SITE INFORMATION AND CORRESPONDENCE

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• i David Stavarek, R.G. June 29, 1998 Page 3 deterministic risk assessment. This assumption is consistent with that described in Cal/EPA (1992) cited in the Workplan. 3. The Workplan states on page 26 that"there is virtually no evidence of surface soil contamination" and"Therefore,the fugitive dust pathway . . . will not be evaluated as an exposure pathway of concern." A number of contaminants have been identified in soil, and therefore this statement is unsupported. Further, it is unclear from the Workplan how extensively surface soil has been sampled analyzed for contamination. The fugitive dust pathway may need to be assessed as an exposure pathway of potential concern. It is recommended that the contribution to overall risk for a fugitive dust exposure scenario (inhalation of PMto) be included for on-site workers. 4. Direct contact with soil. According to the authors, "there are few locations with potential surficial impacts,"and therefore, "direct exposure pathways (e.g., incidental ingestion, dermal contact) will be evaluated for these locations only, and will not be.evaluated for the site as a whole." Exposure scenarios generally assume that exposures occur randomly across receptors and the location as defined in the Conceptual Site Model. Please describe the procedure to be used for estimating the exposure dose at the point of contact. Also, in the text, the word"surficial"is used; the correct word is superficial. 5. In the HRA,please provide details on the extent of soil and groundwater contamination. Specifically, provide information on the depth at which soil samples were taken from, and whether samples were composites. For groundwater, describe whether samples were taken from a screened well, and at what depth the samples were taken from. In both cases,provide some basic QA/QC information. SECTIONS. DATA EVALUATION 1. Representative values for contaminants in soil and groundwater. According to page 9, the HRA will be prepared under the PEA Guidance requirements, which requires that"screening evaluations . . . use . . . the highest concentrations of each contaminant detected on-site to estimate the site's potential threat" (PEA Guidance,page 2-8). The Workplan proposes the use of 95%UCL of the mean,which departs from the PEA Guidance recommendation. Please clearly state the concentration estimate to be used in the HRA, i.e., the maximum for the deterministic approach, and the distributional values for the probabilistic approach. 2. On-site risk assessment. Although there may be evidence that off-site groundwater is contaminated, the risk assessment should not include nor be interpreted as to extending to off-site locations and/or receptors. This is because there is no sufficient nor appropriate evidence on contaminants or conceptual (off)site model beyond property bounds. The risk