Non-Proprietary BMPs

Since the early 1980’s, land developers, particularly in fast-growing regions of the United States, have been required by states and municipalities to manage the stormwater runoff from their development sites.  Stormwater management has aimed at several specific goals:  protecting the biological and physical integrity of stream channels downstream from development sites; protecting from frequent, localized flooding resulting from increased runoff volumes from the new impervious surfaces; and removing pollutants from the site runoff.  Other goals that have been added over the years are mimicking the rate of groundwater recharge that existed prior to development, and protecting streams and properties from extreme flood damage.

An array of BMPs have been developed and used over that period of time.  Probably the most-used practices have been filtering practices such as grass filter strips and channels, infiltration practices such as dry wells and infiltration trenches, permeable pavement, and impoundment practices, such as wet and dry ponds and constructed wetlands.  These earlier practices were largely aimed at controlling the volume and discharge of runoff from the site, as well as providing treatment for the pollutants in the runoff.

In the last decade, a new type of BMP evolved, aimed at reducing the volume of stormwater runoff leaving the development site and, therefore, mimicking the hydrologic patterns that existed at a site before it was developed.  This is a way to minimize our “human footprint” or interference in natural processes.  These new kinds of practices have been labeled “low impact development” (LID) BMPs and include Green Roofs, Bioretention, Rain Gardens, Rooftop Disconnection, Dry Swales and Wet Swales.  LID practices can be linked with Environmental Site Design (ESD) techniques, such as conserving open space and natural areas, and reducing the amount of imperviousness and infrastructure on lots, in residential streets, and in parking areas, to significantly reduce imperviousness and overall development costs while providing greater protection of natural systems and processes.

The movement toward use of LID practices has led to recognition that optimal protection of natural systems is achieved in land development projects by reducing runoff volume and mimicking the pre-development site hydrology, rather than just focusing on treating pollution in the runoff and controlling its release from the site.  This recognition has been validated by a panel of experts at the National Academy of Sciences aimed at improving how we manage stormwater (http://www.nap.edu/catalog.php?record_id=12465#toc ).

DEQ has developed an updated set of non-proprietary BMP standards (stds) and specifications (specs) for use in complying with the Virginia Stormwater Management Law and Regulations.  These updated stds & specs were developed with significant assistance from Tom Schueler of the Chesapeake Stormwater Network (CSN), staff of the Center for Watershed Protection (CWP), the Northern Virginia Regional Commission (NVRC), and the Engineers and Surveyors Institute (ESI) of Northern Virginia.  These standards are based on both the more traditional BMPs and the newer LID practices.  The advancements in these standards and specifications are a result of extensive reviews of BMP research studies incorporated into the CWP’s National Pollution Removal Performance Database (NPRPD).  In addition, we have liberally borrowed from the cutting-edge ideas expressed in the newer BMP stds & specs from other states in the region.

To assist in development of these BMP stds & specs, a literature search was performed to compile data to support updated runoff volume reduction and pollution removal capabilities for different BMPs. Based on the research findings, runoff volume reduction rates were assigned and removal rates for Total Phosphorus were updated for various BMPs, as shown in Table 4.1. The explanation for these decisions can be found in the Technical Memorandum: The Runoff Reduction Method [pdf] developed by the Center for Watershed Protection, in support of DEQ’s regulation and Handbook revision processes.

Table 4.1.  BMP Pollutant Removal Efficiencies (March 1, 2011)

Practice Number

Practice

Removal of TP by Runoff  Reduction
(RR, as %)
(based upon 1 inch of rainfall)1

Removal of TP by Treatment – Pollutant (EMC) Reduction
(PR, as %)1

Total Mass Load Removal of Total Phosphorus
(TR, as %)1

1

Rooftop Disconnection

25 or 50

0

25 or 50

2

Sheetflow to Conservation Area

50 to 75

 0

50 to 75

Sheetflow to Vegetated Filter

50

0

50

3

Grass Channel

10 to 30

15

24 to 41

4

Soil Amendments

Used to decrease runoff coefficient for turf cover at the site. See the design specs for Roof Disconnection, Sheet Flow to Vegetated Filter or Conserved Open Space, and Grass Channels

5

Vegetated Roof 1

45

0

45

Vegetated Roof 2

60

0

60

6

Rainwater Harvesting

Up to 90

0

Up to 90

7

Permeable Pavement 1

45

25

59

Permeable Pavement 2

75

25

81

8

Infiltration 1

50

25

63

Infiltration 2

90

25

93

9

Bioretention 1

40

25

55

Bioretention 2

80

50

90

Urban Bioretention

40

25

55

10

Dry Swale 1

40

20

52

Dry Swale 2

60

40

76

11

Wet Swale 1

0

20

20

Wet Swale 2

0

40

40

12

Filtering Practice 1

0

60

60

Filtering Practice 2

0

65

65

13

Constructed Wetland  1

0

50

50

Constructed Wetland 2

0

75

75

14

Wet Pond 1

0

50 (45) 2

50 (45) 2

Wet Pond 2

0

75 (65) 2

75 (65) 2

15

Extended Detention Pond 1

0

15

15

Extended Detention Pond 2

15

15

31

Notes

1 See design specifications for more information.
2 Lower nutrient removal value in parentheses applies to wet ponds in coastal plain terrain.

Complete standards and specifications are provided for the BMPs listed below, including information needed for design, construction, and long-term maintenance. 

  • Introduction to Virginia’s Non-Proprietary Stormwater Management BMPs (March 1, 2011) [pdf]
    • Appendix A:  Earthen Embankment [pdf]
    • Appendix B:  Principal Spillway [pdf]
    • Appendix C:  Vegetated Emergency Spillway [pdf]
    • Appendix D:  Sediment Forebay [pdf]
    • Appendix E:  Landscaping [pdf]
  • Rooftop (and Impervious Area) Disconnection [pdf]
  • Sheetflow to Filter Areas and Conserved Open Space [pdf]
  • Grass Channels [pdf]
  • Soil Compost Amendments [pdf]
  • Vegetated Roofs [pdf]
  • Rainwater Harvesting [pdf]
    • Cistern Design MS-Excel Spreadsheet, v. 1.6 ) (March 1, 2011) (Excel Spreadsheet; Note: Long download time, in excess of 10 minutes, is possible due to file size of 215MB.)
  •  Permeable Pavement [pdf]
  • Construction products such as porous asphalt, pervious concrete, concrete paving units used for permeable interlocking concrete pavements, as well as concrete and plastic grid paving units are considered approved for use on new development and redevelopment sites in Virginia, pursuant to meeting the requirements in Table 7.6 in the Permeable Pavement BMP design specification.

  • Infiltration [pdf]
  • Bioretention (including Urban Bioretention) [pdf]
    • Example Photo Tutorial (Bioretention Powerpoint Slides) (March 1, 2011) [pdf]
  • Dry Swale [pdf]
  • Wet Swale [pdf]
  • Filters [pdf]
  • Constructed Wetlands [pdf]
  • Wet Ponds [pdf]
  • Extended Detention Ponds [pdf]

USEPA web site for Post-Construction BMPs:
http://water.epa.gov/polwaste/npdes/swbmp/PostConstruction-Stormwater-Management-in-New-Development-and-Redevelopment.cfm.

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