Calculating Bmp Effectiveness Using Unit Processes and a Mass Balance Approach

BACKGROUND The science of treating stormwater pollutants has evolved from simple swales and detention ponds to a whole host of structural and non-structural Best Management Practices (BMPs) promulgated by federal, state, and local authorities. In the 1980’s and 1990’s, required treatment techniques were based upon presumptive criteria that assumed an 80% pollutant reduction of pollutants would be reached using specific design guidelines. While it was acknowledged that this 80% reduction goal was not always attainable for all pollutants and all BMPs, it was the best available science at the time.