Storm-Water Bioretention for Runoff Quality and Quantity Mitigation

In response to water quality and quantity issues within the Stroubles Creek watershed in Blacksburg, Virginia, a retrofit bioretention cell (BRC) was installed to collect and treat runoff from an existing parking lot. The BRC was completed in July 2007, and 28 precipitation events were monitored between October 2007 and June 2008. For each storm, inflow and outflow flow-weighted composite samples were collected and analyzed for suspended sediment, total nitrogen, and total phosphorus. The inflow and outflow concentrations and loads, as well as total inflow and outflow volumes and peak flow rates, were analyzed to evaluate BRC efficiency. Overall, the BRC successfully reduced flow volumes and peak flow rates leaving the parking lot by 97 and 99%, respectively. Cumulative mass reductions for sediment, total nitrogen, and total phosphorus all exceeded 99% by mass. The findings of this study have significant implications for areas with karst geology: (1) current design recommendations of lining the bottom of BRCs with clay may not be sufficient to prevent large amounts of water from infiltrating into surrounding soils; and (2) in areas with significant elevation changes, designing BRCs deeper than the typical 0.6-1.2 m increases the feasibility of retrofits and provides substantial water quality and quantity benefits. DOI:10.1061/(ASCE)EE.1943-7870.0000388. (C) 2011 American Society of Civil Engineers.