N F d l E i C t lNew Federal Erosion Control and Stormwater Regulationsand Stormwater Regulations

and Better Site Planning

Robert Pitt, Ph.D., P.E., BCEE, D. WREDepartment of Civil, Construction, and

Environmental EngineeringTh U i it f Al b T l AL 35487The University of Alabama, Tuscaloosa, AL 35487

Early Regulations

• The Refuse Act of 1899 (33 USC 407) was used in 1970 to establish a discharge permit system (Public Law 92-500). This act prohibited the ) pdischarge of any material, except sewage and runoff, into navigable g , gwaterways without a permit from the Dept. of the Army. p y

Amendments to the Water Pollution Control Act (92-500)

1956 (making the legislation permanent and to fund construction grants for POTWs), 1961 (increased funding for water quality research ( g q yand construction grants), 1965 (increased construction grants and started research concerning combined sewer overflows),g ) 1966 (removed the dollar limit on construction grants), 1972 (the most important advances to this date; act ( p ;renamed “Clean Water Act”), 1977 (to extend some of the deadlines established in the 1972 amendments), and), 1988 (require discharge permits for stormwater).

TMDL Regulations• Another important regulation affecting drainage

and stormwater quality is the TMDL program. • The TMDL program is aimed specifically at

assuring attainment of water quality standards by requiring the establishment of pollutantby requiring the establishment of pollutant loading targets and allocations for waters identified as not now in attainment with those standards.

• Section 303(d)(1) of the Clean Water Act provides that states with EPA review andprovides that states, with EPA review and approval, must identify waters not meeting standards, and must establish total maximum daily loads (TMDLs) for them to restore water quality.

• In general, a TMDL is a quantitative assessment of water quality problems, ycontributing sources, and pollution reductions needed to attain water quality standards.

• The TMDL specifies the amount of pollution or other stressor that need to be reduced to meet ater q alit standards allocatesmeet water quality standards, allocates pollution control, or management responsibilities among sources in aresponsibilities among sources in a watershed, and provides a scientific and policy basis for taking actions needed to p y grestore a waterbody.

Rivers and Lakes, Reservoirs, Bays andE t i

Example Alabama 2006 TMDL Status

Streams (Miles), ,

and Ponds (Acres) Estuaries(Square Miles)

Good Waters 6,984 91,229 79, ,Impaired Waters 2,547 81,838 427TMDL completed 702 28,887TMDL alternative 53Non-pollutant impairment 23TMDL needed 1,770 52,951 427New TMDLs completed 0 0 0R i i TMDL d d 1 770 52 951 427Remaining TMDLs needed 1,770 52,951 427

Total Assessed Waters 9,531 173,067 505Total Waters 77 242 490 472 610Total Waters 77,242 490,472 610Percent of Waters Assessed 12.3 35.3 82.9

http://iaspub.epa.gov/waters10/attains_index.control?p_area=AL

Only about ¼ of the required TMDLs have been completed and only 12%  of the y q p yrivers/streams and 35% of the lakes have been assessed. None of the coastal waters have TMDLs completed, but more that 80% have been assessed. 

• Beginning in 1986, and escalating since 1996, environmental public interest , porganizations have filed numerous lawsuits under the Clean Water Act’s citizen suit provision (section 505) alleging that the EPA had failed to carry g g yout its mandatory duty to disapprove inadequate state section 303(d)(1) lists q ( )( )and/or TMDLs, or to carry out state program responsibilities where states p g phave failed to do so.

“Energy Independence and Security Act of 2007” signed into Law on Dec 19 20072007 signed into Law on Dec. 19, 2007

• Title IV (“Energy Savings in Building and Industry”), Subtitle C (“High Performance Federal Buildings”) Sec. 438 (“Storm C ( g e o a ce ede a u d gs ) Sec 38 ( StoWater Runoff Requirements For Federal Development Projects”):

• “The sponsor of any development or redevelopment project involving a Federal facility with a footprint that exceeds 5,000 square feet shall use site planning, design, construction, andq p g, g , ,maintenance strategies for the property to maintain or restore, to the maximum extent technically feasible, the predevelopment hydrology of the property with regard to the temperature, rate, volume, and duration of flow.”

• This new provision requires much more attention to p qcontrolling runoff volume, in addition to other hydrologic features.

Extremes in Flows cause Infrastructure Damage and Habitat Destruction

Urbanization causes extremes in flows; extended dry periods and short periods of higher flows in many areas

g

periods of higher flows in many areas. In the arid west, urbanization increases dry weather flows in intermittent streams due to excessiveintermittent streams due to excessive irrigation.

Photos of Coyote Creek, San Jose, CA

Failing InfrastructureFailing Infrastructure

Bank instability and WI DNR photos

habitat destruction due to increased flows

It is possible to simplify much ofsimplify much of the receiving water biologicalwater biological data to relate degradation to levels of development.

Urban Steam Classification

Sensitive0 – 10%

Imperviousness

Impacted11– 25%

Imperviousness

Damaged26–100%

Imperviousnesspe ous ess pe ous ess pe ous essChannel Stability Stable Unstable Highly Unstable

Aquatic LifeAquatic Life Biodiversity Good/Excellent Fair/Good Poor

Figure and Table from Center for Watershed Protection

Final Effluent Guidelines to Control Discharge Pollutants from Construction SitesPollutants from Construction Sites

• Published in the Federal Register on Dec. 1, 2009.• Regulation is effective as of Feb. 1, 2010. After this date, g , ,

all permits issued by the EPA or states must incorporate the final rule requirements.Beginning on Aug 1 2011 all sites that disturb 20 or• Beginning on Aug. 1, 2011, all sites that disturb 20 or acres at one time will be affected.

• Beginning on Feb. 2, 2014, the limitation applies to all g g , , ppconstruction sites disturbing 10 or more acres at one time.

• These sites must sample stormwater discharges and l ith i li it ti f t bidit f 280 NTUcomply with a numeric limitation for turbidity of 280 NTU.

• Disturbed areas on construction sites not under active construction activities, can only remain exposed for a co st uct o act t es, ca o y e a e posed o amaximum of 14 days.

• http://edocket.access.gpo.gov/2009/E9-28446.htm

Sediment SourcesNot All Runoff is Sediment LadenNot All Runoff is Sediment-Laden

Birmingham Construction Site Erosion Runoff Characteristics (Nelson 1996)Runoff Characteristics (Nelson 1996)

Low Moderate HighLow intensity rains (<0.25

Moderate intensity rains (about

High intensity rains (>1 (

in/hr)(

0.25 in/hr)(

in/hr)

Suspended 400 2 000 25 000Suspended solids, mg/L

400 2,000 25,000

Particle size (median),

3.5 5 8.5(median), m

Rainfall Energy Index for Eastern US

Controls to Meet Effluent Guidelines (from the Effluent Guidelines document):the Effluent Guidelines document):

• Minimize the amount of soil exposed during construction activityconstruction activity

• Minimize sediment discharges from the site. The design, installation and maintenance of erosion and g ,sediment controls must address factors such as the amount, frequency, intensity and duration of

i it ti th t f lti t t ffprecipitation, the nature of resulting stormwater runoff, and soil characteristics, including the range of soil particle sizes expected to be present on the siteparticle sizes expected to be present on the site

• Provide and maintain natural buffers around surface waters, direct stormwater to vegetated areas to increase sediment removal and maximize stormwater infiltration, unless infeasible

Initial Topography (grubbing and clearing phase)

Pink: low hazardBlue: Moderate hazardYellow: High hazarde o g a a dOrange: High hazard

Sediment SourcesB S il f L P i dBare Soil for Long Periods

Controls to Meet Effluent Guidelines (cont ):Controls to Meet Effluent Guidelines (cont.):

• Minimize soil compaction and, unlessMinimize soil compaction and, unless infeasible, preserve topsoil.

• Soil Stabilization. Stabilization of disturbed areas must, at a minimum, be initiated immediately whenever any clearing, grading, excavating or other earth disturbing activities have permanently ceased on any portion of the site or temporarily ceased on any portionthe site, or temporarily ceased on any portion of the site and will not resume for a period exceeding 14 calendar daysexceeding 14 calendar days

• Etc.

Soil Compaction During Site ActivitiesActivities

Pitt, et al. 1999

General Approach

• The most effective way to meet the numeric effluent guidelines will be through prevention: minimize the amount of disturbed land at any one time and to rapidly stabilize any disturbed groundground.

R ff t l t t th t bidit li it• Runoff controls to meet these turbidity limits in the southeast are likely limited to chemical treatment in conjunction with sediment pondstreatment in conjunction with sediment ponds.

Erosion ControlsDiversion Channels and BermsDiversion Channels and Berms

Erosion ControlsP t t Ch l (Ch k d d li )Protect Channels (Check dams and liners)

Erosion ControlsSlope Protection with Hydroseeding and BlanketsSlope Protection with Hydroseeding and Blankets

Erosion ControlsControl Site Discharges

• Filter fencing for small sites (but only for slope lengths less than about 100 ft). p g )Expect about 10 to 50% control of suspended solids.p

• Sediment ponds for areas larger than• Sediment ponds for areas larger than 10 acres. Expect up to 80% control of suspended solidssuspended solids.

Measured Silt Fence Performance during Alabama Tests (about 54% reductions)

Total Suspended Solids

( )

7000.0

8000.041

d. E

rror

5000.0

6000.0

Mea

n +

Std

3000.0

4000.0 23

0 0

1000.0

2000.0

34

Control Fence Nothing0.0

Lalor, et al. 2003

Construction site sediment ponds can capture significant amounts of sediment, but effluent turbidity is still high.

Chemical Treatment of Exposed SoilsThese newly developed materials act by chemically combining small soil particles into larger discrete particles that are more effective in settling in ponds and in channelsthat are more effective in settling in ponds and in channels. Polyacrylamide (PAM) is the most common chemical being sold now. Polyacrylamide used for erosion control should have a negative (anionic) molecular charge.

Passive chemical addition methods used in New Zealand to enhance sediment and turbidity control of construction site wet detention pondsdetention ponds.

Use of Chemical-Assisted Sedimentation

Auckland Regional Council, New Zealand

Example Performance Data for PAC-assisted Settling

Pond Inflow Outflow SS ReductionFl SS Fl SS

Example Performance Data for PAC-assisted Settling

Flow (L/sec)

SS (mg/L)

Flow (L/sec)

SS (mg/L) (%)

Mason’s Rd 3 26,300 3 144 99.4 M ’ Rd 2 5 100 2 40 99 2Mason’s Rd 2 5,100 2 40 99.2 OVR E 15 1,639 8 51 96 OVR E 2 749 2 56 92 23800E 8 14,800 6 966 93 23800E 1 18,700 2 67 99 B1 Gully 0.3 4,300 0.4 3 99.9B1 Gully 0.3 4,300 0.4 3 99.9 B1 Gully 0.5 16,900 3.0 59 99.6

Many examples of the applicable controls are included in:• Construction Site Erosion and Sediment Controls;

Planning, Design and Performance. R. Pitt, S. Clark, and D. Lake. DESTech Publications, Lancaster, PA, 17601. 381 pages ISBN 1 932078 38 X 2007381 pages. ISBN 1-932078-38-X. 2007. http://unix.eng.ua.edu/~rpitt/Class/Computerapplications/Table.htm

• Alabama Handbook for Erosion Control, Sediment Control and Stormwater Management on Construction Sites and Urban Areas. Volume 1. Alabama Soil and Water Conservation Committee Montgomery AL 2003Water Conservation Committee, Montgomery, AL. 2003. http://unix.eng.ua.edu/~rpitt/Class/Erosioncontrol/Module2/ASWCC June 2003 Alabama Handbook Constructio_ _ _ _ _n_E&S_Control.pdf

Runoff Volume Guidelines

• In addition to requiring pre- and post-d l t k ff t t t hdevelopment peak runoff rates to match, many areas are now requiring runoff volumes after development to match pre-developmentdevelopment to match pre-development conditions.

• This is extremely difficult especially when pre-This is extremely difficult, especially when predevelopment conditions are wooded areas.

• The following examples are based on matchingThe following examples are based on matching the runoff associated with a rain occurring with a two year frequency, having a duration of 24 hrs.

Runoff Curve Numbers for Urban Areas(Average runoff conditions, Ia = 0.2S)

Cover Description CNs for Hydrologic Soil Group

Cover Type Average Percent A B C DCover Type Average Percent Impervious Area

A B C D

Urban districts

Commercial and business 85 89 92 94 95Commercial and business 85 89 92 94 95

Industrial 72 81 88 91 93

Residential district by average lot size⅛ acre or less (town houses) 65 77 85 90 92

¼ acre 38 61 75 83 87

⅓ acre 30 57 72 81 86½ acre 25 54 70 80 851 acre 20 51 68 79 842 acres 12 46 65 77 82

Commercial development with B soils CN = 92

Typical CN Values for Pastures, Grasslands, and Woods

W d i d ditiWoods in good condition with B soils; CN = 55

4.2 inches for central AL4.2 inches for central AL

TR-55, NRDC, June 198

Solution of the SCS Runoff Equation(from TR-55, Urban Hydrology for Small Watersheds, Soil Conservation

Service U S Department of Agriculture):Service, U.S. Department of Agriculture):

Runoff Volume Reduction Goals:Runoff Volume Reduction Goals:

• 0.6 inches pre-development runoff (CN0.6 inches pre development runoff (CN = 55 and P = 4.2 inches)

• 3 3 inches post-development runoff (CN• 3.3 inches post-development runoff (CN = 92 and P = 4.2 inches)Therefore need about 82% runoff• Therefore need about 82% runoff reduction compared to conventional developmentdevelopment.

Porous Pavement• Assume no additional runoff flowing

onto porous pavement (no runon)onto porous pavement (no runon)• Use for walkways and overflow parking

d i d ( ll ) tareas, and service roads (alleys); not used in areas of material storage or for

t i ki t ffi t i i iextensive parking or traffic to minimize groundwater contamination potential.

Madison, WIAustin, TX

Malmo, Sweden

SingaporeEssen, Germany

Potential Problem Pollutants Id tifi d B d W kwere Identified Based on a Weak-

Link Model Having the Following g gElements:

• Their abundance in stormwater,• Their mobility through the unsaturated• Their mobility through the unsaturated

zone above the groundwater, and• Their treatability before discharge.

Links Depend on Infiltration Method(contamination potential is the lowest rating of(contamination potential is the lowest rating of

the influencing factors)• Surface infiltration with minimal pretreatment• Surface infiltration with minimal pretreatment

(grass swales or roof disconnections)– Mobility and abundance most criticalMobility and abundance most critical

• Surface infiltration with sedimentation pretreatment (treatment train: sedimentationpretreatment (treatment train: sedimentation then media filtration)– Mobility, abundance, and treatability all

important• Subsurface injection with minimal pretreatment

( t i ki l t d ll)(porous pavement in parking lot or dry well)– Abundance most critical

Moderate to High Contamination PotentialSurface Infiltration Surface Infiltration Injection after Minimal Su ace t at owith no Pretreatment (rain gardens or swales)

Su ace t at oafter Sedimentation (media filtration and sedimentation)

ject o a te aPretreatment (such as porous pavements)

Lindane, chlordane Lindane, chlordane

Benzo (a) anthracene, bi (2 th lh l

Fluoranthene, pyrene 1,3-dichlorobenzene, b ( ) thbis (2-ethylhexl

phthalate), fluoranthene, pentachlorophenol

benzo (a) anthracene, bis (2-ethylhexl phthalate), fluoranthenepentachlorophenol,

phenanthrene, pyrenefluoranthene, pentachlorophenol, phenanthrene, pyrene

E t i E t i E t iEnteroviruses Enteroviruses Enteroviruses, some bacteria and protozoaNickel, chromium, lead, zinc

Chloride Chloride Chloride

Recommendations to Reduce Groundwater Contamination PotentialGroundwater Contamination Potential when using Infiltration in Urban Areas

• Infiltration devices should not be used in most industrial areas without adequate pretreatment.

• Runoff from critical source areas (mostly in commercial areas) need to receive adequate

t t t i t i filt tipretreatment prior to infiltration.• Runoff from residential areas (the largest

t f b ff i t iti ) icomponent of urban runoff in most cities) is generally the least polluted and should be considered for infiltrationconsidered for infiltration.

Continuous Simulations of Porous Pavement Installations using the 1976 Birmingham rain record (a typical rain period)

About 100 rains, 55 inches total, maximum rain depths of about 4 inches.

Input screen of the pSource Loading and Management Model (WinSLAMM) for porous pavement

Modeling Findings for Porous Pavements in Central Alabama AreaPavements in Central Alabama Area

• Soils having at least 0.1 in/hr infiltration rates can totally remove the runoff from porous pavement areas assumingremove the runoff from porous pavement areas, assuming about 1 ft coarse rock storage layer. Porous pavement areas can effectively contribute zero runoff, if well maintained.

• However, slow infiltrating soils can result in slow drainage times of several days. Soils having infiltration rates of at least 0 5 in/hr can drain the pavement structure and storage area0.5 in/hr can drain the pavement structure and storage area within a day, a generally accepted goal.

• These porous pavements can totally reduce the runoff during the intense 2-year rains.

• Good design and construction practice is necessary to prolong the life of the porous pavements including restrictingprolong the life of the porous pavements, including restricting runon, prohibiting dirt and debris tracking, and suitable intensive cleaning.

Green Roofs• Green roofs can contribute to energy savings

i ti f b ildi l th lifin operation of a building, can prolong the life of the roof structure, and can reduce the amount of roof runoffamount of roof runoff.

• They can be costly. However, they may be one of the few options for stormwater volumeone of the few options for stormwater volume control in ultra urban areas where ground–level options are not available.p

• Irrigation of the plants is likely necessary to prevent wilting and death during dry periods.

Swarthmore College Green R f S th PARoof, Swarthmore, PA

Montgomery Park Green Roof Baltimore, MD.

Photo Courtesy Penn State Center for Green Roof Research

Continuous simulations Co t uous s u at o swere also conducted for green roofs and Birmingham conditions, using WinSLAMM

The main roof runoff removal mechanism for green roofs is evapotranspiration These areevapotranspiration. These are central Alabama monthly ET values and the plant and substrate characteristics used in thesecharacteristics used in these analyses.

Annual Roof Runoff Reductions for Local Green Roofs

70

80

of

Green Roofs

50

60

70

nual

Roo

%)

30

40

50

n in

Ann

unof

f (%

20

30

educ

tion

Ru

0

10

0 20 40 60 80 100

Re

0 20 40 60 80 100

Green Roof as a Percentage of Total Roof Area

Critical Four Inch Rain Roof Runoff Reductions for Local Green Roofs

90

100

ctio

n Reductions for Local Green Roofs

60

70

80

me

Red

ucin

s (%

)

40

50

60

ff V

olum

inch

Rai

20

30

f Run

offo

r 4

i

0

10

0 20 40 60 80 100 120

Roo

0 20 40 60 80 100 120

Green Roof as a Percentage of Total Roof Area

Results from Modeling Local Green Roofs

• Vegetated green roofs can reduce up to about 70% of the annual roof runoff during typical70% of the annual roof runoff during typical conditions, if the complete roof is planted.

• The plants would likely wilt and die as the ET• The plants would likely wilt and die as the ET drives the substrate to the plants’ wilting point during the late summer, early fall period, g , y p ,requiring substantial irrigation.

• Green roofs are capable of controlling all of the p grunoff from the critical four inch rain, if enough storage is provided on the roof, and if at least h lf f h f i l dhalf of the roof is planted.

Rain Gardens for Roof and Paved Area Runoff

• Simple rain gardens with extensive excavations or underdrains can be used near buildings for the control ofunderdrains can be used near buildings for the control of roof runoff, or can be placed in or around the edges of parking areas for the control of runoff from parking areas.

• Rain gardens provide greater groundwater contamination protection compared to porous pavements as the engineered soil fill material should contain significant g gorganic material that hinders migration of many stormwater pollutants. This material also provides much better control of fine sediment found in the stormwaterbetter control of fine sediment found in the stormwater.

• Rain gardens can be sized to control large fractions of the runoff, but maintenance to prevent clogging and to remove contaminated soils is also necessary.

Different types of rain ypgardens for a residential roof, a commercial parking lot and a curb-cut biofilterlot, and a curb-cut biofilter.

WinSLAMM was also used to model rain gardens for local conditionsg

Annual Runoff Reductions from Paved Areas or Roofs for Different Sized Rain Gardens

100

viou

s l I

mpe

rvf(

%)

10

Ann

ual

Run

off

ctio

n in

A

rea

clay (0.02 in/hr)

silt loam (0.3 in/hr)

sandy loam (1 in/hr)

1

Red

u sandy loam (1 in/hr)

0.1 1 10 100

Rain Garden Size (% of drainage area)

Reductions of Runoff from Four Inch Rain from Paved Areas or Roofs for Different Sized

100

a )Rain Gardens

us A

rea

ains

(%

10

mpe

rvio

4 in

ch R

aio

n in

Imdu

ring

4

clay (0.02 in/hr)

silt loam (0.3 in/hr)

d l ( i /h )

10 1 1 10 100R

educ

tiR

unof

f d sandy loam (1 in/hr)

0.1 1 10 100R R

Rain Gardens Size (% of drainage area)

Clogging Potential for Different Sized Rain Gardens Receiving Roof Runoff

10000

g

1000

ggin

g

100

rs to

Clo

years to 10 kg/m2

10Year years to 25 kg/m2

10.1 1 10 100

Rain Garden Si e (% of roof area)Rain Garden Size (% of roof area)

Clogging Potential for Different Sized Rain Gardens Receiving Paved Parking Area Runoff

1000

100

oggi

ng

10ars t

o C

l

10

Yea

years to 10 kg/m2

years to 25 kg/m21

0.1 1 10 100

Rain Garden Size (% of paved parking area)Rain Garden Size (% of paved parking area)

Results from Modeling Local Rain GardensGardens

• Local rain gardens should be located in areas having soil infiltration rates of at least 0 3 in/hr Lower rates result ininfiltration rates of at least 0.3 in/hr. Lower rates result in very large and much less effective rain gardens, and the likely clay content of the soil likely will result in premature l iclogging.

• Rain gardens should be from 5 to 10 percent of the drainage area to provide significant runoff reductions g p g(75+%).

• Rain gardens of this size will result in about 40 to 60% d ti i ff l f th l 4 i h ireductions in runoff volume from the large 4 inch rain.

Rain gardens would need to be about 20% of the drainage area in order to approach complete control of these large rains.

Rain Garden Results (cont.)

• Clogging of the rain garden may occur from particulates entering the device, or from clay in the engineered soil mixengineered soil mix.

• Roof runoff contains relatively little particulate matter and rain gardens at least 1% of the roof area are not glikely to clog (estimated 20 to 50 years).

• Paved area runoff contains a much greater amount of particulate matter and would need to be at least 10%particulate matter and would need to be at least 10% of the paved area to have an extended life (>10 years).

Example Sizing of Stormwater Controls f S ifi P f Obj tifor Specific Performance Objectives

• Estimate source area contributions for large gevents using CN values and areas for each component (roofs, walkways, streets, service

)roads, landscaping, parking)• Apply suitable control practices at each site and

l l t lti ffcalculate resulting runoff• Compare resulting runoff with required runoff goal• Adjust as needed• Layout control on site using landscaping options

Source area curve number values for source areas for large events:source areas for large events:

TR-55, NRCS, 1986

Impervious areas (roofs, walks, streets, parking areas) have CN = 98p ( , , , p g )Pervious areas (landscaped areas in good condition and B soils) have CN = 61

Solution of the SCS Runoff Equation(from TR-55, Urban Hydrology for Small Watersheds, Soil Conservation

Service U S Department of Agriculture):Service, U.S. Department of Agriculture):

23 acre Commercial Site with B Soils

% of site ft2

CN for large

events

Q for 4.2 in

rain (in)total

runoff (ft3)

% of runoff

from area% of site ft events rain (in) runoff (ft ) from area

roofs 21.6 216,506 98 4 72,169 23

access roads 1.8 18,134 98 4 6,045 2

parking lots 61.0 611,347 98 4 203,782 65

streets 6.4 64,020 98 4 21,340 7

walkways 0.5 5,410 98 4 1,803 1landscaping

(good condition) 8.6 86,462 61 0.9 6,485 2

total: 100 1,001,880 311,624 100

Actual CN for site conditions is 96 (3 73 in runoff and 4 2 in rain; Rv = 0 89)Actual CN for site conditions is 96 (3.73 in. runoff and 4.2 in. rain; Rv = 0.89)91% impervious cover; 2.1% of runoff from pervious area, 97.9% of runoff from impervious areas. 6.2X runoff increase with development and 84% reduction needed

First Trial for Stormwater Controls

stormwater control % reductionresulting

runoff (ft3)roofs 10% rain gardens 60 28 900roofs 10% rain gardens 60 28,900

access roads porous pavement 100 0parking lots 10% rain gardens 60 81,500p g g ,

streets 10% rain gardens 60 8,500

walkways porous pavement 100 0landscaping (good

condition) prevent compaction 0 6,500

total: 125,4001.50 inches

60 %

Controls not sufficient

Runoff goal: 50,094 ft3Calculations to determine reduction goals

Runoff goal: 50,094 ftLandscape area runoff: 6,485 ft3

Goal for impervious areas: 43,609 ft3U t ll d i iUncontrolled impervious area

runoff: 305,139 ft3% runoff reduction for

impervious areas needed 85.7 %Therefore need 15% rain

gardens in B soilsgardens in B soils

stormwater control % reduction

resulting runoff (ft3)

area needed (ft2)

15% rainroofs

15% rain gardens 86 10,100 32,500

access roadsporous

pavement 100 0 0access roads pavement 100 0 0

parking lots15% rain gardens 86 28,500 91,70015% rain

streets15% rain gardens 86 3,000 9,600

walkwaysporous

pavement 100 0 0walkways pavement 100 0 0landscaping

(good condition)prevent

compaction 0 6,500 0total: 48,100 ft3 133,800 ft2, ,

0.58 inches 3.1 acres

84.5 % reduction

13.4 % of whole sitereduction whole site

Controls are sufficient; most can fit on landscaped areas with some parking lot islands, and curb-cut biofilters

23 acre Commercial Site with D Soils

% of site ft2

CN for large

events

Q for 4.2 in

rain (in)total

runoff (ft3)

% of runoff

from area% of site ft events rain (in) runoff (ft ) from area

roofs 21.6 216,506 98 4 72,169 23

access roads 1.8 18,134 98 4 6,045 2

parking lots 61.0 611,347 98 4 203,782 64

streets 6.4 64,020 98 4 21,340 7

walkways 0.5 5,410 98 4 1,803 1landscaping

(good condition) 8.6 86,462 80 2.2 156,851 5

total: 100 1,001,880 320,991 100

Actual CN for site conditions is 97 (3 84 in runoff and 4 2 in rain; Rv = 0 92)Actual CN for site conditions is 97 (3.84 in. runoff and 4.2 in. rain; Rv = 0.92)91% impervious cover; 4.9% of runoff from pervious area, 95.1% of runoff from impervious areas. 1.8X runoff increase with development and 45% reduction needed

resulting

First Trial for Stormwater Controls (D soils)

stormwater control % reductionresulting

runoff (ft3)roofs 10% rain gardens 21 57,000

access roads porous pavement 100 0parking lots 10% rain gardens 21 161,000

streets 10% rain gardens 21 16 900streets 10% rain gardens 21 16,900

walkways porous pavement 100 0landscaping (good

condition) prevent compaction 0 18,850

total: 250,7003.00 inches

22%

Controls not sufficient (and rain gardens and porous pavementControls not sufficient (and rain gardens and porous pavement only used in these soils with extreme caution and special design consideration)

Runoff goal: 175,329 ft3Calculations to determine reduction goals

Runoff goal: 175,329 ftLandscape area runoff: 15,851 ft3

Goal for impervious areas: 159,478 ft3U t ll d i iUncontrolled impervious area

runoff: 305,139 ft3% runoff reduction for

impervious areas needed 47.7 %Therefore need 20% rain gardens for D soils (withgardens for D soils (with

caution!)

stormwater control % reduction

resulting runoff (ft3)

area needed (ft2)

20% rainroofs

20% rain gardens 48 37,500 43,300

access roadsporous

pavement 100 0 0access roads pavement 100 0 0

parking lots20% rain gardens 48 106,000 122,00020% rain

streets20% rain gardens 48 11,100 12,800

walkwaysporous

pavement 100 0 0walkways pavement 100 0 0landscaping

(good condition)prevent

compaction 0 15,900 0total: 170,400 ft3 178,400 ft2, ,

2.04 inches 4.1 acres

46.9 % reduction

17.8 % of whole sitereduction whole site

Controls are sufficient; most can fit on landscaped areas with some parking lot islands, and curb-cut biofilters

ConclusionsN l bli h d f d l i i d• Newly published federal construction site and stormwater regulations will require much more careful site planningcareful site planning.

• Runoff volume controls during large events will require extensive use of infiltration practicesrequire extensive use of infiltration practices.

• Sizes of practices for the same land use is not very sensitive to soil conditions (less runoffvery sensitive to soil conditions (less runoff increases compared to pre-development conditions with poorer soils and therefore lower volume reduction goals).

• However, use of infiltration controls in poor soils is not a very robust/sustainable practice, and needs to be done with caution and over-sizing.