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Lopez Property • • December 2013 <br /> 1601 French Camp Turnpike, Stockton <br /> Claim No: 18245 <br /> Downgradient Well (Comfort Air Well <br /> FBENZENE Results for MWBA <br /> s <br /> 5 <br /> J <br /> i 3 I �i <br /> 7 <br /> Z - -_' --__ --- <br /> 1 <br /> wyw ` i <br /> 0- ....,...........,...Z <br /> �•� BENZENE -ww 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 GeoEnvironmental, Inc., May 2011). <br /> • Soil/Groundwater tested for MTBE: Yes. <br /> • Oxygen Concentrations in Soil Vapor: None reported. <br /> • Plume Length: <250 feet. <br /> • Plume Stable or Decreasing: Yes. <br /> • Contaminated Zone(s) Used for Drinking Water: No. <br /> • 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 /> • 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 pg/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 /> • 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 directly substituted for naphthalene concentrations <br /> with a safety factor of eight. Benzene concentrations from the Site are below the naphthalene <br /> Page 10 of 14 <br />