Reductions in Stormwater Quantity and Pollutant Loads Due to Bioretention and CU-Structural Soil Practices

Increases in impervious surfaces associated with urbanization change stream hydrology by increasing peak flows, stream flashiness and flood frequency, and degrade water quality through increases in sediment, nutrient, and bacteria concentrations. In response to water quality and quantity issues within the Stroubles Creek watershed, the Town of Blacksburg and Virginia Tech designed and constructed two innovative stormwater best management practices (BMPs). The goal of this project was to evaluate the effectiveness of a bioretention cell and a CU-Structural Soil^TM infiltration trench. BMP construction was completed in July 2007. Stormwater monitoring, consisting of stormwater runoff rate and volume, and nutrient, sediment, and bacteria concentrations is ongoing. Preliminary results for the bioretention cell indicate average reductions in stormwater quantity, sediment and total phosphorus that exceeded 99% by mass; the CU-Structural Soil^TM infiltration trench produced reductions in stormwater quantity, total phosphorus and sediment that averaged 18%, 45% and 25%, respectively. Preliminary bacteria results for both BMPs are highly variable and require additional analysis. Study results will be used to develop design standards and to estimate runoff volume and pollutant load reductions for water quality management.