Tom Schueler Update on Proposed Virginia Stormwater Regulations and Adapting them for the Ridge and Valley Winchester VA October 28, 2008.

Tom Schueler

Update on Proposed Virginia Stormwater Regulations and Adapting them for the Ridge and Valley

Winchester VA October 28, 2008

New organization launched in September 2007 to improve on the ground implementation of effective stormwater practices in 1300 communities and 7 States in the Chesapeake Bay Watershed

Creating alignment among the local, state, federal and private sectors to solve the Bay stormwater problem through an independent network of concerned stormwater professionals

Chesapeake Stormwater Network

www.chesapeakestormwater.net

Core Themes

Land Development and Impervious Cover Overview of New Stormwater Regulations Adapting Practices for Karst Terrain Discussion

Development is creeping up on us, and will defeat our efforts, if we don’t get our act together soon

0

5

10

15

20

25

30

35

1986 1990 1996 2000 2007 2030

% Dev

76,800 acres of impervious cover and 232,500 acres of turf cover created each year, or nearly 1% of Bay watershed per year

Urban Nutrient Loads Are Fast Becoming a Big Slice of the Bay Pie

Year Total N Total P

1985 2% 5%

2000 9% 15%

2005 19% 30%

2030 ?? ??

Only Bay nutrient load sector where we are seeing reverse progressIn load reductions- source OIG (2007)

The ICM and Urban Subwatershed Management

New National Research Council Report Released

• Flow is a pollutant • Direct relationship land cover and biological degradation • Current piecemeal permitting system does not work• Convert to a watershed based permitting system• Numeric stormwater permit limits • Urban stream classification and management• More Industrial stormwater monitoring

Findings: Urban Stormwater Management in the United States

http://www.nap.edu/catalog.php?record_id=12465

VA DCR Stormwater Regulations• Revised Draft SWM Reg just approved for

administrative review and public comment (est. Spring 2009)

• Currently updating State SWM Handbook, using a stakeholder Technical Advisory Committee

• Currently creating a Virginia SWM BMP Clearinghouse web site and BMP evaluation process (initial draft BMP spec’s posted now)

1. Site Load Standard

• What we do now– Total phosphorus (TP) as

keystone– Most sites meet average

land cover condition (0.45 lbs/acre/year)

– Doesn’t apply to much of state

• What is proposed– TP basis for compliance;

Total Nitrogen also calculated

– Load limit tied to Tributary Strategy goals = 0.28 lbs/acre/year (TP)

– State-wide application

Runoff reduction is defined as the total volume reduced through canopy interception, soil infiltration, evaporation, rainfall harvesting, engineered infiltration, extended filtration or evapotranspiration at small sites

2 .Runoff Reduction (RR)

Stormwater Practices Differ Sharply in Ability to Reduce Runoff Volume

Bioretention, Infiltration, Dry Swales and Related Practices Reduce Runoff Volumes by 50 to 90%

Wet Ponds, ED Ponds and Constructed Wetlands and Filters Reduce Runoff Volumes by zero to 10%

Runoff Reduction Practices *

1. Protected Open Space Receiving Runoff from Developed Areas

2. Rooftop Disconnection (4 options)3. Pervious Parking4. Green Roof5. Grass Channels6. Bioretention & Dry Swales7. Wet Swales8. Infiltration9. Extended Detention* Forest conservation, soil conservation, soil restoration are “self crediting”

Each Practice Must Meet Design Specs to Receive the RR “Credit”

BMPs: Level 1 & 2 BMP Designs

•Level 1: good, standard design

•Level 2: enhanced design to boost nutrient removal

BIORETENTION DESIGN

LEVEL 1 DESIGN LEVEL 2 DESIGN

TV= (Rv)(A) TV= 1.25 (Rv)(A)

Filter media at least 24” deep Filter media at least 36” deep

One form of accepted pretreatment Two or more forms of accepted pretreatment

At least 75% plant cover At least 90% plant cover, including trees.

One cell design Two cell design

Underdrain Infiltration design or underground stone sump

3. Treating Impervious Cover & Managed Turf Areas

• What we do now– Nutrient loads based on

impervious cover

• What is proposed– Nutrient loads &

treatment volume based on impervious cover + managed turf

– Incentives to preserve forest cover

Site Runoff Coefficient (Rv)

Site Rv = RvI * %I + RvT * %T + RvF * %F

Site Cover Runoff Coefficients

Soil Condition Runoff Coefficient

Forest Cover 0.02 to 0.05*

Disturbed Soils 0.15 to 0.25*

Impervious Cover 0.95

*Hydrologic Soil Group (HSG)Forest A: 0.02 B: 0.03 C: 0.04 D: 0.05 Disturbed A: 0.15 B: 0.20 C: 0.22 D: 0.25

4. Spreadsheet – Beta Version

• TN comps included

• Accomodates BMPs in series

• Compliance by site – BMP design by drainage area

• Water quantity compliance

• Accounting for forest treatment volume

• More bells, whistles – not as simple

Water Quality Compliance Spreadsheet 1. Post-Development Project & Land Cover Information

Constants

Annual Rainfall (inches) 43Target Rainfall Event (inches) 1.00Phosphorus EMC (mg/L) 0.28Target Phosphorus Load (lb/acre/yr) 0.28Pj 0.90

Land Cover (acres)A soils B Soils C Soils D Soils Totals

Forest/Open Space -- undisturbed, protected forest/open space or 0.0 2.0 4.0 6.0Managed Turf -- disturbed, graded for yards or other turf to be 6.0 14.0 20.0Impervious Cover (all soil types) 14.0 14.0

Total 40.0

Rv CoefficientsA soils B Soils C Soils D Soils

Forest/Open Space 0.02 0.03 0.04 0.05Managed Turf 0.15 0.20 0.22 0.25Impervious Cover 0.95

Channel ProtectionAllowable QDeveloped = QForested x Vforested / VDeveloped

2.6019,116.22

19.0012,657.08

18.006,459.13

Target Rainfall Event (in)

Drainage Area (acres)

Runoff Reduction Volume (cf)

Drainage Area A

Drainage Area BDrainage Area (acres)

Runoff Reduction Volume (cf)

Runoff Reduction Volume (cf)

Draft VA-DCR BMP Specifications

• Rooftop Disconnection• Filter Strips• Grass Channels• Soil Amendments• Green Roofs • Rain Tanks/Rainwater

Harvesting• Permeable Pavement• Infiltration

• Bioretention– Urban Bioretention

• Dry Swales• Filtering Practices• Constructed Wetlands

– Wet Swales • Wet Ponds• Extended Detention

Ponds

Unique Development Conditions in the Ridge and Valley

Karst TerrainExtremely large lot development Individual development projects are small Surface/subsurface drainage poorly understood Limited public water and sewer serviceRunoff reduction practices are newLimited experience by contractors, designers and

reviewers

Rural Runoff Reduction Practices for Karst Available from CSN Website

Guiding Philosophy for Stormwater Design in Karst

• Detailed on-site geotechnical survey first• LID practices work well in karst• Limited use of infiltration in karst terrain• Avoid big contributing areas and deep trenches/pools• Define stormwater hotspots and ensure full treatment before discharge• No discharge to sinkhole w/o full water quality treatment• Underground injection permits for sinkholes and deep infiltration