The effectiveness of a NPS BMP is a measure of how well it reduces the NPS pollutant production or delivery to water features. Optimal effectiveness is obtained only through the controlled construction and installation of the practice’s structural device, or the precision undertaking of the practice procedure, in accordance with the BMP’s design specifications. Specific practice guidelines can be found, per NPS BMP, in the Virginia Agricultural BMP Cost Share Manual for BMPs that qualify for Virginia’s Cost-Share, Conservation Reserve Enhancement and BMP Tax Credit programs. Similar specifications exist for acceptance into the federal funding programs.
Even when constructed, installed or practiced as per specifications, the effectiveness of NPS BMPs will vary by location owing to each sites’ particular conditions, including weather, soil type, slope, wildlife, stream size and other unique site-specific characteristics. Likewise, the effectiveness of a particular NPS BMP will vary over time for a number of reasons, such as weather, land-use change and level of maintenance. Therefore only rough averages of effectiveness for regional areas are possible. Many of the NPS BMPs in Virginia must be assigned an effectiveness based on limited evaluations and model simulations because the amount of water quality monitoring that would otherwise be needed is cost prohibitive. DCR typically uses values that have been calculated through its involvement with the EPA Chesapeake Bay Program modeling efforts.
Cost-effectiveness can be measured by associating reductions expected per NPS BMP with the cost to implement the practice. This could be done for the total costs or for the funding agency’s portion of that cost.
DCR tracks each BMP in the CREP, Cost-Share and Tax Credit programs in an agricultural BMP database. This database contains much of the information needed to estimate reductions produced by BMPs, either singly or summed by watersheds. Using a stored design lifespan for each BMP, it is also possible to estimate reductions over time or occurring at any specific time. Every practice has an expected design lifespan — a period of time after implementation in which NPS reduction should continue.
The agricultural BMP database can also help officials determine who participates in these programs, compare the acceptance of BMP types across the state, avoid duplication of effort, show areas lacking controls, track finances and provide many other useful insights into the role of NPS BMPs and the success of the programs that promote them. You can query the database.