SITE INFORMATION AND CORRESPONDENCE

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Michael Oliphant -2 - 8 May 2012 HHSE— US Can-Welty Road, Balis According to the HHSE: • Chemicals of potential concern (COPCs) are analytes detected in at least one sample between depths of 0 and 10 feet below ground surface (bgs). Low concentrations of BTEX and certain PAHs are considered Site COPCs and were evaluated quantitatively for the HHSE. Analytical data for 77 soil samples collected from 55 onsite locations and/or borings were evaluated for the HHSE. • Data provided in the HHSE describes exposure point concentrations (EPCs) that were used to calculate the upper confidence limit (UCL) for the mean soil concentration of each COPC. If a high number of non-detect (ND) results occur, it may not be possible to calculate a UCL. The United States Environmental Protection Agency (US EPA) recommends that if this condition occurs, to use the sample median as the EPC. • The conceptual site model (CSM) identifies contaminant sources, release mechanisms, transport media, exposure pathways, exposure routes, and potential human receptors associated with the Site. Potential residential exposure to chemicals in onsite soils were estimated for oral, dermal, and inhalation routes following algorithms in the California Department of Toxic Substances Control (DISC) Preliminary Endangerment Assessment (PEA) Guidance Manual. The algorithms incorporate health protective default exposure parameters promulgated by DTSC and US EPA, that represent reasonable maximum exposure for health hazards and health risks. • An incremental lifetime cancer risk of 1 E-06 (i.e., one- in- one million), in accordance with the National Contingency Plan is used as a point of departure. A cancer risk equal to or below this threshold is considered to be insignificant. If the excess cancer risk is within the acceptable range between 1 E-06 to 1 E-04, a site-specific risk management decision may be considered by the lead regulatory agency. • The additive oral, dermal, and inhalation total potential onsite residential cancer risk determined at 2E-06, is within the range of risk management level of 1 E-06 to 1 E-04. A conservative approach for an onsite residential receptor scenario was utilized in the HHSE. The most likely future onsite use will be for commercial/industrial purposes and/or maintenance trench worker(s). • For non-cancer hazard indices, a hazard index of 1 or less is considered an acceptable health hazard level; the non-cancer hazard index was determined to be 0.02. If regulatory criteria are exceeded based on the findings, the HHSE identifies the chemical and exposure pathways contributing to the elevated risks or hazards. • Since soil and groundwater were delineated, and the characterization dataset adequately describes Site conditions, EPCs were calculated as the UCL of the mean soil concentration for each COPC. • BTEX and PAHs were detected in shallow groundwater samples collected during. characterization activities. Benzene (0.6 micrograms per liter, pg/L) was detected in only one of 35 samples analyzed. Ethylbenzene and xylenes and some PAHs were detected at very low concentrations indicating the potential risks associated with this pathway are low. • Shallow groundwater exceeds numerous California and Federal drinking water and agricultural standards for total dissolved solids. Depth to onsite groundwater is