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d <br /> Guardino — Crawford Company September 2013 <br /> 517 West Fremont Street, Stockton <br /> Claim No : 14349 <br /> Downgradient Well <br /> BENZENE Results for MW2 <br /> 70 .. - <br /> 60 <br /> I <br /> aofir — <br /> 30 <br /> 20 . _ <br /> I <br /> 10 <br /> + <br /> 0 _ - _. - �.: jam....°�.Ir^'a...+ +.�.i•R. <br /> f �•� BENZENE + + T <br /> Evaluation of Current Risk <br /> Estimate of Hydrocarbon Mass in Soil : None reported. <br /> • Soil/Groundwater tested for methyl tert-butyl ether (MTBE) : Yes. <br /> Oxygen Concentrations in Soil Vapor: None reported. <br /> Plume Length : < 100 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 1 . The plume that exceeds water quality objectives is less than 100 feet in length . <br /> There is no free product. The nearest water supply well or surface water body is greater than <br /> 250 feet from the defined plume boundary. <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 /> ug/L while 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 directly substituted 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 9 of 12 <br />