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Virginia Administrative Code
Title 9. Environment
Agency 25. State Water Control Board
Chapter 900. Certification of Nonpoint Source Nutrient Credits
12/1/2021

9VAC25-900-110. Credit calculation procedures.

A. Pursuant to this section, the applicant shall calculate the potential nutrient credits generated by the practices implemented at the nutrient credit-generating projects. The applicable delivery factors, dependent upon the tributary in which the nutrient credit-generating project is located, shall be applied when calculating the potential credits generated.

B. For agricultural practices, except land use conversion, the potential nutrient credits shall be calculated using removal efficiencies for practices approved by the department. In the Chesapeake Bay Watershed, these practices shall be approved by the department based on the efficiencies assigned by the Chesapeake Bay Program. In the Southern Rivers watersheds, these practices shall be approved by the department based on submitted calculations and demonstrations. The standards and specifications for implementation of the practices will be established by the department and shall be in accordance with the VACS BMP Manual or the FOTG, as applicable.

C. For urban practices, the potential nutrient credits shall be calculated using the applicable removal efficiencies pursuant to 9VAC25-870-65 or using the best available scientific and technical information available at the time of nutrient credit certification as approved by the department. Limitations on potential nutrient credits from certain BMPs are:

1. In the Chesapeake Bay Watershed, nutrient load reductions from practices in place prior to July 1, 2005, may not be used to generate credits. Removal efficiencies shall be based upon those efficiencies approved by the Chesapeake Bay Program partnership where applicable. These efficiencies shall be reviewed at the time of certification renewal and adjusted as necessary based upon changes made by the Chesapeake Bay Program Partnership.

2. In the Southern Rivers watersheds, nutrient load reductions from practices in place prior to July 1, 2009, may not be used to generate credits.

D. For land use conversions, conversion of land to a more intensive land use activity will not generate nutrient credits. The number of potential nutrient credits shall be determined by calculating the nutrient credits per acre and multiplying that number by the total acreage that will undergo land use conversion. The nutrient credits per acre is equal to the amount calculated by subtracting the load per acre of nutrient nonpoint source pollution for the proposed land use after conversion from the load per acre for the preconversion land use. The values used for the loadings per acre in this calculation shall be based on the applicable loading levels provided in the WIP or the approved TMDL, where applicable. The preconversion land use shall be based on the land use as of the date specified in 9VAC25-900-100 E. The load per acre for the preconversion land use shall reflect the implementation of any applicable baseline practices necessary to comply with 9VAC25-900-100 B, C, and D. No credits shall be generated from the conversion of land within 35 feet of a water body with perennial water flow as measured from the top of the channel bank.

E. For wetland or stream restoration, an existing conditions assessment survey will be completed prior to restoration activities to use as a pre-restoration condition (baseline pursuant to of 9VAC25-900-100 F) and will be used for comparison to post-restoration conditions. The potential number of credits shall be determined by applying protocols or guidance on a case-by-case basis using the best available scientific and technical information, as approved by the department.

F. For a practice not previously approved by the department, the department will perform a case-by-case review in order to calculate the number of potential nutrient credits generated. The owner shall submit the removal efficiency calculation information for the practice and the calculation of the potential number of credits generated using that efficiency. The department may also request that the submittal include requirements for demonstration projects, the collection of sufficient data to evaluate the results, and any other information the department deems necessary to determine the validity of the credits. In the Chesapeake Bay Watershed, for a practice not approved by the Chesapeake Bay Program Partnership, the department will perform a case-by-case review in order to calculate the number of potential nutrient credits generated on a term basis.

Statutory Authority

§ 62.1-44.19:20 of the Code of Virginia.

Historical Notes

Derived from Virginia Register Volume 36, Issue 23, eff. September 1, 2020.

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