Centralized Impoundments forCentralized Impoundments for Storage of Wastewaters Storage of Wastewaters

Design and ConstructionDesign and Construction

Centralized Impoundments for Centralized Impoundments for Storage of WastewatersStorage of Wastewaters

►Service multiple well sitesService multiple well sites►Regulated part of the well siteRegulated part of the well site►Generally large capacity (10-15 Generally large capacity (10-15

million gallons)million gallons)

Standards For Wastewater Standards For Wastewater ImpoundmentsImpoundments

►Structural StandardsStructural Standards►Liner SystemsLiner Systems

Quality Assurance/Quality ControlQuality Assurance/Quality Control Leak DetectionLeak Detection Action Leakage RatesAction Leakage Rates

►Groundwater MonitoringGroundwater Monitoring

Distance RestrictionsDistance Restrictions

► In the 100-year floodplain of waters of this In the 100-year floodplain of waters of this Commonwealth.Commonwealth.

► In or within 100 feet of a wetland.In or within 100 feet of a wetland.► Within 200 feet from an occupied dwellingWithin 200 feet from an occupied dwelling► Within 100 feet of a perennial stream.Within 100 feet of a perennial stream.► Within 200 feet of a private water source.Within 200 feet of a private water source.► Within 1,000 feet upgradient, and within Within 1,000 feet upgradient, and within

300 feet downgradient, of a public water 300 feet downgradient, of a public water sourcesource

Embankment Design CriteriaEmbankment Design Criteria

► Maximum Particle Size = 6”Maximum Particle Size = 6”► Bottom must be at least 20” above seasonal high Bottom must be at least 20” above seasonal high

groundwater tablegroundwater table► Must meet specific soil type and compaction Must meet specific soil type and compaction

standardsstandards► Minimum embankment top width of 12’ is Minimum embankment top width of 12’ is

requiredrequired► Minimum inside & outside side slopes of 3H:1V Minimum inside & outside side slopes of 3H:1V

are requiredare required► Permanent vegetative ground covering must be Permanent vegetative ground covering must be

established upon completion of dam construction.established upon completion of dam construction.► 2’ of lined freeboard must be maintained at all times.2’ of lined freeboard must be maintained at all times.

Embankment ConstructionEmbankment Construction

►Soils to be used for dam embankment Soils to be used for dam embankment construction must be classified in construction must be classified in accordance with ASTMD-2487. A minimum accordance with ASTMD-2487. A minimum of three samples must be classified.of three samples must be classified.

►Soils acceptable for dam embankment Soils acceptable for dam embankment construction are limited to GC, GM, SC, SM, construction are limited to GC, GM, SC, SM, CL or ML. CL or ML.

►Soils must contain a minimum of 20% of Soils must contain a minimum of 20% of Plus No. 200 sieve materials.Plus No. 200 sieve materials.

Gradation Gradation SheetSheet

GC- Clayey gravels

GM- Silty gravels

SC- Clayey sands

SM- Silty sands

CL- Inorganic clays low to medium plasticity

ML- Inorganic silts and fine sand, slight plasticity

Site PreparationSite Preparation

► Foundation of dam embankment must be stripped and Foundation of dam embankment must be stripped and grubbed to a depth of two feet prior to any placement & grubbed to a depth of two feet prior to any placement & compaction of earthfill.compaction of earthfill.

► Any springs encountered in the foundation area should be Any springs encountered in the foundation area should be drained to the outside/downstream toe of the embankment drained to the outside/downstream toe of the embankment with a drain section two foot by two foot in dimension with a drain section two foot by two foot in dimension consisting of PennDOT Type A sand, compacted by hand consisting of PennDOT Type A sand, compacted by hand tamper. No geotextiles to be used around sand. The last tamper. No geotextiles to be used around sand. The last three feet of this drain at the outside/downstream slope three feet of this drain at the outside/downstream slope should be AASHTO #8 material.should be AASHTO #8 material. 20” Separation must be maintained.20” Separation must be maintained.

CompactionCompaction

► All compaction for embankments must be done with a All compaction for embankments must be done with a sheepsfoot or pad roller. sheepsfoot or pad roller.

► Loose lift thickness must be 9” or less. Loose lift thickness must be 9” or less.

► A minimum of 5 passes of the compaction equipment over A minimum of 5 passes of the compaction equipment over the entire surface of each lift is required.the entire surface of each lift is required.

► Compaction to visible non-movement of the embankment Compaction to visible non-movement of the embankment material is required.material is required.

Soil Placement and CompactionSoil Placement and Compaction

Pad RollersPad Rollers

Embankment Top WidthEmbankment Top Width

Minimum 12’Minimum 12’

Take a closer look…..Take a closer look…..

Failure to properly compactFailure to properly compact movement of the embankment movement of the embankment

materialmaterial

Failure to maintain 2 feet of Failure to maintain 2 feet of lined freeboardlined freeboard

Centralized Impoundment Liner Centralized Impoundment Liner ComponentsComponents

►Sub-baseSub-base►Geo-textile Ventilation LayerGeo-textile Ventilation Layer►Secondary LinerSecondary Liner►Leak Detection SystemLeak Detection System►Primary LinerPrimary Liner

Failed liners Failed liners (two separate locations)(two separate locations)

Failed linerFailed liner

Sub-base

6” Compacted Clay

Particle Size <0.75”

Leak Detection Trench

2% Slope

Minimum Slope = 3H:1V

13

Sub-base RequirementsSub-base Requirements

► Must cover bottom and sidesMust cover bottom and sides► Minimum thickness of 6”Minimum thickness of 6”► Compacted to 90% standard proctorCompacted to 90% standard proctor► Coefficient of permeability < 1 x 10Coefficient of permeability < 1 x 10-6-6 cm/s cm/s

Compaction and permeability testing must be Compaction and permeability testing must be conducted once per 2,500 ftconducted once per 2,500 ft22

► Hard, uniform, smooth and free of debris, Hard, uniform, smooth and free of debris, rock fragments, plant materials and other rock fragments, plant materials and other foreign material.foreign material.

► Free of coarse rock fragments greater than Free of coarse rock fragments greater than 0.75” in diameter.0.75” in diameter.

Like This

Not Like This

Do not utilize organic matter in a Do not utilize organic matter in a subbasesubbase

The Decomposition of organic matter The Decomposition of organic matter produces gas and results in the produces gas and results in the potential for the liner to burst or potential for the liner to burst or

rupture!rupture!

Geotextile Fabric

Leak Detection Pipe

Perforated, 4” Diameter

Schedule 80 Minimum

2% Slope Minimum

Clean Stone

2% Slope

GeotextileGeotextile

► The sub-base shall be covered with The sub-base shall be covered with non-woven geotextile fabric to non-woven geotextile fabric to cushion the secondary liner and cushion the secondary liner and allow for adequate venting between allow for adequate venting between the secondary liner and sub-base to the secondary liner and sub-base to prevent entrapment of gases prevent entrapment of gases beneath the liner system. beneath the liner system.

Secondary Liner

Geo-Synthetic Membrane

Thickness = 40 mil

Anchor Trench

Secondary Liner Secondary Liner RequirementsRequirements

► Must cover bottom and sidesMust cover bottom and sides► Minimum thickness of 40 mil synthetic Minimum thickness of 40 mil synthetic

geo-membranegeo-membrane► Coefficient of permeability < 1 x 10Coefficient of permeability < 1 x 10-7-7

cm/scm/s► Liner compatibility shall satisfy EPA Liner compatibility shall satisfy EPA

Method 9090, Method 9090, Compatibility Test for Compatibility Test for Wastes and Membrane LinersWastes and Membrane Liners

► Installed in accordance with QA/QC planInstalled in accordance with QA/QC plan

Leak Detection

k>1 x 10-2

Leak Detection System Leak Detection System RequirementsRequirements

► Coefficient of permeability of 1.0 x 10Coefficient of permeability of 1.0 x 10-2-2 cm/sec or greater cm/sec or greater► Uses a perforated piping system capable of detecting and Uses a perforated piping system capable of detecting and

intercepting liquid within the leak detection zone and conveying intercepting liquid within the leak detection zone and conveying the liquid to a collection sump. the liquid to a collection sump.

The collection sump shall be equipped with a sump pump The collection sump shall be equipped with a sump pump with an automatic switch.with an automatic switch.

Discharge from the sump pump shall be directed back into Discharge from the sump pump shall be directed back into the impoundment or other suitable containment.the impoundment or other suitable containment.

The pump and sump shall be of sufficient size and capacity to The pump and sump shall be of sufficient size and capacity to convey any leak that may occur without a discharge. convey any leak that may occur without a discharge.

The leak detection zone and sump shall be designed to allow The leak detection zone and sump shall be designed to allow the operator to monitor and record leakage rates.the operator to monitor and record leakage rates.

► The leak detection zone shall have a minimum bottom slope of The leak detection zone shall have a minimum bottom slope of 2%.2%.

► Contain non-carbonate stones or aggregate with no sharp edges.Contain non-carbonate stones or aggregate with no sharp edges.► The operator shall monitor the leak detection zone weekly to The operator shall monitor the leak detection zone weekly to

determine whether liquid is flowing from the zone.determine whether liquid is flowing from the zone.

Leak Detection Piping System Leak Detection Piping System RequirementsRequirements

► The slope, size and spacing of the piping The slope, size and spacing of the piping system shall assure that liquids drain from system shall assure that liquids drain from the leak detection zone.the leak detection zone.

► The pipes shall be installed primarily The pipes shall be installed primarily perpendicular to the flow and shall have a perpendicular to the flow and shall have a minimum post-settlement grade of at least minimum post-settlement grade of at least 2%.2%.

► The minimum diameter of the perforated The minimum diameter of the perforated pipe shall be 4 inches with a wall thickness pipe shall be 4 inches with a wall thickness of Schedule-80 or greater.of Schedule-80 or greater.

Primary Liner

Geo-Synthetic Membrane

Thickness = 40 mil

Primary Liner RequirementsPrimary Liner Requirements

► Must cover bottom and sidesMust cover bottom and sides► Minimum thickness of 40 mil synthetic Minimum thickness of 40 mil synthetic

geo-membranegeo-membrane► Coefficient of permeability < 1 x 10Coefficient of permeability < 1 x 10-7-7

cm/scm/s► Liner compatibility shall satisfy EPA Liner compatibility shall satisfy EPA

Method 9090, Method 9090, Compatibility Test for Compatibility Test for Wastes and Membrane LinersWastes and Membrane Liners

► Installed in accordance with QA/QC planInstalled in accordance with QA/QC plan

Action Leakage RatesAction Leakage Rates

Fluid Height (ft)ALR

(gallons/acre/day)

h ≤ 10 340

10 < h ≤ 15 420

15 < h ≤ 20 490

20 < h ≤ 25 550

25 < h ≤ 30 610

h > 30 case by case

In the event that the flow rate of leakage through the primary liner, as collected in the leak detection sump, exceeds the value above for a given fluid depth, the impoundment shall be drained to the extent necessary and the leak or leaks shall be located and repaired

Allowable leakage rates shall be determined based upon the maximum depth of the impounded fluid as specified in the table below. The area shall be calculated as the area of the liner in contact with the impounded fluid.

Groundwater MonitoringGroundwater Monitoring

► Minimum of 1 monitoring well located up-Minimum of 1 monitoring well located up-gradient and 3 down-gradientgradient and 3 down-gradient

► Must be within 200 feet of the Must be within 200 feet of the impoundment and at least 100 feet closer impoundment and at least 100 feet closer than the nearest drinking water wellthan the nearest drinking water well

► Quarterly monitoring for (as a minimum):Quarterly monitoring for (as a minimum): Total dissolved solidsTotal dissolved solids ChlorideChloride SulfatesSulfates pHpH Specific conductanceSpecific conductance

Monitoring Well ConstructionMonitoring Well Construction► The minimum casing diameter shall be 4 inches The minimum casing diameter shall be 4 inches

unless otherwise approved by the Department in unless otherwise approved by the Department in writing. writing.

► The well shall be equipped with a factory-made The well shall be equipped with a factory-made screen designed to maximize open area and screen designed to maximize open area and minimize entrance velocities and allow rapid sample minimize entrance velocities and allow rapid sample recovery. recovery.

► The well shall be filter-packed with chemically inert The well shall be filter-packed with chemically inert clean quartz sand, silica or glass beads. The material clean quartz sand, silica or glass beads. The material shall be well rounded and dimensionally stable.shall be well rounded and dimensionally stable.

► The casing shall be clearly visible and protrude at The casing shall be clearly visible and protrude at least 1 foot above the ground. least 1 foot above the ground.

► The annular space above the sampling depth shall be The annular space above the sampling depth shall be sealed to prevent contamination of samples and the sealed to prevent contamination of samples and the groundwater. groundwater.

Monitoring Well CasingsMonitoring Well Casings

► Must Be of sufficient strength to protect the well Must Be of sufficient strength to protect the well from damage by heavy equipment and from damage by heavy equipment and vandalism. vandalism.

► Must Be installed for at least the upper 10 feet of Must Be installed for at least the upper 10 feet of the monitoring well, as measured from the well the monitoring well, as measured from the well cap, with a maximum stick up of 3 feet.cap, with a maximum stick up of 3 feet.

► Be grouted and placed with a concrete collar at Be grouted and placed with a concrete collar at least 3 feet deep to hold it firmly in position. least 3 feet deep to hold it firmly in position.

► Be numbered for identification with a label Be numbered for identification with a label capable of withstanding field conditions and capable of withstanding field conditions and painted in a highly visible color. painted in a highly visible color.

► Have a locked cap.Have a locked cap.► Be made of steel or another material of Be made of steel or another material of

equivalent strengthequivalent strength

Typical Typical Monitoring Monitoring

WellWell

screen

Engineer CertificationEngineer Certification

► Design plans for centralized Design plans for centralized impoundments must be developed and impoundments must be developed and sealed by a registered professional sealed by a registered professional engineer in Pennsylvania.engineer in Pennsylvania.

► The design engineer shall provide The design engineer shall provide oversight for all aspects of construction oversight for all aspects of construction to ensure that construction is completed to ensure that construction is completed in accordance with the design and quality in accordance with the design and quality assurance and quality control plan.assurance and quality control plan.

Engineer CertificationEngineer Certification► Upon completion, a facility completion and final certification report Upon completion, a facility completion and final certification report

must be submitted to the Department. The report must be completed must be submitted to the Department. The report must be completed and sealed by the licensed professional engineer who provided and sealed by the licensed professional engineer who provided oversight for construction and contain the following items:oversight for construction and contain the following items: A statement that the engineer provided oversight for all aspects A statement that the engineer provided oversight for all aspects

of construction and that the impoundment was constructed as of construction and that the impoundment was constructed as designed and in accordance with these requirements and the designed and in accordance with these requirements and the quality assurance and quality control planquality assurance and quality control plan

Soils classification testing results for the embankmentsSoils classification testing results for the embankments Soil compaction testing results for the sub-baseSoil compaction testing results for the sub-base As-built drawings noting any deviation from the original plans As-built drawings noting any deviation from the original plans

submitted to the Departmentsubmitted to the Department Quarry tickets for drain materialQuarry tickets for drain material Quality assurance and quality control test resultsQuality assurance and quality control test results Color photographsColor photographs

► The impoundment shall not be filled until the facility completion and The impoundment shall not be filled until the facility completion and final certification report is received and approved by the Department.final certification report is received and approved by the Department.

Contact InformationContact Information

Joseph Adams, P.E.Joseph Adams, P.E. | Environmental  | Environmental EngineerEngineer

Bureau of Oil and Gas ManagementBureau of Oil and Gas Management

Department of Environmental ProtectionDepartment of Environmental ProtectionRachel Carson State Office BuildingRachel Carson State Office Building400 Market Street | Harrisburg, PA 17101400 Market Street | Harrisburg, PA 17101Phone: 717.772.2199 | Phone: 717.772.2199 | josepadams@state.pa.usjosepadams@state.pa.us