SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Harry's Auto Mart y� ' y 2662 North Wilson Way, tT8ckton November 2013 Claim No: 15094 (crossgradient) from the Site. No other water supply wells have been identified within 1,000 feet of the defined plume boundary in files reviewed. Water is provided to water users near the Site by the Stockton East Water District and/or California Water 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. I 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 5. The nearest well, well number 3901122-001, is 201 feet west northwest (crossgradient) from the Site. The tiny amount of hydrocarbons left in the source area does not threaten the crossgradient and inactive well owned by the Frontier Motel. The case otherwise meets Policy Criterion 1 by Class 1. The plume that exceeds water quality objectives is less than 100 feet in length.- There is no free product. The nearest surface water body is greater than 1,000 feet from the defined plume boundary. The regulatory agency determines, based on an analysis of site specific conditions, which under current and reasonably anticipated near-term future scenarios, the contaminant plume poses a low threat to human health and safety and to the environment and water quality objectives will be achieved within a reasonable time frame. • Vapor Intrusion to Indoor Air: The case meets Policy Criterion 2a by Scenario 3a. The maximum benzene concentration in groundwater is less than 100 pg/L. The minimum depth to groundwater is greater than 5 feet, overlain by soil containing less than 100 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 County opposes closure because: • Secondary source remains. RESPONSE: Secondary source as described by the Policy was removed by excavation. • The case fails the Policy groundwater criteria. RESPONSE: The case meets Policy Criterion 1 by Class 5. • The case fails the Policy vapor criteria. RESPONSE: The case meets Policy Criterion 2a by Scenario 3a. Page 2 of 13