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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