Source Control: The Solution to Stormwater Pollution

Another name for source control is pollution prevention. In almost every case, it is easier and cheaper to prevent pollution from occurring in the first place than it is to collect and treat it after the fact. Municipal stormwater managers throughout the United States are coming to grips with the fact that municipal stormwater management requires significant effort and resources and raises numerous legal and financial issues and concerns. More emphasis on source control has the potential to improve system reliability, reduce costs, improve equity, reduce liabilities, as well as improve water quality. When Phase II of the municipal separate storm sewer system permit program under the National Pollutant Discharge Elimination System began, most stormwater managers relied primarily on end of pipe treatment to meet their goals. Under the Clean Water Act, the United States learned that end of pipe treatments are effective in reducing pollutant loads discharging from municipal and industrial wastewater plants. For example, from 1968 through 1996, municipal wastewater treatment plants reduced BOD entering receiving waters by 45 percent in spite of a significant increase in population served (USEPA 2000). Thus it was no surprise that most municipalities formulated and began their stormwater programs based upon the assumption that, if end of pipe treatment worked so well with municipal sewage, then end of pipe treatment should work with urban stormwater. Experience, unfortunately, has demonstrated that this is not the case. The flow and composition of municipal waste generally is well known and predictable. Thus, it is relatively easy to design and operate cost effective treatment systems. However, the flow and composition of urban stormwater is highly variable, both spatially and temporally. Municipal wastewater treatment plants are sophisticated, energy intensive operations equipped with elaborate control systems. On the other hand, end of pipe urban stormwater treatments are relatively simple structures with primitive, if any, operational control. At a modern municipal wastewater treatment plant, BOD removal usually reaches 95 percent or more and nutrient removal rates may exceed 85 percent. Removal rates for BOD at a typical structural stormwater BMP may vary by storm from as little as 16 to as much as 93 percent (Strecker, Quigly, and Urbonas 2000). Removal rates vary nearly as much from BMP to BMP regardless of type, size, location, and climate.