SITE INFORMATION AND CORRESPONDENCE

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Chase Chevrolet December 2014 424 North Van Burren Street, Stockton Claim No: 8294 of drinking water, and it is highly unlikely that the affected shallow groundwater will be used as a source of drinking water in the foreseeable future. Other designated beneficial uses of the affected shallow groundwater are not threatened, and it is highly unlikely that they will be, considering these factors in the context of the site setting. Rationale for Closure under the Policy • General Criteria: The case meets all eight Policy general criteria. • Groundwater Specific Criteria: The case does not meet Policy criteria because no groundwater samples have been collected since 2003, McLeod Lake is approximately 600 feet south (upgradient) of the Site, and the size and stability of the contaminant plume that exceeds water quality objectives is unknown. • Vapor Intrusion to Indoor Air: The case does not meet Policy criteria because the maximum benzene concentration in groundwater is greater than 1,000 micrograms per liter(pg/L), while the minimum depth to groundwater is less than 30 feet. • Direct Contact and Outdoor Air Exposure: The case meets Policy Criterion 3a. Maximum concentrations in soil are less than those in Policy Table 1 for Commercial/Industrial use, and the concentration limits for a Utility Worker are not exceeded. There are no soil sample results in the case record for naphthalene. However, the relative concentration of naphthalene in soil can be conservatively estimated using the published relative concentrations of naphthalene and benzene in gasoline. Taken from Potter and Simmons (1998), gasoline mixtures contain approximately 2 percent benzene and 0.25 percent naphthalene. Therefore, benzene can be used as a surrogate for naphthalene concentrations with a safety factor of eight. Benzene concentrations from the Site are below the naphthalene thresholds in Policy Table 1. Therefore, the estimated naphthalene concentrations meet the thresholds in Table 1 and the Policy criteria for direct contact by a factor of eight. It is highly unlikely that naphthalene concentrations in the soil, if any, exceed the threshold. Objections to Closure and Responses According to the Path to Closure page in GeoTracker, finalized on May 13, 2014, the County objects to UST case closure because: • Inadequate conceptual site model. RESPONSE: Adequate data is available in GeoTracker to develop a conceptual site model as defined by the Policy. • The case does not meet Policy groundwater criteria. RESPONSE: We concur. • The case does not meet Policy vapor criteria. RESPONSE: We concur. • The case does not meet Policy direct contact criteria. RESPONSE: The case meets Policy Criterion 3a. Page 2 of 3