Evaluation of urban non-point source runoff of hazardous metals entering Santa Monica Bay, California.

Significant amounts of non-point source runoff enter the Santa Monica Bay from the Ballona Creek Watershed during wet weather flow. The primary objective of this study was to determine the concentrations of hazardous metal pollutants associated with the aqueous and suspended solid phases during wet weather flow. A calculation of the mass of the pollutants for each storm was conducted. Other objectives of this study were to evaluate during a storm event the relationships between (1) soluble and sorbed metals, (2) storm flow and pollutant loading, including a determination if a first flush was present, and (3) total mass loading of pollutants and relative pollution loading from three watershed sub-basins. This study focused on the urbanized watershed of Ballona Creek, which is approximately 330 km2 (127 miles2) in size and developed primarily with residential and light commercial industries. In the 1997-98 rain season, an El Niño year, two storm events were monitored by the collection of hourly grab samples. An initial storm monitored Ballona creek, while a second storm also monitored Ballona Creek along with two smaller sub-watersheds, Centinela Channel and Sepulveda Channel. The results indicated the suspended solids phase primarily transported the mass for five of the six hazardous metals studied: cadmium, chromium, copper, lead, and nickel. Arsenic was found primarily in the aqueous phase.