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At At

WWetlandetland SStudiestudies andand SSolutions,olutions, IInc.nc.

Wetland

WSSI’s building is serviced by an existing regional pond –NO ON-SITE STORMWATER MANAGEMENT IS REQUIRED.

So, why implement LID?

To mimic the predevelopment hydrology, thereby minimizing stream degradation, because we believe it’s the right thing to do.

To satisfy our curiosity:To see how different types of pervious pavement systems perform relative to

their costTo determine the actual maintenance requirements of an LID projectTo determine the real cost of an LID projectTo determine the barriers to LID implementation

To provide a laboratory for the study of LID performance

To create an integrated LID plan, rather than using a slapdash approach to LID

WWhyhy ddidid wwetlandetland sstudiestudies

iimplementmplement lid?lid?

Wetland

To reduce the post-development curve number to the pre-development curve number by using permeable paving surfaces.

To minimize the effect of increased runoff volume on downstream waters by reducing the post-developed runoff rate below the pre-developed, forested rate through increased storage and time of concentration.

To demonstrate compliance with Chesapeake Bay Preservation Ordinance and stormwater management ordinance regulations without a conventional stormwater management/BMP facility.

WWhathat wwere the ere the TTechnical echnical ggoalsoals

ofof thethe pprojectroject??

Wetland

Conservation and protection of natural features that provide stormwater control.

Minimization of impervious areas and impacts to natural areas.

Direction of runoff to natural areas to slow down and capture water so it can infiltrate natural areas, evaporate, or be reused.

Use of multiple small-scale controls that work to reproduce natural processes with rainfall, including infiltration, detention, retention, evaporation, and groundwater recharge.

Pollution prevention through erosion and sediment control and prevention of soil compaction during site preparation and construction.

Education regarding the practice of LID techniques and maintenance of stormwater infiltration facilities.

WWhathat aarere thethe bbasicsasics ofof lid?lid?

Wetland

HHowow isis lid ilid implementedmplemented

atat thethe wssi bwssi buildinguilding??

Gravel DetentionGravel Detention

Native VegetationNative Vegetation

CisternCistern

BioBio--swaleswale

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Green RoofGreen Roof Pervious ParkingPervious Parking

Rain GardenRain Garden

TThehe ggreenreen rroofoof

1

2

3

1. Steel joist

2. Metal roof deck

3. 5” R-30 foam insulation

4. ½” gypsum protection board

5. 75 mil ethylene propylene diene monomer (EPDM) membrane

6. ½” foam protection board

7. 40 mil high-density polyethylene (HDPE) root barrier

8. Protection fabric

9. 1” drainage layer

10. Filter fabric

11. 3-9” lightweight growing medium

12. Stone features, sedum, and native perennials and shrubs

4

1112

56

78

910

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Green Roof Cross Section

TThehe ggreenreen rroofoofCombination of extensive (3-4” soil) and intensive (4-9” soil) planting areasReduces impervious area by 3,626 sfReduces roof runoffEngineered to support 62 lbs/sfIncreases green area and provides amenityCost: $31.80/sf installed

Wetland

8,000 g8,000 gallonallon ccisternisternCollects the “first flush” of roof runoff (1/2”)Provides irrigation waterOverflows to rain garden and gravel bed detentionCost: $3.88/gal installed

$1.23/ sf impervious area treated(Cistern material only cost: $2.88/gal)

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TThehe rrainain ggardenarden

Treats 34,660 sf of impervious roof and parking lot area1,536 sf bed; 11,693 sf grassed bufferDrains to gravel bed detentionCost: $2.60 /sf impervious area treated

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Pervious Concrete 3,342 sf

GravelPave2 19,862 sf

Gravel Paving 1,273 sf

Concrete Pavers 5,502 sf

Asphalt 55,896 sf

PPerviouservious PParkingarkingWetland

PPerviouservious CConcreteoncreteReduce impervious area by 3,342 sf. (3.9% of total parking area)Drains to gravel bed detentionApproximate cost: $6.00/sf installed(Asphalt cost: $2.56/sf)

Wetland

GGravelravelPPaveave2 2 andand GGravelravel PPavingavingReduce impervious area by 21,135 sf (24.6% of total parking area)Drains to gravel bed detentionGravelPave2 cost: $6.00/sf installed Gravel paving cost: $4.32/sf installed (Asphalt cost: $2.56/sf)(GravelPave2 materials only cost: $3.20/sf)

Wetland

CConcreteoncrete PPaversaversReduce impervious area by 5,502 sf. (6.4% of total parking area)Drains to existing vegetated floodplainCost: $7.10/sf installed + $0.80/sf header curb (Asphalt cost: $2.56/sf)(Paver material only cost: $2.55/sf)

Wetland

GGravelravel BBeded DDetentionetentionOrifice controlled- drains to existing stream systemDetains the 1-yr storm over 24 hours.Cost: $2.28/cf treatment volume installed$0.32/sf impervious area treated

1.6251.625”” OutflowOutflow

Wetland

WWaterater qqualityuality sswalewale

Collects runoff from 12,650 sf of impervious parking surfacesSlows runoffWater quality volume filters through check damsCost: $3.68/sf impervious area treated

Wetland

nnative ative vvegetationegetationMaintains habitatDecreases water consumptionUses a drip irrigation system and captured rainwater Landscape and drip irrigation cost: $125,864 (Typical landscape and irrigation cost: $80,000)

Wetland

DDidid wwetlandetland sstudiestudies mmeeteet itsits

ttechnicalechnical ggoalsoals??

9.5 (71%)Curve Number Reduction87.5Conventional Postdevelopment Curve Number78.0LID Postdevelopment Curve Number74.1Predevelopment Curve Number

Curve Number Reduction:

Chesapeake Bay Ordinance:

51.3%50.0%

Actual phosphorous removalRequired phosphorous removal

Wetland

DDidid wwetlandetland sstudiestudies mmeeteet itsits

ttechnicalechnical ggoalsoals??

Runoff Rate:

Due to limitations with current modeling methods, the time of concentration (Tc) is assumed to be five minutes in both the pre-developed and post-developed case. In reality, the Tc may be less than five minutes in the pre-developed case and may be greater than five minutes in the post-developed case, potentially lowering the peak runoff from the site further than indicated.

7.94 cfsPostdevelopment runoff rate (1.5-year storm)9.42 cfsPredevelopment runoff rate (1.5-year storm)

12,609 c.f.Actual storage provided3,686 c.f. Required storage per Prince Georges County LID Manual

Wetland

Conservation and protection: WSSI conserved on-site wetlands and hardwood areas through the use of retaining walls.

Minimization: WSSI minimized impervious areas through the use of pervious paving systems.

Education: The WSSI building will be used as a showcase piece and a laboratory for the study and promotion of Low-Impact Development.

DDid id wwetlandetland sstudiestudies

ffulfillulfill thethe bbasicsasics ofof lid?lid?

Wetland

DDid id wwetlandetland sstudiestudies

ffulfillulfill thethe bbasicsasics ofof lid?lid?Direction of runoff: WSSI’s gravel bed detention and water quality swale direct runoff

to an existing stream and wetland system on the site. The pervious pavement underdrains direct water to existing vegetated floodplain.

Wetland

Use of multiple small-scale controls:The WSSI site plan includes a green roof, three different pervious pavements, a cistern, a swale, native landscaping, and underground detention to treat stormwater from 3.89 acres of disturbed land.

Pollution prevention: The WSSI site plan called for extensive erosion and sediment controls to protect downstream resources during construction and meets the “no increase” in post-development non-point source pollutant loads requirement.

HHowow mmuchuch ddidid itit ccostost??Rain Garden

Cistern

Green Roof

Pervious Concrete Pavers

Gravel Pavement

GravelPave2 System

Gravel Bed Detention

Swale

Total

Standard Asphalt / Curb and Gutter Estimate

$90,000

$31,000

$115,316

$39,000

$5,500

$143,500

$24,000

$46,525

$360,115

$620,705

Native Landscaping and Drip Irrigation $125,864

Item $/sf impervious Cost

$2.60

$1.23

$31.80

$7.90

$4.32

$6.00

$0.32

$3.68

Wetland

N/A

Pervious Concrete N/A$6.00

WWherehere is theis the pprojectroject llocatedocated??Rte. 29Rte. 29 II--6666

Rte. 29Rte. 29

NN

NN

Wetland

5300 Wellington Branch Drive, Gainesville

FForor ffurtherurther iinformation nformation

on on tthese hese lid plid practicesracticesPervious Pavement Systems:

http://www.uni-groupusa.org/uni-eco-.htmhttp://www.invisiblestructures.comhttp://www.nrmca.org

Green Roofing:http://manual.fsbp.com/Garden%20Roofing%20Systems%20Design%20Guide.pdfhttp://www.greenroofs.comhttp://www.greenroofs.org

Cistern:http://www.xerxescorp.com/index.shtml

General Links:http://www.wetlandstudies.comhttp://www.epa.gov/owow/nps/lid/lid_hydr.pdfhttp://www.lowimpactdevelopment.org

Wetland

TThankshanks to theto the wssiwssi pprojectroject tteameam

Project Management – The Peterson CompaniesConcept Plan – Wetland Studies and Solutions, Inc.General Contracting – EEReed Construction, LPCivil Engineering – Urban Engineering and Associates, Inc.Site Work – S.W. Rodgers Green Roof Installation – The Furbish CompanyPervious Concrete – Virginia Ready Mixed Concrete Association

Wetland