Status of the ASCE/USEPA National Stormwater BMP Database

The ASCE/USEPA National Stormwater Best Management Practices (BMP) Database contains 198 BMPs as of the June 2002. This represents substantial growth of the standardized BMP information contained in the database since the initial 71- BMPs were released to the stormwater management community in June 1999. The Urban Water Resources Research Council of EWRI/ASCE, under a cooperative agreement with the U.S. Environmental Protection Agency (EPA), continues to focus on compilation and entry of high quality BMP data into the national database. The significantly expanded database can now be searched on-line or downloaded through the project web site at http://www.bmpdatabase.org.

The concept of developing a national database arose in the mid-1990s out of the realization that although there was a plethora of published information on BMP performance, the studies did not follow standardized data collection, reporting and performance evaluation protocols, making a scientific and consistent evaluation of this data difficult. The need for BMP performance information is particularly critical now since the EPA has mandated that most municipalities in the United States with populations larger than 10,000 must obtain a stormwater runoff discharge permit by 2003. One of the key requirements of this permit program is implementation of non-structural and structural best management practices (BMPs) appropriate to local conditions. Communities need to know which types of BMPs are appropriate for them (e.g., which BMPs function best in cold climates or in areas of heavy rainfall) and how to monitor the performance of the BMPs they select to ensure they function properly. The National Stormwater BMP Database and data analyses that are being enabled as a result of this database will permit, in the long term, improvement of the BMP selection and design process so that local stormwater management can be much more effective than it is today.

Thus far, key project tasks have included: (1) collecting and evaluating existing BMP design and performance data, (2) designing and creating the national BMP database, (3) developing BMP performance evaluation protocols, and (4) evaluating the data collected and reporting initial findings. A companion project to develop stormwater BMP monitoring guidance was completed when it became apparent that much of the available BMP data was of limited value due to inconsistent BMP monitoring and reporting protocols used in the past, making evaluation of data and transferability of findings difficult and often impossible. The monitoring guidance manual provides practical and comprehensive guidance and is available through the project web site.

The database can be used both to track BMP performance, as well as to research performance of BMPs. Key categories of data requested in the database include (1) test site location characteristics, (2) sponsoring and testing agencies, (3) watershed characteristics, (4) BMP design parameters and cost data, (5) monitoring locations and instrumentation, (6) monitoring costs, (7) precipitation data, (8) flow data, and (9) water quality data. The types of structural BMPs currently accepted in the data entry module are various types of detention basins, retention basins, infiltration basins, wetland basins, wetland channels, biofilters/grass strips, filter media, hydrodynamic devices, percolation trenches/dry wells, and porous pavement. Types of nonstructural BMPs accepted in the data entry module include education, recycling, maintenance practices and source controls. The requested data sets were developed with peer review and input from an international group of experts in the stormwater management field. Based on data received to date, the greatest challenge is to ensure the reporting of accurate precipitation, flow and water quality data. The National Stormwater BMP Clearinghouse reviews new BMP data sets prior to posting to the master database to ensure that required data (e.g., design parameters, flows, water quality data) have been provided and to ensure that the data are technically reasonable (e.g., relationships between peak flows and flow volumes relative to the tributary watershed and precipitation events are evaluated).

Table 1 summarizes the BMPs according to BMP types currently in the database. Table 2 summarizes the types of BMPs in the database by geographic distribution. Some of the preliminary findings include:

• BMP performance should not be based on comparisons using percent removal alone. It may be appropriate to use this measure only on carefully chosen data subsets; for example, sites that have similar stormwater runoff water quality.
• The chosen performance evaluation method can affect reported pollutant removal efficiencies. For example, some BMP types may have been mischaracterized as less effective because of cleaner influent. Most BMPs and biochemical processes will exhibit lower percent removals when the concentrations are low in the influent.
• Retention ponds and wetland basins are not well represented by individual storm-by-storm comparisons because paired inflow and outflow data often are not from the same event.
• Effluent quality is useful for characterizing the effectiveness of the BMP; however, it is still important to determine if the BMP had a statistically significant effect on water quality at each test site.
• Downstream geomorphic and biological responses and aquatic habitat assessment may be better gauges of long-term BMP effectiveness than pollutant removal efficiencies alone, but there is insufficient information at this time to clearly suggest which BMPs may best mitigate the effects of urbanization on receiving waters.
• More BMP performance data are needed for sound statistical analysis of their effectiveness and what design parameters most influence their performance. For more information, please contact the National Stormwater

Table 2. Geographic Distribution of BMPs Posted to the Web Site as of June 2002.
State	Number of BMPs	State	Number of BMPs
AL	13	NJ	3
CA	41	OH	1
CO	4	ON, CAN	1
FL	24	OR	3
GA	2	TX	19
IL	5	VA	29
MD	4	WA	20
MI	5	WI	10
MN	7	Sweeden	1
NC	6	Total	198

BMP Databases Clearinghouse, (303-480-1700 or tlangan@wrightwater.com) or visit the project web site at www.bmpdatabase.org. The Clearinghouse is available to help facilitate electronic transfer of BMP data into the database and welcomes submissions of BMP.