The Virginia Runoff Reduction Method, Version 4.1, is available for use, when used in conjunction with the Virginia Stormwater Management Handbook, as an equivalent methodology under 9VAC25875-590 A of the VESM Regulation.

Key new features of VRRM Version 4.1, which are explained in the VRRM 4.1 User Guide, include:

• Expanding land covers from three to four by adding “mixed open,” a category between “forest/open” and “managed turf;”
• Aligning the four VRRM land covers with applicable Chesapeake Assessment Scenario Tool (CAST) land uses;
• Addressing changes to the Chesapeake Bay Watershed Model (CBWM), reported through CAST, regarding urban phosphorus fertilizer applications;
• Accommodating two new post-development Best Management Practices (BMPs), Regenerative Stormwater Conveyance (RSC) and Tree Planting, which are new in the Handbook; and
• Utilizing a more accurate total phosphorus (TP) load for new development, 0.26 lbs/acre/yr.