No abstract

Dry weather flow can be a substantial source of pollutants, particularly in urbanized areas such as southern California. To effectively evaluate and manage watershed-based pollutants, it is essential to understand the contribution of constituents from both developed and natural areas. Such information can be used by managers to set appropriate regulatory targets and to better evaluate severity of anthropogenic effects. This study quantified levels of suspended solids (TSS), metals, and nutrients from nineteen representative natural (undeveloped) streams in ten watersheds in southern California. Dry-weather concentrations and fluxes were typically one to two orders of magnitude lower than those from developed catchments. Constituent concentrations varied based on the catchment characteristics, with geologic type being the dominant factor that influenced variability among constituent levels. Concentration and flux values were independent of latitude, elevation, and catchment size suggesting that results from this study can be extrapolated to provide regional estimates of background water quality.

A unique flow-weighted composite stormwater sample collection procedure was implemented at The Boeing Company's (Boeing) Santa Susana site, an 11.5-km 2 (2850-acre) facility in Ventura County, California. Customized, high-volume automated flow samplers were deployed at ten outfalls draining watersheds ranging from 0.02 to 3.6 km 2 (5 to 900 acres) in size, some with storage detention and treatment ponds. Autosampler operation programs were designed to capture representative flow-weighted composite samples for the full range of possible hydrologic conditions, and were developed based on hydrologic modeling, anticipated storm patterns and flow volumes, watershed hydrologic characteristics, sample volume requirements, and siting considerations. The autosamplers monitored seven storm flow events during 2009-2010 and were reasonably successful in obtaining representative samples. This autosampling program is believed to be the first of its kind for NPDES permit compliance for storm water, and may serve as a model and provide key lessons for subsequent similar programs.