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Lopez Property March 2014 <br /> 1601 French Camp Turnpike, Stockton <br /> Claim No: 18245 <br /> Downgradient Well Comfort Air Well <br /> BENZENE Results for MWBA <br /> el <br /> 51.__. • _. . .. _ <br /> 41 <br /> K 2 <br /> ..aaT+asa <br /> aaaana a�ili�Itaa'��'a <br /> a•. BENZENE +++ Trend <br /> Evaluation of Current Risk <br /> ® Estimate of Hydrocarbon Mass in Soil: Reportedly, 1,836 pounds of TPHg remain is soil <br /> beneath the former UST area (Advanced GeoEnviron mental, Inc., May 2011). <br /> e Soil/Groundwater tested for MTBE: Yes. <br /> Oxygen Concentrations in Soil Vapor: None reported. <br /> o Plume Length: <250 feet. <br /> e Plume Stable or Decreasing: Yes. <br /> a Contaminated Zone(s) Used for Drinking Water: No. <br /> e Groundwater Risk from Residual Petroleum Hydrocarbons: The case meets Policy Criterion 1 <br /> by Class 2. The contaminant plume that exceeds water quality objectives is less than 250 feet <br /> in length. There is no free product. The nearest water supply well or surface water body is <br /> greater than 1,000 feet from the defined plume boundary. The dissolved concentration of <br /> benzene is less than 3,000 pg/L and the dissolved concentration of MTBE is less than <br /> 1,000 pg/L. <br /> o Indoor Vapor Risk from Residual Petroleum Hydrocarbons: The case meets Policy Criterion 2a <br /> by Scenario 3b. The maximum benzene concentration in groundwater is less than 1,000 ug/L. <br /> The minimum depth to groundwater is greater than 10 feet, overlain by soil containing less than <br /> 100 mg/kg of TPH. <br /> a 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 /> Page 9 of 13 <br />