routine inspections also dem-onstrate the importance the implementingjurisdiction places on the adequacy ofstormwater system construction.


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As stated in Chapter 4, it is important that theland developer/contractor closely coordinateand communicate with the inspection agency.This is especially true when scheduling inspec-tions. Generally, at least 24 hours notice isneeded. Inspections and inspector approvalof work must be completed at the critical stagesof stormwater management system construc-tion. The actual notification of the inspectionagency by the land developer at critical timesmay not always occur, and routine inspectionsare one way to assess timetables. They alsoprovide an opportunity for the inspector to re-mind the contractor of the need for inspectionsat specific times during construction of thestormwater management system. Regardless,it is important for the contractor/developerto recognize the need to contact the inspec-tor when certain stages of construction arereached. This is already recognized in otheraspects of construction, such as electrical orplumbing inspections. The stormwater inspec-tion agency needs to stress to the contractorthe importance of scheduling inspections atimportant stages of construction. The agencymust also convince the land developer/contrac-tor that the inspections are in their best inter-est.

When routine inspections are accomplished,their results must be documented, preferablywith standardized inspection forms. Examplesof a Routine Inspection Form and a Notice toComply Inspection Form are provided in Ap-pendix 6-2. Inspection forms provide a con-sistent record of site inspections and estab-lish a framework for inspection and en-forcement activity. The results should then beprovided to the contractor, transmitted to the de-veloper, and also placed in the project's inspec-tion file. This documentation of the inspectionresults provides feedback to the contractor anddeveloper on the adequacy of erosion and sedi-ment control BMPs and overall facility imple-mentation at various stages of construction.Too often, inspectors visit a site, do not

notify any site personnel, and leave norecord of their inspection. This approachmay reduce confrontation, but provides lim-ited benefit to any individual other than theinspector.

The inspection form details site conditions tothe contractor/developer and provides a ba-rometer of any site inadequacies which mayneed to be addressed. In addition, if site con-struction is proceeding according to the ap-proved plan, it also notifies the contractor/de-veloper that they are doing a good job. Posi-tive feedback is as important as criticism.There are many times when the contractor/developer goes beyond the letter of the lawand is extremely conscientious in their ef-forts. These efforts should be recognizedin the inspection report.

A program may want to use several differentinspection forms. The first inspection reportshould be used to assess general site condi-tions while the second form would be used torequire site correction or compliance accord-ing to an administrative order. The routine in-spection form can be used when the site isgenerally in compliance or where minor cor-rections need to be made to achieve compli-ance. The Notice to Comply or Correction No-tice establishes necessary site improvementconditions and time frames. The Notice toComply establishes a formal paper trail of pro-gressive enforcement. The goal is to improvesite conditions and achieve compliance with ap-proved plans.

5.2. Progress Meetings

In addition to periodic routine inspections, regu-lar progress meetings should be held to dis-cuss construction timetables, problems, neededchanges to the approved plans, and ensurecoordination between the land developer, con-tractor, and inspector. This inspection is pri-marily a meeting between the various parties


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proval activities. The progress meetings alsoensure that the developer and contractor areconstantly aware of their obligations and aregiving them frequent consideration.

5.3. Final Inspection

A final inspection should be required prior tothe contractor being allowed to demobilizeequipment from a site. This inspection shouldbe linked with granting occupancy permits orother required final approvals. As recom-mended in Chapter 4, the stormwater man-agement system bond should not be releasedat this time. The bond should extend for aspecific time frame (warranty period typicallyone year) to ensure short term performance ofthe facility.

Any incomplete items associated with thestormwater management facility should bedetailed in this inspection and provided as aspecific "punch" list to the contractor and de-veloper. A time frame for correction of the listeditems should be decided upon so that a rein-spection can be scheduled at the appropriatetime.

This inspection is critical to the long term per-formance of the stormwater management sys-tem. Final approval of a site should not begiven until all deficient items have beencorrected. When the site receives final ap-proval, the public and eventual site users orowners have an expectation of constructionadequacy. It is important that every possiblestep has been taken to reduce their future ex-penditures for operation, maintenance, andmanagement of the stormwater facility.

6. INSPECTION PROCEDURES

Consistent, meaningful inspection procedures areessential to effective site implementation and suc-cess of the stormwater management program.

as opposed to a site inspection to assessprogress of the stormwater management sys-tem construction. The stormwater managementapproval engineer should attend these meet-ings to provide insight into the appearance,essential components, and any other aspectof the facility design which needs to be em-phasized.

Extra work and needed change orders arethe primary items discussed at theseprogress meetings. These changes willoccur on all construction activities, as de-tailed design review and approval cannotanticipate all possible site conditions thatmay be encountered during construction.The inspector and, where appropriate, the de-sign review engineer should carefully evaluateeach extra work charge and change order toensure its legitimacy. Recommendations ontheir acceptance must be timely. Unnecessarydelays in resolving problems can result in poorrelationships, poor construction quality, andunnecessary extra construction costs. Costsfor the design and implementation of stormwatermanagement systems is a great concern toeveryone. Realistic costs have to be defendedand expected, but unnecessary costs must beavoided. Many excessive costs can be avoidedif there is effective communication during con-struction of stormwater management systems.

The progress meeting provides a number ofbenefits other than assuring proper construc-tion. By having periodic interaction betweenall of the parties involved, all individuals gain agreater understanding of why these facilities arenecessary, how construction needs to be ac-complished, and a greater appreciation regard-ing the relationship between design and con-struction. This is very true of the plan approvalengineer. Too often, these individuals becomeoverwhelmed with the plan review function, anddo not get the necessary experience in actualconstruction of stormwater management sys-tems. Familiarity with construction could havea significant impact on their plan review and ap-


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6.1. Have Necessary InspectionEquipment

Equipment, which should be included in aninspector's inventory, includes the following:

• A Locke level or other surveying equip-ment

• Local erosion and sediment control orstormwater management handbooks.

• Rain and foul weather gear.

• Copies of necessary inspection reportsand forms.

• Business cards or other means of iden-tification.

• A camera to document field conditionsin the case enforcement action becomesnecessary.

Other equipment may be desirable, but is notconsidered essential, such as a vehicle tele-phone that allows an office supervisor to becontacted for guidance on what to do in a givensituation.

6.2. Check In At The Construction Trailer

Too often, inspectors visit a site and do notstop in at the trailer prior to conducting theirinspection. Many times, a contractor will wantto conduct a site inspection with the inspector.This joint inspection can provide an opportu-nity for the inspector to provide some educa-tional tips to the contractor which may pre-clude future problems. In addition, the contrac-tor doesn't want unauthorized people walkingaround the site. Recognition by the contractorthat the inspector is on site will allow he or sheto continue with their activities and not stop whatis being done to inquire why the inspector is onthe site.

6.3. Always Complete An Inspection Formand Give to the Contractor/Developer

Documentation of site conditions, both goodand bad, provides a feedback loop to the con-tractor and developer about their efforts at con-struction of erosion and sediment controls andstormwater management facilities. An inspec-tion report does not have to only discussproblem areas of the site. They should alsobe used for acknowledging good efforts,where the developer can recognize contrac-tor activities. Good inspection reports can pro-vide the contractor with positive feedback, andprove a valuable record for future inspections.If a new or different inspector visits the con-struction site and provides a different empha-sis or evaluation, the previous positive inspec-tion report can demonstrate the intent to com-ply with permit requirements.

Inspection forms also provide the basis for anynecessary enforcement action. By document-ing problems and corrective measures, the in-spector provides the "paper trail" for legal ac-tion, should it become necessary. The formscan provide site documentation to supervisoryindividuals and they also provide a measure ofthe inspectors' work load.

6.4. Generally Speaking - Always Walk theSite in a Consistent Manner

The stormwater program should establish aspecific protocol by which inspections are done.For example, always start at the site entranceand proceed in clockwise manner around thesite. This allows the contractor, another inspec-tor, or any other individual to easily follow thenotation used in an inspection report. This isespecially important on larger sites, where thereare numerous environmental controls. Beingable to follow previous inspection commentscan reduce the time needed to conduct inspec-tions, especially follow ups on a previousinspector's comments and concerns.


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validity of a specific issue or problem. Therewill be times when an inspector must insiston site modification or compliance, even ifit results in a confrontational situation. Theinspector cannot be the contractor's bestfriend. There will be situations where a hardline must be taken. Inspectors must haveconfidence in their actions.

Interest in the function

In too many situations, the erosion and sedi-ment control and stormwater managementinspector has been given the function for areason other than the individual's interest inerosion and sediment control and storm-water management. In these situations, ex-pectations for adequate construction andmaintenance must be lowered. The inspec-tor must recognize their importance to theprogram's overall goals and success.

Being a regulatory program inspector re-quires more than experience in construction.The position is difficult when adversarialroles are established or when hearings,court cases, or meetings are held where theinspector's actions are held under a micro-scope. The inspector must accept thesevarying responsibilities and want to do thejob.

Experience with construction

Inspectors must recognize the real worldimpact of their requirements on site. Thereshould be an awareness of the capabilitiesof various types of construction equipment,and of which equipment may be inappro-priate for a given function. There is a costassociated with equipment and the inspec-tor must recognize these costs when estab-lishing site needs and time frames.

It is important for the contractor to recog-nize that the inspector does have an under-standing of site work and time frames. In

6.5. Wear Safety Equipment, such asSafety Glasses, Hard Hat, and SteelToed Shoes

All individuals at a construction site must meetminimum safety standards. The contractor isoften reluctant to correct an inspector on nec-essary safety equipment, but is still liable forensuring that all site personnel wear the neces-sary equipment. Wearing safety equipment,proactively, can reduce the number of ad-versarial issues and demonstrate the in-spectors' respect for contractor obligationsand site standards.

7. INSPECTOR ATTITUDES AND TRAINING

Inspectors are often placed in a difficult con-frontational position with a developer, con-tractor, and possibly even with their ownsupervisory or plan review staff. The typeof individual best suited for this job wouldbenefit by having the following attitudes.Each of these attitudes and training is im-portant individually, but all are necessary ifthe individual is going to be successful intheir role as an inspector.

Confidence

Inspectors are frequently confronted withreasons why a facility cannot be constructedaccording to the plan or why erosion andsediment control strategies cannot beimplemented according to the approvedplan. The inspector must have the confi-dence to deal with these situations and besure of the necessary responses to eachsituation. At times, the correct response isto discuss the specific issue with a supervi-sor or the appropriate plan approval indi-vidual.

Regardless, inspectors must feel comfort-able with their experience and knowledgeof the construction industry to recognize the


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the same regard, knowledge of constructionwill allow the inspector to recognize when acontractor is giving an excuse for noncom-pliance rather than expressing a real prob-lem. Contractors quickly recognize howmuch latitude they can get from an in-spector. Their recognition of aninspector's awareness of proper con-struction practices will have a positiveimpact on site implementation of neededcontrols.

Training needs

The inspector is expected to deal individu-ally with a wide range of people in the con-struction industry. Often the inspector is theonly individual in a group on-site that repre-sents the program's viewpoints. That indi-vidual must be trained and given the back-ground to enable effective communicationand actions to be taken. In Maryland, it wasonce estimated that approximately 18months were necessary to adequately trainan inspector. The first several months werespent instructing the individual about theprogram's goals, and it's commonly usedindividual practices, strategies, and facili-ties.

Then the training would include travelingaround with experienced inspectors to learnhow to conduct site inspections, what to lookfor on the plans and sites, and how to inter-act with construction-related personnel. In-teraction with construction-related person-nel is extremely important, since these in-teractions determine whether relationshipsare positive or negative. Inspectors mustlearn how to control their personal emo-tions and act in a professional manneron construction sites or the overall pro-gram may be adversely affected.

Communication

An inspector must interact with site person-

nel on a daily basis. Having an inspectorwho is a poor communicator results in mis-information or a lack of understandingby the contractor or developer on specificsite concerns. Communication is an essen-tial inspector function. The more effectivethe ability to communicate, the more poten-tial exists for good site implementation oferosion and sediment control andstormwater management controls.

Commitment

Commitment means accepting limitedresources, having too large a work load,periodically disagreeing with developersand contractors, and accepting that whatthey are doing is important. An adagelocated in the Sussex County ConservationDistrict, Sediment and Stormwater ProgramInspection Office (Delaware) clearly statestheir feelings on inspection:

:"Arguing with an inspector is like wrestlingwith a pig in the mud, after a while you re-alize that the pig enjoys it"

Anti-seep collars, barrel,and riser assembly for a stormwater

management detention basin.


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8. INDIVIDUAL BMP INSPECTIONCONSIDERATIONS

The two site inspection forms in Appendix 6-2are used for general site construction. They arevery appropriate for erosion and sediment con-trol inspection and can be used for stormwatermanagement system construction inspection.However, they must be augmented by inspec-tion checklists specific to each type of storm-water BMP. These checklists highlight criticalconstruction details that need inspection toassure stormwater management system con-struction is in accordance with the approvedplans. They should accompany the project file.They can assist the inspector determine whenspecific sites should be inspected and whatcomponents of the stormwater system may re-quire more individual attention and consider-ation.

Several components of stormwater systemsmay not be visible if inspections are not donewhen these parts are being installed. Examplesinclude core trenches for ponds, anti-seep col-lars or diaphragms, compaction of embank-ments, filter fabric for infiltration facilities, etc. Itis vital that an inspector ensure that these es-sential parts are installed or constructed as theapproved plans detail. Otherwise, there is arisk that an important component is constructedpoorly or even omitted.

Routine inspections are needed to determinesite progress, however, stormwater practiceshave unique elements which require individualattention. Specific inspection needs associ-ated with each type of stormwater managementpractice will be discussed individually in thissection. Detailed facility inspection forms areincluded in the appendices of this chapter.

The following discussions of individual prac-tices are separated into two areas: Design Con-siderations and Construction Considerations.Important aspects in each category are dis-cussed from an inspector's perspective. Com-

munication with the plan approval agency is es-pecially important during design discussions.If the items discussed are not detailed on theapproved plans, the inspector should contactthe plan approval agency to determine the rea-son for an item's omission. Communicationis the cornerstone to proper stormwatersystem implementation.

8.1. Detention and Retention Systems

Detention and retention systems vary in manyways. Retention and dry detention practicesare normally dry, while extended dry and wetdetention systems have a normal pool of wa-ter. Wet detention practices can be further sub-divided into open water ponds and constructedwetlands. The inspection requirements forall of these practices will be summarizedseparately. Thereby, an individual needingspecific information about a certain BMPcan read only that discussion and get a com-prehensive picture rather than looking inseveral places for pertinent information.

Most of the information on wet systems is di-rected towards ponds where the normal poolof water is established by the construction ofan embankment. Excavated ponds typically donot have the same safety concerns related toembankment failure. If unsure, the local Natu-ral Resources Conservation Service can becontacted for technical assistance in determin-ing whether a wet system is an excavated pondor an embankment pond.

8.1.1. Dry Detention Versus Wet Detention

The design and construction of these two typesof detention practices is very similar. There is,however, one very big difference which is im-portant to recognize for inspection purposesduring construction. Detention ponds with anormal pool of water develop a zone of satu-ration through the embankment, which can


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increase failure potential in the future. Con-cerns regarding this zone of saturation (fre-quently detailed on plans as the area below thephreatic line) are alleviated by good quality con-trol during construction. The risk of a potentialhazard is reduced by requiring, during design,safety features in the embankment which reducethe movement of water through the embank-ment. These safety features include anti-seepcollars, diaphragms, core trenches, and claycores. These features are not visible once con-struction is completed. Their construction andquality of construction must be verified by theinspector during their installation. Failure toinspect these features at critical times may re-sult in embankment failure in the future.

Detention or retention practices which are nor-mally dry do not develop a zone of saturation(which results from standing water), and inter-nal water seepage is not a critical concern.However, it is still important to have anti-seepcollars or diaphragms even if embankment fail-ure is not as important an issue.

8.1.2. Important Inspection AspectsRelated to Design

When certain site conditions are encounteredor where the design has an unusual aspect, itis important to communicate with the plan ap-proval entity to ensure that a mistake wasn'toverlooked. Examples of items which should

be discussed include:

A. Encountering sandy soils when buildinga wet pond designed with a normal poolof water without a liner specified on theplans.

B. Stormwater inlets located adjacent to ornear the intended outfall create a "shortcircuit" flow path. While this may be ac-ceptable from a stormwater quantityperspective, the short circuiting will re-duce treatment and lessen water qualitybenefits.

C. Steep slopes into the pond with no slopebreaks (benches) can increase the haz-ard potential and erosion of side slopes.

An example of a pond inflow pointbeing close to the outfall.

Inflow

Outfall

Steep side slopes at a dry pond. Noteplayground equipment at left top of slope.


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D. Essential components normally associ-ated with ponds are not included on theplans. These parts can include anti-seepcollars, trash protection for low flowpipes, principal and emergency spill-ways.

E. Wet detention systems should have ameans to draw the water level downshould draining the pond become nec-essary. From an inspector's viewpoint,a detention pond design without a draw-down mechanism should be brought tothe attention of the plan approval agency.Where ground water provides the per-manent water pool, a drawdown mecha-nism won't be available. The inspectorshould know the expected or designground water elevations at a site, espe-cially the seasonal high level. This infor-mation should be contained on the ap-proved plans.

8.1.3. Important Inspection AspectsRelated to Construction

This section highlights important aspects in theconstruction of ponds. Appendix 6-3 is an ex-cellent example of a Sediment/StormwaterManagement Pond Construction Checklist de-veloped for the State of Delaware. This check-list, or a similarly adapted one, should be usedby inspectors during construction of stormwatermanagement ponds.

A. A major cause of detention and re-tention system failure is water trav-eling along the outside of the princi-pal spillway. This is called piping. Itgenerally occurs along a corrugatedmetal or concrete pipe. This piping ofwater, which is under pressure from thedepth of water in the pond, causes ero-sion of soil adjacent to the pipe. Ero-sion of this material causes the pondembankment to be weakened at that

point and failure of the embankment re-sults. This failure is much more likelyto occur in wet detention systemsthan in retention systems. Detentionponds have a permanent pool of waternext to the embankment. Water will soakinto the embankment and seek a lowerelevation. Failure potential can be pre-vented by proper installation of anti-seepcollars or diaphragms, in conjunctionwith proper compaction of soils adjacentto the principal spillway and collars ordiaphragms.

B. The general minimum standards forconstruction work also apply to theconstruction of stormwater systems.Does the construction comply with localmaterial and equipment requirementsfor earthwork, concrete, other masonry,reinforcing steel, pipe, water gates,metal, and woodwork?

Example of a pond failure due to pipingadjacent to the principal spillway.


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C. Are interior side slopes no steeper than3-to-1(horizontal to vertical) and exteriorside slopes no steeper than 2-to-1? Thereason most stormwater embankmentponds remain stable is that the mass ofearth in the embankment is heavyenough to prevent slippage of materialcaused by water pressure on the up-stream slope. Steep side slopes arenot only more dangerous to the gen-eral public, but they also reduce thetotal mass of earth material in the em-bankment. This can increase the po-tential for embankment failure.

D. Are elevations relatively accurate andaccording to the approved plans? Aninspector should carry a simpleLocke level to determine whether agiven location is at it's proper eleva-tion. The invert elevation of a principalspillway must be lower than the eleva-tion of the pond embankment or troublecan be expected. A Locke level pro-vides a quick, moderately accurate,means to verify field implementation.

E. Are inlet and outlet areas stabilized toprevent erosion? Relying only on veg-etative practices for stabilization is gen-erally inadequate since it takes time forthe vegetation to become well estab-lished. Some form of additional stabili-zation technique is generally necessaryto protect soil until growth of vegeta-tion. This can include erosion controlmatting, riprap, gabions, etc.

F. Are safety features provided? Thesemay include a shallow bench surround-ing the pond edge, barrier plantings todiscourage approach by children, and/or fencing where required.

G. A sequence of construction must be es-tablished and followed. It is just as im-portant that construction be done in

the correct order as having goodquality construction. The sequence ofconstruction includes preconstructionmeetings, temporary erosion and sedi-ment control, core trench, etc. An ex-ample of a typical pond sequence ofconstruction is presented in Appendix 6-4.

H. Upon completion of construction, a finalinspection should be performed. This in-spection provides written documenta-tion to the developer/contractor of thesatisfactory completion of the facility.Depending on local requirements, thisinspection augments the submission ofan "As-Built" Certification or RecordDrawings.

8.2 Constructed Wetlands

Many parts of the discussion in Section 8.1above also are applicable to constructed wet-lands. This BMP often is considered a subsetof wet detention systems. However, they merittheir own separate section because of the com-plexities of their design and construction. Un-like wet ponds, constructed wetlands are shal-low water systems that rely, to a very large ex-tent, on the establishment and propagation of

Pond under construction.Reverse slope bench above waterline and

shallow slope in shallow water areas.


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emergent wetlands plants to provide water qual-ity benefits.


A. Clay or geotextile liners

The shallowness of wetland stormwatertreatment systems means that even asmall alteration in water level can sig-nificantly impact the health of the aquaticplant community. It is important to en-sure that water levels remain some-what consistent. This may necessitatethe use of a clay or geotextile liner tomaintain water levels. When reviewingapproved plans, the inspector must de-termine how water levels in the con-structed wetland are to be maintained.They may be maintained by continualstream baseflow, by high ground waterlevels, or by installation of a liner. Theinspector must know prior to con-struction how water levels will bemaintained.

B. Organic soil conditions

Wetlands are living systems with a widevariety of organisms, each of which re-

quires sources of essential elements forgrowth and propagation. The most com-mon way to provide these elementsquickly is to place organic soils on theconstructed wetland floor. The approvedplans should specify any special provi-sions for placement of organic soils.

Organic soils are not always specified,but their inclusion is highly recom-mended to facilitate plant growth. Nothaving organic soils on the constructedwetland floor results in slower growth andspread of the wetland plants. It often alsoleads to the invasion by nondesirableaquatic plant pioneer species which canout compete more desirable plants.

C. Shallow depth and slight grades

Unlike deeper detention systems, shal-low constructed wetlands need to haveexact grades in the inundated pool area.For the most part, constructed wetlandsare dominated by emergent aquaticplants whose establishment and propa-gation typically depend on water depthsunder two feet. To have a diverse plantcommunity, varying depths are neededsince different plants are best suited forvarious water depths. The plans shoulddetail design elevations throughout theponded area where wetland plants willbe established. They should also clearlyidentify where each type of plant shouldgo.

D. Establishment of forebays

Being shallow water systems, con-structed wetlands are very susceptibleto filling in by sediments generated up-stream. It is important that all principalinflow points be provided with forebaysdesigned to trap the largest volume ofsuspended solids. Forebays providea readily accessible location to allow

Geotextile liner for a constructed wetland.


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periodic removal of accumulatedsediments. Plans should detail the lo-cation, size, and proposed grades of de-signed forebay areas, along with dedi-cated access for maintenance equip-ment.

E. Concern regarding sediment entry intothe system

Because they are shallow water sys-tems, the long term performance of con-structed wetlands can be significantly re-duced by sedimentation. The approvedplan should be reviewed to determine ifthe constructed wetland will be used asa sediment basin during the construc-tion phase of the project. If used as asediment basin, the plans should de-tail the conversion of the sedimentbasin into a constructed wetland. Ifthe constructed wetland is not used forsediment control, the plans shouldspecify:

• Project phasing for overall site con-struction with a timetable for con-struction of the constructed wetland.

• How the constructed wetland will beprotected from sediment entry whenthe drainage area is unstabilized.

• When sediment must be removed

from the forebays or constructedwetland.

• That the wetland will not be planteduntil site stabilization is complete.

F. Reduced concern over saturated em-bankment problems

Most constructed wetlands have a shal-low depth of water against the embank-ment. However, some wetland designsspecify a deep water zone adjacent tothe embankment. The shallow water re-duces water pressure adjacent to theembankment and reduces the numberof anti-seep collars needed to preventpiping along the principal spillway. Theinspector should still expect to see atleast one anti-seep collar on the princi-pal spillway, but safety concerns are re-duced compared to those that exist fordeeper wet detention systems.

G. Reduced safety features

Deeper wet detention systems presentother public safety hazards to those in-dividuals living or working adjacent tothem. Constructed wetlands presentmuch less of a safety concern dueto their denser vegetation, moregradual side slopes, and the shallowwater depth. Plans, therefore, may notprovide specific safety features.

H. Plant materials

Beside the water quality benefits result-ing from detention time of stormwaterwithin the wetland, water quality benefitsalso are provided by the wetland plantcommunity, microbes, and the organicmaterials on the wetland's bottom. Thereare three approaches to establishingaquatic plants in constructed wetlands:plantings of aquatic plants which facili-tates rapid plant growth; providing

Detail of a constructed wetlandshowing designed forebays.

DesignedForebays


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proper hydrology and soil conditions topromote colonization of the system bylocal vegetation; and installing soil hav-ing vegetative plant roots or rhizomes.Of course, these are not mutually exclu-sive, and proper conditions must be pro-vided to sustain plantings.

The approved plan should detail whichapproach is used. If wetland plantingsare to be used, the plan should specify:

• the plant species.• the number of each species.• where the plants will be located.• if the pond water level will be low-

ered to facilitate planting.• a timetable for planting to occur.


A. If the constructed wetland is to be usedas a sediment control basin during con-struction, there are a number of itemswhich must be considered. The outletstructure must be modified by installa-tion of a temporary dewatering device.Final grades are not important to es-tablish at this time, but the minimumvolume needed for sediment control

must be provided for construction gen-erated sediment.

Sediment removal will be needed tomaintain the system's ability to reducesuspended solids. When sedimentcleanout is required, the removed ma-terials should be placed upstream of anysediment trapping facilities to preventtheir movement downstream. The in-spector will generally determinewhen sediment cleanout is neededand should specify where the re-moved sediments are to be placed.

B. The importance of accurate gradeestablishment in shallow con-structed wetland systems cannot beoverstated. During construction, surveystakes must be placed to accuratelyestablish cuts and fills. The final gradesmust be accurate for successful plantestablishment and propagation. Finalgrades should be established prior towater filling the pond, where possible.Once the bottom and side soils have be-come saturated, the movement of earthmaterial becomes much more difficultand the basin may have to be dewateredand dried before final grades can be es-tablished.

Very shallow grades ona constructed wetland.

Temporary sediment trapping deviceattached to a riser assembly.


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a major concern, at this time, with their long termperformance. Detailed evaluations of imple-mented infiltration facilities in Maryland (Pensyland Clement, 1987; Lindsey, Roberts, andPage, 1991) reveal that infiltration systemsare very sensitive to failure due to cloggingof the facility's surface area. Many instancesof premature clogging of infiltration practiceswere attributable to poor site control during thesite construction process. Poor site control re-sults in excess sediment loadings entering theinfiltration system. Therefore, quality control dur-ing construction of infiltration practices is an es-sential responsibility of an inspector.

Infiltration practices can include, by some defi-nition, buffer areas, biofiltration swales, and ri-parian zones. However, in this chapter, infiltra-tion swales, filtration practices, and biofiltrationpractices will be discussed separately. Thenext two sections present general informationon design and construction of infiltration prac-tices. Section 8.3.3 will present specific infor-mation for each of the individual types of infil-tration BMPs.


Design of stormwater infiltration systemsrequires a greater recognition and knowl-edge of specific site conditions, much moreso than for detention systems. Site vari-ables play a much greater role in infiltration fa-cility design. The site variables listed beloware important to assess and evaluate if theimplementation of infiltration BMPs is to be suc-cessful. From an inspector's perspective, theapproved project file should contain informationon each of these parameters. Specific designrecommendations, based on state or local con-ditions, for the parameters discussed below(i.e., maximum slope, depth to water table, mini-mum soil permeability rates, etc.) should be pro-vided in state or local stormwater managementdesign handbooks.

C. Site stabilization must be accom-plished before wetland planting if siterunoff passes through the facility.Excess sedimentation can smother theplants and change wetland elevationswhich would alter planting success andplant composition. Optimally, the plant-ing should be done several months af-ter site stabilization to allow for furtherreduced sedimentation into the wetland,but construction scheduling may reducethat potential.

D. The time of year that plants are placedin the wetland will influence the eventualsuccess of the planting. Ideal times forplanting are in the spring when plants areemerging from dormancy and in the latefall when plants are just entering dor-mancy. Other times for planting are lessrecommended. The inspector shoulddiscuss time frames for planting with thedeveloper/contractor early in construc-tion to establish a timetable for facilityconstruction and wetland planting.

8.3. Infiltration Practices

Infiltration, or retention, practices are widelyrecognized as valuable stormwater manage-ment BMPs because of their multiple benefits.By retaining runoff onsite for percolationor evaporation, infiltration practices are theonly structural stormwater BMPs which re-duce the total volume of stormwater leav-ing an urban site. Infiltration practices includea wide range of BMPs including:

• trenches• basins• drywells• paving (porous pavements, lattice block)• swales

While the multiple benefits of infiltration prac-tices make them very essential BMPs, there is


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A. Soils must be suitable for infiltrating run-off through the soil profile. Soils that havetoo much silt or clay content will tend toclog quicker than more coarse grainedparticles. Each infiltration facilityshould have a soils report attachedto the approved plans which detailsoil conditions at the site of the infil-tration system.

As an initial design consideration, theappropriate Detailed Soil Survey shouldbe consulted to determine whether aspecific site is suitable for infiltrationpractices. If this indicates suitable soils,location-specific soil borings shouldbe taken to verify soil conditions toseveral feet below the bottom of theinfiltration facility. The soils analysiswill indicate the depth of various soils inthe profile in addition to the depth ofwater table or bedrock. The inspectorshould become aware of the soils ex-pected on the site at the proposed loca-tion of the infiltration BMP. This is to en-sure, during construction, that those soilconditions are accurate.

The Stormwater Management Manual

for the Puget Sound Basin, Volume III -Runoff Control (Washington State De-partment of Ecology, 1986) requiresrunoff to pass through at least 18 inchesof soil which has a minimum cation ex-change capacity of 5 milliequivalents per100 grams of dry soil. The intent of thisrequirement is to ensure that pollutantsdo not pass through soils that are tooporous creating ground water pollution.The approved plans should be checkedfor special conditions related to construc-tion of the infiltration system.

B. The design report should contain infor-mation on the depth of soil from the pro-posed bottom elevation of the infiltrationBMP to the water table, bedrock, or im-permeable soil layer. Having limiteddepth of good soil above a barrier to ver-tical water movement may prevent longterm performance of infiltration prac-tices. As these facilities accept runofffrom areas of the project site that havereduced or eliminated infiltration, the ac-cumulation and ponding of runoff in theinfiltration system increases the poten-tial for ground water mounding. Mound-ing can cause ground water levels torise above the design bottom eleva-tion in the vicinity of the facility. Thiscan prevent or significantly reduce in-filtration of runoff.

There are situations where infiltration fa-cilities can be used despite having ahigh ground water table. In very perme-able soils, exfiltration of runoff can oc-cur through the sides of the facility. Thisprocess must be specifically designedfor, and the plans should clearly indi-cate expected site conditions.

C. Site slope must be a consideration inthe implementation of an infiltration BMP.Locating an infiltration system on slopesexceeding 15% could result in infiltratedExample of a soil sample being

taken at an infiltration basin site.


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runoff becoming surface runoff fartherdown the slope and increase site ero-sion problems. Slope can also ad-versely impact the performance of infil-tration trenches. These are linear in na-ture and too steep of a slope may meanthat the uphill portion of the facility neverfills up with water prior to runoff overflow-ing the downstream end of the facility.

D. The proximity of septic fields, structurefoundations, or drinking wells should beconsidered during the design phase toeliminate potential concerns, for obviousreasons.

E. Due to the sensitivity of infiltrationpractices to clogging, the BMP Treat-ment Train concept should be usedto provide pretreatment. This can beaccomplished by swale conveyances,vegetative filters or structural BMPs.Pretreatment is not practical for someinfiltration BMPs such as a porouspavement or dry well. However, when-ever feasible, pretreatment needs to beprovided. The inspector should reviewthe plans to see if pretreatment is pro-vided.

F. The approved plans should detail the

surface covering of the infiltration sys-tem. If vegetation is the cover material,the approval should detail the seedingspecification, ground preparation, andfertilizer application. Other surface cov-ers, such as stone riprap or apron,should also be detailed. If stone is used,the stone should be clean, washed stoneto reduce potential clogging of the facil-ity.


The proper construction of infiltration facilitiesis very important if long term performance is tobe expected. These practices are very suscep-tible to clogging by site generated sediments.It is vital that sediment laden runoff duringconstruction not be allowed to enter thefacility. There is also a time period after sitestabilization has been accomplished that ex-cess sediment loads still are transported down-stream from areas where revegetation is done.These areas of revegetation will not have thebuildup of organic material or the density ofvegetation that will develop eventually. This iswhy pretreatment of runoff before it enters theinfiltration system is needed. The following gen-eral guidelines apply to the construction phaseof all infiltration practices. The guidelines areadapted from those provided in the "Control ofSiltation" Section of the Stormwater Manage-ment Design Manual for the Puget Sound Ba-sin, Volume III - Runoff Control.

A. Infiltration systems should not be con-structed until permanent stabilizationand permanent erosion control of ar-eas draining to the facilities has beenaccomplished.

B. Infiltration facilities, primarily basins,should not be used for temporarysediment traps or basins during con-struction. If an infiltration system must

Combination detention facility andinfiltration basin where exfiltration from

basin occurs through the side walls.


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be used for sediment control, the bot-tom of the facility should be placed atleast one foot above the design bottomelevation. If the system develops a nor-mal pool of water due to bottom clog-ging by finer sediments, it should be de-watered and allowed to dry before ex-cavation to final design bottom eleva-tions. If the material is removed whilewet, there will be the potential for the wa-ter to become turbid and for finer sedi-ments to remain in the water column.This will reduce soil permeability at thefinal bottom elevation.

C. Other than infiltration dry wells and po-rous pavement, all infiltration practicesshall be designed so that the stormwa-ter runoff first passes through a pre-treatment system to remove suspendedsolids before the runoff enters the infil-tration system.

D. The location of infiltration systemsshould be clearly marked at the siteto prevent vehicle traffic across thisarea. The traffic will compact the soilsand reduce soil infiltration rates. As canbe seen from the photograph, identifi-cation without education may not preventa problem from occurring.

8.3.3. Characteristics of IndividualInfiltration Practices WhichWarrant Specific Attention

Although grouped together due to their com-mon goals, infiltration BMPs also are very dif-ferent in their construction and site utilization.Consequently, they will be discussed sepa-rately to provide specific guidance to the in-spector. Probably the best existing source ofinformation on construction inspection of infil-tration systems is the "Inspectors GuidelinesManual for Stormwater Management InfiltrationPractices" (Maryland Department of the Envi-ronment, 1985). Many of the recommendationsin the following section have been adapted fromit. These recommendations need to be con-sidered in addition to those presented in thegeneral discussion in Section 8.3.2 above. Inaddition, detailed construction check sheets areprovided in Appendex 6-5.

A. Infiltration basins often do not have aprincipal spillway since runoff is infil-trated into the ground or evaporated.The primary method of construction isto construct a dam embankment or toexcavate a basin into the ground. Thesefacilities temporarily store (underlined foremphasis) runoff. They are generallyused for larger drainage areas than areother types of infiltration BMPs. Thereare a number of points (See Appendix6-5A) which must be considered by aninspector when inspecting an infiltrationbasin.

1. The infiltration basin dimensions andlocations should be verified onsiteprior to basin construction. Designconsiderations such as distance tofoundations, septic systems, wells,etc. need to be verified.

2. Initial excavation should leave morethan one foot of unexcavated mate-rial above the design bottom eleva-

While the location of the infiltration basinwas marked, construction workers mis-takenly thought the markings identifiedwhere trucks were to enter and leave a

construction site.


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tion if the basin is to be used for sedi-ment control during construction.However, it is recommended thatinfiltration basins not be used forerosion and sediment control dur-ing construction.

3. During initial excavation, the ex-cavated materials should be ob-served by the inspector to verifysoil conditions are consistentwith information in the design re-port. Significant variation of soilsfrom the design report should benoted and the plan approval agencynotified.

4. Excavation should be done by light-weight equipment to minimize the po-tential of soil compaction. Tracked,cleated equipment does less soilcompaction than tired equipment.

5. When inspecting the basin floor atfinal grade establishment, the in-spector should look for any mate-rial, organic or otherwise, which mayreduce basin performance. Ex-amples of such material includestree roots, previously buried mate-rial, or areas of loose stone.

6. Where embankments are required

for basin establishment, the sameconcerns that exist for detentionponds should be considered. Thisincludes:

• clear, grub, and strip topsoil• a cutoff trench• fill material for the embankment

shall be taken from an approvedsource and be clean mineral soilfree of roots or woody vegeta-tion.

• embankment compaction shallbe the same as for detentionponds in terms of degree of com-paction and depth of layers

7. When at final grade, the basinfloor should be deeply tilled torestore the percolation rate ofcompacted soils and to aerate thesoils.

8. Similar to detention systems, infil-tration basins should have a final in-spection performed leading topreparation of written documenta-tion on the adequacy of construc-tion.

B. Infiltration Trenches tend to have alarge length to width ratio and are filledwith stone, gravel, or sand aggregate.Infiltration trenches are generally usedin areas where space available for theBMP is limited. By being linear, and hav-ing the available area filled with stone,etc. they can be fairly deep without hav-ing a comparable width requirement.Runoff entering the facility is stored inthe void areas of the aggregate mate-rial, which normally is between 30 and40% void area. The stored runoff thenexits the trench through the side and bot-tom walls into the soil profile. Appendix6-5B contains an inspector check list forinfiltration trenches.

Example of an infiltration basin beingconstructed.


6-25

1. The infiltration trench dimensions andlocation should be verified onsiteprior to trench construction. Designconsiderations such as distance tofoundations, septic systems, wells,etc. need to be verified.

2. The trench should be excavated us-ing a backhoe or a ladder type tren-cher. Front-end loaders or bulldoz-ers should not be used as theirblades can seal the infiltration soilsurface. Excavated materials shouldbe placed a sufficient distance fromthe sides of the excavated area tominimize the risk of sidewall cave-ins and also to prevent migration ofthe soils back into the trench after thestone, gravel, or sand aggregatehas been placed.

3. The trench bottom and side wallsshould be inspected for removal ofobjectionable material such as treeroots that protrude and could possi-bly puncture or tear the filter fabric.

4. The sides and bottom should belined with filter fabric. The side fab-ric placement will prevent migrationof soil particles from the side wallsinto the trench. The bottom filter fab-

ric will prevent sealing of the aggre-gate soil interface.

5. The fabric should be laid with suffi-cient length to overlap the top of thetrench. Having the trench coveredafter placement of the aggregate willprotect the completed facility by pre-venting excess site sediment fromentering it.

6. An observation well should be in-stalled in the aggregate to allow fu-ture inspections to determinewhether the facility is functioning asdesigned. The observation wellshould consist of a perforated PVCpipe, 4 to 8 inches in diameter andhave a foot plate and a cap. Thefootplate will prevent the entire ob-servation well from lifting up whenthe cap is removed during future in-spections.

Completed infiltration basin; note the lack ofpretreatment measures prior to runoff entry

into the facility.

Infiltration trench showing the observationwell, foot plate, and filter fabric side walls

before placement of the aggregate.


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7. The aggregate material should be in-spected prior to placement to ensurethat it is clean material and free ofdebris. The size of the materialshould be as specified on the ap-proved plans.

8. Upon completion of trench construc-tion, the adjacent areas should bevegetatively stabilized. The overflowof the trench should be directed to anon-erosive outlet channel.

9. A pretreatment BMP should be usedbefore the runoff enters the trench.This pretreatment should be effec-tive at removing suspended solidsand can be a biofiltration swale orother approved method.

10.The observation well should becapped and the initial depth mea-sured and noted on the inspectionchecklist.

C. Infiltration Drywells are similar to in-filtration trenches in that they are exca-vated areas that are filled with an aggre-gate material. The main difference is

that drywells accept runoff from roofs.Therefore, they receive lower loadingsof suspended solids loadings comparedto that expected from ground surfacerunoff. The major concern with infiltra-tion drywells is that, by serving roof ar-eas, they must be located in the vicinityof building foundations. Careful con-sideration must be given to the cor-rect placement of drywells so thatbuilding foundation problems do notresult. A big advantage of a drywellover other runoff controls is that thedrywell is underground and does not rep-resent a loss of site area to the land de-veloper. Appendix 6-5C contains aninspector check list for drywells.

1. The infiltration drywell dimensionsand location should be verified on-site prior to drywell construction.Design considerations such as dis-tance to foundations, septic systems,wells, etc. need to be verified.

2. The drywell should be excavated us-ing a backhoe or ladder type tren-cher. Front-end loaders or bulldoz-

Example of an infiltration trenchtreating highway runoff.

Overflow

Roof Downdrain

Schematic of an infiltration dry well.Adapted from Schueler, 1987


6-27

ers should not be used as the equip-ment blades may cause excessivecompaction of the drywell bottom.

3. Excavated materials should beplaced a sufficient distance from thesides of the excavated area to mini-mize the risk of sidewall cave-ins andalso to prevent migration of the soilsback into the trench after the stone,gravel, or sand aggregate has beenplaced.

4. The drywell bottom and side wallsshould be inspected for removal ofobjectionable material such as treeroots that protrude and could possi-bly puncture or tear the filter fabric.Work should be scheduled so thatthe drywell can be covered in one dayto prevent windblown or water car-ried suspended solids from enteringthe drywell.

5. The sides and bottom should be linedwith filter fabric. The side fabricplacement will prevent migration ofsoil particles from the side walls intothe trench. The bottom filter fabricwill prevent sealing of the aggregatesoil interface.

6. Once the aggregated has beenplaced, filter fabric should be placedover the drywell and final gradingshould be done.

7. An observation well should be in-stalled in the aggregate to allow fu-ture inspections to determinewhether the facility is functioning asdesigned. The observation wellshould consist of a perforated PVCpipe, 4 to 8 inches in diameter andhave a foot plate and a cap. Thefootplate will prevent the entire ob-servation well from lifting up when the

cap is removed during future inspec-tions.

8. The aggregate material should be in-spected prior to placement to ensurethat it is clean material and free ofdebris. The size of the materialshould be as specified on the ap-proved plans.

9. Debris and grit traps consisting offine-mesh screen covering the down-spout (roof leader) should be usedwith dry wells to prevent objection-able materials from entering the ag-gregate subbase through the inflowpipe. Roof gutter screens shouldalso be used to protect gutters andgrit traps from clogging due to wash-off of leaves, pine needles, etc. from

Completed drywell showing overflow device: note total site utilization but also

the lack of observation wells.


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the roof area.

10.The observation well should becapped and the initial depth mea-sured and noted on the inspectionchecklist.

D. Infiltration paving (porous pavementand lattice block) systems are roadand parking lot surfaces whose designallows for stormwater runoff to travelthrough the surface into the ground.Under the porous surface, an aggregatematerial serves as a reservoir base fortemporary storage of the runoff until thewater infiltrates into the ground. Theirbest applications are in areas wherethere is a low volume of traffic orwhere overflow parking is needed ona periodic basis. Appendix 6-5D con-tains an inspection check list for pervi-ous pavements.

Porous Asphalt

This has been the most commonly usedporous paving surface. In porous asphaltthe fines are left out of the mix and theasphalt content is increased slightly to in-crease the binding of the mixture. Leav-ing the fines out of the mixture increasesthe void spaces and allows rainfall to passdirectly through the pavement. The pav-

ing consists of the porous asphalt course,a filter course, the reservoir course, filterfabric, and finally the existing soil.

Lattice Block

Lattice block is a modular unit which isgenerally placed in square sections. It isconcrete with large void areas which arefilled with a porous material, such as sandor pea gravel. Lattice block still shouldhave the filter course, reservoir course,and filter fabric lining, prior to entry intothe soil.

Pervious Concrete

Pervious portland concrete is being usedwidely in Florida to create porous park-ing areas. Like porous asphalt, the finesare left out of pervious concrete creatingan open concrete pavement which allowswater to pass directly through into theground. It avoids some of the pitfalls ofporous asphalt due to its strength to re-sist rutting and compaction. It also hasgreater surface openings to resist sur-face clogging which is such a large con-cern with porous paving. However, spe-cial expertise is required to batch,pour, and finish pervious concrete.

Porous paving being installed showing theporous asphalt course and the filter course.

Lattice block infiltration provided ata parking lot.


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1. To help preserve the natural infiltra-tion rate of the subgrade soils priorto excavation, the infiltration pavingarea should not be excessively trav-eled by heavy construction equip-ment that causes excessive com-paction of soil pores. The areashould be marked off and traffic keptoff it to the greatest extent possible.

2. The infiltration paving dimensionsand location should be verified on-site prior to construction. Designconsiderations such as distance tofoundations, septic systems, wells,etc. need to be verified.

3. The area of the paving should becarefully excavated to prevent ex-cessive compaction of the soils dur-ing the subgrade preparation. Allgrading should be carried out usingwide tracked equipment.

4. Once the subgrade has beenreached, filter fabric should beplaced on the bottom. The type offabric should be specified on the ap-proved plans.

5. Once the fabric has been placed, thereservoir course is placed to the de-sign depth. This course should be

clean, washed stone having a voidratio between 30 and 40%. The res-ervoir course should be laid in 12"lifts and lightly compacted. The ag-gregate should be uniformly spread.

6. The aggregate filter is placed on thereservoir course and is clean washedstone ranging in size from 3/8 to 5/8inch. This stone provides a uniformbase for the asphalt or lattice course.

7. At no time should sediments be al-lowed to enter the infiltration pavingconstruction area.

8. The surface course is then laid. If po-rous asphalt, it should be laid directlyover the aggregate filter course inone lift. The laying temperatureshould be done to local specifica-tions and minimum air temperaturesshould be considered to ensure thatcooling does not occur prior to com-paction. If lattice block is used, tem-perature of the mix or air tempera-ture aren't important. The void areasof the lattice block should be filledwith the appropriately specified ma-terial.Placement of the reservoir base at a

porous pavement site.

Close-up view of lattice block paving withpea gravel filler in the porous areas.


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paction of soil pores. The areashould be marked off and traffic keptoff the area to the greatest extentpossible. This is especially impor-tant at residential construction siteswhere individual residential contrac-tors enter building sites with numer-ous trucks. The driveway areasshould be the access points for con-tractors.

2. The infiltration swale dimensions andlocation should be verified onsiteprior to construction. Design consid-erations such as distance to founda-tions, septic systems, wells, etc.need to be verified.

3. Excavated materials should beplaced a sufficient distance from thesides of the excavated area to pre-vent migration of the soils back intothe swale area.

4. During excavation of the swalecross-section, poor soils, organicmaterial, or rocks should be removedand replaced with permeable soils.

5. Excavation should be done by light-weight equipment to minimize com-paction of the soil profile.

6. The approved design plan will havespecifications for the composition ofthe swale block or check dam (height,slopes, materials, etc.). They willgenerally be earth material andshould be compacted to minimizeseepage. Stone or sod may be re-quired on the face of the check damto prevent possible erosion duringhigh storm flows.

7. The final inspection will verify infil-tration swale dimensions, and as-sure that the number of check dams

9. The inspector should check the over-all workmanship of the pavementarea to ensure smooth transitionsbetween existing and new paving. Asmall compacted section should betested by pouring a few gallons ofwater onto the pavement to ensurethat the water infiltrates into the pave-ment.

E. Infiltration Swales are closely relatedto biofiltration swales. The primary dif-ference is these swales use infiltrationas their primary means of pollutant andtotal runoff volume reduction. However,they are still considered as a subset ofbiofilters since vegetative filtration isalso important. While biofiltration swalesand filters rely on passage of waterthrough vegetation for pollutant reduc-tion, infiltration swales have designedblockages, such as swale blocks orcheck dams, which pond water and pro-motes infiltration. In both situations,slopes must be very gradual to increaseresidence time and reduce flow veloci-ties. Appendix 6-5E contains an inspec-tion check list for infiltration swales.

1. To help preserve the natural infiltra-tion rate of the subgrade soils priorto excavation, the infiltration swalearea should not be excessively trav-eled by heavy construction equip-ment that causes excessive com-

Schematic of an infiltration swale.Adapted from Schueler, 1987


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agrees with the approved plans. Itis absolutely essential that ex-cess sediment loadings be keptout of the swale and that goodvegetative stabilization of theswale be accomplished. Infiltrationswales, due to their small im-pounded areas behind the checkdams, are very susceptible to clog-ging of the pool areas, so good sta-bilization of the site and swales is es-sential.

8.4 Filtration Systems

Filtration systems are becoming more recog-nized and accepted as another option for treat-ment of urban stormwater. There are three pri-mary approaches which are being used aroundthe country. These approaches require very dif-ferent responsibilities for an inspector.

Austin, Texas

The City of Austin has pioneered the use of sandfilter systems as a means to protect their groundwater aquifers. Austin has significant limestoneareas in which discharge of stormwater couldincrease the potential for sinkhole developmentand allow pollution of ground water resourcesby direct discharge of untreated stormwater intothe ground water. They use impermeable lin-

ers under their sand filters to prevent the poten-tial migration of pollutants into the ground wa-ter while treating the runoff. The program re-quires management of both stormwater quan-tity and quality, with treatment of runoff from per-vious and impervious areas.

Washington D.C.

The City of Washington, D.C. is on a combinedsewer system. Their sand filter systems alsoare designed to control the peak rate of dis-charge from a site while providing stormwatertreatment. The stormwater quantity criteria areintended to prevent overloading the combinedsewer capacity. The basic sand filter designused is an underground vault since land is ei-ther very expensive or unavailable for use ofsurface stormwater BMPs.

Infiltration swale adjacent to a highway.

Austin sand filter systemsediment forebays on either side with

sand filter in the center.

Washington, D.C. sand filter.


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Delaware Sand Filter

Delaware's stormwater program has devel-oped a sand filter design for use on highly ur-banized sites where available stormwater treat-ment options are limited. This filter is designedfor water quality only, and is used to treat runofffrom totally impervious drainage areas atsmaller sites. The filter is a shallow systemwhich can be built underground resulting in noloss of site use for buildings.

There are other variations to these three basicdesigns. The City of Alexandria uses variationsof all three approaches. Their variation of theDelaware Sand Filter uses a precast concretetop for the filter which significantly reduces thecost compared to the original Delaware versionwhere cast iron grates are commonly used.Florida's stormwater program pioneered theuse of detention with filtration systems in theearly 1980s. Side bank and vertical recoveryfilters, made of sand and gravel, are used inassociation with detention systems to providestormwater treatment on sites that can not usewet detention.


Design of filter systems is fairly straightforwardwhen compared with ponds or other practices.Their design criteria are clearly detailed in avail-able guidance manuals. One similarity of all ofthe different confined filters is a two chamberfacility. The first chamber is for sediment depo-sition of larger suspended solids. The second,a filtration chamber, contains the filter media,generally sand. Other filter media includingcompost, peat, and alum sludge have been usedon specific projects. Appendix 6-6 is an inspec-tor check list for filtration systems. In addition,the plans should include the following informa-tion:

A. Dimensions and structural details of thefiltration facility.

B. Sequence of construction for overall sitedevelopment and construction of the fil-tration facility.

C. Volumes and size of both the sedimen-tation and filtration chambers.

D. Specifications of the filter media. Themedia should be specified as beingclean, washed material.

Delaware sand filter.

City of Austin sand filter for new highwayconstruction. The chamber in the fore-

ground is the sedimentation chamber, thefiltration chamber is in the background.


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E. Sediment control provisions during con-struction to prevent the facility from pre-mature clogging. The Austin filters in-clude a dry detention component. Ac-cordingly, these facilities may have moreconstruction sediment control notes thanthe other systems.

F. In the Delaware sand filter, the filter maybe prefabricated in standardizedlengths. The means of sealing the jointconnections between units should bespecified on the approved plans.


As can be seen from the illustrations, sand fil-ters may involve reinforcing steel, concrete, andsignificant site preparation prior to construction.The inspector should carefully review the ap-proved plans and discuss any concerns at thepreconstruction meeting. From an inspectionstandpoint the following construction times anditems are important to recognize during the siteinspection.

A. Site location for the filtration facilityshould be staked out. This is especially

important when installing the Austin fil-ter as it encompasses more site areathan do the Washington D.C. orDelaware filters. In general, filters shouldnot be used for sediment control duringconstruction.

B. Structural components should be avail-able on-site to verify adequacy of mate-rials. Reinforcing bars should meetspecifications as should all other struc-tural components such as any pipes, ag-gregate material, and filter fabric.

C. Foundation areas should be cleared ofany organic material which could causeuneven settlement at the material de-composes. Unsuitable foundation mate-rial should be removed and replaced bysuitable material.

D. The foundation area should be com-pacted to sustain the load placed on itby the filtration system. The foundationshould then be leveled as detailed onthe plans to ensure proper drainage ofthe facility.

E. The inspector should be on site when thefacility has been formed up with reinforc-ing bars in place but prior to pouring ofthe concrete.

City of Alexandria variation of the Delawaresand filter using prefabricated concrete

tops for the filter.

Foundation grade being established priorto placement of concrete floor of the

filtration facility.


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F. During concrete pouring, the inspectorshall verify that the concrete meets de-sign specifications for the design load.

G. If the filtration facility is composed ofprefabricated units, the inspector shallapprove the means of joining the sec-tions and the steps taken to preventleakage from between the prefabricatedunits.

H. Delaware and Washington D.C. filtersshould be filled with water once the con-crete has set (or joints sealed on pre-fabricated units) and allowed to sit for24 hours to observe whether the unit hasany leaks.

I. When installation has been completed,meets size and volume requirements,has no leakage, and the contributingdrainage areas have been stabilized,placement of the underdrains shouldthen be done. These drains should beplaced on the proper slope and wrappedin filter fabric to prevent migration of thefiltration material out of the facility.

J. The filter material shall then be placed

in the facility. The material should meetcriteria specified on the design plans.A common material used at this time isC-33 concrete sand. This is clearly de-fined in highway design standards. Thesand should be clean, washed aggre-gate. Other materials, such as peat orcompost, may become more acceptedif their performance demonstrates theirvalue.

K. A final inspection should verify that thefilter material is placed correctly and thefirst sedimentation chamber is clean ofany accumulated sediments or other con-struction debris.

8.5. Biofiltration Systems

Biofiltration practices rely upon several pro-cesses to treat runoff. These include filtration,infiltration, adsorption, and the biological up-take of pollutants from runoff as it flows througha vegetated stormwater treatment system.Biofiltration can effectively function in any lo-cation where natural vegetation and landscap-ing intercept runoff. A key requirement of anyvegetative treatment system is to obtain astand of vegetation that can effectively fil-ter runoff. Ideal vegetation characteristicsinclude a dense, uniform growth of fine-stemmed plants that can tolerate soil satura-tion and the climatological, soil, and pest con-ditions of the area. Drainage areas are gener-ally fairly small, less than 5 to 7 acres. Appen-dix 6-7 is an inspector check list for biofiltrationpractices.

It is essential to maintain proper hydraulicconditions to avoid uneven, channelizedflows through the biofiltration BMP. Unevenflow across the width of a biofilter reduces pol-lutant removal effectiveness because runoffbypasses vegetation, shortening treatmenttime. Channelized flow also may erode biofiltersand exacerbate downstream water quality prob-

Sealing of joints on a prefabricateddelaware sand filter.


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lems that the BMP was intended to mitigate.


Design of biofiltration facilities is fairly straightforward. Their primary treatment process is fil-tering runoff through vegetation. When an in-spector first reviews the approved plans, it isimportant to note the following essential designaspects of biofiltration BMPs.

A. Dimensions and structural details of thebiofiltration system. The bottom widthof swales should be no less than 2 feetif it is to be mowed. The bottom widthshould be no greater than 8 feet unlessit will be hand finished to get a com-pletely level bottom.

B. Sequence of construction for overall sitedevelopment and construction of the bio-filtration system.

C. Do the post-development drainage pat-terns resemble the pre-developmentones? Placement of swales and biofil-ters along natural flow paths and contoursshould be detailed on the approvedplans.

D. To assure even sheet flow in a biofilter,and avoid channelized flow, the bottomof the biofiltration BMP must be flatwith no lateral slope (across the bot-tom of the swale or vegetative filter strip).

E. The design of inflow to the biofiltershould quickly dissipate runoff ve-locity to minimize erosion potential.Dissipation practices such as riprappads and level spreaders should beused.

F. Outflow from biofilters should be diffuseto avoid erosion damage to downstreamfacilities or water bodies. Swales shouldbe equipped with raised storm drain out-lets to prevent erosion.

G. Generally, biofiltration swales are longerthan 100 feet to reduce short circuiting,with their total length depending upon theflow and the minimum required resi-dence time. No minimum width hasbeen established for biofiltration filterstrips since this is a very site specificdesign parameter. All of the above dis-tances are general recommendations toprovide effective stormwater treatment.Exact dimensions and residence timeswill be specified by the state or localstormwater program depending on their

Vegetative swale functioning as abiofiltration facility.

Swale inlet energy dissipator and flow spreader.


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performance standard. These dimen-sions must be specified on the approvedplans. When an inspector finds that abiofiltration system is not built accord-ing to the design plans, the plan approvalagency should be contacted to deter-mine corrections needed to ensureproper performance of the constructedBMP.

H. Longitudinal slopes should be fairlyslight with maximum slopes of 4% (canbe greater with use of check dams).

I. Plant specifications must be containedon the approved plans. Grasses tendto be the superior choice of vegeta-tion as they are resilient, provideabundant surface area, and cansprout through thin deposits of sandand sediments. The plants should bethose of common use in the geographicarea and be somewhat stiff, dense, anda greater leaf area.

J. If the site's soils are sandy, topsoil shouldbe specified on the biofilter's plans.Eliminating hardpan, rocks, and gravelnear the surface will help to prevent per-sistent bare spots in biofilter plant cover.

K. Pretreatment should be provided whenhigh sediment inputs to biofilters are likely.


Construction activities should be phased to en-sure the greatest practical amount of plant coverduring the course of construction. If permanentswales and filter strips are installed during siteconstruction, they either must be protected fromconstruction site runoff or restored for long termuse once site construction is completed. Theinspector should note the following importantaspects of construction:

A. Site location for the biofiltration facilityshould be staked out. This will allow fordimensions, shapes, and slopes to beverified per the design plans.

B. Ensure that lateral slopes are com-pletely level to avoid any tendencyfor the flow to channelize.

C. Ensure that inlets, outlets, and other aux-iliary structures, such as check dams orflow bypasses, are installed as specified.

D. Make sure that vegetation complieswith planting specifications. Ensurethat vegetation becomes uniformlydense for good filtration and to preventerosion. Grass can be established byseeding or using sod. Seeding is gen-erally preferred due to it's lower cost andthe greater flexibility it allows in select-ing grass species. The method of veg-etative stabilization should be dis-cussed and approved at the precon-struction meeting.

E. The biofilter should be placed so thatno portion will be in the shade ofbuildings or trees throughout theentire day, which would cause poorplant growth.

F. Make sure that construction runoff is notentering the biofilter. If it is, require re-

Check dam with energy dissipator.


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moval of sediments and reestablish veg-etation upon the completion of construc-tion.

G. Ensure that measures are in place to di-vert runoff while vegetation is being es-tablished. If runoff is probable and can-not be diverted, ensure that adequateerosion control measures are in place.

H. Inspect liners, underdrains, riprap, andcheck dam spacing, if they are includedin the approved plan.

I. Make sure that any level spreaders arecompletely level and sufficiently stableto remain level during their operation.

J. Check for proper installation of pretreat-ment devices, if required.

K. Ensure that curb cuts and their locationsare as specified. Ensure that the veg-etation is not higher than the curbcut.

9. ONCE CONSTRUCTION IS COMPLETED

Upon satisfactory completion of construction,there are several actions that should be takenwith respect to the completed project and itsfiles. The information can be entered in anymany ways. It can include microfilming the plans,having a data spreadsheet for pertinent infor-mation, or maintaining a physical file of the com-pleted project containing all information neededfor future inspections and actions. It is veryimportant that this process includes ameans of notifying the inspection agencyto make them aware of the need for futureinspections.

This process starts upon completion of the con-struction phase of the project. Specific tasksinclude:

• Entering pertinent information from thecompleted files into a database. Futureretrievals of this information will providethe basis for future maintenance inspec-tions.

• The "As-Builts" or Record Drawingsshould be attached to the file and madean essential part of the permanentrecord. It is becoming more commonfor electronic cad (autocad) drawings tobe required, allowing communities amore efficient means of updating sys-tem-wide stormwater inventory maps.

• Copies of all inspection reports and thefinal inspection report should be placedin the file.

Swale biofilter having erosion controlmatting installed prior to permanent

vegetative stabilization.

The same biofiltration swale with permanent vegetative stabilization

three weeks later.


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• The permanent file should tell who is re-sponsible for subsequent maintenanceinspections and physical maintenanceof the completed facility. These respon-sibilities should be set forth in a legaldocument, signed by the individual as-suming maintenance responsibility. Thiswill help to assure their commitment toassuming and performing these tasks.

• The date for a subsequent maintenanceinspection should be established at thistime to ensure the initiation of perma-nent ongoing inspections of the com-pleted facility.

10. RECOMMENDATION FOR INSPEC-TOR TRAINING AND CERTIFICATIONPROGRAMS

Initial and subsequent on-going training are es-sential for inspectors to learn the initial skills andmaintain their level of understanding. It is alsoimportant that they be aware of their obligationson new types of BMPs or variations in designof existing BMPs.

Inspector training should include a specificcourse designed to provide inspectors withthe minimum information necessary to con-duct site inspections during and after con-struction. This course should be given to pub-lic inspectors and private individuals who areresponsible for inspecting and maintainingstormwater management systems. This train-ing is a mandatory program component if theprogram's law or rules require inspections dur-ing or after stormwater system construction. Theeducational program should include, at a mini-mum, the following items.

• Why implementation of stormwater man-agement facilities is important.

• Applicable laws and regulations.• What the individual types of facilities are

and how they function in various sce-

narios.• How to read a design plan and accom-

panying specifications.• How to inspect a site.• How to complete an inspection form.• How to read a topographic map.• Soils information including knowledge

of soil texture, consistency, etc. to beable to recognize various soils in thefield.

• Site erosion and sediment control strat-egies and practices for consideration inprotection of stormwater managementfacilities.

• Enforcement procedures and penaltyprovisions.

• Detailed information on local vegetationincluding information on suitability ofvarious types of vegetation for differentpurposes. This would include vegeta-tion that is water and drought tolerant.

Education is essential to effective programimplementation. Education on stormwatersystem construction is an important componentof this overall educational process. Withouteducation, the expectations for successfulconstruction of stormwater managementsystems is reduced. The training recom-mended in this chapter could be supplementedwith the educational program discussed inChapter 7. The training probably is best doneby including it in an educational program on siteconstruction which should include erosion andsediment control and stormwater managementsystem construction. The issue of how manyeducational programs and the extent of eachprogram is best made at the local level wherethe programs are most appropriately given.


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APPENDICES

Construction Inspection Formsfor

Stormwater ManagementFacilities


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APPENDIX 6-1

Preconstruction InspectionMeeting Topics Form


6-41

State of New JerseyDepartment of Environmental Protection

Stormwater Management Facility Maintenance Manual

Example Preconstruction Meeting Topics

A. GENERAL INFORMATION

1. Attendance2. Purpose of project and background information3. Emergency telephone numbers4. Construction photograph requirements5. Project sign requirements6. Starting date7. Review of contract documents, including insurance certifications, bonds and subcontrac-

tors documents8. Field office requirements9. Responsibility for notification of affected property owners and residents10. Chain of command for communications and correspondence11. Construction schedules12. Key personnel and their degree of involvement in the project (inspector, owner, engi-

neer, agencies, etc.)

B. POLICE AND FIRE DEPARTMENT CONCERNS

1. Traffic control2. Barricades and signs conforming to the uniform manual3. Noise ordinance considerations4. Working hours, including weekend and holidays5. Vandalism and preventative measures6. Flagmen and traffic control officers7. Equipment storage and vehicle parking8. Emergency vehicle access9. Underground tank locations and precautionary construction procedures10. Storage and use of hazardous materials

C. UTILITIES

1. Utility locations and mark-outs2. Coordination of utility relocations3. Emergency phone numbers of utility companies

D. FUNDING AND PAYMENTS

1. Funding sources and availability2. Procedures and dates for payment estimates3. Dates for payments to contractor4. Breakdown of lump sum items for partial payment5. Policy for payment for materials on site at the close of a payment period


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6. Retained monies during and after construction7. Requirements of funding agencies

E. CHANGE ORDERS AND EXTRA CLAIMS

1. Requirements for additional work and submittal of change orders2. Procedures and schedule for review and recommendations of change orders3. Procedures for negotiating extra claims and change orders

F. CONSTRUCTION ACCESS AND EASEMENTS

1. Easement locations and maps2. Responsibility for locating and staking easements3. Available survey data for the site4. Access requirements and staging areas5. Easement restrictions and restoration requirements

G. CONSTRUCTION DETAILS

1. Unique or complex aspects of the project2. Testing laboratories and sampling procedures3. Cold and hot weather protection measures4. Blasting requirements5. Dump site location for construction related materials6. Shop drawing requirements and review procedures7. Specific construction techniques and procedures8. Review of technical section of the specifications

H. PERMITS

1. Status of all required federal, state, and local permits2. Permit restrictions and conditions3. Start-of-work notifications


6-43

APPENDIX 6-2

General Site Inspectionand

Notice to Comply Forms


6-44

Construction Inspection Report Form(adapted from State of Delaware Sediment and Stormwater Program)

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________

Individual Contacted ____________________________

Weather Conditions _____________________________

Site Status __________________ (active, inactive, completed)

Site Conditions:

acceptable ________Unacceptable ________In compliance with approved plan _________Approved plan is adequate for the site _________

Written Comments:_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Action to be taken:

No action necessary. Continue routine inspections ___________Correct noted site deficiencies by ________________________

1st notice _________2nd notice ________

Submit plan modifications as noted in written comments by _________________________Notice to Comply issued ____________Final inspection, project completed ____________Other ___________________________________________________________________

_________________________ _________________________Received by Inspector

I acknowledge receipt of this inspection Questions or comments regarding this inspectionreport. My signature does not imply agreement report should be directed to the appropriate inspectionor disagreement with its content. agency at the appropriate address and phone number

report.

white: developer/contractor yellow: file pink: legal/enforcement


6-45

Notice to Comply Inspection Report Form(adapted from State of Delaware Sediment and Stormwater Program)

Date ____________

To: _________________________________________Address: ____________________________________________________________________________________________________________________________________________________

Project/Site/Contract Name _______________________________________________________

An inspection of the above referenced project on __________________________(Date) revealedthat the site is not in compliance with the approved Sediment Control and Stormwater Manage-ment Plan, approved Plan amendments, Law, or Regulations, and the following violations exist:

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Notice is hereby given that the above violations shall be corrected in accordance with the ap-proved Sediment Control and Stormwater Management Plan, approved Plan amendments, Law, orRegulations on or before ______________________________ (Date). The site will be re-in-spected at that time to determine if the site has been brought into compliance with the approvedPlan, approved Plan amendments, Law, or Regulations.

Failure to comply with this notice will result in the initiation of legal action by the Departmentin order to bring the site into compliance with the approved Plan, approved Plan amend-ments, Law, or Regulations.

_____________________________ _______________________________Received by Inspector

I hereby acknowledge receipt of this noticeto comply. My signature does not implyagreement or disagreement with its content.

Questions or comments regarding this inspection report should be directed to the appropriate inspectionagency at the appropriate address and phone number



6-46

APPENDIX 6-3

Sediment/Stormwater ManagementBasin Construction Inspection

Checklist


6-47

Sediment/Stormwater Management Basin Construction ChecklistFor Permanent structures per Delaware NRCS Pond Code 378 and Delaware

Sediment and Stormwater Regulations(Developed by Randy Greer, Environmental Engineer)

KEY PROJECT INFORMATION

_____ Item meets standard Project ID: ______________________ Item not acceptable Contractor: _____________________ Item not applicable Inspector: ______________________ Item requires engineer's certification Date(s): __________________

I. Materials and Equipment

_____ Pipe and appurtenances on-site prior to construction and dimensions checked._____ 1. Material (including protective coating, if specified)_____ 2. Diameter_____ 3. Dimensions of metal riser or pre-cast concrete outlet structure_____ 4. Required dimensions between water control structures (orifices, weirs,

etc.) are in accordance with approved plans_____ 5. Barrel stub for prefabricated pipe structures at proper angle for design

barrel slope_____ 6. Number and dimensions of prefabricated anti-seep collars_____ 7. Watertight connectors and gaskets_____ 8. Outlet drain valve

_____ Appropriate compaction equipment available, including hand and small powertamps

_____ Project benchmark near pond site_____ Equipment for temporary de-watering

II. Subgrade Preparation

_____ Area beneath embankment stripped of all vegetation, topsoil, and organic matter_____ Cut-off trench excavated a minimum of 4 feet below subgrade and minimum 4 feet

below proposed pipe invert, with side slopes no steeper than 1:1_____ Impervious material used to backfill cut-off trench

III. Pipe Spillway Installation

_____ Method of installation detailed on plans

A. Bed preparation_____ Installation trench excavated with 1:1 side slopes_____ Stable, uniform, dry subgrade of relatively impervious material (If subgrade

is wet, contractor shall have defined steps before proceeding with installa-tion)

_____ Invert at proper elevation and grade

CN/A


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B. Pipe placement_____ Metal/Plastic pipe

_____ 1. Watertight connectors and gaskets properly installed_____ 2. Anti-seep collars properly spaced and having watertight connec-

tions to pipe_____ 3. Backfill placed and tamped by hand under "haunches" of pipe_____ 4. Remaining backfill placed in max. 8" lifts using small power tamp-

ing equipment until 2 feet cover over pipe is reached_____ Concrete pipe

_____ 1. Pipe set on blocks or concrete slab for pouring of low cradle_____ 2. Pipe installed with rubber gasket joints with no spalling in gasket

interface area_____ 3. Excavation for lower half of anti-seep collar(s) with reinforcing

steel set_____ 4. Entire area where anti-seep collar(s) will come in contact with pipe

coated with mastic or other approved waterproof sealant_____ 5. Low cradle and bottom half of anti-seep collar installed as mono-

lithic pour and of an approved mix_____ 6. Upper half of anti-seep collar(s) formed with reinforcing steel set_____ 7. Concrete for collar of an approved mix and vibrated into place.

(Protected from freezing while curing, if necessary)_____ 8. Forms stripped and collar inspected for honeycomb prior to back-

filling. Parge if necessaryC. Backfilling

_____ Fill placed in maximum 8" lifts_____ Backfill taken minimum 2 feet above top of anti-seep collar elevation

before traversing with heavy equipment

IV. Riser/Outlet Structure Installation

A. Metal riser_____ Riser base excavated or formed on stable subgrade to design dimensions_____ Embedded section of aluminum or aluminized pipe to be painted with zinc

chromate or equivalent on inside and outside surfaces_____ Set on blocks to design elevations and plumbed_____ Reinforcing bars placed at right angles and projecting into sides of riser_____ Concrete poured so as to fill inside of riser to invert of barrel

B. Pre-cast concrete structure_____ Dry and stable subgrade_____ Riser base set to design elevation_____ If more than one section, no spalling in gasket interface area; gasket or

approved caulking material placed securely_____ Watertight and structurally sound collar or gasket joint where structure

connects to pipe spillwayC. Poured concrete structure

_____ Footing excavated or formed on stable subgrade, to design dimensions withreinforcing steel set

_____ Structure formed to design dimensions, with reinforcing steel set as per plan_____ Concrete of an approved mix and vibrated into place. (Protected from freez-

ing while curing, if necessary)_____ Forms stripped and structure inspected for "honeycomb" prior to backfilling.

Parge if necessary


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V. Embankment Construction

A. Fill material_____ Soil engineer's test_____ Visual test by inspector

B. Compaction_____ Soil engineer's test_____ Visual test by inspector

C. Embankment_____ Fill placed in maximum 8" lifts and compacted with appropriate equipment_____ Constructed to design cross-section, side slopes and top width_____ Constructed to design elevation plus allowance for settlement

VI. Impounded Area Construction

_____ Excavated/graded to design contours and side slopes_____ Inlet pipes have adequate outfall protection_____ Forebay(s)_____ Wet pond requirements

_____ 1. 10 feet reverse slope bench one foot above normal pool elevation_____ 2. 10 feet wide level bench one foot below normal pool elevation

VII. Earth Emergency Spillway Construction

_____ Spillway located in cut or structurally stabilized with riprap, gabions, concrete, etc._____ Excavated to proper cross-section, side slopes and bottom width_____ Entrance channel, crest, and exit channel constructed to design grades and eleva-

tions

VIII. Outlet Protection

A. End section_____ Securely in place and properly backfilled

B. Endwall_____ Footing excavated or formed on stable subgrade, to design dimensions and

reinforcing steel set, if specified_____ Endwall formed to design dimensions with reinforcing steel set as per plan_____ Concrete of an approved mix and vibrated into place. (Protected from freez-

ing, if necessary_____ Forms stripped and structure inspected for "honeycomb" prior to backfilling.

Parge if necessaryC. Riprap apron/channel

_____ Apron/channel excavated to design cross-section with proper transition toexisting ground

_____ Filter fabric in place_____ Stone sized as per plan and uniformly placed at the thickness specified


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IX. Vegetative Stabilization

_____ Approved seed mixture or sod_____ Proper surface preparation and required soil amendments_____ Excelsior mat or other stabilization materials, as per plan

X. Miscellaneous

_____ Toe drain_____ Temporary dewatering device installed as per plan with appropriate fabric, stone

size and perforations if included_____ Drain for ponds having a permanent pool_____ Trash rack/anti-vortex device secured to outlet structure_____ Trash protection for low flow pipes, orifices, etc._____ Fencing (when required)_____ Access road_____ Set aside area for clean-out maintenance


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APPENDIX 6-4

Stormwater/Sediment PondTypical Sequence of Construction

forEmbankment Ponds with

Riser/Barrel Outlet Structuresfor

Developers and Contractors


6-52

Stormwater/Sediment PondTypical Sequence of Construction for Embankment Ponds

with Riser/Barrel Outlet Structures forDevelopers and Contractors

(Developed by Randy Greer, Environmental EngineerDelaware Department of Natural Resources and Environmental Control

Sediment and Stormwater Program)

1. NOTIFY PLAN REVIEW/CONSTRUCTION REVIEW AGENCY AS REQUIRED

a. Arrange the preconstruction meetingb. Clear up any questions regarding the approved plan

2. PRE-CONSTRUCTION MEETING WITH CONSTRUCTION REVIEW AGENCY

a. Review the site plan and layout and discuss any problems or changes needed to theplan

b. Obtain approvals for the plan changes from the appropriate inspection or plan reviewagency

c. Discuss the stages of construction which notification to the construction review agency isneeded

3. SITE LAYOUT

a. Make sure site layout agrees with the planb. Check elevation of the proposed outfall structurec. Physically mark any areas not to be disturbed, such as limit of disturbance, wetlands,

property lines, etc.

4. INSTALL PERIMETER EROSION AND SEDIMENT CONTROLS

a. Sediment controls will be needed at the downstream perimeter during the clearing andgrubbing for the pond wherever sediment may leave the site.

5. INSTALL TEMPORARY CHANNEL DIVERSION

a. Divert clean water flow away from pond areab. Stabilize the diversion

6. CLEAR AND GRUB THE POND AREA

7. REMOVE TOPSOIL FROM THE POND AREA

a. Stockpile the soil in an approved locationb. Stabilize the stockpile area

8. FACILITY STAKEOUT

a. Stakeout centerline of embankment, outside and inside toe of slopes


6-53

9. CORE TRENCH/EMBANKMENT AREA

a. Arrange to meet the site reviewer to discuss location of core trenchb. If core trench is needed, determine where material will come from before trench is

opened.c. Make arrangements for de-watering of the core trench if necessaryd. Excavate for core trenche. Fill core trench with suitable material assuring proper compaction to existing ground

elevation

10. CONSTRUCT OUTFALL CHANNEL

a. Rock outlet protection with filter clothb. Remaining channel constructed and stabilized

11. INSTALL BARREL WITH ANTI-SEEP COLLARS

a. This should be done BEFORE any embankment workb. Prepare the bedding for the barrelc. Place barrel and anti-seep collars checking pipe graded. Watertight pipe connections to be checkede. Backfill of barrel with particular attention to the compaction requirements. All structural

backfill shall be completely free of rocks and other objectionable material

12. RISER PLACEMENT

a. Check riser structure for conformance to specificationsb. Check elevation of structurec. Set riser and pour concrete riser base

13. INSTALL ANY EROSION CONTROL STRUCTURES REQUIRED

14. CONSTRUCT REMAINING CORE AND EMBANKMENT

a. Most impervious material placed in core of embankmentb. Material should be checked and approved for suitabilityc. Compact the embankment according to specificationsd. Check UNSETTLED elevation and top width of embankmente. Stabilize embankment

15. DIVERT FLOWS INTO PIPE SYSTEM

16. CONSTRUCT EMERGENCY SPILLWAY

a. If earth spillway, construct in undisturbed groundb. Check elevation of control section and exit channel

17. INSTALL INFLOW CHANNELS

a. Stabilize according to plan including pipe outfalls into pond


6-54

18. COMPLETE EXCAVATION OF POND TO FINAL GRADE

19. VEGETATIVELY STABILIZE ALL DISTURBED AREAS

20. COMPLETE POND CONVERSION

a. Requires approval of inspector to convert from sediment to stormwater controlb. Properly de-water the pond in an approved mannerc. Remove accumulated sediment and restore pond to design grade. Complete final stabili-

zationd. Make any structural modifications to the riser for permanent function


6-55

APPENDIX 6-5

Construction ChecklistsInfiltration Practices

Basins (Appendix 6-5A)Trenches (Appendix 6-5B)Dry Wells (Appendix 6-5C)

Paving (Appendix 6-5D)Swales (Appendix 6-5E)


6-56

Infiltration Basin Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________



1. Pre-constructionSatisfactory Unsatisfactory

Runoff divertedArea stabilized

2. Excavation

Size and locationSide slope stableSoil PermeabilityGroundwater/Bedrock

3. Embankment

Cut-off trenchFill material

4. Final Excavation

Drainage area stabilizedSediment removed from facilityBasin floor tilledFacility stabilized

5. Final Inspection

Pretreatment facility in placeInlets/outletsSite stabilizationAccess to facility provided

Action to be taken:



Submit plan modifications as noted in written comments by _________________________Notice to Comply issued ____________Final inspection, project completed ____________


6-57

Infiltration Trench Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation


3. Filter Fabric Placement

Fabric specificationPlaced on bottom, sides, and top

4. Aggregate Material

Size as specifiedClean/washed materialPlaced properly

5. Observation Well

Pipe sizeRemovable cap/footplateInitial depth = _____ ft.

6. Final Inspection

Pretreatment facility in placeStabilizationOutlet

Action to be taken:No action necessary. Continue routine inspections ___________Correct noted site deficiencies by ________________________




6-58

Infiltration Drywell Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation






5. Observation Well/roof leader


6. Final Inspection

Pretreatment facility in placeDebris/gutter screensStabilizationOutlet



Submit plan modifications as noted in written comments by _________________________Notice to Comply issued ____________


6-59

Infiltration Paving Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation




4. Aggregate Base Course


5. Aggregate Filter Course

SizeClean/washed materialPlaced Properly

6. Porous Surface Course

Proper temperature/compaction

7 Final Inspection

Smooth Surface & TransitionTest sectionFinal stabilization





6-60

Infiltration Swale Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation


3. Check dams

DimensionsCompaction

4. Final Inspection

DimensionsCheck damsProper outletEffective stabilization





6-61

APPENDIX 6-6

Construction Checklistfor



6-62

Filtration Facility Construction Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________




Runoff divertedFacility area clearedFacility location staked out

2. Excavation

Size and locationSide slopes stableFoundation cleared of debrisFoundation area compacted

3. Structural Components

Dimensions and materialsForms adequately sizedConcrete meets standardsPrefabricated joints sealedUnderdrains (size, materials)

4. Completed Facility Components

24 hour water filled testContributing area stabilizedFilter material per specificationUnderdrains installed to grade

5. Final Inspection

DimensionsStructural ComponentsProper outletEffective site stabilization





6-63

APPENDIX 6-7




6-64

Biofiltration Construction Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________




Runoff divertedFacility area clearedFacility location staked outFacility not in heavily shaded area

2. Excavation

Size and locationLateral slopes completely levelLongitudinal slopes within design range

3. Check dams and Level Spreaders

Dimensions, spacing, and materialsCompactionLevel spreaders are completely level


Inlets and outlets installed correctlyFlow bypasses installed correctlyPretreatment devices installedCurb cuts installed per plans

5. Vegetation

Complies with planting specs.Topsoil adequate in composition and placementAdequate erosion control measures in place

4. Final Inspection

DimensionsCheck dams and level spreadersProper outletEffective stand of vegetation and stabilizationConstruction generated sediments removed




STORMWATER MANAGEMENT SYSTEMINSPECTION FORMS

FROM:OPERATION, MAINTENANCE, AND MANAGEMENT OF

STORMWATER MANAGEMENT SYSTEMS

PUBLISHED BY:WATERSHED MANAGEMENT INSTITUTE, INC.

In cooperation with:Office of Water

U. S. Environmental Protection AgencyWashington D. C

Watershed Management Institute410 White Oak Drive

Crawfordville, Florida 32327850/926-5310

Fax: 850/926-1534

Watershed Management InstituteP.O. Box 14

Ingleside, Maryland 21644410/758-2731

Fax: 410/758-0386


F-2

The handbook Operation, Maintenance, and Management of Stormwater ManagementSystems was produced by the Watershed Management Institute, Inc. in cooperationwith the United States Environmental Protection Agency, Office of Water, throughCooperative Agreement CX823621-01-0. The contents do not necessarily reflect theviews or policies of the Environmental Protection Agency, nor does mention of tradenames or commercial products constitute endorsement or recommendation for use.

STORMWATER MANAGEMENT SYSTEMINSPECTION FORMS

From CHAPTER 6: CONSTRUCTION INSPECTION of Operation, Maintenance,and Management of Stormwater Management Systems

Appendices - Construction Inspection Forms F-36-1. Preconstruction Inspection Meeting Topics F-46-2. General Site Inspection and Notice to Comply F-76-3. Sediment/Stormwater Basin Construction Checklist F-106-4. Sediment/Stormwater Pond Typical Sequence of F-15

Construction6-5. Construction Checklists for Infiltration Practices: F-196-5A. Basins F-206-5B. Trenches F-216-5C. Dry Wells F-226-5D. Pervious Paving F-236-5E. Swales F-246-6. Construction Checklist for Filtration Practices F-256-7. Construction Checklist for Biofiltration Practices F-27

From CHAPTER 7: INSPECTION AND MAINTENANCE AFTER CONSTRUCTION ofOperation, Maintenance, and Management of Stormwater Management Systems

Appendices - OMM Forms for Stormwater Management Practices7-1. OMM Inspection Checklist for Ponds F-307-2 OMM Inspection Checklist for Infiltration Practices F-347-2A. OMM Inspection Checklist for Infiltration Basins F-357-2B. OMM Inspection Checklist for Infiltration Trenches F-377-2C. OMM Inspection Checklist for Dry Wells F-397-2D. OMM Inspection Checklist for Pervious Pavement F-407-2E. OMM Inspection Checklist for Swales F-417-3. OMM Inspection Checklist for Filtration Practices F-427-4. OMM Inspection Checklist for Biofiltration Practices F-45

INSPECTION FORMS FOR STORMWATER MANAGEMENT SYSTEMS

F-3

APPENDICESFROM CHAPTER 6

Construction Inspection Formsfor

Stormwater ManagementPractices


F-4

APPENDIX 6-1

Preconstruction InspectionMeeting Topics Form


F-5

State of New JerseyDepartment of Environmental Protection

Stormwater Management Facility Maintenance Manual

Example Preconstruction Meeting Topics

A. GENERAL INFORMATION

1. Attendance2. Purpose of project and background information3. Emergency telephone numbers4. Construction photograph requirements5. Project sign requirements6. Starting date7. Review of contract documents, including insurance certifications, bonds and subcontrac-

tors documents8. Field office requirements9. Responsibility for notification of affected property owners and residents10. Chain of command for communications and correspondence11. Construction schedules12. Key personnel and their degree of involvement in the project (inspector, owner, engi-

neer, agencies, etc.)

B. POLICE AND FIRE DEPARTMENT CONCERNS

1. Traffic control2. Barricades and signs conforming to the uniform manual3. Noise ordinance considerations4. Working hours, including weekend and holidays5. Vandalism and preventative measures6. Flagmen and traffic control officers7. Equipment storage and vehicle parking8. Emergency vehicle access9. Underground tank locations and precautionary construction procedures10. Storage and use of hazardous materials

C. UTILITIES

1. Utility locations and mark-outs2. Coordination of utility relocations3. Emergency phone numbers of utility companies

D. FUNDING AND PAYMENTS

1. Funding sources and availability2. Procedures and dates for payment estimates3. Dates for payments to contractor4. Breakdown of lump sum items for partial payment5. Policy for payment for materials on site at the close of a payment period6. Retained monies during and after construction


F-6

7. Requirements of funding agencies

E. CHANGE ORDERS AND EXTRA CLAIMS

1. Requirements for additional work and submittal of change orders2. Procedures and schedule for review and recommendations of change orders3. Procedures for negotiating extra claims and change orders

F. CONSTRUCTION ACCESS AND EASEMENTS

1. Easement locations and maps2. Responsibility for locating and staking easements3. Available survey data for the site4. Access requirements and staging areas5. Easement restrictions and restoration requirements

G. CONSTRUCTION DETAILS

1. Unique or complex aspects of the project2. Testing laboratories and sampling procedures3. Cold and hot weather protection measures4. Blasting requirements5. Dump site location for construction related materials6. Shop drawing requirements and review procedures7. Specific construction techniques and procedures8. Review of technical section of the specifications

H. PERMITS

1. Status of all required federal, state, and local permits2. Permit restrictions and conditions3. Start-of-work notifications


F-7

APPENDIX 6-2

General Site Inspectionand

Notice to Comply Forms


F-8

Construction Inspection Report Form(adapted from State of Delaware Sediment and Stormwater Program)

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________


Weather Conditions _____________________________


Site Conditions:

acceptable ________Unacceptable ________In compliance with approved plan _________Approved plan is adequate for the site _________

Written Comments:

_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Action to be taken:



Submit plan modifications as noted in written comments by _________________________Notice to Comply issued ____________Final inspection, project completed ____________Other ___________________________________________________________________

_________________________ _________________________Received by Inspector

I acknowledge receipt of this inspection Questions or comments regarding this inspectionreport. My signature does not imply agreement report should be directed to the appropriateor disagreement with its content inspection agency the appropriate address and

phone number.



F-9

Notice to Comply Inspection Report Form(adapted from State of Delaware Sediment and Stormwater Program)

Date ____________

To: _________________________________________Address: ____________________________________________________________________________________________________________________________________________________

Project/Site/Contract Name _______________________________________________________

An inspection of the above referenced project on __________________________(Date) revealedthat the site is not in compliance with the approved Sediment Control and Stormwater Manage-ment Plan, approved Plan amendments, Law, or Regulations, and the following violations exist:

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Notice is hereby given that the above violations shall be corrected in accordance with the ap-proved Sediment Control and Stormwater Management Plan, approved Plan amendments, Law, orRegulations on or before ______________________________ (Date). The site will be rein-spected at that time to determine if the site has been brought into compliance with the approvedPlan, approved Plan amendments, Law, or Regulations.

Failure to comply with this notice will result in the initiation of legal action by the Departmentin order to bring the site into compliance with the approved Plan, approved Plan amend-ments, Law, or Regulations.

_____________________________ _______________________________Received by Inspector

I hereby acknowledge receipt of this noticeto comply. My signature does not implyagreement or disagreement with its content

Questions or comments regarding this inspection report should be directed to the appropriate inspectionagency at the appropriate address and phone number



F-10

APPENDIX 6-3

Sediment/Stormwater ManagementBasin Construction Inspection

Checklist


F-11

Sediment/Stormwater Management Basin Construction ChecklistFor Permanent structures per Delaware NRCS Pond Code 378 and Delaware

Sediment and Stormwater Regulations(Developed by Randy Greer, Environmental Engineer)

KEY PROJECT INFORMATION

_ __ Item meets standard Project ID: __________________ __ Item not acceptable Contractor: _________________N/A_ Item not applicable Inspector: __________________C___ Item requires engineer’s certification Date(s): __________________

I. Materials and Equipment

_____ Pipe and appurtenances on-site prior to construction and dimensions checked._____ 1. Material (including protective coating, if specified)_____ 2. Diameter_____ 3. Dimensions of metal riser or pre-cast concrete outlet structure_____ 4. Required dimensions between water control structures (orifices, weirs,

etc.) are in accordance with approved plans_____ 5. Barrel stub for prefabricated pipe structures at proper angle for design

barrel slope_____ 6. Number and dimensions of prefabricated anti-seep collars_____ 7. Watertight connectors and gaskets_____ 8. Outlet drain valve

_____ Appropriate compaction equipment available, including hand and small powertamps

_____ Project benchmark near pond site_____ Equipment for temporary de-watering

II. Subgrade Preparation

_____ Area beneath embankment stripped of all vegetation, topsoil, and organic matter_____ Cut-off trench excavated a minimum of 4 feet below subgrade and minimum 4 feet

below proposed pipe invert, with side slopes no steeper than 1:1_____ Impervious material used to backfill cut-off trench

III. Pipe Spillway Installation

_____ Method of installation detailed on plans

A. Bed preparation_____ Installation trench excavated with 1:1 side slopes_____ Stable, uniform, dry subgrade of relatively impervious material (If subgrade

is wet, contractor shall have defined steps before proceeding with installa-tion)

_____ Invert at proper elevation and grade


F-12

B. Pipe placement_____ Metal/Plastic pipe

_____ 1. Watertight connectors and gaskets properly installed_____ 2. Anti-seep collars properly spaced and having watertight connec-

tions to pipe_____ 3. Backfill placed and tamped by hand under “haunches” of pipe_____ 4. Remaining backfill placed in max. 8" lifts using small power tamp-

ing equipment until 2 feet cover over pipe is reached_____ Concrete pipe

_____ 1. Pipe set on blocks or concrete slab for pouring of low cradle_____ 2. Pipe installed with rubber gasket joints with no spalling in gasket

interface area_____ 3. Excavation for lower half of anti-seep collar(s) with reinforcing

steel set_____ 4. Entire area where anti-seep collar(s) will come in contact with pipe

coated with mastic or other approved waterproof sealant_____ 5. Low cradle and bottom half of anti-seep collar installed as mono-

lithic pour and of an approved mix_____ 6. Upper half of anti-seep collar(s) formed with reinforcing steel set_____ 7. Concrete for collar of an approved mix and vibrated into place.

(Protected from freezing while curing, if necessary)_____ 8. Forms stripped and collar inspected for honeycomb prior to back-

filling. Parge if necessaryC. Backfilling

_____ Fill placed in maximum 8" lifts_____ Backfill taken minimum 2 feet above top of anti-seep collar elevation

before traversing with heavy equipment

IV. Riser/Outlet Structure Installation

A. Metal riser_____ Riser base excavated or formed on stable subgrade to design dimensions_____ Embedded section of aluminum or aluminized pipe to be painted with zinc

chromate or equivalent on inside and outside surfaces_____ Set on blocks to design elevations and plumbed_____ Reinforcing bars placed at right angles and projecting into sides of riser_____ Concrete poured so as to fill inside of riser to invert of barrel

B. Pre-cast concrete structure_____ Dry and stable subgrade_____ Riser base set to design elevation_____ If more than one section, no spalling in gasket interface area; gasket or

approved caulking material placed securely_____ Watertight and structurally sound collar or gasket joint where structure

connects to pipe spillwayC. Poured concrete structure

_____ Footing excavated or formed on stable subgrade, to design dimensions withreinforcing steel set

_____ Structure formed to design dimensions, with reinforcing steel set as per plan_____ Concrete of an approved mix and vibrated into place. (Protected from freez-

ing while curing, if necessary)_____ Forms stripped and structure inspected for “honeycomb” prior to backfilling.

Parge if necessary


F-13

V. Embankment Construction

A. Fill material_____ Soil engineer’s test_____ Visual test by inspector

B. Compaction_____ Soil engineer’s test_____ Visual test by inspector

C. Embankment_____ Fill placed in maximum 8" lifts and compacted with appropriate equipment_____ Constructed to design cross-section, side slopes and top width_____ Constructed to design elevation plus allowance for settlement

VI. Impounded Area Construction

_____ Excavated/graded to design contours and side slopes_____ Inlet pipes have adequate outfall protection_____ Forebay(s)_____ Wet pond requirements

_____ 1. 10 feet reverse slope bench one foot above normal pool elevation_____ 2. 10 feet wide level bench one foot below normal pool elevation

VII. Earth Emergency Spillway Construction

_____ Spillway located in cut or structurally stabilized with riprap, gabions, concrete, etc._____ Excavated to proper cross-section, side slopes and bottom width_____ Entrance channel, crest, and exit channel constructed to design grades and eleva-

tions

VIII. Outlet Protection

A. End section_____ Securely in place and properly backfilled

B. Endwall_____ Footing excavated or formed on stable subgrade, to design dimensions and

reinforcing steel set, if specified_____ Endwall formed to design dimensions with reinforcing steel set as per plan_____ Concrete of an approved mix and vibrated into place. (Protected from freez-

ing, if necessary_____ Forms stripped and structure inspected for “honeycomb” prior to backfilling.

Parge if necessaryC. Riprap apron/channel

_____ Apron/channel excavated to design cross-section with proper transition toexisting ground

_____ Filter fabric in place_____ Stone sized as per plan and uniformly placed at the thickness specified


F-14

IX. Vegetative Stabilization

_____ Approved seed mixture or sod_____ Proper surface preparation and required soil amendments_____ Excelsior mat or other stabilization materials, as per plan

X. Miscellaneous

_____ Toe drain_____ Temporary dewatering device installed as per plan with appropriate fabric, stone

size and perforations if included_____ Drain for ponds having a permanent pool_____ Trash rack/anti-vortex device secured to outlet structure_____ Trash protection for low flow pipes, orifices, etc._____ Fencing (when required)_____ Access road_____ Set aside area for clean-out maintenance


F-15

APPENDIX 6-4

Sediment/Stormwater PondTypical Sequence of Construction

forEmbankment Ponds with

Riser/Barrel Outlet Structuresfor

Developers and Contractors


F-16

Stormwater/Sediment PondTypical Sequence of Construction for Embankment Ponds

with Riser/Barrel Outlet Structures forDevelopers and Contractors

(Developed by Randy Greer, Environmental EngineerDelaware Department of Natural Resources and Environmental Control

Sediment and Stormwater Program)

1. NOTIFY PLAN REVIEW/CONSTRUCTION REVIEW AGENCY AS REQUIRED

a. Arrange the preconstruction meetingb. Clear up any questions regarding the approved plan

2. PRE-CONSTRUCTION MEETING WITH CONSTRUCTION REVIEW AGENCY

a. Review the site plan and layout and discuss any problems or changes needed to theplan

b. Obtain approvals for the plan changes from the appropriate inspection or plan reviewagency

c. Discuss the stages of construction which notification to the construction review agency isneeded

3. SITE LAYOUT

a. Make sure site layout agrees with the planb. Check elevation of the proposed outfall structurec. Physically mark any areas not to be disturbed, such as limit of disturbance, wetlands,

property lines, etc.

4. INSTALL PERIMETER EROSION AND SEDIMENT CONTROLS

a. Sediment controls will be needed at the downstream perimeter during the clearing andgrubbing for the pond wherever sediment may leave the site.

5. INSTALL TEMPORARY CHANNEL DIVERSION

a. Divert clean water flow away from pond areab. Stabilize the diversion

6. CLEAR AND GRUB THE POND AREA

7. REMOVE TOPSOIL FROM THE POND AREA

a. Stockpile the soil in an approved locationb. Stabilize the stockpile area

8. FACILITY STAKEOUT

a. Stakeout centerline of embankment, outside and inside toe of slopes


F-17

9. CORE TRENCH/EMBANKMENT AREA

a. Arrange to meet the site reviewer to discuss location of core trenchb. If core trench is needed, determine where material will come from before trench is

opened.c. Make arrangements for de-watering of the core trench if necessaryd. Excavate for core trenche. Fill core trench with suitable material assuring proper compaction to existing ground

elevation

10. CONSTRUCT OUTFALL CHANNEL

a. Rock outlet protection with filter clothb. Remaining channel constructed and stabilized

11. INSTALL BARREL WITH ANTI-SEEP COLLARS

a. This should be done BEFORE any embankment workb. Prepare the bedding for the barrelc. Place barrel and anti-seep collars checking pipe graded. Watertight pipe connections to be checkede. Backfill of barrel with particular attention to the compaction requirements. All structural

backfill shall be completely free of rocks and other objectionable material

12. RISER PLACEMENT

a. Check riser structure for conformance to specificationsb. Check elevation of structurec. Set riser and pour concrete riser base

13. INSTALL ANY EROSION CONTROL STRUCTURES REQUIRED

14. CONSTRUCT REMAINING CORE AND EMBANKMENT

a. Most impervious material placed in core of embankmentb. Material should be checked and approved for suitabilityc. Compact the embankment according to specificationsd. Check UNSETTLED elevation and top width of embankmente. Stabilize embankment

15. DIVERT FLOWS INTO PIPE SYSTEM

16. CONSTRUCT EMERGENCY SPILLWAY

a. If earth spillway, construct in undisturbed groundb. Check elevation of control section and exit channel

17. INSTALL INFLOW CHANNELS

a. Stabilize according to plan including pipe outfalls into pond


F-18

18. COMPLETE EXCAVATION OF POND TO FINAL GRADE

19. VEGETATIVELY STABILIZE ALL DISTURBED AREAS

20. COMPLETE POND CONVERSION

a. Requires approval of inspector to convert from sediment to stormwater controlb. Properly de-water the pond in an approved mannerc. Remove accumulated sediment and restore pond to design grade. Complete final stabili-

zationd. Make any structural modifications to the riser for permanent function


F-19

APPENDIX 6-5

Construction Checklistsfor Infiltration Practices




F-20

Infiltration Basin Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation


3. Embankment

Cut-off trenchFill material

4. Final Excavation

Drainage area stabilizedSediment removed from facilityBasin floor tilledFacility stabilized

5. Final Inspection

Pretreatment facility in placeInlets/outletsSite stabilizationAccess to facility provided

Action to be taken:





F-21

Infiltration Trench Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation






5. Observation Well


6. Final Inspection

Pretreatment facility in placeStabilizationOutlet





F-22

Infiltration Drywell Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation






5. Observation Well/roof leader


6. Final Inspection

Pretreatment facility in placeDebris/gutter screensStabilizationOutlet





F-23

Infiltration Paving Construction Inspection Report FormAdapted from the State of Maryland Inspector’s Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation




4. Aggregate Base Course


5. Aggregate Filter Course

SizeClean/washed materialPlaced Properly

6. Porous Surface Course

Proper temperature/compaction

7. Final Inspection

Smooth Surface & TransitionTest sectionFinal stabilization



Submit plan modifications as noted in written comments by _________________________Notice to Comply issued ____________ Final inspection, project completed ____________


F-24

Infiltration Swale Construction Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________





2. Excavation


3. Check dams

DimensionsCompaction

4. Final Inspection

DimensionsCheck damsProper outletEffective stabilization





F-25

APPENDIX 6-6




F-26

Filtration Facility Construction Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________




Runoff divertedFacility area clearedFacility location staked out

2. Excavation

Size and locationSide slopes stableFoundation cleared of debrisFoundation area compacted


Dimensions and materialsForms adequately sizedConcrete meets standardsPrefabricated joints sealedUnderdrains (size, materials)

4. Completed Facility Components

24 hour water filled testContributing area stabilizedFilter material per specificationUnderdrains installed to grade

5. Final Inspection

DimensionsStructural ComponentsProper outletEffective site stabilization





F-27

APPENDIX 6-7




F-28

Biofiltration Construction Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________




Runoff divertedFacility area clearedFacility location staked outFacility not in heavily shaded area

2. Excavation

Size and locationLateral slopes completely levelLongitudinal slopes within design range

3. Check dams and Level Spreaders

Dimensions, spacing, and materialsCompactionLevel spreaders are completely level


Inlets and outlets installed correctlyFlow bypasses installed correctlyPretreatment devices installedCurb cuts installed per plans

5. Vegetation

Complies with planting specs.Topsoil adequate in composition and placementAdequate erosion control measures in place

4. Final Inspection

DimensionsCheck dams and level spreadersProper outletEffective stand of vegetation and stabilizationConstruction generated sediments removed





F-29

APPENDICESFROM CHAPTER 7

Operation, Maintenance, and ManagementInspection Forms

forStormwater Management

Practices


F-30

APPENDIX 7-1

Operation, Maintenance, andManagement

Inspection Checklistfor Ponds


F-31

Inspection Frequency Key A=Annual, M=Monthly, S=After major storm

Operation and Maintenance Inspection Report for Stormwater Management Ponds(Adapted from Anne Arundel County, Maryland)

Inspector Name __________________________ Community _________________________Inspection Date __________________________ Address _________________________Stormwater Pond _________________________

Normal Pool ______ _________________________Normally Dry ______ Watershed _________________________

Items inspected Checked Maintenance Needed Inspection RemarksYes No Yes No Frequency

I, Pond components

A. Embankment andEmergency spillway A,S1. Vegetation and ground

Cover adequate2. Embankment erosion3. Animal burrows4. Unauthorized plantings5. Cracking, bulging, or

sliding of dama. Upstream faceb. Downstream facec. At or beyond toe

UpstreamDownstream

d. Emergency spillway6. Pond, toe & chimney

drains clear and functioning7. Seeps/leaks on

downstream face8. Slope protection or

riprap failures9. Vertical and horizontal

alignment of top of dam asper "As-Built" plans

10. Emergency spillway clearof obstructions and debris

11. Other (specify)B. Riser and principal spillway A

Type: Reinforced concrete ___ Corrugated pipe ___ Masonry ___

1. Low flow orifice obstructed2. Low flow trash rack

a. Debris removal necessaryb. Corrosion control

3. Weir trash rack maintenancea. Debris removal necessaryb. Corrosion control


F-32


4. Excessive sedimentaccumulation inside riser

5. Concrete/Masonry conditionRiser and barrelsa. Cracks or displacementb. Minor spalling (<1")c. Major spalling

(rebars exposed)d. Joint failurese. Water tightness

6. Metal pipe condition7. Control valve

a. Operational/exercisedb. Chained and locked

8. Pond drain valvea. Operational/exercisedb. Chained and locked

9. Outfall channels functioning10. Other (specify)

C. Permanent pool (wet ponds) M1. Undesirable vegetative

growth2. Floating or floatable debris

removal required3. Visible pollution4. Shoreline problems5. Other (specify)

D. Sediment forebays1. Sedimentation noted2. Sediment cleanout when

depth < 50% designdepth

E. Dry pond areas M1. Vegetation adequate2. Undesirable vegetative

growth3. Undesirable woody

vegetation4. Low flow channels clear

of obstructions5. Standing water or wet spots6. Sediment and/or trash

accumulation7. Other (specify)

F. Condition of outfalls into pond A,S1. Riprap failures2. Slope erosion3. Storm drain pipes4. Endwalls/headwalls5. Other (specify)

G. Other M1. Encroachments on pond or

easement areaInspection Frequency Key A=Annual, M=Monthly, S=After major storm


F-33


2. Complaints from residents(describe on back)

3. Aestheticsa. grass mowing requiredb. graffiti removal neededc. Other (specify)

4. Any public hazards (specify)5. Maintenance access

H. Constructed wetland areas A1. Vegetation healthy and

growing2. Evidence of invasive species3. Excessive sedimentation in

wetland area


II. Summary

1. Inspectors Remarks: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Overall condition of Facility (Check one)_____ Acceptable_____ Unacceptable

3. Dates any maintenance must be completed by:

________________________________________________________________________________________________________________________________________________________________________________________________


F-34

APPENDIX 7-2


Inspection Checklistsfor Infiltration Practices:




F-35

Infiltration Basin Maintenance Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________

Individual Conducting the Inspection _______________________ "As Built" Plans available Y/N

Inspection frequency shown in parentheses after item being considered1. Debris cleanout (Monthly)

Satisfactory UnsatisfactoryBasin bottom clear of debrisInlet clear of debrisOutlet clear of debrisEmergency spillway clear of debris

2. Sediment traps or forebays (Annual)

Obviously trapping sedimentgreater than 50% of storage volume remaining

3. Vegetation (Monthly)

mowing done when neededFertilized per specificationsNo evidence of erosion

4. Dewatering (Monthly)

Basin dewaters between storms

5. Sediment cleanout of basin (Annual)

No evidence of sedimentation in basinSediment accumulation does not yet require cleanout

6. Inlets (Annual)

Good conditionNo evidence of erosion

7. Outlets/overflow spillway (Annual, After Major Storm)

Good condition, no need for repairNo evidence of erosion

8. Structural repairs (Annual, After Major Storm)

Embankment in good repairSide slopes are stableNo evidence of erosion

Inspection Frequency Key Annual, Monthly, After major storm


F-36

Satisfactory Unsatisfactory

9. Fences/access repairs (Annual)

Fences in good conditionNo damage which would allow undesired entryAccess point in good conditionLocks and gate function adequate


Action to be taken:

If any of the answers to the above items are checked unsatisfactory, a time frame shall be estab-lished for their correction or repair

No action necessary. Continue routine inspections ___________Correct noted facility deficiencies by ______________________

Facility repairs were indicated and completed. Site reinspection is necessary to verify corrections orimprovements.

Site reinspection accomplished on ________________________

Site reinspection was satisfactory. Next routine inspection is scheduled for approximately:

________________________________

____________________________________ Signature of Inspector


F-37

Infiltration Trench Maintenance Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________



Satisfactory UnsatisfactoryTrench surface clear of debrisInlet areas clear of debrisInflow pipes clear of debrisOverflow spillway clear of debris

2. Sediment traps, forebays, or pretreatment swales (Annual)





Trench dewaters between storms

5. Sediment cleanout of trench (Annual)

No evidence of sedimentation in trenchSediment accumulation does not yet require cleanout

6. Inlets (Annual)


7. Outlets/overflow spillway (Annual)




F-38


8. Aggregate repairs (Annual)

Surface of aggregate cleanTop layer of stone does not need replacementTrench does not need rehabilitation

9. Vegetated surface (Monthly)

No evidence of erosionPerforated inlet functioning adequatelyWater does not stand on vegetative surfaceGood vegetative cover exists


Action to be taken:






________________________________



F-39

Infiltration Dry Well Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________



Satisfactory UnsatisfactoryRoof drains and downspouts clean

2. Vegetation on top of dry well (Monthly)



Dry well dewaters between storms

4. Inlets (Annual)

Good condition of down spoutsNo evidence of deteriorationRoof gutters drain correctly into dry well



Inspection Frequency Key Annual, Monthly, After major stormAction to be taken:






________________________________ ____________________________________ Signature of Inspector


F-40

Infiltration Paving Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________


Inspection frequency shown in parentheses after item being considered1. Debris on infiltration paving parking area (Monthly)

Satisfactory UnsatisfactoryPaving area clean of debris

2. Vegetation (any buffer areas or pervious areas in drainage area)(Monthly)



Infiltration paving dewaters between storms

4. Sediments (Monthly)

Area clean of sedimentsArea vacuum swept on a periodic basis

5. Structural condition (Annual)

No evidence of surface deteriorationNo evidence of rutting or spalling









F-41

Infiltration Swale Well Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________



Satisfactory UnsatisfactorySwales and contributing areas clean of debris


mowing done when neededFertilized per specificationsNo evidence of erosionMinimum mowing depth not exceeded


Swale dewaters between storms

4. Check dams or energy dissipators (Annual, After Major Storm)

No evidence of flow going around structuresNo evidence of erosion at downstream toe

5. Sediment deposition (Annual)

Swale clean of sediments




If any of the answers to the above items are checked unsatisfactory, a time frame shall be established fortheir correction or repair


Facility repairs were indicated and completed. Site reinspection is necessary to verify corrections.





F-42

APPENDIX 7-3

Operation, Maintenance andManagement

Inspection Checklistfor



F-43

Filtration Facility Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________


Warning: If filtration facility has a watertight cover; be careful regarding the possibility offlammable gases within the facility. Care should be taken lighting a match or smoking whileinspecting facilities that are not vented.


Satisfactory UnsatisfactoryContributing areas clean of debrisFiltration facility clean of debrisInlets and outlets clear of debris


Contributing drainage area stabilizedNo evidence of erosionArea mowed and clippings removed

3. Oil and grease (Monthly)

No evidence of filter surface cloggingActivities in drainage area minimize oil & grease entry

4. Water retention where required (Monthly)

Water holding chambers at normal poolNo evidence of leakage


Filtration chamber clean of sedimentsWater chambers not more than 1/2 full of sediments

6. Structural components (Annual)

No evidence of structural deteriorationAny grates are in good conditionNo evidence of spalling or cracking of structural parts


Good condition, no need for repairNo evidence of erosion (if draining into a natural channel)



F-44


8. Overall function of facility (Annual)

No evidence of flow bypassing facilityNo noticeable odors outside of facility


Action to be taken:



Facility repairs were indicated and completed. Site reinspection is necessary to verify correctionsor repairs.





F-45

APPENDIX 7-4

Operation, Maintenance andManagement




F-46

Biofiltration Facility Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________

Individual Conducting the Inspection ______________________ "As Built" Plans available Y/N


Satisfactory UnsatisfactoryBiofilters and contributing areas clean of debrisNo dumping of yard wastes into biofilterLitter (branches, etc.) have been removed


Plant height not less than design water depthFertilized per specificationsNo evidence of erosionGrass height not greater than 6 inchesIs plant composition according to approved plansNo placement of inappropriate plants


Biofilter dewaters between stormsNo evidence of standing water

4. Check dams/energy dissipators/sumps (Annual, After Major Storm)

No evidence of sediment buildupSumps should not be more than 50% full of sedimentNo evidence of erosion at downstream toe of drop structures


Swale clean of sedimentsSediments should not be > than 20% of swale design depth


Good condition, no need for repairNo evidence of erosionNo evidence of any blockages

7. Integrity of biofilter (Annual)

Biofilter has not been blocked or filled inappropriately



F-47

Action to be taken:







Broken up outlet structure.Having the grate on top doesn't really

provide any factor of safety.

Chapter 7Inspection and Maintenance

After Constructionand management.

As discussed in Chapter 5, the owners ofstormwater management systems must beeducated to understand the importance of thefacility, and their obligations to assure its con-tinued function. A case study illustrates theimportance of education in assuring properOMM. One of the authors conducted a sitevisit to an extended dry detention system thatserves a residential subdivision. The facilityhas a perennial or dry weather flow through itwhich it passes through an orifice in the out-let structure. During the winter months, chil-dren in the subdivision plugged up the ori-fices in the outlet structure so water wouldback up in the pond. This ponding let themice skate when temperatures allowed. As aresult, when spring came water could not dis-charge properly, water depths increased, andall of the flow was passing through the emer-gency spillway, which was intended to only

7 - 1

1. OVERVIEW

Once construction is satisfactorily completed,the long term assurance of adequate facilityperformance begins. Stormwater manage-ment systems are expected to perform theirstormwater quality and quantity control func-tions as long as the land use they serve ex-ists. Failure to maintain these systems cancreate the following adverse impacts:

• increased discharge of pollutants down-stream.

• increased risk of flooding downstream.• increased downstream channel instabil-

ity, which increases sediment loadingsand reduces habitat for aquatic organ-isms.

• potential loss of life and property, result-ing from catastrophic failure of the facil-ity.

• aesthetic or nuisance problems, such asmosquitoes or reduced property value,due to a degraded facility appearance.

All of these adverse impacts can be avoidedthrough proper and timely maintenance ofstormwater management facilities. A majorconcern created by these impacts is the gen-eral public's expectations about their qualityof life which is provided, in part, by construc-tion of stormwater management systems. In-adequate maintenance means the generalpublic may have a false sense of security. Ifwe are not going to adequately addressthe maintenance issues of stormwatermanagement system implementation, thefacilities should not be constructed in thefirst place. The most common cause ofstormwater system failure is the lack of ad-equate and proper operation, maintenance,


7-2

convey infrequent emergency flows. As a re-sult, the emergency spillway eroded and theentire pond embankment failed. This was sub-sequently repaired at considerable county ex-pense. This problem could have beenavoided if members of the community hadknown why that facility was built in theircommunity, and knew the importance ofall facility components working properly.

Good design and construction can reducesubsequent maintenance needs and costs,but they cannot eliminate the need for main-tenance altogether. Maintenance will alwaysbe needed. It will require a long term com-mitment of time, money, personnel, andequipment by the individuals responsiblefor operation and maintenance. At thesame time, assuring maintenance repre-sents a long term commitment of publicagency staff. They are needed to conductmaintenance inspections to ensure thatthe responsible maintenance entity is ad-equately performing its responsibilities.

1.1 Intended Readers

This Chapter is equally important to:

• Agency maintenance inspectors,••••• Facility owners, and••••• Facility maintenance personnel.

In addition, individuals responsible for facilitydesign and review should be aware of theequipment used for maintenance and normalmaintenance activities. This awareness willenable them to select stormwater manage-ment system locations and develop designsthat will facilitate, rather than hinder, mainte-nance efforts.

2. HOW MAINTENANCE CAN REDUCEADVERSE DOWNSTREAM IMPACTS

It will be helpful to further discuss the adverseimpacts of maintenance neglect mentioned inthe overview. Understanding the impactscaused by inadequate or improper systemOMM is very important. While some of theseimpacts may be obvious, an expanded dis-cussion may lead to a greater understandingby all individuals responsible, in some way,for stormwater system operation, mainte-nance, and management.

2.1. Increased Discharge of PollutantsDownstream

Stormwater management systems treatstormwater runoff through a number of pro-cesses:

• Gravity settling of particulate materials.This is normally achieved by increas-ing the detention time of water in BMPs,so that the particle settling velocity isgreater than the flow velocity of theparticle towards the facility outlet.

• Filtering of particulate material by veg-etation or media mixtures, such as soil,sand, gravel, compost, or other mate-rials.

• Adsorption of pollutants onto or absorp-tion into organic material.

Any reduction in the volume or area of stor-age reduces detention time or effective areaof flow. This will decrease the ability of theBMP to remove pollutants. For stormwatermanagement facilities that are designed forstormwater treatment only, lack of mainte-nance may negate any benefits derived fromits construction. In these situations, the lackof maintenance means that the original invest-ment of funds for stormwater treatment is, to

CHAPTER 7 Inspection After Construction

7-3

a large extent, wasted.

2.2. Increased Risk of DownstreamFlooding

In addition to water quality reductions, thereis an increased risk of flooding downstream ifthe necessary storage volumes are not avail-able when they are needed. Sediments de-posited on the bottom of ponds gradually ac-cumulate and take up volume that is neededduring flood events. Many times downstreamland use decisions are made with the knowl-edge that upstream stormwater managementsystems reduce (or prevent increases in)floodplain elevations downstream. Develop-ment may be allowed downstream in areasprotected from flooding by the upstream fa-cilities. If these facilities are not maintained,a false sense of security exists within thecommunity which could eventually resultin significant loss of property and evenloss of lives.

Downstream flooding is directly related to thevolume of water traveling through a water-shed, together with the time needed for thewater to flow through it. With respect to flood-ing concerns, stormwater management pro-grams generally do not attempt to significantlyreduce the total volume of water travelingdownstream. Even if infiltration practices areused, they sometimes are sized only forstormwater treatment. They do not have ad-equate volume available to significantly re-duce runoff volumes from larger storms suchas the 50 or 100 year event. Instead,stormwater systems modify the time neededfor water to travel through a watershed. Whilethe volume is the same, stormwater systemsdetain runoff, altering the timing of the deliv-ery of water. The end result is that the in-creased volume of water traveling through thewatershed flows for longer periods of timeeven though the peak discharges are reduced.

2.3 Increased Downstream ChannelInstability

Increased downstream channel instability,which increases sediment loadings and re-duces habitat for aquatic organisms, may re-sult from a lack of facility maintenance.Stormwater management facilities, dependingon the local, regional, or state program, mayhave channel erosion prevention as a majorprogram goal. In these situations, inadequatestormwater system maintenance may notachieve stated goals or may actually exacer-bate channel erosion scour problems. Thismay occur because of increased stormwaterdischarges from sediment filled ponds, or in-creased volumes of stormwater being dis-charged from clogged infiltration practices.

With respect to downstream habitat, thescouring of channel boundaries increaseschannel sedimentation which, in turn, reducesavailable habitat and smothers bottom dwell-ing organisms. Beside sediments resultingfrom channel erosion, improper maintenanceof a stormwater management system may re-sult in the release of eroded sediments fromthe facility itself, or from sediments in up-stream contributing drainage areas travelingthrough the facility and then downstream.

Increased channel erosion in anurban environment.


7-4

2.5. Aesthetic or Nuisance Problems

Aesthetic problems are generally related tothe appearance of a stormwater managementsystem. Landscaping issues such as grassmowing, tree or shrub appearance, and littercontrol are all aesthetic issues. They gener-ally are not a serious concern with respect toproper functioning of a facility. However, fail-ure to take corrective actions on small prob-lems can eventually create a significant facil-ity performance problem.

One common problem frequently seen aroundstormwater management ponds is the dump-ing of grass cuttings along the pond edge. Thecuttings can clog outlets or increase nutrientloadings resulting in increased algae blooms.Another important aesthetic maintenance taskis the management of aquatic vegetation inwet detention littoral zones or constructedwetlands. Often the vegetation will changeover time, sometimes beneficially and some-times not. The landowner must consider theaesthetics of basin maintenance initially andduring the lifespan of the basin.

Mosquitoes, stagnant water, erosion aroundthe shoreline, or vandalism are examples ofnuisance problems. Nuisance problems alsorepresent little structural concern and they arenot considered a safety issue. However, nui-

Erosion around the outlet structure of a stormwater management pond.

2.4. Potential Loss of Life and Property

Interwoven with the increased risk of floodingand channel instability is the issue of loss oflife and property. This can result from a cata-strophic occurrence, such as the sudden fail-ure of a pond embankment, or through thecreation of a hazardous condition such assteep stream banks or water flowing deeperthan expected.

Safety must be the single most importantpurpose of a stormwater management sys-tem. Loss of life associated with OMM of astormwater management facility could havelong term repercussions for the entireprogram. For example, a drowning in a sedi-ment basin in Anne Arundel County, Marylandin the mid-1980's led to a County requirementthat all sediment basins be fenced. The gen-eral public should be aware of any dangersassociated with stormwater management sys-tems, but they should not be adversely im-pacted by a poorly functioning facility.

Loss of property can also occur from streamchannel erosion losses or through increasedfloodplain damage to channel boundaries re-sulting from inadequate performance of up-stream stormwater management systems.

Trees in this stormwater detention basinare an indication that aesthetic

maintenance has not been accomplished.


7-5

sance problems, together with aesthetic prob-lems, can result in reduced property valuesdue to a degraded facility appearance andreduced quality-of-life for people living orworking near the facility.

3. IMPORTANCE OF CHECKLISTS

Checklists are very important to ensure thatall system components are functioning asoriginally constructed. They are important notonly during facility inspection, but they alsoprovide a historical record of facility function.Inspection checklists help to ensure a degreeof consistency. It can be expected that differ-ent individuals will inspect a facility over theyears. By providing common important itemsin an inspection report, continuity is more eas-ily provided. Inspection reports should al-ways be provided to the individual respon-sible for facility maintenance so that theyare aware of the status of their facility.

3.1. Checklists for Inspection

Checklists provide for consistency of siteinspection. They help to assure that allrelevant facility components are in-spected. Any stormwater system will functiononly as well as its component parts. Eachcomponent must be inspected to ensure ef-fective overall OMM and facility performance.

Checklists, when completed and filed with fa-cility information, provide proof that an inspec-tion was done on a routine basis. This docu-mentation is important in case an outside partyrequests to review the information, or for li-ability reduction to demonstrate responsiblecare. The inspection report also identifies anyneeded maintenance activities and estab-lishes a schedule for their completion. Finally,the inspection report forms the basis for rein-spection following maintenance activities toensure satisfactory completion of the activi-

ties in accordance with the initial inspectionreport.

Examples of sample inspection report formsare included in the Appendices at the end ofthis chapter. They should be used as a tem-plate by individuals or entities responsible forfacility maintenance. They should be modi-fied to address additional or modified localcriteria for facility components.

3.2. Checklists to Evaluate StormwaterSystem Function and Performance

When inspections are regularly conducted,checklists can provide a barometer of facilityperformance and they can help to determinemaintenance scheduling and needs. Ratesof sedimentation can be determined by com-paring data from previous inspection reports.This can assist in scheduling periodic sedi-ment removal. In a stabilized watershed, therates of accretion should be fairly consistent.If there is a subsequent increase in the rateof sedimentation, then areas contributingstormwater to the facility should be inspectedfor erosion problems or sediment sources andcorrective steps taken. The responsible main-tenance entity must realize that elevated sedi-ment loadings into the facility will lead to in-creased maintenance costs. In stormwaterBMPs such as infiltration facilities, increasedsedimentation could necessitate costly recon-struction of the entire facility.

Most importantly, OMM budgeting can bemore accurately done if regular inspec-tions and completion of inspection reportsare done. Larger budget items can be plannedfor if inspection reports indicate a growingproblem. An example is a riser assembly fora stormwater pond developing rust problems.This situation can be watched and minor stepstaken to retard deterioration of the riser as-sembly, but the riser must be replaced even-tually. Knowledge of the increasing rate of


7-6

corrosion allows for funding to be generatedover a longer period of time so the impact ofreplacement can be minimized.

4. HIGHLIGHTED EXPECTED OMMNEEDS AS A FUNCTION OFSYSTEM COMPONENTS

This section of the chapter will focus on thelong term operation, maintenance, and man-agement needs of the different types ofstormwater management practices. Sinceeach type of practice includes different com-ponents and processes, the OMM require-ments are best discussed individually. Foreach type of BMP, information will be pre-sented on several types of stormwater pollut-ants and the maintenance activities which ul-timately will be needed to remove them be-fore their accumulation adversely affects BMPperformance. In addition, the sensitivity of apractice to impaired performance resultingfrom capture of pollutants will be discussed.

To a large extent, the type of stormwater man-agement system will depend on the goals ofa specific state/regional/local stormwaterprogram and the problems for which it wasimplemented. If flooding is a major concern,retention and the various types of detentionpractices likely will be used. BMP design willthen be based on stormwater quantity objec-tives. If stormwater quality is an importantgoal, filtration practices, along with retentionand detention systems modified to improvepollutant capture, will be more common. Ineither case, maintenance concerns are bestdiscussed in terms of the type of facility imple-mented.

With regards to pollutant reduction, moststormwater management systems are de-signed to remove sediments. There is enoughvariation in the types of facilities being usedto warrant a more detailed discussion by fa-cility type. One point constantly made is that

stormwater management program implemen-tation is best done by using a BMP treatmenttrain concept. Infiltration facilities can reducethe total volume of stormwater runoff whileother types of facilities would assist in removalof nutrients, toxic materials, metals, and oiland grease. Accordingly, good operation,maintenance, and management of stormwatersystems requires awareness of most availabletypes of BMPs since not just one type may beinstalled on a site.

Individuals need to be aware of the sensi-tivity that individual BMPs have to reducedperformance caused by accumulation ofpollutants. It is important to recognize thatstormwater systems are not equal in termsof their ability to remove pollutants, the oc-currence of storms which could causestructural damage, and their sensitivity toclogging or impaired performance. Imple-menting pretreatment practices can signifi-cantly reduce the potential for impaired facil-ity performance. For facilities impacted by ex-cess sedimentation, the primary concern issediments resulting from construction activi-ties. Construction of facilities must be donewith a sensitivity to their impaired perfor-mance, especially if construction related sedi-ments are allowed to enter the facility while itis being built or after construction but beforeoverall site stabilization.

4.1. Detention and Retention Ponds

Ponds are effective at removing a variety ofpollutants. For some pollutants, the perfor-mance is well documented and can be ex-pected. For other pollutants, removal mecha-nisms and processes are less well defined andmay vary depending on the design, expectedpollutant load, and frequency of maintenance.The variation in performance for some pollut-ants depends, to a large extent, on whetherthe pollutant is in a particulate or soluble form.Ponds are less effective at removing soluble


7-7

pollutants than removing particulates. Ex-ceptions to this rule include BMPs such aswet detention systems or constructed wet-lands, where longer detention times togetherwith the biological processes associated withaquatic plants, provide significant reductionin soluble pollutants. These differences willbe discussed in the sections on individual pol-lutants.

A. Sediments

Ponds are most effective at removing sedi-ments from the water column. Figure 7-1shows that ponds remove sediment byslowing water velocity down, thus allow-ing time for the sediment's downward ve-locity to remove the sediment from the wa-ter column. As a result, ponds need peri-odic maintenance to remove sedimentsdeposited on the bottom. The use of sedi-ment forebays can reduce the mainte-nance problems by reducing the frequencythat sediments must be removed from theentire pond. However, this requires morefrequent maintenance in the forebay ar-eas. As discussed in Chapter 9, morefrequent maintenance can reduce therisk that accumulated sediments maybe considered to be a hazardous waste.

B. Toxic materials and metals

Toxic materials and metals may either be-come attached to sediments as a result ofcation exchange, or they may be in asoluble form. Ponds are very effective atremoving these substances when they areattached to sediments, but they are lesseffective at removing soluble materials.This is especially true for ponds with tra-ditional detention times of 12 to 48 hours.Wet detention systems, with littoral zonesplanted with aquatic vegetation, along withconstructed wetlands can provide greaterremoval of soluble toxics and metals. Pol-lutant removal effectiveness increases withresidence time, with a minimum residencetime of 14 days recommended. Ponds areespecially effective at reducing the releaseof toxic substances that are inadvertentlyspilled during a commercial or industrialaccident. The pond can function as a hold-ing area until cleanup can be accom-plished.

To assure that toxics, especially heavymetals, remain sequestered in the pond'sbottom sediments, it is essential that thebottom environment remain aerobic (haveoxygen) and that the pH remain neutral.Failure to do this will lead to a release of

Figure 7-1. Schematic of a pond and the sedimentation process.


7-8

the pollutants from the sediments and theirreintroduction into the water column.

C. Nutrients

Like metals, nutrients, such as nitrogenand phosphorus, in stormwater can be ineither particulate or soluble forms. Theparticulate form of phosphorus can be veryeffectively removed through adsorptionand sedimentation. As with toxics, pondswill only remain effective at removing par-ticulate nutrients if the bottom sedimentsand water remain aerobic with a pH near7. If the pond bottom develops an anaero-bic (no oxygen) zone or pH rises or falls,phosphorus previously captured can thenbe converted to a soluble form and reen-ter the water column.

Most nitrogen forms, on the other hand,are soluble. They are not removed bysedimentation but through the processeswhich occur during the nitrogen cycle. Akey component of the nitrogen cycle is therole of anaerobic bacteria that live on apond bottom dominated by wetlands veg-etation.

If nutrients in general are of concern in pro-gram implementation, the treatment trainconcept is vital. Phosphorus, in particu-late form, must be removed via settling andadsorption in a facility maintaining an aero-bic environment. Nitrogen could then beremoved in a downstream BMP with a twoweek residence time and anaerobic con-ditions. Two types of facilities are neededfor total nutrient reduction. Biofiltrationpractices, such as vegetative swales,would be effective at reducing particulatepollutants with the stormwater then enter-ing a constructed wetland for soluble pol-lutant reduction.

D. Oils and greases

Ponds provide for reduction in oils,greases, and other hydrocarbons throughvolatilization (vaporization). The effective-ness of this process depends on air andwater temperatures, winds, and surfaceturbulence. One seldom mentioned ben-efit of stormwater management ponds, es-pecially at a commercial or industrial site,is their ability to capture pollutants re-leased during a site spill. For example, aconstructed wetland at a Delaware shop-ping mall received approximately 500 gal-lons of fuel oil that was spilled on the mallparking lot. The oil entered one of the fore-bays of the constructed wetland where itwas fairly easily cleaned up. Without thepond, the oil would have traveled throughthe storm drain system and entered receiv-ing waters. This would have created aserious environmental impact and cleanupwould have been much more difficult andcostly.

On residential sites, oil or automotive flu-ids may be inappropriately disposed by in-dividual property owners. The single mostimportant maintenance recommenda-tion for residential property owners ispollution prevention and pollutantsource control in their day to day ac-tivities at home.

E. The Sensitivity of the Facility to ImpairedPerformance

One of the greatest benefits ofstormwater management ponds is theirresilient performance even when exces-sive pollutant loadings enter the facil-ity. However, performance will suffer ifsediment is introduced in large amountsover a lengthy time frame. Sediments re-duce the volume of storage and reducedetention times which ultimately reducethe pond's pollutant reduction effective-


7-9

ness. This impaired function is not be ex-pected to dramatically occur in a short timeframe, but occurs cumulatively over alonger time period if the incoming pollut-ant loads are consistently elevated.

4.2. Infiltration Facilities

Infiltration facilities, when properly designedand constructed, provide significant pollutantreduction benefits. They also are very effec-tive at reducing the total volume of runoff. Byreducing the runoff volume, they reduce down-stream channel erosion, reduce the declinein stream baseflow, and reduce pollutant de-livery downstream. Infiltration practices aresensitive to pollutant clogging of the sidesand bottom at the soil/stormwater inter-face. Excessive sedimentation can clog thesefacilities quickly.

A. Sediments

Infiltration practices are effective at reduc-ing the downstream movement of sedi-ments. Removing coarser sediments doesnot significantly impair their function, butfiner grained sediments (below 43 ug) cancause clogging of the facility.

B. Toxic materials and Metals

Infiltration facilities can also be effective atremoving toxic materials and metals. Tominimize the potential that pollutants willmove through the soil and into theground water, infiltration practicesshould have an organic layer of soilwhich allows the toxics or metals to at-tach to the soil particles. Additionally,infiltration practices should be vegetatedto help reduce soluble forms of metals.The vegetation's roots also help to main-tain the soil's permeability. Using coarsesandy materials for infiltration will have lim-ited pollutant reduction benefits.

C. Nutrients

Infiltration practices are effective at phos-phorus removal as they capture a largepercentage of particulate phosphorus andmaintain an aerobic environment thatkeeps the particles attached to the soil inthe facility bottom. Nitrogen, on the otherhand, can travel through the infiltrationsystem's soils and into the underlyingground water unless the bottom containsorganic soils. If nitrogen removal is a pro-gram goal, constructed wetlands may bea more appropriate stormwater manage-ment practice, especially in areas withcoarse sandy soils.

D. Oils and greases

Infiltration facilities may not be effective inareas where significant oil and grease de-livery to the facility is expected. Pretreat-ment of runoff to remove oil and greasesshould be done before it enters the infil-tration system. Significant loadings of oiland greases will cause premature cloggingof these facilities and dramatically increasemaintenance obligations.


Infiltration facilities are very sensitiveto impaired performance if excessiveamounts of sediments or oils andgreases are introduced into the facil-ity. The greatest problem is cloggingof soils in the sides and bottom of theinfiltration system. This can occur fairlyrapidly if inflow pollutant levels are not re-duced by pretreatment practices. Otherpollutants which are attached to sedi-ments, such as toxic materials, metals, andphosphorus, are not considered a cloggingconcern. Another problem is poor drain-age as a result of high water table, ground-water mounding, or a confining soil layer.


7-10

Prolonged wetness encourages microor-ganism growths that tend to clog the soils.

4.3. Filtration Facilities

Filtration practices have many variationswhich can enhance their ability to remove avariety of pollutants. Most filters, such asthose used in Austin, Texas, Washington,D.C., Florida, and Delaware, use sand as thefilter media. To be effective in reducingstormwater pollutants, the sand needs to befairly fine grained. However, finer grainedsands have a slower flow rate than coarsersands creating a careful balancing act in thedesign of filters. Other filtering materials be-ing developed around the country includecompost, activated carbon, and peat. The po-tential benefits of using these alternative me-dia will not be discussed in this document asthey are still somewhat experimental and littleis known about their OMM requirements.

Sand filter showing trapped oils and greases.

A. Sediments

Filtration systems are very effective at re-moving sediments from stormwater. Sincemost filter designs include some type ofdetention, sediments are removed fromrunoff through settling and filtration. Mostfilter designs require at least 18 inches of

sand, which has proven effective in trap-ping sediments. Another reason at least18 inches of filter media is recommendedis to allow maintenance by scraping aninch or two of sand from the surface of thefilter. After several maintenance opera-tions reduce the sand thickness to 12inches, new sand can be added to restorethe thickness to 18 inches. Experiencehas shown that most pollutants will onlypenetrate down a few inches into a filtermade of fine sands. However, the coarserthe sand, the farther pollutants will traveland the more filter media that will need tobe removed or replaced when mainte-nance is finally done.


Toxic materials and metals are removedin filters when they attach to sediments orwhen they pass through organic materi-als. This occurs in most sand filters sincethe surface of the filter becomes very or-ganic as a result of trapping fine sedimentsand oils and greases. The organic mate-rial enhances the ability of the sand filtermaterial to remove toxics and metals. Theuse of alternative filter media, such aspeat, also can enhance the ability of fil-ters in removing toxic materials.

C. Nutrients

Filtration systems only remove particulatenutrients. As such, they can be somewhateffective at removing phosphorus fromstormwater. As currently designed, how-ever, they have very little ability to removenitrogen. Experimental systems and vari-ous filter media may improve the nitrogenremoval efficiency of sand filters.

D. Oils and greases

Filtration facilities are very effective at re-moving oil and greases. The Delaware fil-


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ter was developed primarily for removal ofhydrocarbons from small, intensely urbansites, such as gas stations or fast food res-taurants. The sedimentation chamber isimportant in removing hydrocarbons as oiland solids adhere to each other. Oils andgreases penetrate only an inch or so intothe filter media before being bound up inthe sand. However, expectations of per-formance depend on the gradation of thefilter media. Several filter designs recom-mend C-33 concrete sand as the speci-fied filter media.


With respect to maintenance, the ques-tion is not if a filter system will clog,but when. Filter systems are very sensi-tive to excessive loadings of oil and greasewhich can clog the surface of the filter.The sand filter in Rehoboth Beach, Dela-ware, provides a good case study. Thefilter normally requires monthly inspection,with cleanout of the sand surface twice peryear. In one instance, an individualdumped waste oil into the facility and im-mediately caused the sand filter to clog.On one hand, the filter was effective at pre-venting the downstream migration of wasteoil, but this effectiveness caused it toquickly clog.

Sediments can also be a problem forstormwater filters, especially if they are finegrained sediments in the silt/clay category.Coarser sediments do not cause a signifi-cant reduction in permeability of the sandand they are generally removed in thesedimentation chamber of the facility.

4.4 Biofiltration Facilities

Biofiltration facilities generally include vegeta-tive filter strips and swales. Physical filtration

by vegetation is an important pollutant removalcomponent of biofiltration facilities. Anotherimportant filtration mechanism, depending ontheir character, may be infiltration of storm-water runoff through the surrounding surfaceand subsurface soils.

A. Sediments

Biofiltration facilities are very effective atremoving sediments from stormwater.Their effectiveness is based, to a large ex-tent, on the duration of flow through them.The longer the flow path and residencetime, the higher the effectiveness in remov-ing sediments.


There is little information available on theeffectiveness of biofiltration facilities in re-moving organic toxic materials. They aremoderately effective (60-75%) at remov-ing metals from stormwater. Removals arefairly low for soluble metals such as zincor copper.

C. Nutrients

Biofiltration facilities are not very effectiveat nutrient removal. Phosphorus removalis very modest while nitrogen removal isnegligible. A greater level of performancecan be expected for nutrient reduction ifthe biofilter is mowed and the grass cut-tings removed from the drainage system.This may not be a realistic expectation asit may rely on numerous individual prop-erty owners to do, especially for biofiltra-tion facilities located in residential com-munities.

D. Oils and greases

Biofiltration practices are effective at oiland grease reduction. They are most ef-fective in removing fairly low levels of oil


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and grease and can be overwhelmed byexcessive loadings.

E. The sensitivity of the facility to impaired per-formance

Biofiltration facilities are susceptible to im-paired performance primarily as a resultof excess sediment loadings smotheringvegetation. Oils and greases can also bea serious concern as their entry could killvegetation. These impacts could occurvery quickly if large amounts of these pol-lutants are introduced in a short timeframe.

5. INSPECTION FREQUENCY

Suggested inspection frequencies are in-cluded in the inspection forms in the Appen-dices at the end of this chapter. These fre-quencies should be considered as the maxi-mum interval between inspections. It is im-portant to remember that inspections cannever be done frequently enough. Morefrequent inspections, especially for certainpractices such as filters and infiltration prac-tices, should be done whenever possible.

Inspection frequency for stormwater manage-ment system maintenance depends on twoprincipal factors:

• local climate and precipitation• the type of stormwater system

The influence of local climate and precipita-tion on maintenance frequency will be dis-cussed in the following section, while the in-fluence of practices was discussed in the pre-vious section.

5.1. Local Climate and Precipitation

The frequency of maintenance depends on

how much and how often it rains, the poten-tial for large events, and the occurrence ofsnow and ice. Climate provides one of thefoundations upon which stormwater manage-ment systems are designed and constructed.The recommended time frames for inspec-tion and maintenance will vary dependingon local climate and rainfall conditions. Itis very important to carefully considerthese factors when determining inspectionfrequencies for a specific stormwatermanagement program.

A. Local climate

An important local climate consideration is theseasonal aspect of rainfall. A region of thecountry having a defined wet or dry seasonwill need to consider the maintenance require-ments associated with these distinct seasons.This is especially true of practices for whichinspections are recommended monthly. Dur-ing a normal wet season, inspections shouldbe done according to the recommendedschedule. However, monthly inspections areprobably too frequent during a normal dry sea-son when less frequent inspections will suf-fice. There is value to conducting inspectionsmore frequently. However, unless they aredone voluntarily by an assigned maintenanceentity, public inspections will cost money andrequire staff resources typically unavailableto most stormwater programs. Reducing thefrequency of inspections during a dry sea-son may be appropriate and allow re-sources to go farther. However, the ap-propriateness of less frequent inspectionsduring the dry season ultimately will de-pend on the type of practices and thedrainage area it serves. The recommendedinspection frequencies presented in thisHandbook are for those areas which receiverainfall throughout the year.

In addition to the seasonality of rainfall, veg-etation growing seasons, especially the dor-mant seasons, will have an impact on how of-


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ten a biofiltration or constructed wetland willneed to be inspected. The dormant seasonmay provide a good opportunity to inspect afacility for erosion problems due to a winterdie back of the vegetation. Areas which couldnot be inspected during the growing seasonmay be visible when the vegetation dies back.

B. Precipitation

The characteristics of storms, such as rainfallintensity, depth, inter-event time, and percent-age of annual precipitation as snow or rain, isalso an important factor in determining inspec-tion frequency. Total annual precipitation inthe Pacific Northwest is similar to rainfalldepths in the mid-Atlantic region, but the na-ture of rainfall in terms of inter-event dry pe-riod, average depth of individual storms, andthe seasonal nature of the rainfall is very dif-ferent. Thus, far different inspection frequen-cies are merited.

Simply stated, the more rainfall events andthe greater the pollutant loading, the morework a stormwater management facility mustdo. Increased use or loading is directly re-lated to the need for maintenance. Inspec-tions may be needed more frequently inareas having a greater number of stormsand greater depths per event.

6. AESTHETIC AND FUNCTIONAL MAIN-TENANCE

Maintenance can be broken down into a num-ber of different categories, but two primary cat-egories are aesthetic/nuisance maintenanceand functional maintenance. These two cat-egories can overlap at times. They are mutu-ally important to each other and each isequally important. Functional maintenanceis important for performance and safetyreasons, while aesthetic maintenance isimportant primarily for public acceptanceof stormwater facilities, and because it

may also reduce needed functional main-tenance activities.

Both forms of maintenance are needed andboth must be combined into an overallstormwater management system maintenanceprogram. Both forms of maintenance are in-cluded in the checklists in the Appendices tothis chapter.

6.1. Aesthetic Maintenance

Aesthetic maintenance primarily enhances thevisual appearance and appeal of a stormwaterfacility. A stormwater system with a good ap-pearance will allow the facility to more easilybecome an integral part of a community. Aes-thetic maintenance is obviously more impor-tant for those facilities that are very visible.Underground stormwater systems do not havethe need for aesthetic maintenance that aboveground, open air systems have. Generally,aesthetic maintenance is more important atponds and biofiltration facilities, although itmay also be important for certain types of fil-tration and infiltration facilities, such asAustin's sand filter design or landscape infil-tration basins. The following activities can beincluded in an aesthetic maintenanceprogram:

A well landscaped pond in Newark, Dela-ware is a centerpiece for the office park.


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6.2. Functional Maintenance

Functional maintenance is necessary to keepa stormwater management system operationalat all times. Functional maintenance has twocomponents:

• Preventive maintenance• Corrective maintenance

6.2.1. Preventive maintenance

Preventive maintenance is the maintenancewhich is done on a regular basis as detailedin the checklists contained in the Appendicesto this chapter. Preventive maintenance tasksinclude upkeep of any moving parts, such asoutlet drain valves or hinges for grates, ormaintenance of locks. Preventive mainte-nance can also include maintenance of veg-etative cover to prevent erosion. Examples ofpreventive maintenance include:

A. Grass mowing

Actual mowing requirements at a facilityshould be tailored to the specific site con-ditions, grass type, and seasonal variationin climate. Local soil conservation districtsor cooperative extension service officescan provide assistance in determiningmaintenance requirements for varioustypes of vegetation.

A. Graffiti removal

The timely removal of graffiti will improvethe appearance of a stormwater system.Timely removal will also tend to discour-age further graffiti or other acts of vandal-ism.

B. Grass trimming

Trimming of grass around fences, outletstructures, hiker/biker paths, and struc-tures will provide a more attractive appear-ance to the general public. As much aspossible, the design of stormwater facili-ties should incorporate natural landscap-ing elements which require less cuttingand/or trimming. However, there often areareas where mowing will be necessary tomaintain attractiveness as perceived bythe average individual.

C. Control of weeds

In situations where vegetation has beenestablished, undesirable plants can be ex-pected. These undesirable plants can ad-versely impact the aesthetics of astormwater facility. This can also apply towetland stormwater systems and wet de-tention littoral zones which may be invadedby undesirable aquatic plant species.These undesirable plants can be removedthrough mechanical or chemical means. Ifchemicals are used, the chemical shouldbe used as directed and left over chemi-cals disposed of properly.

D. Miscellaneous details

Careful, meticulous, and frequent attentionto performing maintenance tasks such aspainting, tree pruning, leaf collection, debrisremoval, and grass cutting (where intended)will allow a stormwater management systemto maintain an attractive appearance andhelp maintain its functional integrity. Routine mowing of a detention facility.


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B. Grass maintenance

Grass areas require limited periodic fertil-izing, de-thatching, and soil conditioningin order to maintain healthy growth. Provi-sions may have to be made to reseed andreestablish grass cover in areas damagedby sediment accumulation, stormwaterflow, or other causes.

C. Vegetative cover

Trees, shrubs, and other ground cover re-quire periodic maintenance, including fer-tilizing, pruning, and pest control.

D. Trash and debris

A regularly scheduled program of debrisand trash removal will reduce the poten-tial for outlet structures, trash racks, andother facility components from becomingclogged and inoperable during stormevents. In addition, removal of trash anddebris will prevent possible damage tovegetated areas and eliminate potentialmosquito breeding habitats. Disposal ofdebris and trash must comply with all lo-cal, county, state, and federal waste con-trol programs. Only suitable disposal andrecycling sites should be used.

E. Sediment removal and disposal

Accumulated sediments should be re-moved before it threatens the operationor storage volume of a stormwater man-agement system. Disposal of sediments isdiscussed in Chapter 9 and must complywith local, county, state, or federal require-ments. Only suitable disposal areas shouldbe used. Sediment removal in infiltrationsystems must also include monitoring theporosity of the subbase, replacing orcleaning the pervious materials as neces-sary, and reestablishing vegetation.

F. Mechanical components

Valves, sluice gates, pumps, fence gates,locks, and access hatches should remainfunctional at all times. Regularly sched-uled maintenance should be performed inaccordance with the manufacturers' rec-ommendations. All mechanical compo-nents should be operated during eachmaintenance inspection to assure contin-ued performance.

G. Elimination of mosquito breeding habi-tats

The most effective mosquito control pro-gram is one which eliminates potentialbreeding habitats, or, in the case of open

Example of clogged inlet causing erosionwhen water overflowed onto vegetatedareas adjacent to a stormwater pond.

Potential mosquito habitat resultingfrom inadequate drainage.


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water ponds or wetlands, ensures thatoptimal conditions are maintained for thesurvival of mosquito control organisms.Any stagnant pool of water can becomea mosquito breeding area within a mat-ter of days. Ponded water in open cans,tires, and areas of sediment accumulationsor ground settlement can become mos-quito breeding areas. Local mosquito con-trol programs can be contacted for assis-tance and advise on minimizing mosquitoproblems.

H. Facility maintenance

A maintenance program for monitoring theoverall performance of the stormwater man-agement system should be established. Wetdetention and wetland systems, are espe-cially, complex environments. They requirea healthy aquatic ecosystem to provide maxi-mum benefits and to minimize needed main-tenance. It is important to remember thatpotentially large problems can be avoided ifpreventive maintenance is done in a timelyfashion.

6.2.2. Corrective maintenance

Corrective maintenance is required on anemergency or non-routine basis to correctproblems and to restore the intended opera-

tion and safe function of the stormwater man-agement system. Corrective maintenance isnot done on a scheduled basis but on an asneeded basis. Failure to promptly address acorrective maintenance problem may jeopar-dize the performance and integrity of the fa-cility. It may also present a potential safetyproblem to those living adjacent to or down-stream of the facility. Corrective maintenanceactivities include:.

A. Removal of debris and sediment

Sediment, debris, and trash which threatenthe ability of the facility to store or conveywater should be removed immediately andproperly disposed of to restore properfunctioning of the facility. A blocked inletor outlet means that stormwater will travelin an area that was not normally designedas a flow path. In the case of an inlet, thestormwater could travel over a curb ontoa grassed area and scour that area. If theoutlet is blocked, water will back up in thefacility and may travel through the emer-gency spillway or overflow area. Theseareas are not designed for frequent flowand may become eroded. If sediments areclogging a facility component, the lack ofan available disposal site should not de-lay removal of the sediments. Temporaryarrangements should be made for handlingRermoval of debris from the entrance of

an outlet structure in a detention facility.

Sediment cleanout of a stormwatermanagement pond.


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the sediments until a more permanent ar-rangement is made.

B. Structural repairs

Repairs to any structural component of thefacility should be made promptly. Equip-ment, materials, and personnel must bereadily available to perform repairs onshort notice. The immediate nature of therepairs depends on the type of damageand its effects on the safety and operationof the system. Where structural damagehas occurred, the design and conduct ofrepairs should be undertaken only bequalified personnel.

C. Dam, embankment and slope repairs

Damage to dams, embankments, andslopes must be repaired quickly. Typicalproblems include settlement, scouring,cracking, sloughing, seepage, and rutting.A concern in an embankment with a bar-rel assembly or outflow pipe through it isseepage around the outside of the barrel.This can also cause movement of embank-ment soils, which can weaken the embank-ment. Repairs need to be made promptly.Other temporary activities may be needed,such as drawing down the water level inthe facility to relieve pressure on a dam orembankment, or to facilitate repairs. Crackrepair in a concrete structure may neces-sitate draining the facility and cleaning thearea of the crack prior to repair. If the fa-cility is to be dewatered, pumps may benecessary if there is no drain valve.

D. Elimination of mosquito breeding areas

If neglected, a stormwater system can be-come a mosquito breeding area, especiallyfacilities which are designed to drain anddry out, but which do not. Corrective ac-tion may be needed if a mosquito prob-lem exists and the stormwater facility is

the source of the problem. Local mosquitocontrol experts should be consulted foradvice. If mosquito control in a facility be-comes necessary, the preventive mainte-nance program for mosquitoes should bereevaluated, and more emphasis placedon control of mosquito breeding habitats.

E. Erosion repair

Vegetative cover is necessary to preventsoil loss, maintain the structural integrityof the facility, and maintain it's pollutantremoval benefits. Where a reseeding pro-gram has been ineffective, or where otherfactors have created erosive conditions(i.e., pedestrian traffic, concentrated flow,etc.), corrective steps should be taken toprevent further loss of soil and any subse-quent danger to the performance of thefacility. There are a number of ways thatcorrective action can be taken. These in-clude erosion control blankets, riprap, sod-ding, or reduced flow through the area. Lo-cal experts should be consulted to addresserosion problems if the solution is not evi-dent.

F. Fence repair

Fences can be damaged by any numberof factors, including vandalism and stormevents. Timely repair will maintain the se-curity of the site.

G. Elimination of trees, woody vegetationand animal burrows

Woody vegetation or animal burrows canpresent problems for dams or embank-ments. The root system of woody vegeta-tion can undermine dam or embankmentstrength. If the vegetation dies and the rootsystem decomposes, voids can be createdin the dam or embankment which weakenthe structure. Preventive maintenance canavoid this problem. However, when it oc-


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curs through lack of a preventive mainte-nance program, steps must be taken toeliminate the problem. Vegetation, includ-ing root systems, must be removed fromdams or embankments and the excavatedmaterials replaced with proper material ata specified compaction (normally 95% ofthe soils maximum density). Animal bur-rows should be filled and steps taken toremove the animals if burrowing problemscontinue to occur. In an urban environ-ment, animals of concern are usuallymuskrats or beavers. If the problem per-sists, local wildlife officials should be con-sulted regarding removal steps. This con-sulting is necessary as the threat of ra-bies in some areas may necessitate theanimals being destroyed rather than relo-cated.

H. Snow and ice removal

Accumulations of snow and ice canthreaten the functioning of a stormwatermanagement system, particularly at inlets,outlets, and overflow emergency spillways.Providing equipment, materials, and per-sonnel to monitor and remove snow andice from these critical areas is necessaryto assure the continued functioning of thefacility during the winter months.

I. General facility maintenance

In addition to the above elements of cor-rective maintenance, general correctivemaintenance should address the overallfacility and it's associated components. Ifalgae growth becomes a problem forponds, or if an infiltration facility does nottotally drain, steps must be taken to rees-tablish the original performance of the sys-tem. Stormwater facilities often are verycomplex systems. They will work onlyas long as each individual elementfunctions correctly. If corrective main-tenance is being done to one facility

component, other components shouldbe inspected to see if maintenance isneeded. There may be a cost savingsin conducting numerous maintenanceactivities if equipment is on site whichcould improve a number of neededmaintenance items.

7. TRAINING NEEDS, INCLUDING ANINSPECTOR TRAINING ANDCERTIFICATION PROGRAM

There are going to be many individuals whoare involved in stormwater management sys-tem maintenance activities. Having individu-als conduct these activities, including inspec-tion, without training reduces the potential forproper facility inspection and maintenance.

What individual would have three differentkeys to open the gate to enter a facility?


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It is important that educational programsbe developed and implemented to ensurelong term performance and function ofstormwater management facilities.

7.1. Mandatory Versus VoluntaryEducational Programs

It is recommended that an inspector's train-ing program be mandatory. An inspector mustknow what components of a stormwater man-agement facility are integral to proper func-tion and safety. This recommendation is con-sistent with that made in Chapter 4.

A training program for owners and operatorsof stormwater facilities is best done on a vol-untary basis where the appropriate regulatoryagency provides educational materials andprograms for facility owners and operators.In addition to these materials and programs,annual interaction is important. When publicagency inspections are done on stormwatersystems, the owner and/or operator shouldalso be present. This interaction can provideowners and operators with a greater under-standing of various facility components andtheir importance to overall facility function.

The inspection agency should also con-tact all facility owners and operators andoffer to conduct an inspection with themat the convenience of the owner or opera-tor. This may represent somewhat of a hard-ship on the inspection agency, especially forresidentially-owned facilities, since inspec-tions may be necessary after normal workhours or on weekends. It is vital to makeowners and operators aware of their obli-gations and responsibilities for theirstormwater systems. Meetings on site arenecessary to instill that recognition.

7.2. Components of an InspectorTraining Program

A required inspector training program mustbe structured, have classroom or lecture ses-sions that must be attended, and a programmanual that is kept by those taking the course.The course curriculum should include muchof the material in this Handbook and shouldinclude the following components:

1. Institutional background for the storm-water management program.

2. Discussions of why stormwater facili-ties are important for stormwater quan-tity and quality control.

3. Basic soils and geology information.4. Basic hydrology and hydraulics so in-

spectors have an understanding of theprocesses involved in rainfall and run-off).

5. Explanation of the specific legal author-ity and regulatory requirements of thestormwater management program.This should detail the inspection re-quirements and penalty options.

6. Discussion of the different types ofstormwater management facilities be-ing used in a given jurisdiction. Thisdiscussion will include the treatmentprocesses of the individual facilitiesand the maintenance issues associ-ated with each type of facility.

7. The impacts of maintenance on waterquality, including disposal of waste ma-terial.

8. How to read plans and understandspecifications.

9. How to inspect a stormwater manage-ment facility. This will include use ofthe maintenance inspection checklistssimilar to those presented in the ap-pendices at the end of this Chapter.

10.Enforcement options including avail-able inspection and enforcement reportforms.

11. Case studies showing construction and


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maintenance of stormwater manage-ment facilities. The case studies shouldinclude construction techniques andsequences so the inspectors would un-derstand the importance of compo-nents that are not normally visible.

12. Issues related to actual maintenanceof stormwater management facilities.This would include disposal of materi-als removed from the facility and anyconcerns regarding the hazardous na-ture of removed sediments.

7.3 Components of an OperatorsTraining Program

For the most part, individuals responsible formaintenance of stormwater management sys-tems seldom have that job as their primaryresponsibility. For example, this may includethe officers of a residential property ownersassociations, or staff charged with overallproperty maintenance at commercial or indus-trial sites. These individuals need basiceducation about stormwater managementsystems, their operation, and mainte-nance. They do not need to know aboutmore "abstract" topics such as institu-tional backgrounds, etc. That informationshould be available upon request, but isn't im-portant during a workshop or training sessionwhere they are giving up their own time to at-tend.

An operator's training program will have manyof the same components as the inspector'straining program but with less emphasis insome areas. The training program should fo-cus instead on practical aspects of stormwaterfacility operation, maintenance, and manage-ment. The focus should be on matters whichare directly applicable to OMM situations. Theoperators program should consist of astormwater system operator's manual, in con-junction with classroom or lecture sessionswhere the individual course topics can be

added or removed depending on the audi-ence. The manual would be more comprehen-sive than the training course, and would pro-vide information that is not necessary in atraining course but which could be beneficialdepending on an individual's interest. Thecourse could consist of the following compo-nents:

1. Discussions of why stormwater facili-ties are important for stormwater quan-tity and quality control.

2. Specific legal authority and regulatoryrequirements for the maintenance ofstormwater management systems. Thiswould clearly state the obligations as-sociated with facility ownership.

3. Discussion of the different types ofstormwater management facilitieswhich are being used in a given juris-diction. This discussion will include thetreatment processes of the individualfacilities and the maintenance issuesassociated with each type of facility. Itshould include a series of modules foreach type of facility which would be pro-vided in a specific discussion.

4. The impacts of maintenance on waterquality, including disposal of waste ma-terial.

5. How to read the plans and understandappropriate specifications.

6. How to inspect a stormwater manage-ment facility. This includes the use ofmaintenance inspection checklistssimilar to those in this chapter's appen-dices. This would also consist of top-ics or presentations for individual typesof facilities which could be presenteddepending on the BMPs of particularinterest to the attendees.

7. Issues related to actual maintenanceof stormwater facilities. This would in-clude disposal of materials removedfrom the facility and any concerns re-garding the hazardous nature of re-moved sediments.


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spections, offer an opportunity to use privateinspectors who have attended and passed theinspector certification course. As part of thepermit approval process, a stormwater sys-tem approval should require the land owneror developer to establish a legal maintenanceinfrastructure. This could include requiringthe permittee to retain the services of a certi-fied private inspector to conduct annual in-spections of completed stormwater systems.Copies of the inspection reports would betransmitted to the public agency responsiblefor maintenance and the property owner orstormwater system operator. This approachmay reduce the necessity for public agencyinspection. However, public inspectors will stillbe needed to periodically ensure the accu-racy of the private inspector's reports and toinitiate necessary enforcement action.

Another key requirement of all stormwa-ter management programs is requiring op-erators to have the financial capability toensure that they meet their facility main-tenance obligations. The agreements pro-vided at the end of Chapter 4 contain legalauthority to conduct needed maintenance inthe event of default by the responsible pri-vate entity. Chapter 8 provides cost informa-tion for many maintenance tasks. Stormwatersystem owners or operators must be madeaware of these costs, how often they can beexpected to be incurred, and have a mecha-nism to collect money to accomplish the main-tenance. These can be in the form of monthlyor annual assessments within a community,or the ability to assess individual owners whenthe need arises.

9. TYPICAL OMM TOOLS

There are a number of tools which are usedin the maintenance of stormwater manage-ment systems. These are discussed to assistinspectors and facility owners in developingspecific facility maintenance programs. Actual

8. EQUIPMENT AND RESOURCESNEEDED

Inspector equipment needs are discussed inChapter 6 and they are again provided andexpanded on here for inspectors who may beresponsible for stormwater management fa-cility maintenance only. Essential equipmentfor an inspector includes:

• A locke level or other surveying equip-ment.

• Flashlight• Crowbar• Tape measure and other measuring de-

vice (survey rod), such as a clear PVCtube, to determine sediment accumu-lation depths in facilities.

• Local erosion and sediment control orstormwater management handbooks.

• Rain and foul weather gear.• Copies of necessary inspection reports

and forms.• Business cards or other means of iden-

tification.• A camera to document field conditions

in case an enforcement action be-comes necessary.

Insufficient staff is a chronic problem for moststormwater system inspection and mainte-nance programs. Since most public agen-cies will never have enough inspectors,the issue of public versus private inspec-tors to conduct annual maintenance in-spections should be considered. Regard-less of the program structure, some indi-vidual must be responsible for conduct-ing maintenance inspections or assuringthat some qualified entity or person is per-forming inspections. The public entity re-sponsible for ensuring maintenance of storm-water facilities must have resources availableto conduct periodic inspections to ensure fa-cility performance.

Maintenance inspections, like construction in-


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equipment and material requirements shouldbe determined on an individual basis for eachfacility. The information presented here isadapted from the "Stormwater ManagementFacilities Maintenance Manual" (NJDEP,1989).

Grass maintenance equipment

1. Tractor-mounted lawn mowers2. Riding lawn mowers3. Hand mowers4. Gas powered trimmers5. Gas powered edgers6. Seed spreaders7. Fertilizer spreaders8. De-thatching equipment9. Pesticide and herbicide application

equipment10.Grass clipping and leaf collection

equipment

Vegetative cover maintenance equipment

1. Saws2. Pruning shears3. Hedge trimmers4. Wood chippers

Transportation equipment

1. Trucks for transportation of materials2. Trucks for transportation of equipment3. Vehicles for transportation of person-

nel

Debris, trash, and sediment removal equipment

1. Loader2. Backhoe3. Grader4. Dragline5. Vacuum equipment

Miscellaneous equipment

1. Shovels

2. Rakes3. Picks4. Wheel barrows5. Fence repair tools6. Painting equipment7. Gloves8. Standard mechanics tools9. Tools for maintenance of maintenance

equipment10.Office space11. Office equipment12.Telephone13.Safety equipment14.Tools for concrete work (mixers, form

materials, etc.)

Inspector equipment during a routine mainte-nance inspection

1. Flashlight2. Locke level or survey equipment3. Approved facility plans4. Measuring rod (to determine depth of

sediment accumulation)5. Crowbar (removal of cast iron covers)5. Inspection report form6. Pen or pencil

Inspector equipment (when on site during themaintenance of a stormwater facility)

1. Gloves2. Safety hat3. Safety glasses4. Safety boots5. Inspection report form6. Pen or pencil7. Lock level or survey equipment8. Approved facility plans

Materials

1. Topsoil2. Fill material3. Seed4. Soil amendments (fertilizer, lime, etc.)5. Chemicals (pesticides, herbicides, etc.)


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tive maintenance is a high priority wheneverit is needed. Preventive maintenance is next,followed by aesthetic maintenance. All ofthese forms of maintenance are needed, butprioritizing is necessary, especially whenthere is a safety or potential safety con-cern, or when there is limited staff and/orequipment.

The items previously considered as correc-tive maintenance include, in order of priorityfrom most important to least important:

• Structural repairs• Dam, embankment and slope repairs• Erosion repair• Removal of debris and sediment• Elimination of mosquito breeding areas• Elimination of trees, woody vegetation,

and animal burrows• General facility maintenance• Fence repair• Snow and ice removal

Preventive maintenance importance and pri-ority depends to a large extent on the type ofBMP. Biofiltration facilities perform only ifmowing is routinely accomplished, yet wetponds may only need mowing on an annualbasis. As such, prioritizing is not as importantas ensuring that preventive maintenance isaccomplished. Preventive maintenance, asdiscussed earlier, includes::

• Grass mowing• Grass maintenance• Vegetative cover• Trash and debris• Sediment removal and disposal• Mechanical components• Elimination of mosquito breeding

habitats• Other specific facility maintenance

items

The City of Bellevue, Washington has devel-oped a stormwater facility maintenance

6. Mulch7. Paint8. Paint removers (for graffiti)9. Spare parts for equipment10.Oil and grease for equipment and

stormwater management facility main-tenance of mechanical components

11. Concrete

10. IMPORTANCE OF TRACKINGOPERATION, MAINTENANCE, ANDMANAGEMENT

Facility tracking and recording are importantcomponents of stormwater facility mainte-nance programs. In this day and age, there isno reason why maintenance cannot betracked using computerized data bases. Thiswould allow inspectors to be assigned an in-ventory of facilities to inspect and provideeasily accessible information on when OMMwas done last and when the next inspectionmay be needed. The data entered into thecomputer tracking system could include iden-tification numbers for each facility, facility type,facility locations, special maintenance needs,and data from previous inspections. At theconclusion of each site visit, the inspectorenters a maintenance needs assessment intothe computer data base. The computer couldthen generate a maintenance work order.

This approach would help to ensure that prob-lems are corrected in the order of the risk thatthey pose. This type of system would alsoensure that no facilities "fall through thecracks" in terms of annual inspections andmaintenance. Tracking of when a facilitywas last inspected and the facility's sta-tus should never rely on the memory ofindividual inspector.

11. PRIORITIZING MAINTENANCE TASKS

In terms of prioritizing maintenance, correc-


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TABLE 7-1. BELLEVUE (WA) STORM FACILITY MAINTENANCE PRIORITIZATION SYSTEM

Priority Criteria Example

A Hazard to life or health - a situation Partial collapse of an occu-presenting substantial likelihood of pied structure creates road-injury. way hazard which has a

reasonable likelihood ofcausing a traffic accident;hazardous working conditionsfor utility crews

B Hazard to structures - a situation Damage to buildings,presenting a reasonable liklihood roadways,utilities, etc.of damage to structures.

C Hazard to property - a situation Erosion; landscape damage;presenting a reasonable likelihood sedimentationof property damage

Inconvenient situation for D Nuisance maintenance crews, small

amounts of standing water.

prioritizing system, which is shown in Table 7-1.

12. SAFETY ISSUES DURINGMAINTENANCE INSPECTIONS ANDDURING ACTUAL MAINTENANCE

The importance of inspector and maintenancepersonnel safety when conducting mainte-nance inspections and activities cannot beoveremphasized. Individual safety must be aparamount consideration when conductingmaintenance inspections or performing main-tenance.

12.1 Safety Issues During MaintenanceInspections

Safety issues during maintenance inspectionsare, for the most part, common sense itemswhich should be considered in any outdooractivity. Possible concerns or issues include:

• Look out for holes. A hole can be verysmall in circumference but deep. In thevicinity of a stormwater managementfacility a hole can be an indication of aserious problem. When conducting a

Example of a hole on a stormwater pondembankment. This indicates two concerns:(1) watch where you walk; and (2) the pondhas serious problems with piping aroundthe barrel assembly. If you see this, get

assistance.


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maintenance inspection, look whereyou walk.

• Animals can present a serious concern.Rabies is a concern with wildlife andanimal bites which could have severeconsequences. Be careful aroundgeese. Geese are very territorial, andcan be extremely aggressive. Look outfor snakes.

• Be careful lifting manhole covers orother structural covers in stormwaterfacilities. These items can be veryheavy, can slip, and cause serious in-jury, such as the loss of a finger. Inaddition, since they are heavy, backproblems can occur if covers are liftedalone or incorrectly.

• Poison ivy, poison oak, or other plantscan present a problem depending onthe individual's allergic reaction tothem. This can also present a problemduring maintenance when vines fromcutting woody vegetation may lie allover a site.

• Never enter a confined space unlessyou have been trained and have propersafety equipment in accordance withOSHA Regulations. Do not enter pipesor conduits unless another individualis present during the inspection. Donot enter a pipe or conduit, even withothers present, if there is any concernregarding the structural strength of thepipe or conduit.

• Be careful not to walk in water whenthe depth is unknown or where theremay be steep slopes below the waterline.

• Be careful of nails, broken glass, orother sharp objects. Soft bottom shoes,such as athletic shoes, may be morecomfortable for general wear, but theyare not as safe as hard soled shoes.Fences can tear clothing or cause cuts,which may necessitate medical treat-ment.

• Gloves should be worn if any mechani-cal parts or structural components aregoing to be handled. This should bedone for safety reasons (cuts, abra-sions, etc.) and for health reasons,especially where pollutants or othermaterials can coat the hands then getrubbed into eyes or the mouth. Alwayswash hands after an inspection whereitems are manipulated, especially ifgloves are not worn.

• In systems which are somewhat sealedwith poor ventilation, be careful withcigarettes, lighters, or other openflames. Also be sure to allow a facilityto vent for a period of time if a peculiarodor is present. Do not enter any con-fined space unless the atmosphere hasbeen checked and proper safety equip-ment is worn and/or erected.

Inspectors lifting a manhole cover of aWashington, DC sand filter. Care must betaken in cover removal and replacement.


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12.2. Safety Issues During MaintenanceActivities

During maintenance activities, the typical con-cerns exist around any construction equip-ment. Remember, you can see equipmentwhile they are operating, but equipmentoperators may not see you.

• Equipment should always be operatedsafely and in accordance with manu-facturers specifications.

• Call utility companies before initiatingany maintenance activity involving anyexcavation. Look for overhead wiresbefore operating any equipment whichcould touch the wires.

• Before starting any maintenance activ-ity, be sure that all necessary equip-ment or replacement parts are onsiteor are readily available. In the case ofsediment removal, have the disposallocation staked out or identified.

• Excavated areas that cannot be filledat the end of a work day should be cov-ered, when possible, or clearly identi-fied and marked off.

• When working in a residential commu-nity, the residents should be educatedabout the maintenance activity and howlong it will take.

• Don't cut corners when doing mainte-nance activities. Be careful. Alwaysbe aware of what is around you. Takethe time needed to do the job right.Recognize that things go wrong, andtaking time to do quality work will savetime and money in the long run.

• Wear a hard hat, steel toed shoes,safety glasses, ear plugs, etc. if in anarea where construction equipment (or

operating equipment) is operating.

• Mowing can be hazardous so be care-ful around mowers that are running.Take special care when mowing steepslopes. Be sure to wear safety glasses,steel toed shoes, and ear plugs whilemowing.

• Gloves should be worn if any mechani-cal parts or structural components aregoing to be handled. As stated before,this needs to be done for both safetyand health reasons. Always washhands after an inspection where itemsare manipulated, especially if glovesare not worn.

13. SPECIFIC MAINTENANCE ACTIVI-TIES FOR EACH TYPE OF FACILITY

Specific BMP design criteria varies from ju-risdiction to jurisdiction, so the frequency ofmaintenance for the range of BMPs will varyalso. An example of this variation in criteriamay be the design of sediment forebays inponds, or the requirement for pretreatmentpractices. This section will provide informa-tion that is generally applicable to the indi-vidual types of facilities. However, it cannotbe too specific regarding time frames sincethey are influenced by local criteria. Recom-mended frequency of inspections is providedin the checklists in the chapter's appendices.

This section will also present specific ex-amples of maintenance problems associatedwith individual practices. It is extensively il-lustrated to clearly show examples of func-tional maintenance problems that may occurat different types of BMPs. Some general rec-ommendations on the frequency of mainte-nance activities will be provided. However,maintenance needs are so specific to theland being served by the stormwater facil-ity and the pollutant load being delivered


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to the facility, that actual conditions willvary from site to site. Actual maintenancefrequency should depend on the resultsof routine inspections which can deter-mine the rate of accumulation of materi-als in the individual facility.

The discussion will be broken down into thefour main classes of stormwater practices:

• Detention and retention ponds, includ-ing wetlands

• Infiltration facilities• Filtration facilities• Biofiltration facilities

13.1 Detention and Retention Ponds

Maintenance activities for detention and re-tention ponds have many similarities, but therealso are some differences in the types of main-tenance that are needed. Dry detention sys-tems have more lawn areas that must bemowed. Mowing of dry detention facilitiesshould be done at least once per year to pre-vent the growth of woody vegetation on theembankment. Monthly or more frequent mow-ing is necessary if good turf grass cover isexpected or desired.

In addition, dry detention systems frequently

have pilot or low flow channels to conveysmaller flows. These pilot channels may be-come undermined, if made of concrete, or ifmade of stone, may become choked with veg-etation and require chemical treatment to re-establish flow conveyance ability. Mainte-nance efforts for pilot channels will be doneon an "as needed" basis. Careful inspectionshould be done on concrete pilot channels,as their undermining will jeopardize the struc-tural integrity of the pilot channel.

Wet detention systems with their normal wa-ter pool are effective at converting inorganicnitrogen to organic nitrogen. Consequently,

Example of trees all around the detentionfacility perimeter. It is obvious that

maintenance has not been done in years.

Example of a dry detention facility showingthe degree of mowing required and the

riprap pilot channel.

A constructed wetland without sedimentforebays filling in. This facility is about 10years old and will need to be dredged ofsediments within the next 10 years. Con-structed wetlands are very susceptible to

filling in if inflow sediments are significant.


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this may create algae problems unless littoralzones are planted with aquatic vegetation.Wet detention systems also more commonlyhave forebays to remove heavier sediments.As such, forebay maintenance is an impor-tant issue for wet detention systems whichmust be considered. Frequency of forebaymaintenance depends on the incoming pol-

Example of debris which is beginning toclog the outlet structure of a detention

facility.

lutant load and the forebay size.

Both dry and wet detention systems have thepotential for debris clogging an inlet or outletstructure. There can be a surprising amountof debris generated in residential communi-ties, and commercial facilities can expect de-bris of all sorts. Inspections for debris shouldbe made on a monthly basis or after rainevents to ensure that all components of thestormwater facility are operating as required.

Removal of sediments will also be needed ona periodic basis. Coarser sediments can beexpected to be found close to the pond inlet,with finer sediments expected to be depos-ited closer to the pond outfall. In terms of vol-ume, the coarser sediments will occupy agreater volume and maintenance removal ofthese sediments will be needed more fre-quently than removal of finer sediments.Studies of detention ponds used by theFlorida Department of Transportation in-dicate that sediments need to be removedabout once every 10 to 20 years. Usingforebays, which can be more easily cleanedout more frequently, can increase the timebefore sediments will need to be removed fromthe entire pond. Recommendations for dis-posal of collected sediments are presentedin Chapter 9.

Example of a forebay prior to flow enteringthe wet pond, which is located in the rear of

the picture.

Extended detention facility where waterquality is provided by the small orifice at thebottom of the weir. Maintenance should bemainly concerned with keeping the grate

unclogged.


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Removing sediment from a wet pond shouldbe done by draining the water down to thelowest possible elevation. If possible, a smallpool of water should be left to provide habitatfor the resident fish population. Removingsediment while having a normal pool of waterwill cause significant turbidity with the finersediments traveling downstream. When thesediments are removed from the pond, theyshould be placed at a location where they candry prior to final placement. It is important tohave sediment control provisions included inthe maintenance costs to prevent downstreamincreases in pollutant loadings or to preventremoved sediments from reentering the facility.Sediment removal from dry detention systemsis more straightforward. Since these facili-ties are normally dry, sediments can be re-moved by an appropriate means and disposedof properly. Experience has shown that itis easier and more effective to removesediments when they are dry and cracked,and thereby separated from the vegetation.Sediment control during maintenance is stillnecessary in case of storms that could mobi-lize stockpiled materials or erode exposedsoils.

Erosion problems can occur with either dry or

Pond inflow point clearly showing thecoarser sediments dropping out of

suspension .

Erosion behind the grouted riprap wingwallwill eventually cause failure of the riprap,

which will increase sediment loadingsdownstream negating the BMP's benefit.

Gate valve for a stormwater managementpond. When maintenance inspections aredone, the valve should be operated and

lubricated to ensure proper function.

wet detention systems. For the most part theystart as small problems which, if uncorrected,can grow into large problems and possiblythreaten the integrity of the detention facility.Inspections to locate erosion problems shouldbe done at least annually or after majorstorms. Evidence of significant foot or biketraffic in areas where vegetation has died in-dicate potential erosion areas in the future.These areas should be protected from traffic


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or provided with a more erosive resistantground cover.

Periodic maintenance of structural com-ponents must be done to ensure their con-tinued operation. This includes inspectingany joints for possible leakage or seepage.Areas should also be checked for corrosion,valves should be manipulated and lubricatedwhen needed, and all moving parts inspectedfor wear and tear.

The most important concern of stormwatermanagement detention and retention ponds

is safety. Situations may occur which, if noaction is taken, may cause imminent struc-tural failure of the facility. Inspections mustbe made at least annually to ensure the safetyof a facility. If there is any concern that thefacility is unsafe, assistance must be re-quested from an individual who has expertisein dam safety. Failure to take action, whenconfronted with a potential problem, canincrease liability if a failure occurs. Com-plete failures of stormwater management sys-tems generally do not occur overnight. Theystart as small problems and increase gradu-ally.

Ponds are rather unique when compared toother types of stormwater systems. If filtra-tion, biofiltration, or infiltration facilities fail orclog, their reduced performance generally willnot result in downstream safety concerns.Ponds provide effective water quality perfor-mance, but that performance is gained at thecost of increased safety concerns. They mustbe designed correctly, built satisfactorily, and

Leakage around the barrel and riser assem-bly. This could cause piping of water adja-cent to the barrel which would jeopardize

the structural strength of the facility.

Water piping around a barrel. The wateris flowing with considerable velocity.

This may be as bad as it gets. This retentionfacility was in a state of failure. The em-bankment had to be breached and com-

pletely rebuilt. The problem resulted fromseepage around the barrel causing embank-

ment soil to move with the flow of water.This failure resulted from poor construction.


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actively maintained. A failure in any one ofthe three aspects of detention or retentionfacilities could result in significant problems.Ponds are a valuable tool in controlling storm-water runoff, but care must be taken to en-sure that the service they were constructedto provide continues.

13.2 Infiltration Practices

Infiltration facilities encompass a wide rangeof BMPs as previously discussed. Mainte-nance issues are generally related to one ortwo major concerns:

• clogging• standing water

Clogging of these practices can occur fromsediments entering the facility and sealing thesoil surface, preventing infiltration of runoff.Clogging can also occur from excess oils andgreases entering the facility, or from microor-ganism growth which results when waterstands too long in the facility. As water infil-trates into the soil, the algae can clog the soilsurface and prevent infiltration. Whatever thereason, clogging will cause failure of infiltra-tion practices creating long term problems.

Infiltration facilities must go dry between

storm events to provide maximumstormwater management benefits. Theirclogging means less runoff is infiltrated andmore goes into the overflow system on a morefrequent basis. Clogging may also mean thatwater is permanently present in the facility, whichcan then become a mosquito breeding area.

Close up sediments clogging an infiltrationbasin. Silt and clay sediments are thegreatest concern since they can seal

the basin/soil interface area.

Excessive silt-clay sediments have cloggedthe basin floor causing this infiltration basin

to fail.

Algae on an infiltration basin floor hascaused failure of the facility by preventing

infiltration of stormwater.


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Standing water results from clogging whichobstructs the flow of water into the ground.Standing water can also result from seasonalhigh water tables or ground water moundingin the vicinity of the facility. If either of theseproblems occur, the facility's performance willdepend on exfiltration out of the sides insteadof the bottom.

If ground water problems persist at the facil-ity, contingency plans may be needed. Thesecould include conversion of the infiltration sys-tem to a practice which includes a permanentpool of water such as a wet detention or con-structed wetland system. Another alternativeis to provide the facility with a structural out-let to prevent seasonal or permanent waterpooling. If either of these options are neces-sary, the appropriate inspection and/or ap-proval agency should be contacted to ensureapproval of the modifications. In such cases,future inspections will be based on the modi-fications rather than maintaining expectationsassociated with the originally approved andconstructed facility.

With respect to maintenance activities, the firststep is to inspect the infiltration facility to de-termine if there is standing water during a pe-riod of time when it hasn't rained. If standingwater exists, then it needs to be deter-

Infiltration basin constructed in the watertable. Excellent exfiltration out of the basin

sides maintaind proper functioning.

Example of a failed infiltration basin causedby clogging and not seasonal or mounded

water table. The basin should be pumped ofwater and allowed to dry out before

sediment is removed.

mined whether the cause is clogging of thefacility, seasonal water table conditions,or ground water mounding. This analysisis crucial for determining the next steps. If theproblem is caused by a high water table ormounding, an entire new strategy will beneeded to correct the problem. If clogging isthe reason, maintenance activities will needto be performed to restore desired infiltrationrates.

Ideally, the inspection will find only partial clog-ging, allowing sediments to be removed whenthe facility dries out. If the facility is totallyclogged, correction is much more difficult. Thefacility should be drained and allowed to dryout before removing sediments. If sedimentremoval is attempted while water is standingin the facility, the finer sediments will becomesuspended and not be removed from the fa-cility. These suspended sediments are re-sponsible for the initial clogging of the prac-tice, and their resuspension will last only untilquiescent conditions allow for resettlement.


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The facility will never achieve the desired re-establishment of infiltration rates.

Safeguards should be installed during con-struction to reduce maintenance concerns.However, even with design and constructionbeing sensitive to future maintenance, main-tenance problems will occur as they do for allstormwater management facilities. For ex-ample, to facilitate maintenance, rock filled in-filtration trenches should be designed to havefilter fabric placed approximately one foot be-low the surface of the facility. This fabric is adesign point of failure which allows the un-derlying stone to remain clean. If standing

water persists on the surface of the facility,the top foot of stone should be removed andthe filter fabric removed and replaced. Thisdesign prevents the need to replace the en-tire stone reservoir base.

The use of vegetative filters as a pretreatmentBMP to improve long term performance of in-filtration facilities cannot be stressed toomuch. The pictures on this page of infiltra-tion trenches at the same site clearly showthe partial clogging of the trench abutting theparking lot. The ten feet wide buffer strip be-tween the paved surface and the trench sig-nificantly reduces the maintenance concernsassociated with trench clogging.

Of primary importance to the long termfunction of infiltration practices is the needto keep all contributing drainage areasstable. Sediment loadings into the facilitymust be kept to a minimum. All inspections ofthese facilities must include inspection for sitestabilization. All areas draining to the infiltra-tion facility must be stabilized or prematureclogging of the facility will result. The infiltra-tion system checklists recommend annual in-spections for sediment accumulation. Thefrequency of actual maintenance activitiesdepend on loadings from contributing drain-age areas.

Two infiltration trenches on the same site.The value of the vegetative buffer strip

can clearly be seen.

Clogged infiltration swale. The individualswale blocks must be dewatered before

accumulated sediments are removed.


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Porous paving or lattice block systems aresomewhat unique. Reduced maintenancecannot be designed into the BMP as is donefor other infiltration facilities by usingbiofiltration, fabrics, or forebays to help pre-treat runoff. Design options to reduce main-tenance for infiltration paving is predominantlylimited to using them in areas of low traffic,where paving is still necessary, or criteriaspecifying a certain frequency of vacuumsweeping. In general, vacuum sweepingshould be done weekly with an annual pres-

sure washing using biodegradable cleaners.

Education is especially important in reducingOMM of infiltration paving practices. It is veryimportant that owners are aware of the pervi-ous nature of the paving surface. A commonapproval condition is to require that signs beplaced around the parking area to notify allusers that the surface is pervious, and thatsediment tracking needs to be minimized.Signage also alerts owners of the need for in-kind replacement of the pervious pavement,if needed.

One type of porous parking surface is latticeblock paving. This surface comes in modularunits which can be placed down in blocks.Lattice block paving can include filter fabricunder the blocks to facilitate future mainte-

Porous paved parking lot clogged due toexcess sediment on parking surface.

Sign at a hotel porous pavement parkinglot. If paving needs to be replaced, the signclearly states maintenance requirements.

Lattace block infiltration system at acommercial parking lot. The open areas are

filled with pea gravel to provide supportfor shoe heels.


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nance. When maintenance is necessary, thelattice block can be lifted up in individual sec-tions, the filter fabric under the block replaced,and the blocks restored to their original places.However, some form of maintenance will prob-ably be necessary on an annual basis. Po-rous paving facilities may require more fre-quent maintenance, depending on the vehicu-lar traffic using the paved area. In heavilytrafficked areas, vacuum sweeping should bedone on a monthly, or at least quarterly basis.

13.3 Filtration Practices

There are three distinctly different types of fil-tration systems, depending on whether theAustin, Delaware, or Washington, DC ap-proaches are used. The Austin filter acceptsrunoff from entire drainage areas, which in-cludes pervious areas where sediments maybe finer sized than sediments from impervi-

ous areas only. The Washington, DC filterprovides stormwater quantity and quality man-agement from smaller drainage areas. TheDelaware filter only provides stormwater qual-ity treatment from impervious drainage areas.In a similar fashion, though, the frequency ofmaintenance of all of these facilities dependson the loadings entering the facilities, regard-less of the type of facility.

All three approaches have two major compo-nents of their systems which include:

• a sedimentation chamber• a filtration chamber

The sedimentation chamber provides a vol-ume of storage for coarser sediments anddebris. Maintenance inspections should con-sider the depth of materials which have beendeposited in the sedimentation chamber andthe potential for those trapped materials to

Sedimentation chamber

Filter chamber

Sedimentation chamber

Austin sand filter serving a commercial facility. The sediment chambers are on both sides ofthe filter with the sand filter accepting flow through the gabion baskets.


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migrate to the filtration chamber. The depthof accumulated sediments will be relativelyeasy to measure in all three types of facilities.

A. Austin Sand Filter

The sedimentation chamber for the Austinsand filter is designed for larger drainage ar-eas and normally remains dry between storms.Consequently, it is normally maintained in thesame fashion and with the same equipmentas a dry detention facility. The frequency ofmaintenance depends on the stabilization ofsoils in the contributing watersheds. Mainte-nance of the sedimentation chamber is gen-erally not needed more frequently than everyfive to ten years. It is important that accessbe provided to the sedimentation chambersfor maintenance equipment to enter and per-form needed maintenance.

The frequency of maintenance for the filtercomponent of the Austin sand filter dependson the magnitude of the incoming pollutantloadings. However, in general, filters may re-quire cleanout every year. The finer sedi-ments may be raked from the surface of thesand and removed, or a flat bottom shovelcould skim the surface of the sand to rees-tablish sand permeability.

B. Washington, DC and Delaware Sand Filters

The Washington, DC and the Delaware sandfilter sedimentation chambers are normallywet. As such, the accumulated material willbe wet and removal is best accomplished byusing vacuum type equipment. In general,the volumes of water to be removed from eachsystem are fairly small since the facilities servesmaller drainage areas than the Austin ap-proach. This makes vacuuming a practicalalternative. The frequency of vacuuming willdepend on the loading contributed from thedrainage areas. However, experience indi-cates that maintenance cleanout of the sedi-mentation chambers is not often needed inless than 10 years of active service.

The filtration chambers are more sensitivethan the sedimentation chambers to cloggingby sediments and other fine grained materi-als, such as oils and greases. While the sedi-mentation chamber functions primarilythrough gravity settling of the incoming mate-rials, the filtration chamber is where filteringof pollutants occurs. This chamber will bemore effective at removal of the finer sedi-ments, which will be retained in the top sev-eral inches of the filter media.

Filtration chamber of an Austin sand filtershowing overflow spillway. The sand

media needs to be inspected regularly todetermine if design permeabilities are

reduced.

Delaware sand filter showing both thesedimentation and filtration chambers. Thesedimentation chamber is permanently filled

with water to prevent resuspension of theaccumulated sediments.


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The filtration chamber will need maintenanceon a much more frequent basis than will thesedimentation chamber. If the sand filter is inan area with a significant pollutant loading,filter maintenance may be needed at leasttwice per year to ensure that the design flowstravel through the facility. Diminished perme-ability of the sand will result in more frequentoverflows into the conventional drainage sys-tem with less stormwater treatment. Replace-

ment of the filter media is most easily accom-plished with a flat bottom shovel to removethe accumulated materials. It will be fairlyeasy to see the depth of penetration of thepollutants and how much filter media needsremoval. Usually, it is not necessary to replaceall of the filter media, only the top layer.

C. Information Applicable to all ThreeFilter Designs

When portions of the filter media must be re-placed, only materials which meet the storm-water program's filter specifications should beused. There is a lot of research being doneEvidence of scour at the entrance to the

filtration chamber from the sedimentationchamber. The connecting areas between

chambers should be protected with anonerosive material, such as stone or a

splash pad.

Sand filter in Auckland, New Zealand. Thesand filter serves a commercial parking lot.Vegetation growing in the filtration chamber

may indicate a need for maintenance.

Waste oil was dumped in this Delawaresand filter and sealed the filter mediaalmost immediately. The top several

inches of sand had to be replaced. On thegood side, if the filter were not present,

the oil would have been discharged on thecommunity beach.


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with alternative filter media such as compost,activated carbon, alum, etc. If the approvingagency allows or specifies an alternative fil-ter media as a replacement, there must bedocumentation in the inspection and owner'sfiles on the use of a media different than speci-fied on the approved plans. Most commonlyused at this time for filter media sand is ASTMdesignation C-33 concrete sand.

Depending on the pollutants which can be ex-pected in the filter system, testing of the ma-terial to be removed should be done to deter-mine a suitable location for its disposal. Ingeneral, existing information indicates that dis-posal at a landfill is appropriate, but if the fil-tration facility serves an industrial facility, thesediments should be tested to determine ifthey are considered hazardous materials.There is a greater discussion of sediment test-ing and disposal in Chapter 9.

As with all stormwater management facilities,there is always the potential for vandalism.This can include damage to the facility itself,theft of facility components, or illegal dump-ing of waste products such as waste oil.These problems must be expected, and al-though not specifically anticipated, remedialaction must be quickly accomplished.

A primary method to reduce vandalism is a

community education program explainingstormwater pollution generation, the impor-tance of BMPs such as filter systems, and theneed to limit pollutant entry into BMPs. Onecomponent of this education program couldbe stenciling of the inlets to the filter. Thismay limit some individuals conducting the van-dalism through ignorance of the facility's pur-pose.

Other maintenance concerns such as scour,leakage, spalling of concrete, cracks in con-crete or grates need to be addressed whenthey are discovered. Washington, DC andDelaware filter systems have a permanentpool of water in the sedimentation chambers.If these chambers become dry, there is leak-age, and the leakage must be stopped for thefacility to function correctly. If the leaking area

Stenciled pollution message adjacent toa filtration facility.

Delaware filtration facility subject to liveloads at a gasoline station.


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cannot be identified, a dye test may be nec-essary to track the flow of water in the leakingchamber. In addition, all three of these typesof filters use concrete in their construction.Concrete will deteriorate over time, especiallyif subject to live loads. The concrete must beroutinely inspected, and repaired when nec-essary.

13.4 Biofiltration Systems

Biofiltration facilities treat runoff by filtering itthrough dense growths of vegetation. Thisfiltering can be done by passing stormwaterthrough a vegetated swale or through a de-signed buffer strip. Biofiltration functions relyprimarily on flow traveling through the facilityin a dispersed condition, preventing concen-trated flow of runoff. Besides vegetative fil-tration, treatment in biofilters often also reliesupon infiltration of runoff into underlying soils.Therefore, maintenance of biofiltration facili-ties is primarily concerned with:

• Maintenance of dispersed flow throughthe biofilter.

• Maintaining a thick growth of vegeta-tion.

• Preventing undesired overgrowth veg-etation from taking over the area.

• Removal of accumulated sediments.

• Debris removal.

Maintenance of dispersed flow through thebiofiltration facility is critical if itsstormwater treatment effectiveness is tobe maintained. Concentrated flow travels ata higher velocity than does dispersed flow,and may transport pollutants through thebiofiltration system before they are removedfrom the runoff.

A dense growth of vegetation enhances bio-filtration facility performance for stormwatertreatment. Therefore, vegetation maintenancewill require close attention by system ownersor operators. Mowing is needed on a periodicbasis, but mowing must be correctly done.Mowing grass too short will damage the grass,increase runoff flow velocities, and therebydecrease pollutant removal effectiveness. Ifthe grass grows too tall, it may lie down dur-ing a storm instead of filtering runoff, alsodecreasing treatment effectiveness.

Inspections must be done to ensure that thedesired vegetation remains in the facility. Theinvasion of undesired vegetation can occur ifsite conditions promote its growth. In somesituations the replacement of the planted veg-etation by a volunteer species may be ben-eficial, but only if the invasive species pro-

Well maintained biofiltration swale serving acommercial development. There is someevidence of oil staining of the vegetation.

Biofiltration swale showing mowing wearand other signs of spotty vegetation

demonstrating the need for maintenance.


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vides equal or increased water quality ben-efits and is accepted by the owners of the site.If site slopes are very flat, the biofiltration fa-cility could become dominated by wetlandplants. The dense growth of wetland plantsmay be desired for stormwater treatment andalso will reduce the typical mowing costs as-sociated with biofiltration facilities. In this situ-ation, the maintenance file documents theshift in the plant community and provideguidelines for how to take care of the modi-fied site condition.

Sediments will accumulate in biofiltration sys-tems and their removal may be the most ex-pensive aspect of biofiltration maintenance.

When sediments are to be removed, it is es-sential to restore the slope and elevations tothe originally constructed condition. Sedimentremoval will necessitate disturbance of thevegetation in the facility, so steps will have tobe taken to reestablish the vegetation uponcompletion of sediment removal. Erosioncontrol in the contributing drainage area alsowill be necessary to prevent scour of the fa-cility until there is once again a dense standof vegetation. Examples of erosion controltechniques are shown in Chapter 6.

Sediment may also impeding effective perfor-mance of a biofiltration facility by clogging itsinlets, preventing design storms from beingtreated in the facility. If stormwater backs upinto the upstream drainage area, overflow mayoccur to an area not designed to accept addi-tional flow. In this situation, erosion and siteinstability may result from an inlet becomingclogged with sediments.

Similar to other types of practices, debris re-moval is an ongoing maintenance function atall biofiltration systems. Debris, if not re-moved, can block inlets or outlets, cause flowto become concentrated, and can be unsightlyif located in a visible location. Inspection andremoval of debris should be done on a monthly

Sediment accumulation in a biofiltrationfacility reduces the effectiveness of that

facility in removing pollutants. This swaleis in need of maintenance to reestablishdesired water quality control conditions.

Biofiltration swale with little slope, poordrainage, and baseflow. The swale is well

vegetated with wetland plants.

A clogged curb cut impedes flow enteringthe biofiltration system. A better designwould have a wider opening with a small

vertical drop to prevent sediment cloggingof the opening.


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basis, but debris should be removed when-ever it is observed on site.

Just as it is important to know when a fa-cility needs to be maintained, it is impor-tant to know when you don't have to domaintenance. The original plan for the siteprovides the best information at that time onthe design and construction of the biofiltrationfacility. Over time the facility may change inappearance and function. These changes maynot necessarily be bad. Having a knowledge-able inspector conduct regular inspectionsmay be one way to allow a facility to evolveinto an improved facility with reduced mainte-nance costs. The emergence of wetland

plants in a biofilter, or the growth of nativevegetation, may improve its value and perfor-mance.

If you are unsure of the value of perform-ing a maintenance activity, discuss thespecific situation with the inspector orplan approval agency to see if there canbe an improvement made to the facility.

14. GENERAL DISCUSSION

If there is any confusion about the type ofstormwater management facility, it's pur-pose, or what specific maintenance activi-ties are important, ASK FOR HELP!Stormwater systems can be simple in conceptand function, but they can also be complexand confusing to the average individual whois far too often responsible for the facility'slong term performance.

The inspection agency and approval agencymust be available and receptive to public re-quests for assistance with stormwater man-

An unmaintained, but well vegetated biofiltra-tion system. Debris needs to be removed

from the facility.

This is a natural well vegetated biofiltra-tion facility. It is not regularly mowed butis performing its water quality function.

The design and operation of this facility willneed to be clearly understood if effectivemaintenance is to occur. The taller riser

contains a pump to drain the water qualityvolume to a higher elevation for discharge.


7-42

agement system operation, maintenance, andmanagement. Often, this technical assistancewill include conducting site inspections withthe owner or operator to go over the approvedplan, discussing maintenance inspectionchecklists, and providing advice to the owneror operator.

It is expected by this time, that the inspectorknows to ask the plan review agency aboutspecific aspects of facility design and con-struction, but that information must also betransmitted to the eventual owner/operator. Asite meeting between the inspector and ownerupon the owner's assumption of maintenanceresponsibility is very important. At this time,checklists can be given to the owner alongwith other educational information that mayprovide the owner with increased awarenessabout the need for proper maintenance andhow it can be accomplished. At the same time,the inspector should give the owner a list of

individuals who can provide assistance ifproblems are encountered.

Design and approval of a stormwater man-agement system is done to the best degreepossible without complete awareness of indi-vidual site development characteristics. In ad-dition, development of a specific site may ne-cessitate a different approach to stormwatermanagement. In such situations, the ap-proved plan is a springboard to water re-sources protection. As the developed site ma-tures, changes may be necessary to thestormwater facility. A good relationship be-tween the approval agency, inspectionagency, owner, and operator can provide theflexibility needed to assure resource protec-tion while allowing consideration of specificsite conditions. Communication and com-mitment are essential for assuring the longterm operation, maintenance, and manage-ment of stormwater management systems.

The operation of this stormwater management system appears very confusing. Theinspector must work closely with the owner/operator to ensure that proper performance

is maintained.


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APPENDIX 7-1


Inspection Checklist for Ponds


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Operation and Maintenance Inspection Report for Stormwater Management Ponds(Adapted from Anne Arundel County, Maryland)

Inspector Name __________________________ Community _________________________Inspection Date __________________________ Address _________________________Stormwater Pond _________________________

Normal Pool ______ _________________________Normally Dry ______ Watershed _________________________


I, Pond components

A. Embankment andEmergency spillway A,S1. Vegetation and ground

Cover adequate2. Embankment erosion3. Animal burrows4. Unauthorized plantings5. Cracking, bulging, or

sliding of dama. Upstream faceb. Downstream facec. At or beyond toe

UpstreamDownstream

d. Emergency spillway6. Pond, toe & chimney

drains clear and functioning7. Seeps/leaks on

downstream face8. Slope protection or

riprap failures9. Vertical and horizontal

alignment of top of dam asper "As-Built" plans

10. Emergency spillway clearof obstructions and debris

11. Other (specify)B. Riser and principal spillway A

Type: Reinforced concrete ___ Corrugated pipe ___ Masonry ___

1. Low flow orifice obstructed2. Low flow trash rack

a. Debris removal necessaryb. Corrosion control

3. Weir trash rack maintenancea. Debris removal necessaryb. Corrosion control



7-45


4. Excessive sedimentaccumulation inside riser

5. Concrete/Masonry conditionRiser and barrelsa. Cracks or displacementb. Minor spalling (<1")c. Major spalling

(rebars exposed)d. Joint failurese. Water tightness

6. Metal pipe condition7. Control valve

a. Operational/exercisedb. Chained and locked

8. Pond drain valvea. Operational/exercisedb. Chained and locked

9. Outfall channels functioning10. Other (specify)

C. Permanent pool (wet ponds) M1. Undesirable vegetative

growth2. Floating or floatable debris

removal required3. Visible pollution4. Shoreline problems5. Other (specify)

D. Sediment forebays1. Sedimentation noted2. Sediment cleanout when

depth < 50% designdepth

E. Dry pond areas M1. Vegetation adequate2. Undesirable vegetative

growth3. Undesirable woody

vegetation4. Low flow channels clear

of obstructions5. Standing water or wet spots6. Sediment and/or trash

accumulation7. Other (specify)

F. Condition of outfalls into pond A,S1. Riprap failures2. Slope erosion3. Storm drain pipes4. Endwalls/headwalls5. Other (specify)

G. Other M1. Encroachments on pond or

easement areaInspection Frequency Key A=Annual, M=Monthly, S=After major storm


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2. Complaints from residents(describe on back)

3. Aestheticsa. grass mowing requiredb. graffiti removal neededc. Other (specify)

4. Any public hazards (specify)5. Maintenance access

H. Constructed wetland areas A1. Vegetation healthy and

growing2. Evidence of invasive species3. Excessive sedimentation in

wetland area


II. Summary

1. Inspectors Remarks: ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Overall condition of Facility (Check one)_____ Acceptable_____ Unacceptable

3. Dates any maintenance must be completed by:

________________________________________________________________________________________________________________________________________________________________________________________________


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APPENDIX 7-2


Inspection Checklistsfor Infiltration Practices:




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Infiltration Basin Maintenance Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________



Satisfactory UnsatisfactoryBasin bottom clear of debrisInlet clear of debrisOutlet clear of debrisEmergency spillway clear of debris

2. Sediment traps or forebays (Annual)





Basin dewaters between storms

5. Sediment cleanout of basin (Annual)

No evidence of sedimentation in basinSediment accumulation does not yet require cleanout

6. Inlets (Annual)




8. Structural repairs (Annual, After Major Storm)

Embankment in good repairSide slopes are stableNo evidence of erosion



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9. Fences/access repairs (Annual)

Fences in good conditionNo damage which would allow undesired entryAccess point in good conditionLocks and gate function adequate


Action to be taken:






________________________________



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Infiltration Trench Maintenance Inspection Report FormAdapted from the State of Maryland Inspector's Guidelines Manual

Date _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________



Satisfactory UnsatisfactoryTrench surface clear of debrisInlet areas clear of debrisInflow pipes clear of debrisOverflow spillway clear of debris

2. Sediment traps, forebays, or pretreatment swales (Annual)





Trench dewaters between storms

5. Sediment cleanout of trench (Annual)

No evidence of sedimentation in trenchSediment accumulation does not yet require cleanout

6. Inlets (Annual)






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8. Aggregate repairs (Annual)

Surface of aggregate cleanTop layer of stone does not need replacementTrench does not need rehabilitation

9. Vegetated surface (Monthly)

No evidence of erosionPerforated inlet functioning adequatelyWater does not stand on vegetative surfaceGood vegetative cover exists


Action to be taken:






________________________________



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Infiltration Dry Well Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________



Satisfactory UnsatisfactoryRoof drains and downspouts clean

2. Vegetation on top of dry well (Monthly)



Dry well dewaters between storms

4. Inlets (Annual)

Good condition of down spoutsNo evidence of deteriorationRoof gutters drain correctly into dry well











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Infiltration Paving Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________


Inspection frequency shown in parentheses after item being considered1. Debris on infiltration paving parking area (Monthly)

Satisfactory UnsatisfactoryPaving area clean of debris

2. Vegetation (any buffer areas or pervious areas in drainage area)(Monthly)



Infiltration paving dewaters between storms

4. Sediments (Monthly)

Area clean of sedimentsArea vacuum swept on a periodic basis

5. Structural condition (Annual)

No evidence of surface deteriorationNo evidence of rutting or spalling









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Infiltration Swale Well Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________



Satisfactory UnsatisfactorySwales and contributing areas clean of debris


mowing done when neededFertilized per specificationsNo evidence of erosionMinimum mowing depth not exceeded


Swale dewaters between storms

4. Check dams or energy dissipators (Annual, After Major Storm)

No evidence of flow going around structuresNo evidence of erosion at downstream toe


Swale clean of sediments




If any of the answers to the above items are checked unsatisfactory, a time frame shall be established fortheir correction or repair







7-55

APPENDIX 7-3





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Filtration Facility Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________


Warning: If filtration facility has a watertight cover; be careful regarding the possibility offlammable gases within the facility. Care should be taken lighting a match or smoking whileinspecting facilities that are not vented.


Satisfactory UnsatisfactoryContributing areas clean of debrisFiltration facility clean of debrisInlets and outlets clear of debris


Contributing drainage area stabilizedNo evidence of erosionArea mowed and clippings removed

3. Oil and grease (Monthly)

No evidence of filter surface cloggingActivities in drainage area minimize oil & grease entry

4. Water retention where required (Monthly)

Water holding chambers at normal poolNo evidence of leakage


Filtration chamber clean of sedimentsWater chambers not more than 1/2 full of sediments

6. Structural components (Annual)

No evidence of structural deteriorationAny grates are in good conditionNo evidence of spalling or cracking of structural parts


Good condition, no need for repairNo evidence of erosion (if draining into a natural channel)



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8. Overall function of facility (Annual)

No evidence of flow bypassing facilityNo noticeable odors outside of facility


Action to be taken:



Facility repairs were indicated and completed. Site reinspection is necessary to verify correctionsor repairs.





7-58

APPENDIX 7-4





7-59

Biofiltration Facility Maintenance Inspection Report FormDate _________________ Time _____________________

Project _______________________________________________________________________

Location _____________________________________

Individual Conducting the Inspection ______________________ "As Built" Plans available Y/N


Satisfactory UnsatisfactoryBiofilters and contributing areas clean of debrisNo dumping of yard wastes into biofilterLitter (branches, etc.) have been removed


Plant height not less than design water depthFertilized per specificationsNo evidence of erosionGrass height not greater than 6 inchesIs plant composition according to approved plansNo placement of inappropriate plants


Biofilter dewaters between stormsNo evidence of standing water

4. Check dams/energy dissipators/sumps (Annual, After Major Storm)

No evidence of sediment buildupSumps should not be more than 50% full of sedimentNo evidence of erosion at downstream toe of drop structures


Swale clean of sedimentsSediments should not be > than 20% of swale design depth


Good condition, no need for repairNo evidence of erosionNo evidence of any blockages

7. Integrity of biofilter (Annual)

Biofilter has not been blocked or filled inappropriately



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Action to be taken:







Chapter 8Costs and Financing of Stormwater

Facility Operation and Maintenancetion on the costs of stormwater system op-eration, maintenance, and management to:

••••• Stormwater system owners.

••••• Directors of stormwater utilities,public works, stormwater programs,and other public and private agenciesresponsible for stormwater systemmaintenance.

••••• Purchasing agents, managers, anddirectors.

The chapter also discusses various methodsof obtaining adequate public and private fundsfor required stormwater system operation,maintenance, and management. This infor-mation is intended specifically for:

••••• Elected officials and other leaders ofstate, regional, and local governmentsresponsible for stormwater systemmaintenance.

••••• Stormwater program administrators,business administrators, comptrollers,financial directors, and other public andprivate sector officials responsible forfinancing stormwater system mainte-nance.

2. STORMWATER SYSTEMMAINTENANCE COSTS

To develop sound stormwater system opera-tion, maintenance, and management budgetsand determine adequate funding levels, acomprehensive data base of OMM costs is

8-1

1. OVERVIEW

Even if a stormwater management programhas established effective institutional mecha-nisms to help assure that stormwater systemsare operated and maintained properly, prob-lems can arise because of inadequate knowl-edge about the costs of maintenance. An-nual program budgets must include adequatestaffing and financial resources to conduct themaintenance activities needed to assure thatstormwater systems operate properly. Addi-tionally, the stormwater program must assurethat financial mechanisms are implementedto provide the needed funding.

The fundamental role that proper budget-ing and financing plays in the successfulperformance of effective stormwater sys-tem maintenance cannot be overempha-sized. The specific objectives of this chapterare:

• To provide operating and maintenancecost information from several stormwaterprograms around the country.

• To provide methods by which stormwaterprograms can estimate operation andmaintenance costs.

• To provide general information on variousalternative methods of financingstormwater system operation, mainte-nance, and management.


This chapter is intended to provide informa-


8-2

needed. Unfortunately, there is very little harddata on the actual costs of stormwater sys-tem OMM, especially for stormwater treatmentBMPs. This chapter will present data ongeneral OMM costs along with specific costdata from several stormwater programsaround the country.

It is important to remember that the cost ofstormwater system OMM is very site specific.Factors that determine the frequency, type,and cost of OMM include the type and size ofBMP, use of source controls, land use, con-tributing drainage area, rainfall characteristics,climate, vegetation growing system, mainte-nance access, and disposal requirements.

Table 8-1 presents cost estimates for variousequipment and materials used in typicalstormwater management system OMM. Costsare provided both for equipment purchase andrental. In many cases, renting equipment,is a preferred alternative. This is especiallytrue for infrequently used equipment orlarger, very expensive equipment. Addi-tionally, local governments often find itadvantageous to contract for the use ofhighly specialized equipment since staffmay not have the experience needed tooperate it. Purchasing these types of equip-ment, and especially more commonly usedequipment, may be justified when it can beused for activities other than stormwater facil-ity maintenance, such as by road, publicworks, or recreation departments. For largerequipment, it may be less expensive to leasefor a short time instead of renting by the day.

These cost estimates are intended to providegeneralized cost data to those in both the pub-lic and private sectors involved either in theactual OMM of stormwater systems, or in theplanning, budgeting and financing forstormwater system OMM. The reader shoulddevelop more detailed cost estimates basedupon local data or data pertaining to a spe-cific program or type of stormwater system.

Sources of more specific data include localequipment sales, lease, and/or rental compa-nies, and local maintenance and constructioncontractors. Valuable information can be ob-tained from local government stormwater,public works, parks, or road departments.Consultation and coordination between thesevarious departments within local governmentsor private companies is strongly recom-mended.

Table 8-2 summarizes the estimated per-son-hours associated with many of themore common stormwater system opera-tion, maintenance, and management activi-ties. These values can be used with ap-plicable personnel rates to determine la-bor costs for a specific stormwaterprogram or facility. The reader should notethat the estimates are based on the entire areaof a stormwater system. Additionally, dryBMPs are assumed to be entirely covered withgrass which requires regular mowing, fertil-izer, and other management. Appropriateadjustments should be made for wet BMPsand for facilities that are larger than one acre.

In addition to labor and materials costs,an additional allowance needs to be madefor the disposal of trash, debris, leaves,and sediments. These costs can be mini-mized by having a dedicated area where ma-terials can be composted or where sedimentscan be dewatered and reused. These areascan either be on-site near the stormwater sys-tem or at a centrally located materials yardwithin the community. Disposal of these ma-terials must comply with federal, state, and/orlocal regulations (See Chapter 9). Accord-ingly, costs and requirements can vary widely.

3. OMM COSTS FROM SPECIFICSTORMWATER MANAGEMENTPROGRAMS

This section will present cost information from

CHAPTER 8 Operation and Maintenance Costs and Financing

8-3

TABLE 8 -1.Stormwater System OMM Equipment and Material Costs (1997).

GRASS MAINTENANCE EQUIPMENT

EQUIPMENT PURCHASE RENT (Per Day)

Hand mower $300 - $500 $25 - $50

Riding mower $3,000 - $7,000 $75 - $150

Tractor mower $20,000 - $30,000 $150 - $450

Trimmer/edger $200 - $500 $25 - $35

Spreader $100 - $200 $20 - $30

Chemical sprayer $200 - $500 $25 - $40

VEGETATIVE COVER MAINTENANCE EQUIPMENT

Hand saw $15 - $20 $5

Chain saw $300 - $800 $15 - $35

Pruning shears $25 - $40 $5

Shrub trimmer $200 - $300 $25 - $35

Brush chipper $2,000 - $10,000 $100 - $300

SEDIMENT, DEBRIS, AND TRASH REMOVAL EQUIPMENT

Vactor truck $100,000 - $250,000 $700 - $1200

Front end loader $60,000 - $120,000 $250 - $500

Backhoe $50,000 - $100,000 $250 - $500

Excavator >$100,000 $400 - $1,000

Grader >$100,000 $400 - $1,000

TRANSPORTATION EQUIPMENT

Van $18,000 - $30,000 $50 -$100

Pickup truck $15,000 - $25,000 $50 - $100

Dump truck $40,000 - $80,000 $100 - $200

Light duty trailer $3,000 - $6,000 $50 - $100

Heavy duty trailer $10,000 - $20,000 $100 - $250


8-4

TABLE 8 -1.

Stormwater System OMM Equipment and Material Costs (Cont.).

MISCELLANEOUS EQUIPMENT

EQUIPMENT PURCHASE RENT (Per Day)

Shovel $15 $5

Rake $15 $5

Pick $20 $5

Wheel barrow $100 - $250 $15 - $25

Portable compressor $800 - $2,000 $50 - $150

Portable generator $750 - $2,000 $50 - $150

Concrete mixer $750 - $1,500 $50 - $100

Welding equipment $750 - $2,000 $50 - $100

MATERIALS

MATERIAL PURCHASE

Topsoil $35 - $50/cubic yard

Fill soil $15 - $30/cubic yard

Grass seed $5 - $10/pound

Soil amenties (fertilizer, lime, etc) $0.10 - $0.25/sq. ft.

Chemicals (ie,pesticides, herbicides, etc) $10 - $30/gallon

Mulch $25 - $40/cubic yard

Dry mortar mix $5/50 pound bag

Concrete delivered $60 - $100/cubic yard

Machine/motor lubricants $5 - $10/gallon

Paint $20 - $40/gallon

Paint remover $10 - $20/gallon


8-5

TABLE 8 - 2.

Typical Hours Needed To Perform Stormwater OMM Tasks.

PREVENTATIVE MAINTENANCE TASKS(Values expressed in person-hours)

TASK SMALL FACILITY(Total area < 0.25 acre)

LARGE FACILITY(Total area > 1 acre)

Grass cutting 1 1 - 4

Grass management 0.5 1 - 2

Trash & debris removal 0.5 1 - 2

Sediment removal 4 6 - 10

Mobilization 1 1

Inspection & reporting 1 2

CORRECTIVE MAINTENANCE TASKSTrash & debris removal 4 6 - 10

Sediment removal 8 -12 8 - 40

Dewater ing 4 8 - 16

Aquatic vegetativemgmt.

4 6 - 16

Structural repairs 24 36 - 72

Erosion repair 1 - 4 3 - 8

Fence repair 2 - 4 4 - 10

Snow & ice removal 1 - 4 2 - 6

Mosquito extermination 1 2 - 4

Mobilization 2 2 - 4

AESTHETIC MAINTENANCE TASKSGrass trimming 0.5 - 1 1 - 4

Weed control 0.5 - 1 2 - 4

Landscape maintenance 1 - 2 2 - 8

Graffiti removal 2 - 4 4 - 8


8-6

country associated with their facility operation, maintenance, and management activities.Because the information from each program varies so greatly, information from each programwill be presented separately and in different formats.

3.1. City of Orlando, Florida

Orlando has required the treatment of stormwater since 1984, with recent emphasis on retro-fitting older drainage systems to reduce stormwater pollutant loadings into the City's lakes.The City conducts a wide range of operation, maintenance, and management activities on itsstormwater systems and has a very active lake management program. Summarized beloware costs associated with major OMM activities:

Activity CostHerbicide (Rodeo) application to ditch bottoms $170.00 per acreStreet grass control with herbicide (Roundup) $ 6.40 per city blockDitch mowing by hand using weed-eaters and mowers $ 60.00 per acreDitch mowing by large tractor $ 12.00 per acreCleaning of stormsewers and catch basins with Vactor $160.00 per hourRepair of structures (less materials) $ 50.00 per hour

3.2. City of Fresno, California

Fresno developed and is implementing a stormwater master plan which relies upon regionalstormwater retention (infiltration) facilities. The city's facilities are classified as "stormwatersystems", "recharge systems" or " fully landscaped systems", with the latter also serving as10 to 20 acre parks. The respective annual OMM costs for these facilities are $125/acre(stormwater systems), $197/acre (recharge systems), and $1,506/acre (landscaped systems).When accumulated sediments need to be removed from any of these systems the annualcost is approximately $275/acre. Table 8-3 provides a more detailed summary of thesecosts.

3.3. Somerset County, New Jersey

The primary focus of the stormwater management program in Somerset County is flood con-trol. The program, which began in 1975, operates an extensive flood control network withradiotelemetry controls of its main drainage structures. As part of its stormwater manage-ment system, a large number of dry detention basins, with concrete low flow channels, havebeen constructed. Maintenance of these systems primarily consists of grass trimming andmowing. When mowing is performed, erosion problems are identified and repaired, debrisand litter are removed, as is sediment which has accumulated in the low flow channel. TheCounty is responsible for the OMM of 52 dry detention systems with a land area of 164.5acres. These range in size from 0.5 to 21.5 acres.

Until 1992, the County used its own maintenance crew to perform all OMM operations. In


8-7

TABLE 8 - 3.

Maintenance Activities and Costs for Stormwater Management Systems in Fresno, California (1996).

STORMWATER SYSTEMS(No landscaping, 10 systems, 92.2 acres)

Activity Cost

Weeding $110/acre/year

Special (erosion control) $ 6/acre/year

Extra work (structural repairs) $ 4/acre/year

Miscellaneous $ 4/acre/year

FULLY LANDSCAPED SYSTEMS(10 basins, 84.1 acres)

Mowing $770/acre/year

Water $416/acre/year

Extra work (erosion, structuralrepairs)

$185/acre/year

P G & E $130/acre/year

Rodent control $ 5/acre/year

RECHARGE BASINS

Basin/Size Cost Cost/Acre/Yr

A - 10.0 acres $3,500 $350

S - 26.9 acres $4,000 $149

OO - 9.3 acres $ 57 $ 61

AC - 10.4 acres $2,500 $240

AE - 21.6 acres $1,728 $ 80

BO - 15.0 acres $4,112 $274

CL - 14.7 acres $4,400 $299

CN - 21.0 acres $5,000 $238

CO2 - 13.2 acres $1,535 $116

CW 15 3 acres $3 602 $235


8-8

1993, the county solicited bids for the work and hired a private contractor who did an excellentjob. In 1994, the county once again solicited bids and received the following bids:

Bidder Bid Price $/OMM Visit $/AcreCounty $68,236 $ 312 $414.81Bidder A $62,200 $ 284 $378.12Bidder B $56,100 $ 256 $341.03Bidder C $51,635 $ 236 $313.89

The three bid prices include $8,000 in County costs for supervision and inspection. This costis based on three hours of supervision/inspection per day, assuming 2 to 3 basins per day, fora total of 110 days at $25 per hour personnel costs. Based on these bids, the County awardedthe work to the low bidder, a different contractor than the County had used in 1993. Thiscontractor did not perform as well as the previous contractor. The County received manycomplaints from residents about the contractor's poor OMM work. Consequently, Countystaff performed many remedial OMM tasks resulting in $6,000 in additional costs. In 1995,the County's elected officials decided to allow the County maintenance crew to once againperform all OMM operations. Even though the cost was about $5,000 more than using aprivate contractor, advantages of using the County crew included better workman-ship, quicker response time to resident requests, fewer complaints from residents,and greater accountability.

Table 8-4 summarizes the activities and costs associated with the maintenance of 52 drydetention systems in Somerset County. The table shows the costs of maintenance for all basinsand for those with an area of 2 to 2.5 acres, the size of the typical system. It also shows the costsof performing stormwater maintenance activities two, three, and five times per year.

TABLE 8 - 4.Summary of 1994 Stormwater System OMM Costs

in Somerset County, New Jersey.

ITEM ALL1994

BASINS

2 - 2.5 ACREBASINS

2 OMM/YR 3 OMM/YR 5 OMM/YR

Total cost $62,450 $22,037 $6,039 $2,792 $53,669

Total #OMM 219 89 22 12 185

Total area 164.5 49 25.5 8 131

# Basins 52 22 11 4 37

$/OMM $285.16 $247.61 $274.50 $232.67 $290.10

$/Acre $379.64 $449.73 $236.82 $349.00 $409.69

$/Basin $1,200.9 $1,001.68 $549.00 $698.00 $1,450.51

OMM/Basin 4.21 4.04 2 3 5

Acre/Basin 3.16 2.23 2.32 2 3.54

$/Acre/OM $90 18 $111 32 $118 41 $116 33 $81 94


8-9

3.4. City of Austin, Texas

Austin, Texas began requiring the treatment of stormwater in 1984 as part of the city's programto protect its surface and ground water resources. The city's stormwater program annualbudget has varied in recent years from $16.28 million in FY93-94 to $16.76 million in FY94-95to $15.28 million in FY95-96. Stormwater OMM costs within these three budget years amountedto $3.16 million, $3.69 million, and $4.34 million. The primary funding source is from the city'sstormwater utility which collected $14.87 million, $15.42 million, and $13.56 million respec-tively in these three budget years. Additionally, stormwater OMM funding is obtained frominspection and maintenance fees which brought in $128,241, $170,000, and $260,131. Thenumber of employees at the utility has increased from 74 FTEs in FY93-94 to 78 in FY94-95to 86 in FY95-96, with increased maintenance of stormwater systems accounting for five ofthe eight new positions in this last year.

Tables 8-5 A-E present information from the city's most recent five year stormwater mainte-nance plan. The city's budget also includes the following performance measures for OMM:

Outcome 1993-94 1994-95 1995-96(goal)Removed sediments from creeks (cyds) n/a n/a 10,000Restore water quality ponds 8 12 20# restored ponds/maintenance FTE 0.8 2.0 4.0# water quality ponds maintained 161 273 327

3.5. Urban Drainage and Flood Control District (Denver, Colorado)

The UDFCD coordinates regional stormwater management in the metropolitan Denver area,covering 1608 square miles and 36 local governments. The District charges an annual drain-age fee which raises approximately $4 million per year. The District is responsible for OMMoperations at selected regional, multi-jurisdictional stormwater facilities, primarily drainageconveyances and dry detention systems. The District contracts most OMM work and con-ducts inspections to assure that the work is performed satisfactorily.

Routine OMM activities include mowings of non-irrigated natural grasses along drainage chan-nels, regularly scheduled collection and disposal of debris and litter from the drainageway,and unscheduled debris removal that become necessary because of large storms. Non-routine OMM activities include erosion repair and construction to rehabilitate or replace exist-ing drainage structures.

Table 8-6 summarizes information on the cost of OMM operations conducted for the UDFCD.It is important to note that the per foot costs of maintenance varies greatly depending on thewidth of the channel and its associated right of way, the type of bottom, the slope of thechannel sides, the type channel side slope stabilization, the type and extent of vegetation,and the ease of maintenance access.


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Activity Inventor EstimatedNeed

ActualOutput

ActualBudget

RESOURCE SERVICES

Contract channel vegetationremoval

300 miles 82 miles 3X 64 miles 3X $700,000

Contract pond vegetation removal 161 161ponds 3X 136 ponds4X

$100,000

Complaint handling N/A 1,500 1,500 $199,169

Storm sewer locating (utility coord) N/A 2,000 loc./yr 2,000 loc./yr $91,152

Maintenance scheduling/planning N/A N/A $206,239

Street drainage repairs unknown unknown unknown $175,000

WATERWAY MAINTENANCE

Channel dredging/cleaning 300 miles 20miles 5 miles $578,984

Bridge/culvert clearing 1,000 2,400 1,800 $579,384

Erosion control projects 150 150 6 $200,548

INLET MAINTENANCE

Storm sewer inlet inspection 18,000 18,000 2X 2,000 4X $51,073

Storm sewer inlet cleaning 18,000 13,500 2X 1,500 4X $207,542

Storm sewer inlet filter cleaning 178 7,476 7,476 $34,048

Wet debris dewatering N/A 300 100 $293,097

STORM SEWER MAINTENANCE

Storm sewer repair/installation 400 miles unknown 2,400 feet $277,145

Storm sewer cleaning 400 miles unknown 10,000 feet $102,145

Storm sewer inspection 400 miles unknown 6 miles/yr $151,073

POND MAINTENANCE

Water quality pond restoration 142 35 4 $212,078

Water quality/detention pond OMM 161 126 50 N/A

TOWN LAKE CLEANUP N/A 200 130 $34 048

TABLE 8 - 5 A.City of Austin

Stormwater Maintenance PlanFY 1995

(Note: 2X,3X,4X =two times, three times, four times).


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TABLE 8 - 5 B.City of Austin

Stormwater Maintenance PlanFY 1996.


ProposedOutput

ProposedBudget

RESOURCE SERVICES



Contract pond vegetation removal 273 273 ponds 3X 136 ponds4X

$100,000






Channel dredging/cleaning 300 miles 20miles 8 miles $1,010,061



INLET MAINTENANCE









Special projects N/A unknown 6 projects $89,238

POND MAINTENANCE





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TABLE 8 - 5 C.City of Austin



ProposedOutput

ProposedBudget

RESOURCE SERVICES




$240,441









INLET MAINTENANCE










POND MAINTENANCE





8-13

TABLE 8 - 5 D.City of Austin



ProposedOutput

ProposedBudget

RESOURCE SERVICES




$240,441









INLET MAINTENANCE










POND MAINTENANCE





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TABLE 8 - 5 E.City of Austin



ProposedOutput

ProposedBudget

RESOURCE SERVICES




$300,000






Channel dredging/cleaning 300 miles 20 miles 17 miles $1,106,248



INLET MAINTENANCE










POND MAINTENANCE





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TABLE 8 - 6.

Stormwater System OMM Costs in Denver, Colorado.

Channels with Earth Bottoms

Years ChannLength

ChanneWidth

ROWWidt

SideSlopes

Slope/ROMaterial

# Mows/Debris

PU

TotalCost

$/Ft $/Ft/Yr

91-9 14,000 40 60 Flat Grass 0/3 $14,189 $1.01 $0.25

86-9 7,750 25 150 4:1 Riprap/Grass

5/3 $117,108 $15.11 $1.68

86-9 17,315 35 80 Flat Boulder/grass

6/30-40 $397,022 $22.93 $2.55

86-9 7,550 15 100 Flat Grass 5/5 $110,990 $14.70 $1.63

89-9 10,300 20 40 Flat Earth 0/3 $9,945 $0.97 $0.16

86-9 22,750 45 65 1:1/Flat

Earth 0/3 $59,895 $2.63 $0.29

88-9 4,600 20 40 Flat Earth 0/5 $7,374 $1.60 $0.23

Channels with Concrete Trickle Channels90-9 4,700 8 125 4:1 Grass 3/3 $15,759 $3.35 $0.67

86-9 4,550 6 50 2.5:1 Grass 3/3 $35,071 $7.71 $0.86

86-9 1,100 12 150 Flat Grass 3/3 $11,387 $10.35 $1.15

86-9 4,150 6 100 4:1 Grass 3/5 $52,821 $12.73 $1.41

Dry Detention Systems with Grass BottomsYears Channel

LengthSedimentRemoval

Area(Acres

ChannelMaterial

# Mows/Debris

PU

TotalCost

$/Acre $/Acre/Yr

88-9 253 No 1.4 Concrete 4/4 $7,983 $5,702 $814.59

89-9 752 No 6.6 Concrete 3/3 $15,353 $2,326 $387.70

86-9 3,700 No 9.3 Earth 0/2 $9,076 $976 $108.43

86-9 3,085 Yes 15.5 Earth 0/2 $29,521 $1,905 $211.62


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3.6. City of Bellevue, Washington

Bellevue's stormwater program has required the construction of facilities to minimize flooding andreduce pollutants since 1984. The City's Surface Water Management program maintains thestormwater management system . The system consists of a combination of 146 miles of openstreams, ditches, and culvert, 290 miles of enclosed storm pipe, 14,000 catch basins and man-holes, and 225 neighborhood and ten regional detention facilities. Program staff install, clean,repair, and inspect all components of the system and respond to emergency flooding situations.

In 1974 the City was one of the first local governments to implement a stormwater utility in 1974,providing a dedicated funding source for stormwater management and the OMM of the city'sstormwater system. The budget for stormwater system OMM for the past three years is summa-rized below:

Year Salary/Benefits Supplies/Services Capital Total1994 $ 636,171 $ 330,485 $ 247,621 $1,381,5081995 $ 664,267 $ 383,043 $ 184,325 $1,422,2321996 $ 661,801 $ 434,415 $ 67,280 $1,305,543

Table 8-7 summarizes Bellevue's stormwater OMM costs during 1994 and 1995. As part of itsstormwater OMM planning process, City staff have been compiling cost information on specificBMPs. Annual OMM costs for some of these BMPs are summarized below:

Constructed wetland Sediment removal = $1,500Staff vegetation removal = $ 530Contracted vegetation removal = $ 975Total cost with overhead = $3,846

Coalescing plate filters = $ 832API filters = $ 512Small wet vaults Sediment removal = $ 300

In addition to these costs, the city has installed several innovative stormwater treatment systemsfor which some OMM cost information is available, and has collected OMM data from nearbycities which are using other types of stormwater treatment BMPs. This information is summarizedbelow:

A. Alum Injection SystemAlum injection within stormsewer to precipitate stormwater pollutants has been used inFlorida since 1986. In 1995, the City of Bellevue constructed an alum injection system totreat runoff from 5.4 acres of a new development at a cost of $92,000. The estimatedannual OMM costs are:

Personnel (1 person, 12 hrs weekly @ $35/hr) = $21,840Aluminum sulfate (600 gallons/year) = $ 1,000Magnesium hydroxide (Buffer, 55 gal/yr) = $ 240pH probes (replacements, two/yr) = $ 300Electricity = $ 504Total annual OMM costs $23,884


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TABLE 8 - 7.Stormwater System OMM Costs in Bellevue, Washington.

OMMACTIVITY

1994COMPLETED

1994LABORDAYS

1994TOTALCOST

1995COMPLETED

1995LABORDAYS

1995TOTALCOST

VacuumC/B, inlets

1,457 62.44 $21,586 2,134 101.06 $29,355

VacuumManholes

308 46.94 $15,877 436 58.69 $19,372

VacuumDitch

2653 ft 23.94 $7,244 3,582 40.63 $11,114

VacuumRes. Pond

106 75.31 $26,690 41 30.25 $9,841

JetrodPipelines

29,620 ft 88.94 $31,196 38,750 ft 116.00 $39,413

Root SawPipelines

4,706 ft 45.63 13,863 5,356 ft 56.19 $16,064

VacuumOil Separator

8 4.63 $1,441 8 3.00 $965

BrushRes. Pond

43 163.56 $33,484 42 212.75 $36,350

BrushRegion.Pond

7 34.00 $7,143 11 36.81 $7,942

ManuallyClean Basins

4,897 165.63 $31,943 2,795 125.50 $24,117

DitchCleaning

9802 ft 63.25 $12,766 16,643 ft 96.63 $35,478

Repair CBInlets, MH

249 141.56 $33,433 326 193.34 $41,263

RepairPipelines

76 ft 20.56 $6,333 222 73.31 $32,420

RepairRes. Pond

62 hrs 33.25 $8,320 642 hrs 80.19 $17,331

RepairRegion.Pond

532 hrs 66.44 $13,794 506 hrs 63.19 $14,316

Clean/repairStreams

53 hrs 93.69 $21,668 877 hrs 109.59 $26,247

InspectRes. Pond

222 59.69 $11,597 251 56.38 $12,737

Inspect OilSeparators

70 8.25 $1,505 64 8.97 $1,897

Customer 362 81 38 $19 320 504 102 94 $24 205


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B. Lakemont Filter SystemPart of the stormwater system for the Lakemont Development, a single and multifamilyresidential development, included a BMP treatment train to serve 252.3 acres. Thestormwater system consists of an underground wet vault, two filters, and a dry deten-tion system. The total construction costs of this system in 1992 was $4.6 million. Theestimated annual OMM costs are:

Personnel (2 people, total of 15 hrs/week @ $35/hr) =$13,650Phone for telemetry, flow gages =$ 1,200Electricity =$ 720Contracted maintenance of electrical controls =$ 2,500Filter media replacement =$20,000Vault sediment removal =$ 1,500Total =$39,570

C. Compost Stormwater FiltersKing County, Washington performed a cost study of these stormwater treatment sys-tems (Table 8-8). Additionally, CSF Treatment Systems, Inc. which construct andmaintain these systems, provided King County staff with the following estimates fortwo potential applications of this innovative BMP:

Assumptions:Average annual OMM cost is based on a four year service contract with a 5% inflationfactor. Maintenance includes two annual inspections and two minor OMM visits in thespring and early fall.

Disposal cost of $35 per cubic yard although often the material can be used for on-sitelandscaping or erosion control.

Cost estimates:Filter 1 treats 12 acres of residential area with a peak discharge rate of 1.49 cfs. Thefilter area is 12' by 30' (360 sf) with a construction cost of $18,800 and an averageannual OMM cost of $2,480.

Filter 2 treats 5 acres of commercial development with a peak discharge rate of 1.22cfs. The filter area is 10' by 31' (310 sf) with a construction cost of $16,200 and anaverage annual OMM cost of $2,175.

3.7. Kitsap County, Washington

Like many local governments within the Puget Sound watershed, Kitsap County began re-quiring the treatment of stormwater in 1994. To provide a dedicated funding source for itsstormwater management program, the county implemented a stormwater utility which gener-ates $4 million through its user fees. Stormwater system OMM is a major component of thecounty's program, receiving 24% of the annual budget. Table 8-9 summarizes cost informa-tion on stormwater system OMM in Kitsap County. Costs are based on a labor cost of $25 perhour and a $55 per ton handling and disposal cost.


8-19

TABLE 8-8.

Stormwater Compost Filter System Costs(Compiled by King County Surface Water Management).

TABLE 8 - 9.

Stormwater OMM Costs in Kitsap County, Washington.

4. FINANCING STORMWATER SYSTEM OPERATION, MAINTENANCE, ANDMANAGEMENT

To provide the flood control, water quality protection, and other benefits for which stormwatersystems are constructed, it is essential that maintenance and management be performed ona regular basis. As both the number of systems and the reliance upon them grows, theimportance of stormwater system OMM grows accordingly. Unfortunately, experience through-

TributaryArea

Flow Rate(2 yr storm)

ConstructioCost

Cost perTributaryAcre

AnnualOMM Cost

12 Acres,Residential

1.49 cfs $18,800Drop-In Filter

$1,570 $2,480

5 Acres,Commercial

1.22 cfs $16,200Drop-In Filter

$3,240 $2,175

50 AcresResidential

5.5 cfs $47,900Open Filter

$960 $5,600

CATCH BASIN SEDIMENT REMOVAL

FACILITIE # OMM/YR PERSONHRS

PERSONNELCOSTS

CUBIC FEETSEDIMENT

DISPOSALCOSTS

ANNUAL$/FACILIT

549 549 (Onceeach)

284.3 $7,107.50 2,611.50 $9,797.75 $30.79

CONTROL STRUCTURE SEDIMENT REMOVAL

49 49 (Once each) 147 $3,675.00 696 $2,587.44 $127.81

VEGETATION CONTROL

$27.00 47 (1-4 each) 860 $2,150.00 $45.77/Operation N/A $79.63


8-20

out the country has shown that, for severalreasons, stormwater system OMM is often ne-glected or, at best, performed only sporadi-cally. This maintenance deficiency poses aserious threat to the safe and effective opera-tion of the stormwater systems we have cometo rely upon and to the health and safety ofthe people and water bodies the facilities areintended to protect.

While there are several reasons for thismaintenance neglect, including lack of in-spectors or institutional mechanisms, theprimary cause is a lack of adequate main-tenance funding. The problem of inadequatefunding manifests itself in several ways, in-cluding insufficient staffing, inadequate equip-ment, lack of or inattentive facility inspections,and ineffective operation, maintenance, andmanagement efforts.

Similarly, the problem of inadequatestormwater maintenance (or program) fund-ing also has several causes. These includelegal and regulatory constraints, a shortageof overall operating funds, poor stormwaterprogram planning, and a lack of commitmentby elected officials and by citizens. Unfortu-nately, stormwater management has al-ways been "the orphan infrastructure" -only receiving public attention and fund-ing in times of crisis. At budget time,stormwater program funding seldom com-petes well against other community needssuch as police protection, fire protection, am-bulance service, etc. Accordingly, fundingstormwater maintenance and managementprograms from traditional general fund sourceshas led to inadequate funding.

These causes signify an overall failure to rec-ognize stormwater system OMM as a keycomponent of any stormwater managementprogram. The only way to solve this di-lemma is through a comprehensive publicinformation program which educateselected officials, citizens, and the private

sector about the importance of stormwatermanagement programs, proper stormwatersystem OMM, and the need for adequatefunding. Because of limitations on traditionalgeneral funding sources, the solution requiresboth commitment and creativity.

4.1. Public Financing of Stormwater OMM

A major policy issue facing local govern-ments is whether they should assume re-sponsibility for stormwater system OMM.Assumption of stormwater OMM may take theform of direct involvement by local governmentstaff or by contracting with private mainte-nance services.

Where local governments already have as-sumed such maintenance, the lack of ad-equate funding has led to a seriously high levelof facility maintenance default. This not onlycreates severe health and safety hazards fortheir residents and threatens the health of theirwater bodies, but it may also threaten the con-tinuation of the overall stormwater manage-ment program. It is extremely difficult togenerate the vital public support that a suc-cessful stormwater program requires if thelocal residents are surrounded bystormwater systems that are unsightly,unsafe, and ineffective.

In addition, a local government may wish toassume the maintenance of all or some of theprivately constructed stormwater systemswithin its borders. Traditionally, this has beenthe exception rather than the status quo. Mostlocal governments prefer to require sys-tems serving private land uses to beowned, operated, and maintained by pri-vate landowners or property owner asso-ciations. Unfortunately, history has shownthat most private owners do an inadequatejob of stormwater system OMM. Conse-quently, as a last resort, more local govern-ments are considering assumption of OMM


8-21

responsibilities to restore and maintain exist-ing systems which have already suffered con-tinued neglect from owners or to avert antici-pated defaults by potentially negligent own-ers. In either case, a lack of adequate fundswill prevent the local government from assum-ing this maintenance, which in turn will onlyadd to the growing list of unsightly, unsafe,and ineffective stormwater management sys-tems within the community.

The problem of inadequate stormwatersystem OMM funding described above in-dicates that the traditional methods of pub-lic financing may either be ill-suited for thispurpose or are not being used to their full-est extent. In response to these factors, fourstormwater funding sources have been iden-tified and are being used widely around thecountry. These funding sources, individuallyor in combination, offer a greater opportunityto provide an adequate source of funds tomeet local government stormwater systemOMM obligations. These four recommendedfunding sources are:

••••• General tax revenues••••• Stormwater utility fees••••• Inspection or permit fees••••• Dedicated contributions

Details about these four funding sources willbe subsequently presented, along with sug-gested criteria for evaluating the suitability ofeach. Prior to a discussion of each one, how-ever, it is important to note some fundamen-tal aspects of public stormwater system OMMfinancing.

The success or failure of any proposed fi-nancing program which must receive pub-lic support and approval is often deter-mined by the degree of information thepublic receives. For many reasons, the pub-lic is generally protective of its dollars and ini-tially suspicious of any new public programwhich proposes to spend them. Often, this

suspicion is beneficial, for it helps promotesound fiscal planning and spending programs.

However, where this suspicion is unwarrantedand cannot be overcome, it may also preventa valuable and fiscally sound program formadvancing beyond the proposal stage. There-fore, the value of a comprehensive publicinformation program can not be overem-phasized. Such a program must explain thebasis, purpose, and details of the financ-ing proposal and must convince the pub-lic and their elected officials that it is bothnecessary to implement and beneficial totheir interests. Experience has shown thatcitizens and elected officials don't mind spend-ing money if they know exactly what the moneywill be used for and what benefits the expen-ditures will provide to the community.

All successful stormwater management main-tenance (or program) funding programs shouldpossess certain fundamental elements orcharacteristics. These include:

• Be based upon a stable source of con-sistent funds. Proper stormwater systemOMM must be continually and consistentlyperformed on a regularly scheduled basis.This requires a long term commitment ofpersonnel, equipment, and materials. Asa result, the funds to support this commit-ment must be based upon a stable, se-cure, and reliable source.

• Be compatible with the local organiza-tional structure. The overall effectivenessof a stormwater OMM program is based toa large extent upon the efficiency of itsfunding program. The most efficient fund-ing program is that which is most compat-ible with the organizational structure of themanaging department, agency, or author-ity. Wherever possible, the fundingprogram should use the billing, collection,and bookkeeping operations of an exist-ing public system.


8-22

• Include provisions for the four essen-tial operations - Program Administra-tion, Accounting and Budgeting, Rev-enue Management, and InformationManagement. Program Administrationis needed to insure the effective and effi-cient operation of the overall program.Accounting and Budgeting procedures areneeded to accurately track operations anddetermine required funding levels. Thismay include the use of detailed work or-ders and time sheets by maintenance andinspection personnel and their supervisors.Revenue Management must insure a se-cure and reliable source of program fundsto meet expenses and oversee their ex-penditure. Information Management mustprovide all of the above with comprehen-sive and accurate data upon which opera-tional decisions can be based. It must alsofoster program understanding and supportby providing government leaders and thepublic with timely information, explana-tions, and answers.

• Be based upon an equitable, under-standable, and defensible fee or ratestructure. Stormwater OMM funding pro-grams may require complex proceduresand operations in order to provide ad-equate funding levels. However, to obtainpublic acceptance and support, theprogram's fees or rates must be basedupon a formula or method that can bereadily explained to and understood by thepublic. The fees or rates must be per-ceived as being both reasonable and eq-uitable and based upon accurate data andsound decisions.

• Be continually reviewed and updated.Program costs, revenues, and responsi-bilities must be regularly evaluated andadjusted as needed to maintain maximumcost effectiveness. The do this, theprogram must possess a flexibility of ap-proach which will allow it to quickly respond

to such changes. This is especially truewhen a large storm occurs and OMMneeds are increased significantly.

• Be consistent with applicable state lawsand regulations. The final details of aspecific public stormwater OMM financingprogram will depend to a great extent uponthe general authorities and requirementsestablished in state law or regulations.Prior to the adoption of any financingprogram, the local government's generalcounsel should review all details of theprogram to assure it is compatible withstate law.

4.1.1. General Tax Revenues

Around the nation, the general tax fund isthe most commonly used source of fund-ing for stormwater programs andstormwater system OMM. General tax rev-enues are an obvious source of funding sincethe purpose of local government taxes is tofund activities necessary to provide for thecommunity's health, safety, and welfarethrough the implementation of a number ofsocial, economic, recreational, and environ-mental programs. Accordingly, since prop-erly functioning stormwater systems providepublic heath, safety, and environmental ben-efits, and since neglect of stormwater systemOMM can create serious health, safety, andenvironmental hazards, the use of general taxrevenues to provide for the maintenance ofstormwater systems can be construed as be-ing consistent with this purpose.

However obvious, general tax revenues mayalso be the least suitable source ofstormwater program or maintenance fund-ing. As the name implies, "general" tax rev-enues originate at a number of sources andare used to finance an equally diverse num-ber of public programs, including police andfire protection, civil and criminal courts, social


8-23

often successful after a recent "crisis"such as a major flood or contamination ofan important community water body.These calamities present an opportunity togain public support and to prevent futuredisasters. They are an excellent time tobreak the "hydro-illogical cycle" andimplement the "hydro-rational cycle".

4.1.2. Stormwater Utility Fees

The unreliability of using general tax fundsto finance stormwater programs orstormwater system OMM has led manycommunities around the country to imple-ment either a stormwater utility fee or astormwater special assessment. The useof utility charges to finance publicly owned wa-ter and sewer systems began in the early1900s and, today, provides a stable source offunds for local utility authorities and agenciesaround the nation. In recent years, with theadoption of tax limitations, utility charges and

and economic support programs, roadways,utilities, and recreational activities and facili-ties. This combination of broad base and usecreates two distinct problems which must beovercome if general tax funds are to be usedto support public OMM of stormwater systems.

First, with such a broad base, it may be diffi-cult to justify the expenditure of general fundsto maintain a stormwater system that will onlybenefit a portion of the taxpaying community.Second, with an equally broad use,stormwater programs and maintenancemust compete against a large number ofother vital public programs for a very lim-ited number of tax dollars. This is one rea-son why so many stormwater programs areinadequately funded and why so manystormwater systems are improperly operatedand maintained. This problem has been com-pounded in recent years by tax caps and thepublic's general opposition to new or highertaxes.

Elected officials have discretionary authorityin allocating general tax revenues through theannual budget process. However, both a gov-ernment' s responsibilities and its political re-alities tend to define how these funds are ac-tually spent. Mandatory services such as po-lice and fire protection must receive priorityover more discretionary budget items suchas stormwater system OMM. Therefore, towin use of general tax funds to financestormwater system OMM, it must be demon-strated to the public and to elected officialsthat this activity has greater importance thanother discretionary budget items.

The success of this effort will depend uponmany factors, including the overall costs andcommunity benefits of the maintenanceprogram, the severity and extent of the main-tenance neglect problems, and the effective-ness of the methods used to inform and edu-cate the public and their elected officials.Experience has shown that this effort is


8-24

special assessments have become increas-ingly popular as local governments attempt tomaintain an adequate level of public servicesin the face of limits on expenditure growth.

The concept of a utility charge to publicly fi-nance stormwater system OMM is a soundone in several respects. Unlike general taxrevenues, utility charges are not subject tostate "tax cap" limitations. The public is usedto utility charges because of the precedent setby water and sewer charges. Most impor-tantly, a more direct relationship betweencosts and benefits of stormwater system OMMcan be demonstrated than through the gen-eral assessment of local taxes. Finally, simi-lar to general tax revenues, the stormwaterutility charge can be used to publicly financethe maintenance of both new and establishedstormwater systems.

A variation of a city or county-widestormwater utility fee is the establishmentof a stormwater benefit area in which allproperty owners pay a special assessmentcharge. The charge generally is assessedon a per acre basis to fund construction andOMM of stormwater facilities within the ben-efited area. Additionally, if different land useswithin the benefit area receive substantiallydifferent levels of stormwater benefits, theassessment of per acre fees from subarea tosubarea should vary in proportion to the ben-efits received. The boundaries of the benefitarea should be based on the contribution ofrunoff to the stormwater system. This mayinclude the tributary drainage area for a singlestormwater system, especially if it is a regionalfacility, or more commonly, for an entire net-work of facilities within a watershed or sub-watershed.

Special assessment charges within a benefitarea should meet the following criteria:

• Fees should not exceed the amount of thebenefit received by any particular property.

• Fees should be properly allocated to thebenefited properties.

• Property owners should have an opportu-nity to comment, or even vote, on how theassessments are allocated to their prop-erties.

Whether for a stormwater utility fee or aspecial assessment fee, an important needis to establish a relationship between thefee and the benefits received. Unlikecharges for water or sewer, a readily mea-sured commodity is not delivered to thestormwater utility or benefit area customer. Toa lesser extent, the service provided bystormwater system OMM is not as readily per-ceived or quantified as the service provide bya wastewater system which continually dis-poses of sanitary wastes from homes or busi-nesses. As a result, the services provided to,and the benefits received by, the utility cus-tomer or special benefit property owner mustbe more broadly defined if an acceptable andequitable utility charge or special assessmentis to be developed. The goal is to show thatassessed fees are used to cover costs ofstormwater system OMM or otherstormwater services benefiting each prop-erty and that the benefits to each propertyare at least equal in value to the assess-ment fee. Constitutional standards requirethat property owner benefits be special ben-efits which are generally not shared by thecommunity as a whole.

The utility rate structure for a stormwater fa-cility maintenance district should be based onseveral considerations. The most fundamen-tal of these is the concept of payment basedupon contribution to the need for the mainte-nance rather that the benefits provided by it.For example, a typical stormwater systemOMM charge may be based upon the size ofthe property contributing runoff to the facility.This rate may be refined to reflect the per-centage of impervious surfaces on the prop-


8-25

erty, the runoff potential of the remaining per-vious areas, the type of land use, and otherfactors affecting the rate, volume, or pollutantloading of stormwater. For example, a oneacre property containing a single family resi-dence with 20 percent impervious area wouldpay proportionally less than a similarly sizedindustrial property with 80 percent imperviouscover for the OMM of the stormwater systemto which these lands contributes runoff .

While a certain degree of complexity may berequired to equitably distribute OMM coststhroughout the community or special district,the rate structure should remain as simple aspossible. This simplicity will help make therate structure more understandable to the ratepayer and, as a result, more acceptable. Therate structure should also retain a degree offlexibility to accommodate changes in programrevenues, expenses, and responsibilities.

The rate structure also must reflect the costsof providing the essential stormwater programelements listed in pages 8-21 and 8-22. Theseadministrative and support costs are estimatedto range from 10 to 25 percent of total programcosts.

If a local government does not wish to own,maintain, and operate private stormwatersystems, stormwater utility fees can pro-vide an economic incentive to increase thelikelihood that the private property own-ers will actually conduct OMM activities.Several local stormwater utilities provide "cred-its" if a property or subdivision has an on-sitestormwater management system which isbeing maintained properly. An administrativeproblem with this system that must be ad-dressed is how to assure that the private sys-tems are being maintained properly. Somelocal governments have establishedStormwater Operating Permits which requirean annual inspection by staff or certificationby a private inspector that the facility is beingmaintained and is operating as constructed.

Since state and local government stormwaterprograms often have too few inspectors, theprograms in Delaware and Florida have imple-mented training and certification programs forpublic and private sector personnel who wishto conduct inspections.

4.1.3. Inspection or Permit Fees

Similar to utility fees or special assessments,the use of inspection or permit fees to pub-licly finance stormwater system OMM repre-sents a relatively new application of an estab-lished component of government revenues.In many states, local governments have thegeneral authority to establish fees and othercharges to pay for the operational expense ofvarious programs and services. Often, thesefees are associated with the issuance of a per-mit, such as a building permit, clearing or grad-ing permit, stormwater permit, or sewer con-nection permit. Alternatively, these fees maybe associated with building or stormwaterprogram requirements for inspections.

Implementing a successful stormwatersystem OMM program funded entirely orpartially by inspection or permit fees re-quires the establishment of two primary re-lationships. First, the permit program it-self must be directly related in some man-ner to stormwater systems and, preferably,their operation and maintenance. For ex-ample, the use of fees from a sanitary sewerconnection permit program to financestormwater system OMM may not be feasible,permissible, or acceptable to the public. How-ever, the use of fees from a storm sewer con-nection program may be. Other potentiallyfeasible permit fees include those for a localconstruction permit, stormwater permit, orstormwater discharge permit. Inspection feescan be required when the local government'sstormwater program requires a periodic in-spection of private stormwater systems. Thepublic inspections can determine whether the


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owner is maintaining the facility properly. Ifnot, they can help identify what OMM activi-ties are needed and notify the owner. A per-mit program based upon fees for annual in-spections, such as a stormwater discharge orstormwater operating permit, can provide acontinuing source of funds. However, manypermit or inspection fees are a one timecharge, typically when the facility is first con-structed. These are not a good funding sourcefor continuing stormwater system OMM.

Second, a relationship should be estab-lished, if possible, between the payer ofthe inspection or permit fee and the use ofthe fee itself. For stormwater inspection fees,this relationship is relatively easy to establish.For permit fees, it is recommended that thefees be placed into dedicated accounts. Todemonstrate that the fees are being used forthe OMM of specific facilities, it is recom-mended that computer data bases be estab-lished to track facility maintenance activitiesand costs. This data base will also allow thestormwater program to more accurately esti-mate future resources and funding needed toadequately maintain stormwater systems. Themore directly either of the above relationshipscan be established, the greater the chancesof public acceptance.

Similar to utility charges, inspection andpermit fees should reflect the concept ofpayment based upon contribution to theneed for facility OMM rather than the ben-efits provided by it. For example, factors toconsider in establishing a stormwater con-struction permit fee might include the size ofthe proposed facility, its contributing drainagearea, the number of BMPs or structures, andwhether it is for stormwater quantity control,stormwater quality control, or both. Therefore,a relatively small facility serving a residentialarea and intended only for quality controlwould be charged a proportionately lower per-mit fee than a larger facility providing bothquantity and quality control to a commercial

area. The same factors could be consideredwhen establishing an inspection fee along withthe number of inspections, time to conduct in-spections, and time to travel to the site.

As with stormwater utility fees, permit or in-spection fees need to be as simple as pos-sible but still provide for an equitable distribu-tion of costs. The fee schedule should alsoprovide flexibility to accommodate changes inprogram revenues, expenses, and responsi-bilities. It also needs to reflect the costs ofprogram administration, accounting and bud-geting, and revenue and information manage-ment.

4.1.4. Dedicated Contributions

The use of dedicated contributions from landdevelopers to finance public maintenance ofstormwater systems represents an extensionof an established procedure in a new direc-tion. Under this program, the local govern-ment assumes the OMM of a stormwater sys-tem constructed as part of a private develop-ment. The actual OMM can be provided ei-ther by local government staff or through con-tract with a private maintenance service. Allor a portion of the required funding for theOMM is obtained through a one-time con-tribution by the land developer to a dedi-cated account which is controlled by thelocal government. Often the developer isresponsible for OMM during a "warrantyperiod", frequently the first two years.

The amount of contribution to the dedicatedaccount could be based upon several factorsincluding:

1. The type of stormwater BMP and the an-ticipated OMM activities.

2. The total number of years in which facilityOMM would be provided.

3. The present annual maintenance, admin-istrative, insurance, and support costs.


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4. The anticipated annual increase in presentcosts due to inflation, equipment depre-ciation and replacement, increases in la-bor and insurance rates, rising disposalcosts, and other factors.

5. The anticipated interest earned by thededicated contribution.

6. The percentage, if any, of cost sharingbetween the developer and the local gov-ernment.

The type of stormwater BMP will determinethe frequency and types of needed OMM op-erations. Unfortunately, an extensive database on this information is not available. How-ever, the information presented earlier in thischapter can help to develop cost estimates ofstormwater facility OMM. Administrative andsupport function costs are estimated to rangefrom 10 to 25 percent of total program costs.An annual cost of 2 percent of the dedicatedfunds may be required to cover the adminis-trative costs of the dedicated accounts them-selves. This information can be used to helpestimate the present annual OMM, adminis-trative, insurance, and support costs.

The total number of years for which OMM willbe provided will vary with the policies of eachlocal stormwater program. Often the dedi-cated contribution is based on public OMMfor 25 years, after which stormwater OMMcosts are financed through either the localgovernments general tax revenues orstormwater utility fees.

The Township of West Windsor, New Jerseyhas established a Dedicated ContributionProgram and will be used as an example forcalculating the developer's contribution. Theprogram is based upon the Township provid-ing 25 years of OMM after which thestormwater OMM will be financed through theTownship's general tax revenues. Participat-ing developers are required to furnish 75 per-cent of the estimated annual stormwater sys-tem OMM costs in the form of a one-time pay-

ment. The amount of this payment is calcu-lated for each facility through the use of a stan-dardized Developer Contribution Worksheet(Table 8-10).

In the West Windsor program, annual OMMcosts are based upon the performance of fourmajor maintenance tasks by Township per-sonnel. These tasks are grass mowing; land-scape maintenance; general maintenance,which includes trash and debris removal anderosion repair; and periodic sediment removaland bottom restoration. Grass mowing is es-timated at the rate of one acre per hour. Otherrequired tasks are estimated based upon anhourly, yearly, or per task basis. Appropriatefactors are used to reflect infrequent OMMtasks such as sediment removal and bottomrestoration. Annual liability insurance costsare also estimated and combined with theestimated annual costs of the four major main-tenance tasks to produce a total first-yearOMM cost for the facility. This value is multi-plied by an appropriate Present Worth Fac-tor and then by 0.75 to determine the actualamount of the developer's dedicated contri-bution. This Present Worth Factor is basedupon an average annual interest rate on thededicated funds of 8 percent and an averageannual cost increase of 6 percent over the 25year OMM period.

The use of dedicated contributions to financestormwater OMM has many advantages. Firstand foremost, they provide a secure, dedi-cated funding source for future stormwaterOMM activities. Unlike general tax revenues,contributions to dedicated accounts are notsubject to state tax cap limits. A disadvan-tage is that dedicated contributions are onlyapplicable to new stormwater systems. Theuse of these funds and the activities they payfor need to be closely tracked. This is fairlyeasily done through account and expenserecords. This information can be used to dem-onstrate a direct relationship between the con-tributed funds and their use for facility OMM.


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Equally important, this type of a data base can help the local government to better estimatethe OMM costs of future new facilities and to estimate funding needs for OMM of olderstormwater systems. To minimize overall administrative costs, it is recommended that asingle dedicated account be established for all developer contributions.

TABLE 8 - 10.

Sample Worksheet for Calculating Dedicated Contribution To Stormwater Management System OMM.

NAME OF DEVELOPMENT: ______________________________________________LOCATION: ___________________________________________________________TYPE OF STORMWATER SYSTEM: _______________________________________NUMBER OF ACRES OF STORMWATER SYSTEM: ___________________________NUMBER OF ACRES CONTRIBUTING TO THE SYSTEM: ______________________

1. MOWING

A. Rate per hour for labor and equipment =$___________B. Base number of hours for labor and equipment

for mobilization and mowing up to one acre: __________C. Number of hours for mowing additional

area (based on one hour per acre) __________D. Hours needed for mowing = B + C =____________E. Cost per mowing = A X D =$___________F. Number of mowings per year: __________G. Annual mowing cost = E X F =$___________H. Materials cost =$___________I. Total cost = G + H =$___________

2. LANDSCAPE MAINTENANCE

A. Rate per hour for labor and equipment =$___________B. Number of hours of required landscape

maintenance per year: __________C. Annual landscape maint. cost = A X B =$___________D. Materials cost =$___________E. Total cost = C + D =$___________


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3. GENERAL MAINTENANCE

A. Rate per hour for labor and equipment =$___________B. Number of required hours of trash and

debris removal per occurrence: __________C. Number of required hours of erosion

and sediment repair per occurrence: __________D. Number of required hours of sediment

removal per occurrence: __________E. Number of required hours of other

specific maintenance per occurrence: __________F. Cost per occurrence = A X (B + C+ D+ E) =$___________G. Number of occurrence per year: __________H. Total cost = F X G =$___________

4. INSURANCEA. Annual insurance cost =$___________

TOTAL FIRST YEAR COST

1. MOWING (1.I.) =$___________2. LANDSCAPE MAINTENANCE (2.E.) =$___________3. GENERAL MAINTENANCE (3.H.) =$___________4. INSURANCE (4.A.) =$___________TOTAL FIRST YEAR MAINTENANCE COST =$___________

CALCULATION OF DEVELOPER CONTRIBUTION

A. TOTAL FIRST YEAR COST =$___________B. FOR 25 YEARS = x 19.79C. TOTAL REQUIRED AMOUNT = A X B =$___________D. DEVELOPER CONTRIBUTION PERCENTAGE = X 0.75E. DEVELOPER CONTRIBUTION = C X D =$___________

Chapter 9Disposal of Stormwater Sediments

posed.


This chapter is intended primarily for:

• • • • • Public Officials and Regulatory Person-nel, who need to be aware of the applicabilityof federal and state regulations which may ap-ply to the disposal of stormwater sediments.

• • • • • System Owners or Operators, who needto know how to properly test and dispose ofsediments which accumulate in their stormwatersystems.

2. POTENTIALLY APPLICABLE LAWSAND REGULATIONS

Stormwater pollutants include a wide variety ofsubstances that are deposited on pervious andimpervious surfaces and then transported by thenext rainfall. Additionally, especially in olderurbanized areas, there are often connectionsto the stormwater system which should go tothe sanitary sewer system. Consequently, awide variety of contaminants that may be clas-sified as hazardous or toxic may enterstormwater management systems. These con-taminants include heavy metals, petroleum hy-drocarbons, pesticides, and a wide variety oforganic chemicals. Consequently, severalfederal and state laws and regulations mayapply to the disposal of sediments whichaccumulate in stormwater systems orwhich are captured by street sweepers.

Unfortunately, few state or local governmentshave established clear policies, guidance, or

9-1

1. OVERVIEW

Assuring that stormwater management systemswill provide their desired benefits is no easytask. There are many challenges to overcome.The stormwater management system must beproperly designed and constructed. Thestormwater program's institutional frameworkmust assure that periodic inspections occurduring and after construction of the stormwatersystem, and that an operation and maintenanceentity is clearly identified and legally responsiblefor the long term operation, maintenance, andmanagement of the stormwater system.

Once these hurdles are cleared, new challengesarise. A growing concern, as more and morestormwater treatment systems are con-structed, is how should the sediments thataccumulate in them be disposed. Thestormwater pollutants that accumulate in thesediments are highly variable, but they ofteninclude several contaminants such as heavymetals, petroleum hydrocarbons, and other or-ganic compounds, such as pesticides or sol-vents, which may be considered hazardouswastes.

This chapter will discuss the applicability offederal and state solid and hazardouswaste laws which may affect the proper dis-posal of stormwater sediments. It will alsosummarize data on stormwater sedimentsfrom the few studies which have been con-ducted to characterize them. Recommen-dations will be provided on whetherstormwater sediments need to be charac-terized before disposal and what types oftests need to be conducted. Finally, recom-mendations will be made on howstormwater sediments should be safely dis-


9-2

rules on disposal of stormwater sediments orthe applicability of federal, state, or local lawsand rules. Seldom do current laws, ordinances,rules, or guidelines governing solid waste han-dling and disposal address waste removedfrom stormwater systems. This ambiguitymakes it difficult for public and private opera-tors to comply with relevant laws and regula-tions in their stormwater management systemmaintenance programs. As a result of theseunanswered handling and disposal questions,many stormwater management agencies havebeen discouraged from performing routinemaintenance of stormwater systems.

This section will discuss laws and regulationsthat may be potentially applicable to stormwatersystem sediment disposal.

2.1. Federal Laws and Regulations

A. Resource Conservation and Recovery Actof 1976 (RCRA)

RCRA requires generators of hazardouswastes to monitor and manage them in accor-dance with specified procedures. A solid wastemay be considered a hazardous waste if it con-tains materials which are specifically listed inSections 261.31 through 261.33 of 40 CFR orbecause it possesses any of four hazardouscharacteristics (ignitability, corrosivity, reactiv-ity, or toxicity). In nearly all cases concerningstormwater sediments, the reason that theycould be classified as hazardous wastes isbecause they contain listed chemicals ratherthan because the sediments are hazardous bycharacteristic. However, it is possible forstormwater sediments to be classified haz-ardous wastes because they exhibit toxic-ity. Stormwater sediments would exhibittoxicity if, using the Toxicity CharacteristicLeaching Procedure (TCLP), the extractcontains contaminant concentrationswhich exceed the limits listed in Table 1 ofSection 261.24 of 40 CFR (See Table 9-3 for

a partial listing of these limits).

Key aspects of RCRA and its implementingregulations which may affect stormwater sedi-ment disposal include (Jones et. al., 1995):

• The Mixture Rule. RCRA regulations in-clude lists of a number of chemicals andtheir by-products that are considered haz-ardous wastes when used and discarded(see Sections 261.31 through 261.33 of 40CFR). Under the mixture rule, a mixture ofany solid waste (including dirt) and thelisted waste is considered by regulation tobe a hazardous waste. Even small con-centrations of a listed waste can renderlarge volumes of material hazardous waste.

• The Derived-From Rule. If solid waste isconsidered hazardous waste, even if byoperation of the mixture rule, then any resi-due from the treatment, storage, or disposalof the hazardous waste is also consideredto be hazardous waste.

• The Contained-In Policy. Under existingEPA policy, environmental media, such assoil, water, or debris, that contain a haz-ardous waste must be handled as a haz-ardous waste.

• The Nature of the Source Material. Sim-ply because a chemical listed in RCRArules is detected in stormwater sedimentsdoes not make the sediments hazardouswaste, even after discard. For example, ifa spent halogenated solvent listed as haz-ardous waste is detected in stormwatersediments, the sediments would be haz-ardous waste under the mixture rule only ifthe source of the spent solvent containedmore than ten percent of that solvent by vol-ume.

The Mixture and Derived-From rules do notapply to stormwater sediments until they areremoved from the BMP. Only then are the sedi-ments considered to be discarded. It is the

CHAPTER 9 Disposal of Stormwater Sediments

9-3

Contained-In Policy, rather than the mixture orderived-from rules, that is most likely to bringstormwater sediments within the scope ofRCRA regulations. A de minimis exception tothe contained-in policy can be used on a site-specific basis. EPA must then demonstratethat contaminated media contain hazardouswaste before applying RCRA requirements. Itis likely that EPA will apply the Contained-Inpolicy to stormwater sediments, but the policy,as applied to contaminated media, has notbeen adopted as a rule.

B. Federal Water Pollution Control Act -NPDES Regulations

Discharges of pollutants to waters of the UnitedStates or to certain master stormwater systemsowned or operated by local government mayrequire a NPDES permit from EPA or the statewater quality agency. For example, these regu-lations would apply to discharges of vactortruck water to storm sewers.

2.2. State Laws and Regulations

The owner, operator, or responsible mainte-nance entity of a stormwater management sys-tem should request the stormwater permittingor program agency to provide informationabout the potential applicability of state or locallaws and regulations to the disposal ofstormwater system sediments. This requestmay not bring a quick or simple answer depend-ing on how long the stormwater program hasbeen in operation and whether this issue hasbeen addressed.

The laws and regulations in different statesand local governments are going to varyconsiderably. Be sure to consult your ap-propriate local or state agency. The follow-ing discussion will summarize how laws andrules in two states - Washington and Florida -address the issue of stormwater sediment dis-posal.

A. Washington State

The Washington State Solid Waste Manage-ment Act (R.C.W. 70.95) classifies solids col-lected from stormwater systems and streetcleaning as solid wastes. The Act definesthese wastes as street waste solids. Suchwastes must be stored and handled accordingto relevant solid waste regulations.

One of the highest priorities of the Act is to en-courage waste recycling over landfill disposal.Government agencies can frequently use streetwaste solids for fill or other uses permitted bylocal health departments. To be designated asstreet waste solids in Washington state, andavoid handling as a hazardous waste, contami-nant concentrations in solids must not exceedthe levels presented in Table 9-1.

If garbage, refuse, and other contaminants areremoved from stormwater facility sediments,they may not even require handling as solidwaste. Such solids must consist only of soil,sand, gravel, or sediment. However, these ma-terials should not be used as residential top-soil or in locations where they could have con-tact with wetlands, surface waters, ground wa-ter, wells, or utility trenches.

The Washington State Model Toxics ControlAct (MTCA) establishes waste contaminationthresholds, above which materials must behandled as hazardous waste (see Table 9-2).The hazardous waste threshold of 200 mil-ligrams per kilogram (mg/kg) total petroleumhydrocarbons (TPH) is particularly relevantto disposal of stormwater sediments.Wastewater treatment plants typically set maxi-mum influent pollutant concentration levels (seeTable 9-2). These pretreatment standards areestablished to avoid disruption to plant opera-tions by toxic substances and impacts to receiv-ing waters by contaminants that the plant can-not adequately remove. The applicability of


9-4

TABLE 9-1. Maximum Contamination Limits for Street Waste Solids1 in Washington State

Contaminant Analytic Method Max. Concentration (ppm)2

Heavy fuel hydrocarbons (C24 -C30) EPA WTPH 418.1 2000Diesel (C12-C24) EPA WTPH-D 500Gasoline (C6-C12) EPA WTPH-G 250Benzene EPA 8020 0.5Ethylbenzene EPA 8020 20Toluene EPA 8020 40Xylenes (total) EPA 8020 20

1Solids collected from stormwater facility and street cleaning 2ppm = parts per million

TABLE 9-2. Standards for Disposal of Wastes under TCLP1, MTCA2, andPretreatment Standards3 in Washington State.

Type of Waste/Contaminant Legal Standard Maximum Concentration Limits

SolidsLead TCLP1 5.0 mg/L = 100 mg/kgTPH MTCA2 200 mg/kgVactor WaterCopper (daily average) Pretreatment standards3 2.00, 3.00 mg/LCopper (grab maximum) Pretreatment standards3 8.00 mg/LLead (daily average) Pretreatment standards3 1.50, 2.00, 3.00 mg/LLead (grab maximum) Pretreatment standards3 4.00 mg/LZinc (daily average) Pretreatment standards3 1.50, 4.00, 5.00 mg/LZinc (grab maximum) Pretreatment standards3 10.00 mg/L

1 Toxic Characteristic Leaching Procedure (US Environmental Protection Agency)2 Model Toxics Control Act (enacted in Washington state)3 Pretreatment standards are from Lynnwood, Everett, and Seattle, WA.

TABLE 9-3. Florida Criteria for Clean Soils, Rule 62-770, F.A.C.

Parameter Max. Conc. Max. Conc. Parameter Max. Conc. Parameter Max. Conc. TCLP (mg/l) (mg/kg)(1) (mg/kg)(1) (mg/kg)(1)

Arsenic 5 0.8 Benzene 1.1 PAHs 2300Barium 100 87000 Toluene 300 TRPHs 370Cadmium 1 640 Xylenes 290 MTBE 350Chromium 5 290 Pyrene 2200 Anthracene 19000Lead 5 500 Fluorene 2100 Naphthalene 1000Mercury 0.2 3.7 Chrysene 140 Phenanthrene 1900Selenium 1 390 Dibenzo(a,h)- Benzo(a)pyrene 0.1Silver 5 390 anthracene 0.1 Benzo(a)anthracene 1.4

(1) Values based on residential land use assumptions.


9-5

these pretreatment standards is especiallyrelevant to discharges of water collected byvactor trucks.

B. State of Florida

Florida was the first state in the country to re-quire the use of best management practices totreat stormwater from all new development. Theadoption of Section 17-4.248, Florida Admin-istrative Code (F.A.C.), in 1979, and the sub-sequent adoption of Chapter 17-25, F.A.C.(now 62-25), in 1981, along with the incorpora-tion of stormwater treatment requirements intothe Management and Storage of Surface Wa-ters (MSSW) regulations of the water manage-ment districts has led to the construction of tensof thousands of BMPs throughout the state.These stormwater treatment practices are anessential component of the state’s manage-ment programs to protect, maintain, or restorethe quality of Florida’s surface and ground wa-ters.

In response to numerous questions concerningproper procedures for disposing of sedimentswhich accumulate in stormwater BMPs, theStormwater/Nonpoint Source ManagementSection at the Florida Department of Environ-mental Regulation published Guidelines forSampling, Analyzing, and Disposing ofStormwater Sediments in November 1992. Theguidelines outline biological, chemical, and tox-icity leaching testing procedures which couldbe used to determine the characteristics of thestormwater sediments. The paper also outlinesrecommendations for disposal of the sedimentsafter they have been characterized.In developing these guidelines, staff coordi-nated with the staff in the Divisions of WasteManagement and Water Facilities to assurecompatibility with the rules and policies im-posed by other Department programs. A ma-jor policy issue concerned which program’s cri-teria to apply to stormwater sediments. Rulesand criteria used by the following programs

were reviewed and analyzed for applicability todisposal of stormwater sediments:

• Domestic wastewater residuals• Solid waste management facilities• Compost made from solid waste• Soil thermal treatment facilities• Interim soil cleanup goals• Sediment quality assessment

guidelines

Ultimately, the stormwater sediment disposalrecommendations were based on the WasteClean Up Program's "Clean Soil Criteria" foundin Chapter 62-775, F.A.C. (Table 9-3).

The Florida Department of Environmental Pro-tection currently is reevaluating the applicabil-ity of the limits of the various above programsto stormwater sediments. One of the majorproblems is the lack of consistency be-tween programs and the apparent conflictbetween the values for allowable concen-trations of metals in materials to be land-applied. One reason for the differences inallowable concentrations is that the as-sumed risk level varies depending on theprogram. The Clean Soils Criteria were de-veloped using a risk level of 1 x 10-6. The Re-siduals criteria also are based on a 1 x 10-6 in-cremental cancer risk goal for carcinogens, butuse a 1 x 10-4 incremental cancer risk for non-carcinogens. EPA's proposed Bright Line con-centrations were developed using a 1 x 10-3 riskfactor.

3. CHARACTERISTICS OF STORM-WATER SEDIMENTS AND WASTES

This section will present a summary of data, pri-marily from Washington and Florida, on the con-centrations of different contaminants typicallyfound in stormwater sediments and vactor wa-ter.


9-6

Preliminary studies have indicated that vactorwastes can surpass dangerous waste levels forseveral metals and petroleum hydrocarbons. Astudy by Herrera Environmental Consult-ants (1991) found that vactor truck sedi-ments generally exceeded the WashingtonModel Toxics Control Act criteria forpolyaromatic hydrocarbons (PAHs) andTPH. Concentrations of the most oftendetected compounds were greater in wastesfrom industrial areas than from residentialand commercial areas.

Disposal of decant water, the liquid fraction ofstorm facility wastes removed by vactor trucks,also poses risks to water quality. Decant waterhas the potential to carry solids, metals, tolu-ene, xylenes, and volatile and semi-volatile com-pounds. Total suspended solids (TSS) are aprincipal pollutant in street waste liquids. Manycontaminants, particularly metals, bind to fineparticles, organic material, and clay particles.

Total Kjedahl nitrogen is associated with par-ticles in the 250 to 2000 micron size range.Total phosphorus and nitrate-nitrogen bind toparticles smaller than 100 microns, but mostnitrate-nitrogen is in solution. Liquids can alsocontain large numbers of fecal coliform bacte-ria. Toluene, xylene, and ethylbenzene areamong the most frequently detected organiccompounds in decant water. Table 9-4 presentspollutant ranges for street waste solids and liq-uids, as reported by Serdar (1993). Illicit dump-ing and property owner practices can greatlyincrease contaminant concentrations instormwater management facilities.TABLE 9-5. Ranges of Pollutant Contami-nation in Washington State Catch Basin

and VactorWastes, by Land Use (from Jacobson,1993).

Type of Waste/ ResidentialCommercial IndustrialHighway

Vactor truck crew removing stormwater sediments and liquids from a catch basin.


9-7

TABLE 9-4. Ranges of Toxics and Other Materials Concentrations in Street WasteSolids and Liquids (from Serdar, 1993)

Substance Concentration Ranges Concentration Rangesin Solids in Liquids

Solids 61 - 85% -Gravel fraction 1 - 33% -Sand fraction 57 - 90% -Silt fraction 4 - 28% -Clay fraction 0 - 3% -Fecal coliforms - 400 - 9000 MPN/100 mLTSS - 265 - 111,000 mg/LSettleable solids - 2 - 234 mL/L/hourDissolved solids (total) - 95 - 550 mg/LArsenic Undetected - 24 mg/kg 0.030 - 1.240 mg/LCadmium 0.5 - 1.8 mg/kg -Chromium 19 - 241 mg/kg 0.013 - 1.81 mg/LCopper 18 - 560 mg/kg 0.081 - 7.6 mg/LLead 24 - 194 mg/kg 0.255 - 13 mg/LMercury 0.04 - 0.16 mg/kg Undetected-0.022 mg/LNickel 33 - 86 mg/kg -Zinc 80 - 558 mg/kg 0.401 - 18 mg/LTPH 0.040 - 4.600 mg/kg -PAHs (total) 0.890 - 146 mg/kg -Toluene - 0.096 - 0.180 mg/LXylenes (total) - 0.020 - 0.360 mg/LPhenol - 0.002 - 0.075 mg/L

A paper produced by the Center for UrbanWater Resources Management at the Univer-sity of Washington collected and summarizeddata from Washington state research on catchbasin and vactor waste contamination(Jacobson, 1993). The objective of the studywas to determine any correlations betweenland uses and pollutant concentrations instorm facility wastes. Results of the studyare presented in Tables 9-5 and 9-6.

Contamination levels in sediment wastes andvactor liquids from residential and commer-cial areas were quite similar. Solids and vactorliquids from industrial areas were generally sig-nificantly more polluted than those of residen-tial and commercial areas. However, severalcommercial and industrial results overlapped,

indicating that these two land uses sometimeshave similar pollution potential.

The Jacobson study concluded thatstormwater system solids must be dis-posed of with caution because of high TPHconcentrations. Similar results were foundin a 1995 analysis of vactor sediments thathad been stockpiled at a maintenance yard inBellevue, Washington. Although such wastesare probably not so contaminated that theyrequire hazardous waste landfilling, they aretoo polluted for some standard landfills.

Although copper and lead concentrations invactor water from residential and commercialareas were not high enough to cause concern,zinc frequently exceeded standards. Vactor


9-8

Contaminant (ppm)1 (ppm)1 (ppm)1 (ppm)1 Catch Basin Solids

Copper 20-126 18-117 165-456 -Lead 101-636 95-1726 230-500 -Zinc 174-336 165-997 228-455 -TPH 499 52,400-60,000 5400 -

Vactor SedimentsCopper 24-28 36 88-229 -Lead 69-92 91 109-175 -Zinc 106-138 208 219-338 -TPH 401-1293 - 2197 276

Vactor WaterCopper 0.120-0.933 0.265 1.481-3.418 5.456Lead 0.600-1.300 0.510 3.835-5.775 28.478Zinc 0.608-2.498 3.057 5.672-10.200 26.754TPH 5.2 - 8.2 7.7

1ppm = parts per million (mg/kg for solids; mg/L for liquids)

TABLE 9-6. Percentages of Washington State Catch Basin and Vactor WasteSamples Exceeding TCLP1, MTCA2, and Pretreatment3 Standards,

by Land Use (from Jacobson, 1993).

Type of Waste/ Residential % Commercial % Industrial % Highway % Contaminant × No. of × No. of × No. of × No. of (Legal Standard) Samples Samples Samples SamplesSolidsLead (TCLP) 43% × 35 60% × 35 71% × 21 -TPH (MTCA) 78% × 14 100% × 5 80% × 5 -Vactor Water3Copper (2.0 mg/L standard) 0% × 11 0% × 4 50% × 12 44% × 9Copper (3.0 mg/L standard) 0% × 11 0% × 4 25% × 12 44% × 9Copper (8.0 mg/L max. grab) 0% × 11 0% × 4 17% × 12 22% × 9Lead (1.5 mg/L standard) 9% × 11 0% × 4 100% × 12 89% × 9Lead (2.0 mg/L standard) 9% × 11 0% × 4 92% × 12 78% × 9Lead (3.0 mg/L standard) 0% × 11 0% × 4 75% × 12 78% × 9Lead (4.0 mg/L max. grab) 0% × 11 0% × 4 50% × 12 78% × 9Zinc (1.5 mg/L standard) 36% × 11 25% × 4 100% × 12 100% × 9Zinc (4.0 mg/L standard) 27% × 11 25% × 4 92% × 12 78% × 9Zinc (5.0 mg/L standard) 9% × 11 25% × 4 92% × 12 67% × 9Zinc (10.0 mg/L max. grab) 0% × 11 0% × 4 25% × 12 55% × 9

1Toxic Characteristic Leaching Procedure (US EPA) 2Model Toxic Control Act (enacted inWashington state) 3Pretreatment standards are from Lynnwood, Everett, and Seattle, WA.water samples from industrial and highway areas frequently surpassed the highest waste-water treatment plant pretreatment standards for all three metals. Thus, vactor liquids fromthese land uses would certainly require pretreatment before discharge to wastewater treatmentplants.


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Sediments collected from Tacoma, Washing-ton catch basins one year after they werecleaned were significantly less contaminatedthan samples collected from the same catchbasins before cleaning. These resultsstrongly suggested that annual cleaning ofcatch basins helps to reduce contaminantlevels in wastes. By controlling contamina-tion levels in catch basin wastes through regu-lar cleaning, stormwater utilities could reducehazardous waste disposal costs. Similar re-sults are likely to be attained in larger treatmentfacilities, which can accumulate sediments overa longer periods than catch basins.

As part of the reevaluation of Florida's policyon the land application of solid wastes, includ-ing sediments from stormwater systems, Liv-ingston and Cox (1995) summarized data fromFlorida stormwater investigations. A compre-hensive review of the stormwater literaturefound 17 reports which included data on the con-centrations of contaminants within stormwatersystem sediments. These investigations con-tained considerable data on concentrations ofheavy metals and nutrients in stormwater sedi-ments but relatively little data on organic con-taminants such as petroleum hydrocarbons.More data were available on stormwater sedi-ments from wet detention systems than from in-filtration or filtration practices.

Table 9-7 summarizes the concentrations ofheavy metals in stormwater sediments from dif-ferent types of BMPs, while Table 9-8 summa-rizes the concentrations of heavy metals in thesediments of BMPs serving different land uses.The data in both tables are for surficial sedi-ments - the top one inch. Five ofthe sites also included data from different lay-ers of the stormwater sediments. As with thedata from Washington state, the concentra-tions of heavy metals were highest insurficial layers, but diminished rapidlywithin the top eight inches of sediments.

Livingston and Cox (1995) presented the fol-lowing conclusions on the concentrations ofcontaminants in stormwater system sedimentsin Florida:

• Stormwater sediments, especially in the topone inch of sediment, can exceed Florida'sClean Soil Criteria for chromium and lead.The average chromium concentration in thetop inch of sediments from wet detention sys-tems (83.3 ug/g) and from dry swales (69.7ug/g) exceeded the 50 mg/kg clean soil cri-terion. However, of the 430 samples fromwet ponds, less than 20 percent had chro-mium concentrations above the clean soilcriterion. In sediments from dry swales,chromium concentrations exceeded 50 mg/kg more frequently. All nine top layersamples and two of the 0-4 inch sampleshad chromium concentrations above thisvalue. The average chromium concentra-tion in the top inch of swale sediments was69.7 mg/kg while the average in the 0-4 inchsamples was 51.3 mg/kg.

• The average lead concentration in the topinch of sediments from a retention system,wet ponds, dry swales, wet swales, androadside shoulders exceeded the 108 mg/kg clean soil criterion as did sediments col-lected by street sweepers. Sediment leadconcentrations greater than this level werefound in the sediments from seven wetponds, all three dry swales, the lone wetswale, all four highway shoulder sites, andin one street sweeper investigation, oneconducted in 1977 when leaded gas wasstill available. Even the deeper sedimentlayers exceeded the clean soil criteria forlead in the FDOT highway ponds (0-4 inchlayers), and at both the East-West Express-way dry swales and the Interstate 4 wetswale (0-4 and 0-8 inch layers).

• Table 9-8 compares the levels of heavymetals in sediments from stormwater sys-tems serving different land uses. Similar to


9-10

Land Use No. Obs./Sites

Cd Cr Cu Ni Pb Zn

SF Residential 75/3 2.10 17.40 9.10 8.00 29.20 29.90

MF Residential 15/1 1.20 3.20 21.20 7.20 32.00 22.20

Commercial 17/4 2.30 14.20 26.30 6.40 110.20 150.90

Mixed Com/Res. 57/3 2.70 14.80 26.10 4.00 351.60 176.10

Highways 313/14 5.70 51.30 54.00 26.10 676.80 298.40

TABLE 9-7. Comparison of Heavy Metal Concentrations (ug/g) in the Top One Inch of Sediments from Various Types of Stormwater Systems in Florida.

TABLE 9-8. Comparison of Heavy Metal Concentrations (ug/g) in the Top One Inch of Sediments from Florida Stormwater Systems Serving Various Land Uses.

BMP No. Obs/ Sites

Cd Cr Cu Ni Pb Zn

Dry Retention Basin 3/1 1.00 4.00 13.00 NA 200.00 100.00

Wet Detention Basin 430/21 3.60 83.30 25.60 13.10 227.00 150.30

Grassed Swale - dry 9/3 5.50 69.70 89.50 35.60 1060.0 497.30

Grassed Swale - wet 5/1 1.60 8.40 14.60 6.00 438.60 112.60

Exfiltration Trench 2/1 3.00 14.50 8.00 NA 80.00 80.00

stormwater loadings, concentrations of tracemetals in sediments increased with the in-tensity of the land use and the associatedstormwater loadings. As expected, be-cause of the characteristics of pollutants lefton surfaces over which motor vehiclestravel, sediments in BMPs capturing high-way runoff have the highest concentrationsof trace metals. The average chromium con-centration in highway BMP sediments barelyexceeds the clean soil criterion (51.3 mg/kg vs 50 mg/kg). However, the average leadconcentration in sediments from BMPs serv-ing highways (676.8), industrial (578), mixedcommercial/residential (352),and commercial (110.2) land uses exceedsthe clean soil criterion for lead (108 mg/kg).

• Table 9-9 contains data allowing a compari-

son of heavy metal concentrations in threedifferent layers of stormwater BMP sedi-ments. As expected, concentrations declineas the loose surface sediment is combinedwith more consolidated deeper sediments.However, even in the samples compositingthe top 0-8 inches of BMP sediments, leadconcentrations in sediments from highwaywet ponds and dry swales can exceed theclean soil criterion.

• A growing concern among ecologists is theeffects of petroleum hydrocarbons and vola-tile organic compounds on the biota of wa-ter bodies receiving stormwater discharges.Unfortunately, few investigations have beenundertaken to determine the ecological ef-fects of these materials, which have becomealmost ubiquitous in the urban environment


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Table 9-9. Concentrations of Heavy Metals (ug/g) in the top 1 inch, top 0-4 inches,and top 0-8 inches of Sediments from 6 Florida Stormwater Systems.

Land Use/Site Name/Reference

Metal SF Res. MF Res. SF Res. Comm. Hwy. Hwy SwalesEssex Point Unknown Greenview Int. Mkt. Pl. FDOT Ponds Harper 88Harper 1988 Harper 1988 Yousef 1990 Harper 1988 Yousef 1990 USGS 88

( Sites/Obs.) (1/6) (1/15) (1/48) (1/4) (9/161) (3/9)

Cd 1.6 1.2 2.3 2.9 15.0 5.51.5 0.9 2.7 1.8 7.4 3.51.5 0.3 ND 1.1 ND ND

Cr 7.2 21.2 9.5 12.2 61.0 69.75.8 9.8 8.7 11.3 28.5 51.35.2 6.2 ND 8.9 ND ND

Cu 9.0 3.2 11.8 6.8 28.0 89.57.5 1.8 7.0 4.7 10.6 77.47.3 1.4 ND 3.4 ND ND

Ni 3.0 7.2 8.0 6.4 52.0 35.62.5 3.8 4.7 5.1 33.9 20.92.0 2.7 ND 6.3 ND ND

Pb 13.8 32.0 34.2 46.0 374.0 106011.2 14.0 17.7 31.5 141.9 653.59.9 9.3 ND 22.8 ND ND

Zn 11.6 22.2 31‘.0 127.0 161.0 497.36.9 13.3 12.4 68.5 48.4 269.05.7 10.4 ND 36.8 ND ND

ND = Not determined for the soil profile listed due to insufficient data.

because of civilization’s reliance upon themotor vehicle. Additionally, very few inves-tigations have determined the levels of vola-tile organic aromatics or petroleum hydro-carbons in stormwater BMP sediments.Only six Florida studies included measure-ments of these contaminants, with only theLake Tuscawilla project in Ocala providingdata that allows a comparison of stormwatersediment characteristics to the clean soilcriteria. The levels of total recoverable pe-

troleum hydrocarbons and the polynucleararomatic hydrocarbons in sediments fromLake Tuscawilla greatly exceeded the cleansoil criteria. The cause of these elevatedlevels is believed to be a leaking under-ground fuel tank. This required the City ofOcala to “treat” these sediments by spread-ing them in sludge drying beds, exposingthem to light and oxygen.

• Another interesting observation can be


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made with respect to lead concentrationsin the soil along the edges of highways. Atthe edge of the pavement and in a swalelocated 18 feet away from the pavement’sedge, the lead concentrations greatly ex-ceeded the clean soil criteria in the top twoinches of soil. Does this mean that all soilsadjacent to highways need to be cleanedup or disposed? Of course, this investiga-tion was conducted back in 1978 beforeleaded gas had been eliminated, and theresults should be different today.

• A key question that must be addressed iswhether sediments taken from stormwaterBMPs are a “hazardous waste” becauseof their toxicity? Based on Florida data,stormwater sediments generally are nottoxic based on the results of TCLP tests.Not a single sample in the data base ex-ceeded the TCLP limits that would causestormwater sediments to be classifiedas a hazardous waste.

To augment the information summarized above,the Florida Dept. of Environmental ProtectionStormwater Section conducted additional sam-pling of stormwater sediments in late 1996. Aprimary goal of this effort was to obtain data onorganic contaminants such as petroleum hydro-carbons and pesticides. Samples were col-lected from twelve different stormwater BMPsserving eight different land uses. A total of 102samples were collected by 14 different localstormwater programs throughout the state ofFlorida.

Each sample was analyzed for physical char-acteristics and 128 pollutants including:• Total solids• Sediment grain size• Total Organic Carbon• Metals - As, Cd, Cr, Cu, Ni, Pb, Zn• 26 Chlorinated pesticides and PCBs• 34 Volatile Organics• 60 Semivolatile PAHs, phthlates, phenols• Total recoverable petroleum hydrocarbons

In addition, Toxicity Characteristic LeachingProcedure (TCLP) was conducted on sedi-ments collected at 44 sites.

The results of this project confirm the results andrecommendations of Livingston and Cox(1995). Notable results include (Cox et. al.1997):

• Only about 10% of the 15,506 analyses per-formed resulted in levels above the labora-tory minimum detection levels (MDL).

• Only 53 pollutants were found in detectableconcentrations. Similar to previous studies,several traffic related metals (chromium,lead, and zinc) were found at all sites, whilecopper, cadmium, nickel, and arsenic weredetected in samples at frequencies of 94%,72%, 67%, and 64% respectively.

• Of the 35 organic compounds detected, only8 were found in at least half of the 87 sites.These include total recoverable petroleumhydrocarbons (TRPH), chlordane,pyrene,benzo(b)fluoranthene, fluoranthene,chrysene, DDE-p,p', and benzo(a)pyrene.

• TRPH were found at 78 sites while the pesti-cide Chlordane was found at 71 sites (82%).Chlordane previously was widely used fortermite control but was banned in 1989.While detectable levels of Chlordane wouldbe expected in sediments from olderstormwater BMPs, high concentrations alsowere found in sediments recently collectedby street sweepers and catch basins.

• The NURP results found that only about 20%of stormwater samples had detectable lev-els of organic pollutants and that only fourPAHs were found in more than 10% of thesamples (EPA, 1983). However, these samefour PAHs were found in 47 to 64% of thestormwater sediment samples. A total of 13PAHs, 2 pesticides, 2 phthalates, and PCB


9-13

1260 were found in 10 percent of more ofthe sediment samples.

• Only 3 of the 36 organic pollutants tested forTCLP were detected at levels above the mini-mum detection limit. These included toluene,total xylenes, and m,p-cresols. None of thelevels exceed RCRA levels.

• All four metals (As, Cd, Cr, Pb) tested forTCLP were detected in levels above theMDL. Only two lead samples from canals inSouth Florida exceeded TCLP levels for haz-ardous wastes.

3.1. Contaminants Levels in Sedimentsof Ultra-Urban BMPs

Confined sand filters and baffle boxes are twoBMPs which often are used on highly impervi-ous, land-limited sites. Because of their inher-ent design and limited storage volume, thesetwo BMPs typically require frequent mainte-nance to remove accumulated sediments orclogged filter sand.

In a Seattle, Washington study to monitor the

performance of a sand filter system, filter sandand sediment were analyzed for TCLP metals,copper, zinc, FOG, and TPH. After sevenmonths of filter operation at a busy ship-ping facility, no sample came close to vio-lating hazardous and dangerous wastestandards for metals. However, TPH con-centrations in settling chamber sedimentsgreatly exceeded the Washington ModelToxics Control Act hazardous waste crite-rion of 200 mg/kg. Results for the two moni-tored filters were close, 25,454 and 34,018 mg/kg, despite their divergent water quality condi-tions. None of the full sand cores closely ap-proached the Model Toxics Control Act limit forTPH. However, the two most concentrated seg-ments, taken from the 0 to 1.2 inch segment ofthe sand cores, did exceed the criterion.

Baffle box used to retrofit stormwater systems along the Indian River Lagoon, Florida.


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posal method. Field test kits are available todetect petroleum and polyaromatic hydrocar-bons.

Maintenance workers should also note theland uses in the catchment of a stormwaterfacility. Stormwater sediments from indus-trial areas and highways are much morelikely to exceed hazardous waste standardsthan those from residential and commercialareas. Personnel should be particularly vigi-lant when any of the following activities arepresent in a catchment: electroplaters; indus-trial parks; vehicle repair facilities; wreckingyards; cemeteries; golf courses; pesticideblending and mixing areas; electrical vaults;hydraulic lift pumps; animal product handlers;and waste storage areas.

Characterization of stormwater facility wastesis a central feature of the Washington State De-partment of Transportation's (WSDOT) strategyto minimize waste disposal costs by usingclean wastes in maintenance activities.WSDOT follows a two-step disposal process,consisting of interim and final disposal. In theinterim stage, waste will be characterized to de-termine proper final disposal. Vactor waste willbe placed a minimum of 100 feet from propertyboundaries, surface water bodies, and watersupply wells. Following the decanting of vactorliquids, the solids are to be placed on imper-meable surfaces surrounded by berms of strawbales or dirt. The piles will be covered by plas-tic or other impervious materials to minimizethe amount of water that drains through the sol-ids. Waste piles are not to exceed 100 cubicfeet in volume. The dirtiest wastes will be seg-regated from those that are relatively cleaner.Wastes will be characterized by appearance,odor, and field test kits that detect total petro-leum and polyaromatic hydrocarbons.

WSDOT will perform periodic laboratory analy-ses to confirm the results of the test kits. Theselection of stormwater sediment pollut-ants for laboratory analysis depends on the

As part of the Indian River Lagoon (Florida) Na-tional Estuary Program's efforts to reducestormwater pollutant discharges to the lagoon,local governments have installed several threechambered baffle boxes. These are under-ground, "on-line" systems installed at the endof existing storm sewers before they dischargeto the Indian River Lagoon. The treatment ef-fectiveness of these baffle boxes was investi-gated by Royal and Vanderbleek (1994). Theycollected samples from each of the three cham-bers of a baffle box and analyzed them for heavymetals. The concentrations of all heavy metalswere extremely low. This probably reflects thefrequent pumping out of the baffle boxes. Theboxes, which accumulated over 8,500 poundsof sediment in less than six month of opera-tion, are cleaned out approximately every fourmonths. The interval between pump outs hasvaried from one to six months.

4. RECOMMENDATIONS ON SEDIMENTTESTING

4.1. Storm Facility Solids and LiquidWaste Testing

Maintenance personnel should examine the ap-pearance and odor of solids and liquids re-moved from stormwater BMPs to determinewhether chemical analyses are necessary. Per-sonnel should be alert to an especially oily ap-pearance, coloration by antifreeze, or odors ofgasoline, solvents, hydrogen sulfide, or othernoxious substances. Hazardous waste willstain, corrode, or otherwise alter the look ofcatch basins. These characteristics could besigns of illicit dumping.

Material from a contaminated catch basinshould not be pumped into a vactor truckcontaining cleaner wastes. Mixing wastesof differing qualities could contaminate thewhole load and make its disposal more dif-ficult. The suspected hazardous waste shouldbe analyzed to determine the appropriate dis-


9-15

location of the facility and the initial charac-terization of the waste. Sediments fromstormwater systems in heavily urbanized andindustrial catchments should be analyzed for pe-troleum hydrocarbons (TPH), FOG, toxic met-als (e.g., lead, zinc, copper, and cadmium), nu-trients (e.g., phosphorus), and, if appropriate,organic pesticides, which can accumulate onpond bottoms. The Washington Departmentof Ecology recommends that street wastesolids be tested for chromium, TPH, andPAHs, the pollutants that are the most likelyto exceed the criteria for street waste sol-ids designation (i.e., acceptable for reuse).Vactor wastes collected by the WSDOT will beperiodically analyzed for total metals, TCLPmetals, TPH, gasoline, diesel, heavy fuel hydro-carbons, PAH, and benzene-toluene-ethyl ben-zene-xylene (BTEX).

4.2. Testing of the Sand Filter Mediumand Accumulated Sediments

Key analytes to determine sediment and sanddisposal requirements are fats, oils, and grease(FOG), TPH, and the TCLP and other metals.If TCLP metals concentrations in solids are re-ported in mg/kg, they can be compared to TCLPstandards (defined in mg/L) by multiplying theTCLP standard by 20 to convert to mg/kg. Thisapproximate equivalents method is used by theUS EPA. The equivalents method implicitlyassumes that the analytic method for determin-ing metals concentrations in solids was followedprecisely and that the metals were completelyextracted. The presence of oil and grease insediments can reduce extraction efficiency.Because the dilution factor of 20 is extremelyconservative, samples found to exceed hazard-ous waste standards according to the equiva-lents method frequently do not exceed TCLPstandards in reality.

5. RECOMMENDATIONS ON THEDISPOSAL OF STORMWATER

SEDIMENTS

5.1. Waste Collection Considerations

A drawback to vactor trucks is that they can mixwastes that are relatively clean with those thatare very dirty. An effective, but costly solutionwould be to have “clean” and “dirty” trucks. Al-ternatively, cleaning only facilities associatedwith a single type of land on a given vactor truckrun would reduce the risk of mixing wastes withdifferent contaminant levels. Because of theirgreat potential to cause contamination,vactor wastes should never be mixed withstreet sweepings or debris from ditch clean-ing.

5.2. Disposal Methods

Guidelines are necessary, but generally do notexist, for disposing sediments from stormwaterBMPs. The best programs now send them tolined municipal landfills unless they fail a “looksbad and smells bad” test. If wastes fail to passthis subjective test, they are treated as hazard-ous wastes and tested.

Reuse, recycling, and other non-landfill end so-lutions for stormwater sediments can help toreduce disposal costs. Many state solid wastelaws, such as Washington's Solid Waste Man-agement Act and its Model Toxics Control Act,give the highest priority to this waste handlingstrategy. When disposal of stormwater systemwastes is necessary, they should be transportedto lined landfills where they can be used for covermaterial or, if necessary, to hazardous wastedisposal facilities.In Washington state, some entrepreneurs haveset up an incineration facility at an old, unusedcement plant kiln to cook vactor wastes. Thishas been shown to be a cost-effective optionwhen compared to landfilling the wastes.

Where only petroleum hydrocarbon contami-nation prevents the recycling of storm facility


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trucks is another important problem. Not onlydo storm drain liquids contain pollutants in theirown right, but the vactoring process could fur-ther contaminate the water column by resus-pending solids. Vactor trucks must decant wa-ter two or three times per day to make room formore solids. A common and practical methodof decant water disposal is to drain it into catchbasins in nonsensitive areas. Another practiceis to discharge decant water into sanitary sew-ers. However, discharge of vactor waste intosanitary sewers may still allow pollutants to en-ter surface waters if treatment at the wastewa-ter treatment plant is inadequate. Moreover,high toxics loadings can also upset biologicalprocesses at wastewater treatment plants.

The three options that have been suggested formanaging decant water are (1) reducing theamount of liquids removed from storm facilities;(2) eliminating discharges in the field; and (3)using field settling sumps. There is a lack ofdata on the filtration of vactor liquids in the field,so this method is not recommended. Similarly,data on the treatment efficiencies or the main-tenance safety of stormwater inserts and on-line filtration systems are not widely available.

Reducing the amount of liquids removed fromstormwater facilities (option 1) would be accom-plished by modifying vactor suction tubes toreduce the amount of liquid removed duringcleaning. To eliminate field discharges (option2), liquids are transported in vactor trucks withthe solids and treated at decant stations. De-cant station treatment techniques include (1)using drying pads and lagoons to eliminate alldischarges; (2) gravity settling of solids andpossible treatment with a coalescing plate oil/water separator, followed by discharge to a sani-tary sewer; and (3) treatment with a sand or asand/peat filter. One decant station design in-cludes a 9-foot deep sump for the settling ofsolids from decant water. Solids are removedapproximately every other day. Some cities de-water combined liquid and solid street wastesand filter the liquids before discharging to sani-

wastes, they could be bioremediated at an ap-proved pit site. The WSDOT (1994) classifiestreated soils as follows:

Class 1 Soils — These soils contain residualconcentrations of petroleum contaminants at orbelow analytical detection limits. They are con-sidered clean and can be used as fill for anyproject.

Class 2 Soils — These soils contain detectablelevels of petroleum contaminants below theCleanup Regulation Method A cleanup standard— 100 parts per million of TPH. Appropriateuses include fill or other uses that will not causea threat to human or environmental health.

Class 3 Soils — These are soils with high lev-els of heavy hydrocarbons that may not meetcleanup standards even after treatment. Soilsreceiving adequate treatment should be ableto meet the cleanup levels for light petroleumfractions. Those soils that cannot attain cleanupstandards should be used at the original site ordisposed of in an existing, permitted municipallandfill.

Class 1 soils can be used in the following ap-plications: road and parking lot subgrade; roadconstruction fill; street sweeping sand; pipebedding, except for drinking water pipes; utilitytrench backfill, except for drinking water pipes;controlled density fill; fill in commercial and in-dustrial zones; prefabricated concrete manufac-turing; Portland cement manufacturing; asphaltmanufacturing; daily cover or fill in permittedlandfills, provided they are dewatered; or otherend uses approved by local health departments.Street waste solids should not be reused forsurface mining reclamation, in a wastewaterdisposal mound system, or as cover or fill in aninert demolition waste landfill.

5.3. Decant Water Disposal

Disposal of decant water picked up by vactor


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tary sewers.

The field sump method (option 3) would usegravity settling over 4 to 8 hours to reduce de-cant water contamination. The sump could beany type of detention or retention BMP. Sumps,vaults, and tanks are the most practical facili-ties for settling because they can be installedin a wide variety of locations, are easily main-tained, and solids can be removed by vactortruck. A modified catch basin could also serveas a sump. Use of twin sumps would allow oneto settle solids and drain while the other re-ceived new wastes.

The removal of solids from vactor liquids by set-tling has been found to occur at the followingrates: 54% removed after 0.5 hour; 67% after 1hour; 79% after 2 hours; 87% after 3 hours;90% after 4 hours; and 97% after 8 hours. Infive hours, the settling of 1750 pounds (795 kg)of solids from 1500 gallons (5678 liters) of wa-ter reduced pollutants by the following amounts:

sediments -- 55 to 85%; chemical oxygen de-mand -- 11 to 54%; total organic carbon -- 6 to35%; total phosphorus -- 4 to 50%; total nitro-gen -- 2 to 61%; zinc -- 4 to 60%; and lead -- 31to 83%.

5.4. Sand Filter Waste Disposal Methods

The researchers in the Seattle sand filter moni-toring study decided that settling chamber wa-ter could be drained through the sand bed in-stead of removed for off-site disposal whencleaning of the chamber became necessary.The rationale for this decision was that, becausesand filters are flow-through systems, settlingchamber water normally is treated by the sandbed anyway. Thus, disposal regulations do notdirectly affect the settling chamber water, pro-vided that it is treated by the sand bed. How-ever, when siphoning liquid out of the settlingchamber, maintenance personnel should becareful not to resuspend sediments. Alterna-

Settled vactor solids at Bellevue, WA. vactor decant station.Photo courtesy of Ventilation Power Equipment, Inc. , Seattle.


9-18

tively, if costs are not an objection and appro-priate methods are available for disposal of theliquid and sediment, removing both materialssimultaneously could reduce time and laborcosts.

The variable sand core sampling results fromthe Seattle study created a dilemma about howto dispose of filter sand, when removal becamenecessary. Because inconsistencies in concen-trations could make identifying the portions thatare hazardous waste difficult, occasional dis-posal of the entire upper layer might be the bestoption. Maintenance should be fairly infrequent,only every few years, and generate a relativelysmall volume of waste (top few centimeters ofthe soil column). Bioremediation, the decom-position of organic molecules by microorgan-isms, has been well demonstrated for hazard-ous material and contaminated soil renovation.However, this technique needs to be assessedfor use in stormwater sand filters. Full rejuve-nation by bioremediation might not be possiblewhen mineral solids cause the filter to clog.

Sediments from stormwater dischargesaccumulated on the bottom of Megginnis

Arm, Lake Jackson, in Florida beforeimplementation of the state's stormwater

treatment rules in 1982. Removal ofsediments from water bodies and the

restoration of water bodies is much moredifficult and expensive than the imple-

mentation of BMPs and their propermaintenance.

Chapter 10Information Sources

Information used in this publication was obtained from a variety of sources which are listed inthis chapter. The interested reader is urged to review these information sources if moredetailed information is desired. Additionally, because of the rapid growth of the stormwatermanagement state-of-the-art, readers are encouraged to consult more recent literature toassure that they have the most recent data and information.

Chapter 1, Introduction, and Chapter 2, Stormwater Management Practices

Avellaneda, E. 1985. Hydrologic Design of Swales. M.S. Thesis, University of CentralFlorida, Orlando, Florida.

Bell, W., L. Stokes, L.J. Gavan, and T.N. Nguyen. 1995. Assessment of the Pollutant Re-moval Efficiencies of Delaware Sand Filter BMPs. Department of Transportation andEnvironmental Services, Alexandria, Virginia.

Camp Dresser & McKee; Larry Walker Associates; Uribe and Associates; and ResourcePlanning Associates. 1993. California Storm Water Best Management Practices Hand-books. State of California, Sacramento, California.

Carr, D. W. and B.T. Rushton. 1995. Integrating a Native Herbaceous Wetland into StormwaterManagement. Final report, Contract WM 434, submitted by the Stormwater ResearchProgram, Southwest Florida Water Management District to Florida Department of En-vironmental Protection (FDEP) SW/NPS Management Section, Tallahassee, Florida.

City of Alexandria, Department of Transportation and Environmental Services. 1992. Supple-ment to the Northern Virginia BMP Handbook. Alexandria, Virginia.

City of Olympia, Department of Community Planning and Development. 1994. DrainageDesign and Erosion Control Manual for Olympia, 1994 edition. City of Olympia, WA.

City of Portland, Environmental Services, Clean River Works and Woodward-Clyde Consult-ants. 1995. City of Portland Stormwater Quality Facilities: A Design Guidance Manual.City of Portland, OR.

Cullum, M.G. and P.J. Whalen. 1988. An Assessment of Urban Land Use/Stormwater Run-off Quality Relationships and Treatment Efficiencies of Selected Stormwater Manage-ment Systems. SFWMD Technical Publication 88-9, West Palm Beach, Florida.

Dyer, Riddle, Mills and Precourt, Inc. 1985. Orlando Urban Stormwater Management Manual.Stormwater Management Bureau, Orlando, Florida.

10 - 1


10- 2

Eaker, W.M. 1994. Stormwater Management in North Carolina: A Guide for Local Officials.Land-of-Sky Regional Council, Asheville, North Carolina.

Engineering Technologies Associates, Inc. and Biohabitats, Inc. 1993. Design Manual forUse of Bioretention in Stormwater Management. Prepared for Prince George's CountyWatershed Protection Branch, Landover, Maryland.

Galli, J. 1991. Thermal Impacts Associated with Urbanization and BMPs in Maryland. Met-ropolitan Washington Council of Governments, Washington D. C.

Harper, H.H. 1985. Fate of Heavy Metals from Highway Runoff in Stormwater ManagementSystems. Ph.D. Dissertation, University of Central Florida, Orlando.

Harper, H.H. 1987. Stormwater Treatment by Natural Systems. Final Report, ContractWM127, submitted to FDER SW/NPS Management Section, Tallahassee, Florida.

Harper, H.H. 1994. Stormwater Loading Rate Parameters for Central and South Florida.Environmental Research and Design Inc., Orlando, Florida.

Harper, H.H. 1988. Effects of Stormwater Management Systems on Groundwater Quality.Final Report, Contract WM 190, submitted by Environmental Research and DesignInc., Orlando, Florida to FDER SW/NPS Management Section, Tallahassee, FL.

Harper, H. H., B. M. Fries, D. M. Baker and M. P. Wanielista 1986. Stormwater Treatment byNatural Systems. Final Report STAR Project 84-026 submitted by the University ofCentral Florida Engineering School to FDER SW/NPS Management Section, Talla-hassee, Florida.

Harper, H. H., Murphy, M.P. and Livingston, E.H. 1986. Inactivation and Precipitation ofUrban Runoff by Alum Injection in Stormsewers. Presented at 6th Symposium onLake and Reservoir Management, North American Lake Management Society, Port-land, Oregon.

Harper, H. H. and J. L. Herr. 1993. Treatment Efficiencies of Detention with Filtration Sys-tems. Final report, Project 90B103, submitted by Environmental Research and De-sign Inc., Orlando, Florida to SJRWMD, Palatka, Florida.

Harper, H. H. and J. L. Herr. 1995. Evaluation of the Stormwater Treatment and Manage-ment Program in Orange County. Final report submitted by Environmental Researchand Design Inc. to Orange County Stormwater Management Department, Orlando,Florida.

Horner, R.R. 1988. Biofiltration Systems for Storm Runoff Water Quality Control. Finalreport submitted to the City of Seattle, Washington.

Horner, R.R. 1996. Infiltration Facilities for Stormwater Quality Control - Course Manual.Course sponsored by University of Washington, center for Urban Water Resources

CHAPTER 10 Information Sources

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Management and Professional Engineering Practice Liaison Program, Seattle, WA.

Horner, R.R. 1996. Constructed Wetlands for Stormwater Quality Improvement - CourseManual. Course sponsored by University of Washington, center for Urban Water Re-sources Management and Professional Engineering Practice Liaison Program, Se-attle, WA.

Horner, R.R. 1996. Biofiltration for Stormwater Quality Control - Course Manual. Coursesponsored by University of Washington, center for Urban Water Resources Manage-ment and Professional Engineering Practice Liaison Program, Seattle, WA.

Horner, R.R., J.J. Skupien, E.H. Livingston, and H.E Shaver. 1994. Fundamentals of UrbanRunoff Management: Technical and Institutional Issues. Terrene Institute, Washing-ton, DC.

Kehoe, M.J., C.W. Dye, and B.T. Rushton. 1994. A Survey of the Water Quality of Wetlands-Treatment Stormwater Ponds. SWFWMD, Brooksville, Florida.

Kulzer, L. 1990. Water Pollution Control Aspects of Aquatic Plants: Implications for StormwaterQuality Management. Municipality of Metropolitan Seattle, Seattle, WA.

Lindsey, G., L. Roberts and W. Page. 1992. Inspection and Maintenance of InfiltrationFacilities. J. Soil Water Conserv. 47 (6): 481-186.

Livingston, E.H. 1988. State Perspectives on Water Quality Criteria. In Design of UrbanRunoff Controls, an Engineering Foundation Conference, Potosi, Mo. ASCE, New York,New York.

Livingston, E.H. 1989. Use of Wetlands for Urban Stormwater Management. In ConstructedWetlands for Wastewater Treatment, D.A. Hammer, editor, Lewis Publishers, Chelsea,Michigan.

Livingston, E.H. 1995. Lessons Learned From a Decade of Stormwater Treatment in Florida.In Stormwater Runoff and Receiving Systems: Impact, Monitoring, and Assessment,E. Herricks, editor, CRC Press, Inc., Boca Raton, Florida.

Livingston, E.H., McCarron, E., Cox, J.H., and P.A.Sanzone. 1988. The Florida Develop-ment Manual: A Guide to Sound Land and Water Management. Stormwater/NPSManagement Section, Florida Department of Environmental Regulation, Tallahassee,Florida.

Livingston, E.H., H. Harper, and J. Herr. 1994. The Use of Alum Injection to Treat Stormwater.In Proceedings of the Second Annual Conference, Soil and Water Management forUrban Development - Creative Stormwater Management. Sydney, Australia.

Martin, E.H. and J.L. Smoot. 1986. Constituent - Load Changes in Urban Stormwater RunoffRouted Through A Detention Pond - Wetlands System in Central Florida. U.S.G.S.,


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WRI Report 85-4310, Tallahassee, Florida.

Maryland Water Resources Administration. 1984. Standards and Specifications for Infiltra-tion Practices. Annapolis, Maryland.

Maryland Water Resources Administration. 1986. Maintenance of Stormwater ManagementStructures: A Departmental Summary. Annapolis, Maryland.

Miller, R. A. 1985. Percentage Entrainment of Constituent Loads in Urban Runoff, SouthFlorida. USGS WRI 84-4329, Tallahassee, Florida.

Municipality of Metropolitan Seattle, Engineering Department. Maintenance Standards forRetention/Detention Facilities. Information sheets. City of Seattle, Washington.

Municipality of Metropolitan Seattle. 1992. Biofiltration Swale Performance, Recommenda-tions, and Design Considerations. Publication 657. Seattle, Washington.

Peterson, A., R. Reznick, S. Hedin, M. Hendges, and D. Dunlap. Guidebook of Best Manage-ment Practices for Michigan Watersheds. Michigan Department of Natural Resources,Surface Water Quality Division, Lansing, Michigan.

Rushton, B. T. and C. W. Dye 1993. An In-Depth Analysis of a Wet Detention StormwaterSystem. Final report, Contract WM435, submitted by the Stormwater ResearchProgram, Southwest Florida Water Management District to FDER, SW/NPS Manage-ment Section, Tallahassee, Florida.

St. Johns River Water Management District. 1996. Rule 40C-42 and associated Applicant’sHandbook. Palatka, Florida.

Schiffer, D. M. 1989. Effects of Three Highway - Runoff Detention Methods on Water Qualityof the Surficial Aquifer System in Central Florida. U.S.G.S., WRI Report 88-4170,Tallahassee, Florida.

Schueler, T.R. 1987. Controlling Urban Runoff: A Practical Manual for Planning and Design-ing Urban BMPs. Metropolitan Washington Council of Governments, Washington,DC.

Schueler, T.R. and J. Galli. 1995. Environmental Impacts of Stormwater Ponds. In StormwaterRunoff and Receiving Systems: Impact, Monitoring, and Assessment, E.E. Herricks,Editor, CRC Press, Inc. Boca Raton, Florida.

Shaver, H. E. 1986. Infiltration as a Stormwater Management Component. Proceedings ofthe Urban Runoff Technology, Engineering Foundation Conference, Henniker, NewHampshire, June 1986, pp.270-280.

Shaver, H.E. Sand Filter Design for Water Quality Treatment. In Stormwater Runoff andReceiving Systems: Impact, Monitoring, and Assessment, E.E. Herricks, Editor, CRCPress, Inc. Boca Raton, Florida.


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South Carolina Land Resources Conservation Commission. 1992. A Guide to Site Develop-ment and Best Management Practices for Stormwater Management and SedimentControl. Columbia, South Carolina.

Southwest Florida Water Management District. 1995. Proceedings of the 4th BiennialStormwater Research Conference, October 18-20, 1995. SWFWMD, Brooksville,Florida.

Strecker, E.W., J.M. Kersnar, E.D. Driscoll, and R.R. Horner. 1992. The Use of Wetlands forControlling Stormwater Pollution. US Environmental Protection Agency, Region 5,Chicago, IL.

Stockdale, E.C. 1986. The Use of Wetlands for Stormwater Management and NonpointPollution Control: A Review of the Literature. Final report submitted to the Washing-ton State Department of Ecology, Olympia, Washington.

Stockdale, E.C. 1986. Viability of Freshwater Wetlands for Urban Surface Water Manage-ment and Nonpoint Pollution Control: An Annotated Bibliography. Final report submit-ted to the Washington State Department of Ecology, Olympia, Washington.

U. S. EPA. 1983. Water Quality Standards Handbook. Office of Water Regulations andStandards, Washington, D.C.

U. S. EPA. 1991. Guidance for Water Quality-based Decisions: The TMDL Process. Officeof Water, Washington, D. C. EPA 440/4-91-001.

U. S. EPA. 1993. Water Quality Standards Handbook - Second Edition. Office of Water,Washington, D. C. EPA-823-B-93-002.

W and H Pacific. 1992. Compost Storm Water Filter System: Technical Summary, Methodsand Results. W and H Pacific, Portland, Oregon.

Wanielista, M. P. 1977. Quality Considerations in the Design of Holding Ponds. StormwaterRetention/Detention Basins Seminar, University of Central Florida, Orlando, Florida,August 1977.

Wanielista, M.P. and E. Shannon. 1977. Stormwater Management Practices Evaluation.Report prepared as part of the Orlando Metropolitan 208 study for the East CentralFlorida Regional Planning Council, Orlando, Florida.

Wanielista, M. P., R. N. Gennaro and J. H. Bell. 1978. Shallow Water Roadside Ditches forStormwater Purification. University of Central Florida, Orlando, Florida.

Wanielista, M.P. and Yousef, Y.A. 1986. Best Management Practices Overview. Proceed-ings of the Urban Runoff Technology, Engineering Foundation Conference, Henniker,New Hampshire, June 1986, pp.314-322.


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Wanielista, M.P., Yousef, Y.A., Van DeGroaff, L.M., and Rehman-Koo, S.H. 1986. En-hanced Erosion and Sediment Control Using Swale Blocks. Final report submitted bythe University of Central Florida, Department of Civil and Environmental Engineeringto the Florida Department of Transportation, Bureau of Environment and Environmen-tal Research, Tallahassee, Florida. Report FL-ER-35-87.

Wanielista, M.P., Y.A. Yousef, G.M. Harper, T.R. Lineback, and L. Dansereau. 1991. Pre-cipitation, Inter-Event Dry Periods, and Reuse Design Curves for Selected Areas ofFlorida. Final Report, Contract WM346, submitted by the University of Central Florida,Department of Civil and Environmental Engineering to the FDER SW/NPS Manage-ment Section, Tallahassee, Florida.

Wanielista, M.P., M.J. Gauthier, and D.L. Evans. 1991. Design and Performance of ExfiltrationSystems. Final report, Contract C3331, submitted by the University of Central Florida,Department of Civil and Environmental Engineering to the Florida Department of Trans-portation, Bureau of Environment and Environmental Research, Tallahassee, Florida.

Washington Department of Ecology. 1992. Stormwater Management Manual for the PugetSound Basin. 4 volumes. Washington Department of Ecology, Olympia, WA.

Washington State Department of Transportation. 1994. Highway Runoff Manual. RevisedDraft, M31-16, May 1994. Washington State Department of Transportation, Olympia,Washington.

Water Pollution Control Dept. 1992. Biofiltration Swale Performance, Recommendations,and Design Considerations. Publication 657, Seattle, Washington.

Yousef, Y.A., et al. 1985. Fate of Pollutants in Retention/Detention Ponds. In StormwaterManagement: An Update, Publication 85-1, University of Central Florida, Orlando,Florida, pp.259-275.

Yousef, Y.A., M.P. Wanielista, H.H. Harper, D.B. Pearce and R.D. Tolbert. 1985. Removal ofHighway Contaminants by Roadside Swales. Final report submitted by the Universityof Central Florida, Department of Civil and Environmental Engineering to the FloridaDepartment of Transportation, Bureau of Environment and Environmental Research,Tallahassee, Florida. Document No. FL-ER-30-85.

Yousef, Y. A., M. P. Wanielista, H. H. Harper and T. H. Jacobsen. 1986. Effectiveness ofRetention/Detection Ponds for Control of Contaminants in Highway Runoff. Final re-port submitted by the University of Central Florida, Department of Civil and Environ-mental Engineering to the Florida Department of Transportation, Bureau of Environ-ment and Environmental Research, Tallahassee, Florida. Document No. FL-ER-34-86.

Yousef, Y. A., M. P. Wanielista, J. D. Dietz, L. Y. Lin, and M. Brabham. 1990. Efficiency Optimi-zation of Wet Detention Ponds for Urban Stormwater Management. Final report, ContractWM159, submitted by the University of Central Florida, Department of Civil and Environ-mental Engineering, Orlando, Florida to FDEP SW/NPS Management Section, Tallahas-see, Florida.


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Chapter 4, Programmatic and Regulatory Aspects

Horner, R.R., J.J. Skupien, E.H. Livingston, and H.E Shaver. 1994. Fundamentals of UrbanRunoff Management: Technical and Institutional Issues. Terrene Institute, Washing-ton, DC.

Maryland Water Resources Administration. 1986. Maintenance of Stormwater ManagementStructures: A Departmental Summary. Annapolis, Maryland.

Shaver, H.E. and E.H. Livingston. 1993. Midwest Urban Runoff Workshop Materials. Hand-out material for two day workshop sponsored by Terrene Institute, Watershed Man-agement Institute, and U. S. EPA, Region 5, Water Division, Wetlands and WatershedSection.

Chaper 40, Title 7, Delaware Code - Erosion, Sediment, and Stormwater Control Act

Department of Natural Resources and Environmental Control, State of Delaware. 1993.Sediment and Stormwater Management Regulations.

Chapter 373, Florida Statutes

Chapter 403, Florida Statutes

Chapter 62-25, F.A.C., Stormwater Regulations, Florida Department of Environmental Pro-tection, Tallahassee, Florida.

Chapter 62-40, Florida Administrative Code, State Water Policy, Florida Department of Envi-ronmental Protection, Tallahassee, Florida.

Chapter 40C-42, F.A.C, Regulation of Stormwater Management Systems, St. Johns RiverWater Management District, Palatka, Florida.

Environmental Management Ordinance, Chapter 28, Part 1, Tallahassee, Florida.

Environmental Management Act, Leon County, Tallahassee, Florida.

Chapter 7, Inspection After Construction

Reinelt, L.E. 1992. Inspection and Maintenance of Permanent Stormwater ManagementFacilities: Training Manual. University of Washington, Department of Civil Engineer-ing, Center for Urban Water Resources Management, Seattle, WA; and WashingtonState Department of Ecology, Olympia, WA.


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Chapter 8, Costs and Financing of Stormwater Facility O & M

Bellevue Operations and Maintenance Division. 1995. Annual Report and Plan. UtilitiesDepartment, Bellevue, Washington.

Bellevue Operations and Maintenance Division. 1996. Annual Report and Plan. UtilitiesDepartment, Bellevue, Washington.

Evertsen, J. January 2, 1996. Maintenance Costs. Internal memorandum to Bill Chamberlin,Chief, Stormwater Utilities, Orlando, Florida.

Harrison, D. February 29, 1996. Costs to Maintain Stormwater Basins. Information sent toEric Livingston from the Executive Director, Fresno Flood Control District, Fresno,California.

Hunter, M.R. February 15, 1996. Maintenance Cost Information. Letter to Eric Livingstonfrom the Chief of Maintenance, Urban Drainage and Flood Control District, Denver,Colorado.

Hoffman, P.A. January 12, 1996. Drainage Utility Budget and Work Plan. Letter to EricLivingston from the Chief Financial Manager, Public Works and Transportation De-partment, Austin, Texas.

Skupien, J.J. 1995. Estimates of Typical Maintenance Costs. Internal analysis for theSomerset County Public Works Department.

Watson, R. December 28, 1995. BMP Cost Data. Internal memorandum to Joanna Richey,Retrofit Study Project Manager, Bellevue, Washington.

Chapter 9, Disposal of Stormwater Sediments

Camp, Dresser and McKee, Inc. 1993. Letter Report to FDEP, Lake Tuscawilla Demon-stration Project, Contract WM473, prepared for Florida Department of EnvironmentalProtection, Stormwater and NPS Management Section, Tallahassee, Florida.

Cox, J. H., S. Allick, and E. Be. 1997. Characterization of Stormwater ContaminatedSediment and Debris for Determining Proper Disposal Methods. Final report submit-ted to EPA Region 4, Atlanta, Georgia

.Fernandez, M. and C. B. Hutchinson. 1993. Hydrogeology and Chemical Quality of Water

and Bottom Sediment at Three Stormwater Detention Ponds, Pinellas County,Florida. WRI Report 92-4139, U.S.G.S. Tallahassee, Florida.

Harper, H. H. 1993. “Evaluation of Sediment Loadings From the Dolphin Cove Outfall,Hypoluxo, Florida.” Environmental Research and Design Inc., Orlando, Florida.


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Herrera Environmental Consultants, Inc. 1991. Vactor Truck Operations and DisposalPractices. Prepared For Washington Department of Ecology. Herrera Environmen-tal Consultants, Inc., Seattle, WA.

Horner, R.R., and C.R. Horner. 1995. Design, Construction, and Evaluation of a SandFilter Stormwater Treatment System: Part II — Performance Monitoring. Report toAlaska Marine Lines, Seattle, WA.

Jacobson, M.A. 1993. Data Summary of Catch Basin and Vactor Waste Contamination inWashington State: Final Report — Prepared for the Washington Department ofEcology, Urban Nonpoint Management Unit. University of Washington, Departmentof Civil Engineering, Center for Urban Water Resources Management, Seattle, WA.

Jones, J., S. Anderson, J. Fognani, and F. R. McGregor. 1995. BMPs and HazardousSediment. Public Works, May, 1995, pp.51-54.

Livingston, E.H. and J.H. Cox. 1995. Stormwater Sediments: Hazardous Waste or DirtyDirt? In Proceedings of the 4th Biennial Stormwater Research Conference, October18-20, 1995. SWFWMD, Brooksville, Florida.

MacDonald, D. D. 1994. Development and Evaluation of Sediment Quality AssessmentGuidelines. Final report submitted by MacDonald Environmental Sciences, Ltd.,Ladysmith, British Columbia to the FDEP Sediment Research Group, Tallahassee,Florida.

Royal, J.C. and R.D. Vanderbleek. 1994. Sediment Control Project Assessment forIndialantic basin and Micco basin. Final report submitted by Surface Water Improve-ment Division, Brevard County, Florida to SJRWMD and Indian River Lagoon NEP.

Serdar, D. 1993. Contaminants in Vactor Truck Wastes. Washington Department ofEcology, Olympia, WA.

U.S. Environmental Protection Agency. 1983. Results of the Nationwide Urban RunoffProgram. Water Planning Division, Washington, D.C.

Washington Department of Ecology. 1994. Draft Report on Storm System Waste Charac-teristics and Handling. Washington Department of Ecology, Olympia, WA.

Yousef, Y. A., L. Y. Lin, J. V. Sloat and K. Y. Kaye. 1991. Maintenance Guidelines forAccumulated Sediments in Retention/Detention Ponds Receiving Highway Runoff.Final report submitted by the University of Central Florida, Department of Civil andEnvironmental Engineering to the Florida. Department of Transportation, Bureau ofEnvironment and Environmental Research. Document No. FL-ER-47-91.

operation, maintenance, & management

Documents