Strecker, Eric, Marcus Quigley, and Ben Urbonas, 2003. "A Reassessment of the Expanded EPA/ASCE National BMP Database, " AGU 2003 Fall Meeting, 8-12 December, San Francisco, California.
The purpose of the National Stormwater BMP Database is to improve the quality and consistency of information on the performance of BMPs. The USEPA/ASCE National BMP Database has grown significantly since the first evaluation of BMP performance data in the database was completed in 2000. The project team is currently performing a re-evaluation of the data contained in the database to assess the overall performance of BMPs as well as compare BMP design attributes to performance. To date the project has included: 1. Development of scientifically developed protocols for collection and reporting of BMP performance information 2. Establishment of database to store BMP monitoring and design data in standard format 3. Establishment of standard techniques for data collection, storage, reporting, and analysis 4. Evaluations of BMP performance and potential technical BMP design improvements The evaluations include the assessment of various BMP types as categorized in the database with regards to their ability to reduce runoff volumes as well as improve effluent quality. Certain BMP types may reduce the volume of runoff through evapotranspiration and/or infiltration, as opposed to BMPs that are more "sealed," such as wet ponds, wetlands, and vaults. Runoff reductions directly reduce pollutant loading as does improved effluent quality. On average, dry detention basins were found to reduce runoff volumes by an average of 30% (comparison of inflow to outflow), while biofilters reduced volumes by almost 40%. As expected, wet ponds, wetlands, and hydrodynamic devices, and retention ponds show little or no runoff volume reductions. BMP types vary with regards to effluent quality that is achieved. BMPs such as wet ponds and wetlands appear to achieve lower concentrations in effluent quality than other BMPs such as detention ponds (dry) and hydrodynamic devices. These differences vary with pollutant type. With more data available, analyses of BMP design versus performance show statistically valid results. For example, a relationship (ratio) between the treatment volume of retention ponds (with wet pools) versus the average size storm event volume monitored has been established, showing that those with a ratio of 1 or greater have been observed to achieve significantly better effluent quality. One of the key project findings is that pollutant percent removal reporting is not a valid indicator of performance, unless treatability information (such as settling velocity data) is provided. The recommended measures for BMP performance include: 1. How much stormwater runoff is prevented? (Hydrological Source Control) 2. How much of the runoff that occurs is treated by the BMP or not? (bypass or beyond treatment flows) 3. Of the runoff treated, what is the effluent quality? (Are water quality objectives being met?) This paper also briefly overviews the Urban Stormwater BMP Performance Monitoring ("Manual") (Strecker, et. al., 2002) that was developed by integrating experience gleaned from field monitoring activities conducted by members of ASCE's Urban Water Resource Research Council and through the development of the ASCE/EPA National Stormwater Best Management Practices Database. The Manual is intended to help achieve stormwater BMP monitoring project goals through the collection of more useful and representative rainfall, flow, and water quality information.