Urban Stormwater BMP Performance and Cost-Effectiveness

Eighteen stormwater best management practice (BMP) structures were constructed in 2006 for the Arlington Pascal Stormwater Improvement Project by the Capitol Region Watershed District (CRWD) and partners in effort to alleviate localized flooding and improve water quality in a local impaired water body. The BMPs constructed include eight rain gardens, eight infiltration trenches, an underground stormwater storage and infiltration facility, and a stormwater pond. Since construction, the BMPs have been monitored and maintained by CRWD to ensure long term performance of each structure.The objective of this study was to conduct a performance and cost-benefit analysis for each BMP structure, from 2007 through 2010, to determine: annual volume and pollutant load reductions; annual volume and pollutant removal efficiencies; and annual volume reduction and pollutant removal costs. Water quality and quantity data collected through monitoring of the eighteen BMPs was used to model annual BMP performance for volume and pollutant load reductions. Annual operation and maintenance (O & M) costs have been tracked overtime, as well as, actual construction costs. The cost-benefit analysis was performed based on the BMP performance results, annual maintenance costs, and actual construction costs.Modeling showed that the overall performance of each BMP was exceptional with nearly all annual volume and pollutant load reductions meeting or exceeding annual projected load reductions. High volume reduction and pollutant removal efficiencies were observed for the underground system (100%), all infiltration trenches (75%-100%), and all rain gardens (83%-100%), for all four years. The cost-benefit analysis showed that volume reduction and pollutant removal costs are directly affected by annual loading and O & M costs and that each BMP structure type varied in its overall cost-effectiveness. However, costs have generally been decreasing over time. Based on this study, it can be concluded that the Arlington Pascal Project has been a cost-effective strategy for achieving target volume and pollutant load reduction goals.