WQv
|
=
|
(c)(P)(A)
12
|
Where:
| ||
WQv
|
=
|
Water quality volume in acre-feet
|
c
|
=
|
Rational method post-development runoff coefficient for the
two-year storm
|
P
|
=
|
1.25 inches
|
A
|
=
|
Area in acres of proposed regulated activity
|
REv = (0.25)*(I)/12
|
Where:
| ||
REv
|
=
|
Recharge volume in acre-feet
|
I
|
=
|
Impervious area in acres
|
Best Management Practice
|
Design Reference NumberC
|
---|---|
BioretentionA
|
4, 5, 11, 16
|
Capture/reuseB
|
4, 14
|
Constructed wetlands
|
4, 5, 8, 10, 16
|
Dry extended detention ponds
|
4, 5, 8, 12, 18
|
Minimum disturbance/minimum maintenance practices
|
1, 9
|
Significant reduction of existing impervious cover
|
N/A
|
Stormwater filtersA (sand, peat,
compost, etc.)
|
4, 5, 10, 16
|
Vegetated buffers/filter strips
|
2, 3, 5, 11, 16, 17
|
Vegetated roofs
|
4, 13
|
Vegetated swalesA
|
2, 3, 5, 11, 16, 17
|
Water quality inletsD
|
4, 7, 15, 16, 19
|
Wet detention ponds
|
4, 5, 6, 8
|
NOTES:
| |
A
|
This BMP could be designed with or without an infiltration component.
If infiltration is proposed, the site and BMP will be subject to the
testing and other infiltration requirements in this chapter.
|
B
|
If this BMP is used to treat the entire WQv, then it is the
only BMP required because of this BMPs superior water quality performance.
|
C
|
See table below.
|
D
|
Water quality inlets include such BMPs as oil/water separators,
sediment traps/catch basin sumps, and trash/debris collectors in catch
basins.
|
Design Reference Title
| |
1
|
"Conservation Design For Stormwater Management — A Design
Approach to Reduce Stormwater Impacts From Land Development and Achieve
Multiple Objectives Related to Land Use," Delaware Department of Natural
Resources and Environmental Control, The Environmental Management
Center of the Brandywine Conservancy, September 1997.
|
2
|
"A Current Assessment of Urban Best Management Practices: Techniques
for Reducing Nonpoint Source Pollution in the Coastal Zone," Schueler,
T. R., Kumble, P. and Heraty, M., Metropolitan Washington Council
of Governments, 1992.
|
3
|
"Design of Roadside Channels with Flexible Linings," Federal
Highway Administration, Chen, Y. H. and Cotton, G. K., Hydraulic Engineering
Circular 15, FHWA-IP-87-7, McLean Virginia, 1988.
|
4
|
"Draft Stormwater Best Management Practices Manual," Pennsylvania
Department of Environmental Protection, January 2005.
|
5
|
"Evaluation and Management of Highway Runoff Water Quality,"
Federal Highway Administration, FHWA-PD-96-032, Washington, D.C.,
1996.
|
6
|
"Evaporation Maps of the United States," U.S. Weather Bureau
(now NOAA/National Weather Service) Technical Paper 37, Published
by Department of Commerce, Washington D.C., 1959.
|
7
|
"Georgia Stormwater Manual," AMEC Earth and Environmental, Center
for Watershed Protection, Debo and Associates, Jordan Jones and Goulding,
Atlanta Regional Commission, Atlanta, Georgia, 2001.
|
8
|
"Hydraulic Design of Highway Culverts," Federal Highway Administration,
FHWA HDS 5, Washington, D.C., 1985 (revised May 2005).
|
9
|
"Low Impact Development Design Strategies An Integrated Design
Approach," Prince Georges County, Maryland Department of Environmental
Resources, June 1999.
|
10
|
"Maryland Stormwater Design Manual," Maryland Department of
the Environment, Baltimore, Maryland, 2000.
|
11
|
"Pennsylvania Handbook of Best Management Practices for Developing
Areas," Pennsylvania Department of Environmental Protection, 1998.
|
12
|
"Recommended Procedures for Act 167 Drainage Plan Design," LVPC,
Revised 1997.
|
13
|
"Roof Gardens History, Design, and Construction," Osmundson,
Theodore. New York: W.W. Norton and Company, 1999.
|
14
|
"The Texas Manual on Rainwater Harvesting," Texas Water Development
Board, Austin, Texas, Third Edition, 2005.
|
15
|
"VDOT Manual of Practice for Stormwater Management," Virginia
Transportation Research Council, Charlottesville, Virginia, 2004.
|
16
|
"Virginia Stormwater Management Handbook," Virginia Department
of Conservation and Recreation, Richmond, Virginia, 1999.
|
17
|
"Water Resources Engineering," Mays, L. W., John Wiley and Sons,
Inc., 2005.
|
18
|
"Urban Hydrology for Small Watersheds," Technical Report 55,
US Department of Agriculture, Natural Resources Conservation Service,
1986.
|
19
|
US EPA, Region 1 New England web site (as of August 2005) http://www.epa.gov/NE/assistance/ceitts/stormwater/techs/html.
|
Hot Spot Land Use
|
Pretreatment Method(s)
|
---|---|
Vehicle maintenance and repair facilities, including auto parts
stores
|
Water quality inlets
|
Use of drip pans and/or dry sweep material under vehicles/equipment
| |
Use of absorbent devices to reduce liquid releases
| |
Spill prevention and response program
| |
Vehicle fueling stations
|
Water quality inlets
|
Spill prevention and response program
| |
Storage areas for public works
|
Water quality inlets
|
Use of drip pans and/or dry sweep material under vehicles/equipment
| |
Use of absorbent devices to reduce liquid releases
| |
Spill prevention and response program
| |
Diversion of stormwater away from potential contamination areas
| |
Outdoor storage of liquids
|
Spill prevention and response program
|
Commercial nursery operations
|
Vegetated swales/filter strips
|
Constructed wetlands
| |
Stormwater collection and reuse
| |
Salvage yards and recycling facilities*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Fleet storage yards and vehicle cleaning facilities*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Facilities that store or generate regulated substances*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Marinas*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Certain industrial uses (listed under NPDES)*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
NOTES:
| |
*
|
Regulated under the NPDES Stormwater Program
|
Pretreatment Method
|
Design ReferenceA
|
---|---|
Constructed wetlands
|
4, 5, 8, 10, 16
|
Diversion of stormwater away from potential contamination areas
|
4, 11
|
Stormwater collection and reuse (especially for irrigation)
|
4, 14
|
Stormwater filters (sand, peat, compost, etc.)
|
4, 5, 10, 16
|
Vegetated swales
|
2, 3, 5, 11, 16, 17
|
Water quality inlets
|
4, 7, 15, 16, 19
|
NOTES:
| |
A
|
These numbers refer to the Design Reference Title Chart in Subsection O, above.
|
Area Tributary to infiltration BMP
| |
*100%
| |
Base area of infiltration BMP
| |
The area tributary to the infiltration BMP shall be weighted
as follows:
| |
All disturbed areas to be made impervious:
|
weight at 100%
|
All disturbed areas to be made pervious:
|
weight at 50%
|
All undisturbed pervious areas:
|
weight at 0%
|
All existing impervious areas:
|
weight at 100%
|
Permeability Range*
inches/hour
|
Thickness Factor
|
---|---|
6.0 to 12.0
|
0.8
|
2.0 to 6.0
|
1.0
|
1.0 to 2.0
|
1.4
|
0.75 to 1.0
|
1.2
|
0.5 to 0.75
|
1.0
|
NOTES:
| |
*
|
If the permeability rate (as measured by the adapted 25 PA Code
§ 73.15 percolation test in Appendix G) falls on a break
between two thickness factors, the smaller thickness factor shall
be used.
|
Sites with soil permeability greater than 12.0 in/hr or less
than 0.5 in/hr, as measured by the adapted 25 PA Code § 73.15
percolation test in Appendix G, are not recommended for infiltration.
|
Return Period
|
24 Hour Rainfall Depth
|
---|---|
1 year
|
2.40 inches
|
2 year
|
3.00 inches
|
5 year
|
3.60 inches
|
10 year
|
4.56 inches
|
25 year
|
5.52 inches
|
50 year
|
6.48 inches
|
100 year
|
7.44 inches
|
NOTES:
|
A graphical and tabular presentation of the Type II twenty-four-hour
distribution is included in Appendix C.
|
v = 1.486/n*r2/3*s1/2
|
"v" is the mean velocity of flow in feet per second.
|
"n" is the coefficient of roughness.
|
n equals 0.013 for concrete pipe.
|
n equals 0.021 for asphalt coated corrugated metal
pipe, 25% paved.
|
"r" is the hydraulic radius in feet.
|
"s" is the slope of the energy grade line.
|
"Q" equals VA where "A" equals cross-sectional area in square
feet.
|
Q = V * A
|