Simulated Effectiveness of 12 Wet Weather Best Management Practices in an Urban Watershed

12 types of stormwater and combined sewer control measures were simulated with a representative oneyear rainfall record for an urban watershed in southeastern Pennsylvania. Simulated best management practices (BMPs) included porous pavement, dry wells, retention and infiltration basins, rain barrels, bioretention, green rooftops, constructed wetlands, structural storage facilities, and real time control of sewer flows. For each BMP type, a range of coverage was simulated, extending from existing conditions to the maximum theoretical impervious cover that could drain to the BMP. The results were extended to estimate loads of water quality constituents by applying typical concentrations of pollutants found in untreated stormwater, treated stormwater, and combined sewage. The hydraulic modeling results and pollutant load estimates were combined with construction cost estimates to produce a measure of BMP cost-effectiveness suitable for long-term planning in the watershed studied.The results of the simulations support a number of general conclusions about the implementation of BMPs in the watershed. The cost of runoff volume reduction is higher in separate-sewered than in combined-sewered areas because temporary storage and release results in additional capture at CSO regulator structures. If pollutant removal is significant for a given BMP, the cost difference between separate-sewered and combined-sewered areas is smaller. For the combined-sewered areas, real time control (RTC) is among the most competitive options in terms of both volume (5th) and load (4th) reduction. Wet retention, wetlands, infiltration basins, and rain barrels are among the most costeffective options in separate-sewered areas. In highly urbanized areas, storage under parking facilities may be the only practical option to achieve large storage volumes. The choice of BMPs ultimately is a balance between effectiveness, feasibility, cost, and intangible factors.