SITE INFORMATION AND CORRESPONDENCE

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Lopez Property • • 1601 French Camp Turnpike, Stockton December 2013 Claim No: 18245 Service. The affected groundwater is not currently being used as a source of drinking water, and it / is highly unlikely that the affected groundwater will be used as a source of drinking water in the foreseeable future. Other designated beneficial uses of impacted groundwater are not threatened, and it is highly unlikely that they will be, considering these factors in the context of the site setting. Remaining petroleum hydrocarbon constituents are limited and stable, and concentrations are decreasing. Corrective actions have been implemented and additional corrective actions are not necessary. Any remaining petroleum hydrocarbon constituents do not pose a significant risk to human health, safety or the environment. Rationale for Closure under the Policy • General Criteria: The case meets all eight Policy general criteria. • Groundwater Specific Criteria: The case meets Policy Criterion 1 by Class 2. The contaminant plume that exceeds water quality objectives is less than 250 feet in length. There is no free product. The nearest water supply well or surface water body is greater than 1,000 feet from the defined plume boundary. The dissolved concentration of benzene is less than 3,000 micrograms per liter (Ng/L) and the dissolved concentration of methyl tert- butyl ether (MTBE) is less than 1,000 pg/L. • Vapor Intrusion to Indoor Air: The case meets Policy Criterion 2a by Scenario 3b. The maximum benzene concentration in groundwater is less than 1,000 pg/L. The minimum depth to groundwater is greater than 10 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 directly substituted 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, the Regional Water Board opposes Closure because: • Secondary source remains. RESPONSE: Secondary source as defined by the Policy was removed by excavation in 1987. • The case does not meet Policy groundwater criteria. RESPONSE: The case meets Policy Criterion 1 by Class 2. • The case does not meet Policy indoor vapor criteria. RESPONSE: The case meets Policy Criterion 2a by Scenario 3b. • The case does not meet Policy direct contact criteria. RESPONSE: The case meets Policy Criterion 3a. Page 2 of 14 1