Tools and Guidance

Stormwater Spreadsheet Tool

The Center for Watershed Protection has developed a spreadsheet tool for the WVDEP to aid in appropriately sizing runoff reduction stormwater management practices. This spreadsheet tool will allow users to ascertain and verify compliance with the provisions of the MS4 permit to reduce runoff from the first one inch of rainfall. WVDEP conducted two workshops in 2010 to provide training to attendees on how to use the spreadsheet.

Based on the comments WVDEP recieved at both workshops the spreadsheet underwent several revisions. The spreadsheets (below) available for download contain the most recent revisions.

Some of the revisions include:

  • Managed turf has been included as a possible land cover in the drainage area for residential rain gardens. (For a detailed explanation of managed turf, go to the document below).

  • Each Drainage Area tab includes a calculation of runoff produced by the one inch rain event, and the runoff volume remaining from the one inch storm after runoff reduction practices are selected. This can be used as a tool to check compliance for each drainage area, but if redevelopment or other credits apply, a designer will not need to achieve the full runoff reduction amount on each tab.

  • All of the tabs have been formatted for printing. The Drainage Area tabs work best on 11" x 17" landscape.

WV Mitigation and Pay In Lieu of Guidance

In January 2013, West Virginia DEP released the Guidance for Developing an off-site stormwater compliance program. This guidance document is specifically for MS4s who wish to develop their own off-site mitigation or payment in lieu program to meet the requirements contained within the MS4 general permit.

The Runoff Reduction Method

The Runoff Reduction Method was developed in order to promote better stormwater design and as a tool for compliance to meet new stormwater runoff volume reduction requirements in the United States.

Runoff reduction has benefits beyond pollutant load reductions. BMPs that reduce runoff volumes can do a better job of replicating predevelopment hydrologic conditions, protecting downstream channels, recharging groundwater, and, in some cases, reducing overbank (or “nuisance”) flooding conditions.

When utilizing runoff reduction stormwater practices the designer experiments with combinations of several runoff reduction practices (BMPs) on the site. In each case, the designer estimates the area to be treated by each runoff reduction practice to incrementally reduce the required treatment volume for the site. The designer is encouraged to use runoff reduction practices in series within individual drainage areas (such as rooftop disconnection to a grass swale to a bioretention area) in order to achieve a higher level of runoff reduction.

West Virginia's spreadsheet tool works very well in determining the amount of runoff volume to capture in order to meet the provisions of the MS4 permit.

Extended Filtration Memorandum of Understanding

Recently WVDEP clarified MS4 permit language regarding extended filtration stormwater practices.