Automated Flow-Weighted Composite Sampling of Stormwater Runoff in Ventura County, CA

A unique flow-weighted composite stormwater sample collection procedure was implemented at The Boeing Company's (Boeing) Santa Susana site, an 11.5-km2 (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 km2 (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.