California's First Chemical Human Health Risk Assessment on Stormwater – Results from the Santa Susana Field Laboratory
« All Publications

A quantitative evaluation of human health risks associated with potential surface water discharge contact was conducted for the Santa Susana Field Laboratory (SSFL) (Site), in response to a unique Los Angeles Regional Water Quality Control Board (LARWQCB) order associated with The Boeing Company's (Boeing's) National Pollutant Discharge Elimination System (NPDES) permit for industrial stormwater discharges.

The Human Health Risk Assessment (HHRA) evaluated exposure associated with activities that could occur according to beneficial use designations contained in the Los Angeles Water Quality Control Plan (Basin Plan) including non-swimming water contact recreational activities (hiking, rafting and other limited recreational uses that fall under the Basin Plan designation). Direct exposures to surface water – i.e., incidental ingestion and dermal contact – were identified as the most likely potentially complete exposure pathways and were evaluated quantitatively in the risk assessment. In addition, the inhalation pathway and fish consumption (at downstream locations) pathways were evaluated. Over 50 organic and inorganic chemicals were evaluated, and both cancer and non-cancer endpoints considered.

Similar to many areas of California, surface water runoff at SSFL's ephemeral drainages is typically limited to winter months. A challenge in developing the exposure assessment for the HHRA was the intermittent nature of the flow from the majority of the NPDES outfalls at the Site and the limited and uncertain frequency a recreational user may encounter these natural drainages where flow is occurring during the winter months. Flow monitoring data from the outfalls were used to estimate annual discharge frequencies, which were then used to estimate the number of days per year that exposure to surface water exiting each outfall could occur (i.e., exposure frequency). Another challenge was the estimation of surface water concentrations at downstream offsite locations where water is present in sufficient quantity year-round, edible fish are present and there is the potential for fishing and fish consumption.

The results of this risk assessment indicate that potential recreational exposures to constituents in surface water runoff exiting the SSFL are below levels of concern as established by the California Environmental Protection Agency and the United States Environmental Protection Agency. This includes those constituents that have had NPDES permit limit exceedances, including lead and dioxins. The final HHRA was approved by the LARWQCB and the California Office of Environmental Health Hazard Assessment, and the results were presented to the public by the SSFL Stormwater Expert Panel.

This presentation will describe the risk assessment and hydrologic methodologies that were used to develop this first of its kind chemical human health exposure assessment on stormwater. The approaches used in the risk assessment can be applied to other sites where surface water runoff may be present in areas that are used for recreational purposes. The audience will be invited to participate through a Q&A session to understand how this human health exposure assessment may relate to their sites or projects and better understand the research and analyses performed. This presentation addresses the conference theme of "Stormwater… Why We Do What We do: Looking Back and Looking Forward" by presenting the results of the first stormwater human health risk assessment that can be used in the future as a basis to demonstrate whether stormwater discharges pose a human health risk during contact and non-contact recreation near or within recreational receiving waters.

Publication Summary

  • Geosyntec Authors: Ruth Custance, Brandon Steets
  • All Authors: Ruth Custance, Brandon Steets, Geosyntec Consultants; Jeffrey Wokurka, Boeing; Michael Stenstrom, UCLA
  • Title: 2019 CASQA Annual Conference
  • Event or Publication: Event
  • Practice Areas: Urban Stormwater Management Planning and Design
  • Citation: Geosyntec will make substantial technical contributions at the California Stormwater Quality Association (CASQA) Annual Conference at the Monterey Conference Center in Monterey, California on October 7-9, 2019.
  • Date: October 7-9, 2019
  • Location: Monterey, California
  • Publication Type: Platform Presentation