water to receiving waters during a storm event (WPCF 1989; Moffa 1990; EPA 1992, 1993b). The use of structural controls for combined sewer overflow management often involves significant costs when applied in dense, highly developed, older urban areas.
Most urban BMPs are designed to control parameters other than just nutrients, such as heavy metals, solids, and oxygen demanding constituents. Hence, their design will also be predicated upon removal of these other constituents, as well as for management of stormwater quantity.
A large number of nonstructural BMPs are available (ASCE and WEF 1998). In general, nonstructural BMPs emphasize source controls and “good housekeeping”. Many such options are routinely implemented as part of stormwater master plans in cities, although their effectiveness has not generally been quantified, especially for nutrient control. Examples include:
use of alternative products;
vehicle use reduction;
storm drain system signs (e.g., “dump no waste, drains to stream”);
control of illicit connections to storm sewers;
street cleaning and catchbasin cleaning;
control of leaking sanitary sewers; and
land use controls.
Overall, post-construction monitoring data is lacking so there is little concrete evidence of the effectiveness of urban BMPs. Management practices are often implemented under the assumption that they will be effective in reducing the load of targeted pollutants, without any follow up on how well they actually perform. Hence, good design information is lacking. In response to the need to assemble and evaluate available effectiveness data, the American Society of Civil Engineers is conducting such a study for EPA (Strecker et al. 1999), due to be completed sometime in 2000 (Box 9-1). When finished, this study will provide a definitive statement about the effectiveness of urban BMPs.
Location as well as type of BMPs play an important role in control of nonpoint source runoff. For example, stormwater and combined sewer