Retrofitting Residential Streets with Stormwater Control Measures over Sandy Soils for Water Quality Improvement at the Catchment Scale

Impervious cover (IC) has been shown to increase runoff volumes, peak discharges, and pollutant loads to streams, which can lead to degraded water quality and biological integrity. Stormwater control measures (SCMs) have been developed to mitigate the hydrologic and water quality impacts of urban areas and IC. This paired watershed study evaluated the impacts of multiple SCM retrofits on water quality at a catchment scale in a 0.53 ha urban residential drainage area. In February 2012, an in-street bioretention cell (BRC) retrofit, four permeable pavement parking stalls, and a tree filter device were installed to treat residential street runoff inWilmington, North Carolina. In the retrofitted catchment, 94% of the directly connected impervious area (DCIA) and 91% of the total drainage area were retrofitted for water quality treatment. Underlying soils in the study area were sand. After the SCM retrofits were constructed, concentrations of total Kjeldahl nitrogen (TKN), total phosphorous (TP), total suspended solids (TSS), copper (Cu), lead (Pb), and zinc (Zn) significantly decreased by 62%, 38%, 82%, 62%, 89%, and 76%, respectively. Concentrations of dissolved pollutants [nitrate-nitrite-nitrogen (NO2,3-N), total ammoniacal nitrogen (TAN), and orthophosphate (O-PO43-)] did not change. Mass exports of TKN, TAN, O-PO43-, TP, TSS, Cu, Pb, and Zn significantly decreased by 79%, 60%, 54%, 72%, 91%, 54%, 88%, and 77%, respectively. Improvements in water quality were due to decreases in particulate and particulate-bound pollutant concentrations and loads. This study has shown that a limited number of SCMs installed within a street right-of-way can mitigate a substantial portion of the water quality impacts caused by existing residential development. (C) 2014 American Society of Civil Engineers.