SITE INFORMATION AND CORRESPONDENCE

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Ocampo Property February 2015 821 South Wilson Way, Stockton Claim No: 18916 Rationale for Closure under the Policy • General Criteria: The case does not meet all Policy general criteria; the conceptual site model is incomplete because the extent of the groundwater plume is not adequately defined. • Groundwater Specific Criteria: The case does not meet Policy criteria because the extent of groundwater contamination is undefined to the east(downgradient) of the Site. • Vapor Intrusion to Indoor Air: The case meets Policy Criterion 2a by Scenario 1. There are high concentrations of petroleum hydrocarbons in the groundwater. The minimum depth to groundwater beneath the foundation of existing or potential buildings is greater than 30 feet, overlain by soil containing less than 100 milligrams per kilogram (mg/kg)of TPH. • 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 June 19, 2014, the County objects to UST case closure because: • Inadequate conceptual site model. RESPONSE: We concur. • Secondary source remains. RESPONSE: Secondary source as defined by the Policy was removed by active remediation. • The case does not meet Policy groundwater criteria. RESPONSE: We concur. • The case does not meet Policy vapor criteria. RESPONSE: The case meets Policy Criterion 2a by Scenario 1. Recommendation The Fund recommends that the County direct the Responsible Party to define the extent of groundwater contamination to the east. � - _ �� , � Kirk tarson, P.G. Date Robert Trommer, C.H.G. Date Engineering Geologist Senior Engineering Geologist Technical Review Unit Chief, Technical Review Unit (916) 341-5663 (916) 341-5684 Page 2 of 2