Written by: Jay Mosley, PE, CFM, CPESC, Project Manager
The latest Ohio EPA General Permit for Storm Water Discharges Associated with Construction Activity (CGP) became effective on April 22nd of this year. It includes, for the first time, a means for engineers and developers to reduce the size of structural post-construction practices used to capture and treat a project’s Water Quality Volume (WQv). This reduction is now permitted by incorporating Runoff Reduction Practices into the design of the site’s drainage system. Credits of up to 100% of the required WQv are obtainable depending on the practice selected and the soils in the area of the practice. The allowable Runoff Reduction Practices in the CGP and the Rainwater and Land Development Manual include:
- Infiltration Trench/Basin
- Infiltration Trench
- Permeable Pavement with Infiltration
- Underground Storage with Infiltration
- Grass Swale
- Sheetflow to Grass Filter Strip
- Sheetflow to a Conservation Area
- Impervious Surface Disconnection
- Green Roofs
- Rainwater Harvesting
These new Runoff Reduction Practices in the CGP allow designers to reconsider how proposed sites are developed and laid out. For example, expanding the grassed areas along the edges of parcels, or within internal drainage areas that sheetflow to grass filter strips or conservation areas, can now help reduce the size of the Extended Detention and Infiltration Practices typically used on most developed sites.
In addition, the use of properly designed infiltration trench/basins, permeable pavement with infiltration, underground storage with infiltration and green roofs can now achieve up to 100% of the WQv for a site!
The use of some of these new Runoff Reduction Practices can also reduce project construction costs by minimizing or eliminating the need for large structural storm water Best Management Practices!
Need help? Environmental Design Group can help you maximize the use of Green Runoff Reduction Practice Credits on your site. Learn more here!