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Chevron #9-4054 May 2014 <br /> 2103 Country Club Boulevard. Stockton <br /> Claim No: 12729 <br /> Evaluation of Current Risk <br /> • Estimate of Hydrocarbon Mass in Soil: Approximately 137 pounds of benzene (Arcadis, 2012). <br /> • Soil/Groundwater tested for methyl tert-butyl ether (MTBE): Yes. <br /> • Oxygen Concentrations in Soil Vapor: None reported. <br /> • Plume Length: Undefined in the B zone, <250 feet in zones A, C, and D. <br /> • Plume Stable or Decreasing: No. <br /> • Contaminated Zone(s) Used for Drinking Water: No. <br /> • Groundwater Risk from Residual Petroleum Hydrocarbons: The case does not meet Policy <br /> criteria because the contaminant plume that exceeds water quality objectives is not defined. <br /> • Indoor Vapor Risk from Residual Petroleum Hydrocarbons: The case does not meet Policy <br /> criteria because the maximum benzene concentration in groundwater is greater than 1,000 <br /> pg/L and the minimum depth to groundwater is less than 30 feet. <br /> • Direct Contact Risk from Residual Petroleum Hydrocarbons: The case meets Policy Criterion <br /> 3a. Maximum concentrations in soil are less than those in Policy Table 1 for <br /> Commercial/Industrial use, and the concentration limits for a Utility Worker are not exceeded. <br /> There are no soil sample results in the case record for naphthalene. However, the relative <br /> concentration of naphthalene in soil can be conservatively estimated using the published <br /> relative concentrations of naphthalene and benzene in gasoline. Taken from Potter and <br /> Simmons (1998), gasoline mixtures contain approximately 2 percent benzene and 0.25 percent <br /> naphthalene. Therefore, benzene can be used as a surrogate for naphthalene concentrations <br /> with a safety factor of eight. Benzene concentrations from the Site are below the naphthalene <br /> thresholds in Policy Table 1. Therefore, the estimated naphthalene concentrations meet the <br /> thresholds in Table 1 and the Policy criteria for direct contact by a factor of eight. It is highly <br /> unlikely that naphthalene concentrations in the soil, if any, exceed the threshold. <br /> Page 11 of 15 <br />