Water Quality and Hydrological Benefits of a Natural Treatment System in an Urban Watershed in Southern California.

Bioretention systems are important tools for capturing and infiltrating polluted runoff, but more data are needed on their effectiveness within Mediterranean climates. A two-year study investigated water retention and pollutant loading in the Ballona Creek Rain Garden during 28 storms. This system was constructed to infiltrate runoff from light industrial and commercial operations bordering the Creek. Study goals were to measure flows and pollutant concentrations in runoff entering and leaving the garden and integrate these to calculate mass loading. Nine pollutants were measured at all flowing inlets/outlets two to three times per storm. Infiltration rates ranged from 18% to 100% and averaged 74% across 28 storms. Average pollutant retention across all nine pollutants for all nine sampled storms was 71.6%. Results demonstrate that bioretention systems can be effectively used in urban Mediterranean climates to promote infiltration, capture pollutants, and prevent polluted stormwater from reaching impaired water bodies. [ABSTRACT FROM AUTHOR]