Optimization of stormwater filtration at the urban/watershed interface

Environmental pollution from cities is a major ecological problem attributed to contaminated runoff from nonpoint sources. The U.S. Environmental Protection Agency's guidance on implementation of total maximum daily loads (TMDL) does not adequately cover methods to improve waters impaired by nonpoint sources. To comply with TMDLs, cities may install filters in curb inlets, or use other Best Management Practices (BMPs). We tested 10 different filters and found their effectiveness in retaining pollutants ranged from 0 to > 90%, depending on combinations of pollutant types (metals, pathogens, and total suspended sediments (TSS)) and filter materials. Hence, the decision to deploy filters into curb inlets must consider land use patterns associated with specific categories of pollutants generated within cities. We developed a geographic information system (GIS)-enabled model for estimating and mitigating emissions of pollutants from urban regions into watersheds. The model uses land use categories and pollutant loadings to optimize strategic placement of filters to accommodate TMDLs. For example, in a city where the landuse pattern generates 4 × 10⁶ kg of TSS, 55 kg of Cd, and 2 × 10 ³ kg of Zn per year into 498 curb inlets that discharge into a sensitive watershed, the optimized placement of 137, 92, and 148 filters can achieve TMDL endpoints for each pollutant, respectively. We show further that 158 strategically placed filters effectively meet the requirements simultaneously for all three pollutants, a result at least 5 times more effective than random placement of filters.