SITE INFORMATION AND CORRESPONDENCE

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Mr. Wayne Henry • • Page 2 of 3 Rei United Rental 15 December 2011 2911 E. Fremont St., Stockton, California The CHHSLs guidance document provides that "if the results of the Tier 1 assessment indicate that further evaluation of human health risks is warranted, site-specific exposure assumptions, target risks, etc., can be substituted for default parameter values used to develop the Tier 1 CHHSLs and alternative screening levels developed under a Tier 2 assessment. This assessment can be incorporated into the guidelines presented in the DTSC (Department of Toxic Substances Control) PEA (Preliminary Endangerment Assessment) document. Prior to modifying the Tier 1 default assumptions, concurrence from the appropriate regulatory agency should be obtained. Site data can then be compared to the revised screening levels." L&P stated that the CHHSLs and ESLs were developed on the residential exposure scenario and performed the Tier II evaluation by modifying the default parameters to those of an indoor worker. L&P determined that the resulting hazard quotients indicated an insignificant health risk for all samples and that the incremental cancer risk was in a potentially acceptable range. The EHD has some concerns that need to be addressed. 1. L&P states in the report that the residual contamination in the soil beneath the warehouse is probably contributing to the detected contaminant concentrations in the air samples collected in the warehouse - TPHg, BTEX and naphthalene. However, they also state that the warehouse was closed during the air sampling, and that a truck was parked inside the closed building for over 24 hours before and during the collection of the samples. Please explain how can one determine whether or not the detected contaminants were from either impacted soil beneath the building or the vehicle parked within the building, or that they are a combination of these two — or more — potential sources? 2. L&P interprets a comparison of the detected analyte ratios of the two indoor air samples versus the two ambient air samples to indicate that they may have different sources, and infer from that interpretation that the indoor air sample concentrations were from the soil under the building. The EHD considers the number of samples too small to make a statistical interpretation that the two ambient (outdoor) samples and the two indoor samples had different sources and does not think it follows that even if the samples had different sources that the indoor contaminants were derived from impacted soil underlying the building. The EHD is actually impressed by how similar the contaminant ratios in each of the four samples resembles the others, despite a distance of approximately 300 feet between the easternmost outdoor sample and the westernmost indoor sample; could the similarity of analytical results among the four samples be due to a similarity of sources, such as parked vehicles slowly releasing hydrocarbons? 3. L&P stated that they modified the CHHSLs from the residential scenario to an indoor worker scenario by modifying the default parameters. The EHD notes that the CHHSLs and ESLs utilized in Table 3 of the report were Tier I values derived for commercial/industrial land use. The EHD was not party to modifying the input parameters and is not aware of what the modified parameters were changed from and what authoritative source was used to set the modified parameters; please provide this information. Please also note how these values specifically were changed. Comment Letter December 2011