Dayton Canyon is the site of a proposed Centex Homes housing development called Sterling Properties. It is located west of the intersection of Roscoe Boulevard and Valley Circle Boulevard in West Hills and is less than a mile from the eastern property boundary of the Santa Susana Field Laboratory (SSFL).
Dayton Canyon was extensively sampled in 2005 and 2006 for perchlorate and radionuclides.
Sampling was performed in October 2005 for cesium-137, and gross alpha and gross beta, and again in January 2006 for strontium-90, plutonium-238 and plutonium-239. The results were reported by Allwest Remediation. The survey results were reviewed by Cabrera Services.
- Allwest Remediation, "Radiological Investigation Report - Dayton Canyon Site, West Hills, California", June 7, 2006, (Revised September 2006). Allwest concluded, "The results of the radiological investigation and evaluation do not indicate any radionuclide concentrations above the referenced background values."
- Cabrera Services, "Technical Memorandum - Review and Evaluation of Radiological Survey and Laboratory Results for the Sterling Project, West Hills, California", May 23, 2006." Cabrera concluded, "Cabrera recommends that no additional radiological investigations be performed. It is unlikely that concentrations of the radionuclides of concern at the West Hills Project site result from activities at the SSFL. Based on the data available, it appears unlikely that any radioactivity has migrated from the SSFL onto the Sterling Property. Laboratory results, including those farthest west in the creek, did not indicate any radionuclide concentrations above the referenced background values."
The Department of Health Services was asked to review the 2005/2006 soil radionuclide data. In their report they concluded, “These concentrations and risks are below those that would pose an undue health and safety concern for residential land usage.”
Nevertheless, the DTSC recommended further sampling and Allwest Remediation prepared a supplemental sampling and analysis plan in September, 2006.
Allwest Remediation published the results of the new round of sampling in June 2007.
- "Supplemental Radiological Investigation Sampling and Analysis Results - Sterling Homes Development, West Hills, California." June 4, 2007
Auxier & Associates were then commissioned to interpret the radiological data and calculate a risk assessment. They issued their report in February 2008. Auxier concluded that, "Using the available information presented in this report, no areas of radiological concern were identified in the canyon. Visual examination of concentration data plotted on aerial photos of the site indicates that the higher results are scattered across the site and not clustered together. A statistical comparison of surface and subsurface concentrations failed to prove that they were different populations. These two observations indicate soil concentrations of the radionuclides investigated are relatively uniform across the entire study area. The soil concentration data was used to calculate the exposure potential to a hypothetical receptor living on the property. Risks to this postulated receptor from Cs-137, Pu-238, Pu-239/240, and Sr-90 are relatively small, with the calculated upper-bound risk above background about 4 x 10-7. Risks of this magnitude are less than the 10-6 to 10-4 risk range generally considered by EPA to be acceptable at Superfund sites."