Draft Preliminary Site Evaluation
Santa Susana Field Laboratory (SSFL)
Ventura County, California
In this preliminary evaluation of available data and information, ATSDR has not identified an apparent public health hazard to the surrounding communities because people have not been, and are currently not being exposed to chemicals and radionuclides from the site at levels that are likely to result in adverse health effects.
Available environmental data indicate that chemicals and radionuclides have been released to air during rocket engine testing and waste handling and disposal activities at the SSFL. Quantitative air monitoring data and verified site-specific meteorological data are not available. Releases in the past were probably higher than at present. Given that the nearest communities are located more than one half mile from any onsite release sources, it appears unlikely that onsite releases would migrate to offsite areas at levels that would pose a health hazard to the surrounding community.
Ground water under the site is contaminated by trichloroethylene (TCE) that has migrated offsite of the northwestern and northeastern facility boundaries. Contamination was first recognized in the 1980s and concentrations of TCE, and its degradation products, have declined over time. The majority of the local water supply is provided by purveyors who obtain water from surface water sources distant from the SSFL. These purveyors have supplemental water supply wells that are located more than two miles from the SSFL. Some privately-owned water wells are located in the Santa Susana Knolls and unincorporated areas of Simi Valley. Available data and information provide no indication that municipal and privately-owned water wells have been adversely impacted by chemicals or radionuclides from the SSFL. As a result of the ongoing ground water remediation at the SSFL site, it is unlikely that there will be future exposure to contaminated ground water. Because the potential for deep fracture flow from the site has not been adequately characterized, there is a potential for substances in ground water to discharge at springs or down-gradient water wells along the margins of Simi and San Fernando Valleys.
Available data and information indicate that chemical and radionuclide releases to soil and sediment have occurred at the SSFL. One important source of releases is the Former Sodium Disposal Facility located in Area IV. There has been limited soil and sediment migration of chemicals and radionuclides from the Disposal Area to offsite areas north of the facility boundary. Concentrations are highest close to the facility boundary and decrease rapidly with increasing distance from the property boundary. Because the area surrounding the SSFL is hilly and rugged, it is not easily accessible to persons in the nearby community. Any human exposure to these maximum offsite concentrations is not likely to result in adverse human health effects. Based on available data and information, there is no indication that offsite residential areas, including the Brandeis-Bardin Institute, Santa Monica Mountains Conservancy, and Bell Canyon, have been adversely impacted by chemicals and radionculides from the SSFL. Therefore, there is no apparent likelihood for human exposure to chemicals and radionuclides in soil and sediment in these offsite areas. In response to comments made by the Las Vegas EPA office on the sampling techniques used to characterize radionuclides in Area IV of the facility, further characterization of Area IV radionuclides is being proposed by EPA and the Department of Energy.
ATSDR acknowledges that this report is a preliminary assessment of the potential for human exposure and public health hazard posed by the SSFL. On the basis of our preliminary conclusions, we make the following recommendations:
- A more in-depth evaluation of exposure pathways that addresses past, current, and future exposure to chemicals and radionuclides from the SSFL should be conducted to improve the assessment of potential offsite exposures and public health implications associated with this site. Such an assessment must be facilitated through community outreach and participation and must include health education activities. We further recommend that this assessment address the following related issues:
- More in-depth evaluation of airborne chemical releases from SSFL operations, including air dispersion modeling of past accidents and disposal activities, and compilation and use of a consistent, site-specific meteorological data set to improve the assessment of past exposures to these substances.
- Development of a regional hydrogeological flow model and additional monitoring at down-gradient springs or seeps in Simi Valley and Santa Susana Knolls to evaluate the potential for deep fracture flow and potential future exposure. Also, even though it may not be related to SSFL, additional source characterization of the perchlorate detection in Simi Valley should be conducted.
- Additional radiological characterization of Area IV with more sensitive instrumentation and appropriate grid spacing to assure a lower detection limit.
- A re-analysis of the cancer registry data including additional years of newly available cancer data and updated demographic information should be conducted to see if the apparent increase in the incidence rates of bladder and lung cancers persist. A more in-depth evaluation of cancer data should be conducted that addresses environmental exposures from the SSFL, possible confounding exposures from other nearby contaminant release sources, and residential histories.
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