SITE INFORMATION AND CORRESPONDENCE

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David Stavarek, R.G. June 29, 1998 Page 2 P=Ose of thp,Workplan The purpose of the Workplan is to describe the methodology proposed by Sierra-Pacific for conducting a health risk assessment(HRA) for the Former PuroGroBrea Facility site. According to the Workplan, the purpose of the HRA is"to evaluate potential risks to human health associated with chemical substances that have been detected in on-site soil and in ground water both on- and off-site" (see comment 2 for Section 5,below). A HRA has been requested by the California Regional Water Quality Control Board (CRWQCB) as partial requirement for evaluating the need for soil and/or groundwater remediation or cleanup of this site. General Comments The Workplan is a well-organized document. A number of statements need to be clarified, though. The comments below are issues and statements based on current practices in health risk assessment as used by the Office of Environmental Health Hazard Assessment(OEHHA). We would like to see these comments addressed in the final HRA prepared by Sierra-Pacific rather than in a new draft of the Workplan. In the text,the acronym"Cal-EPA" is used;the correct acronym is Cal/EPA. SECTION 4.0 CONCEPTUAL SITE MODEL(CS4 1. Current use and zoning of land. According to page 13, the authors state that". . . for the purposes of the CSM and HRA, current on-site land use is characterized as a standard `industrial/commercial' facility,which will continue as such for 30 years into the future (deterministic HRA)." The Preliminary Endangerment Assessment (PEA) Guidance Manual (page 2-17), however,requires the use of a residential use of the land, regardless of the current use and zoning of the site. OEHHA supports this guidance unless there is a deed restriction placed on the use of this land. The probabilistic approach,however,may use other exposure scenarios in addition to the residential. 2. Surface soil and contaminant levels. According to Section 4.2,"surface soils are considered to include only the top three feet of soil" (page 14). PEA Guidance requires that"The sampling strategy should ensure that locations which would likely contain the highest contaminant concentrations will be sampled"and"The maximum depth of sampling will depend on the potential for migration of the contaminants through soil." (page 2-9). For this purpose, PEA Guidance incorporates the "swimming pool construction" scenario in the residential use of land. As a result,PEA Guidance implicitly assumes a depth of up to 10 feet as "surface soil" containing the maximum observed concentration of contaminant. It is recommended that the 0-3 ft depth proposed in the Workplan be extended to 10 ft in the