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Guidance Document Change: The Virginia Erosion and Stormwater Management Regulation (VESM Regulation, 9VAC25-875-590) requires the use of the Virginia Runoff Reduction Method (VRRM) or another equivalent methodology that is approved by the department to demonstrate compliance with the water quality technical criteria Article 3, Part V (9VAC25-875-570 et seq.). This guidance revises the Virginia Runoff Reduction Method: Instructions & Documentation (March 28, 2011) and Virginia Runoff Reduction Method Compliance Spreadsheet User’s Guide & Documentation (Version 3.0, April 2016), updates the VRRM Excel spreadsheets, and confirms that the Virginia Department of Environmental Quality (DEQ) approves the use of VRRM Version 4.1 and a target total phosphorus load of 0.26 lbs/acre/yr, when used in conjunction with the Virginia Stormwater Management Handbook, Version 1.0 (effective July 1, 2024) as an equivalent methodology under 9VAC25875-590 A of the VESM Regulation . The Virginia Runoff Reduction Method Compliance Spreadsheet User’s Guide & Documentation, Version 4.1, July 2024 (VRRM 4.1 User Guide) provides stepwise user instructions as well as a thorough explanation of the spreadsheet logic, equations, and reference information. The Excel spreadsheets are available from the DEQ webpage: https://www.deq.virginia.gov/our-programs/water/stormwater/stormwater-construction/guidance-vrrm, and are also accessible from the webpage for the Virginia Stormwater Management Handbook, Version 1.0 (Handbook): https://online.encodeplus.com/regs/deq-va/index.aspx. 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. DEQ held an informal public comment period on proposed updates to the VRRM and TP load for new development from June 22 to August 21, 2023. DEQ received 71 unique comments from 20 people and/or organizations. The comments and responses are available for download at: https://www.deq.virginia.gov/our-programs/water/stormwater/stormwater-construction/guidance-vrrm. As a result of the public comments, DEQ, working with its consultant on the model, Virginia Tech, made several revisions which are incorporated in VRRM 4.1. A presentation from Virginia Tech, which provides a summary of the updates from VRRM 3.0 to VRRM 4.1, is also available on the DEQ website. Information and documents that were posted on the DEQ website for the informal public comment period are available upon request. For this 30-day public comment forum, comments on the Handbook may be submitted through the Town Hall website or by email to the contact address provided with this notice. As guidance, VRRM 4.1 does not replace the VRMM instructions and document (March 28, 2011) that was incorporated by reference into the VESM Regulation. Further, DEQ will continue to accept results from VRRM 1.0 and VRRM 3.0, using a TP load of 0.41 lbs/acre/yr, when calculated using specifications in the 1999 Virginia Stormwater Management Handbook, until July 1, 2025 or such later date that the State Water Control Board adopts amendments to the VESM Regulation that change the TP load. Members of the regulated community are encouraged to use VRRM 4.1 in conjunction with the accompanying TP load for new development of 0.26 lbs/acre/yr as an alternative to VRRM 1.0 and 3.0.

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