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Ocampo Property September 2013 <br /> 821 South Wilson Way, Stockton <br /> Claim No: 18916 <br /> Groundwater Trends <br /> • Since 2004, six groundwater monitoring wells have been installed and regularly monitored. <br /> Benzene trend is shown below: Source area (MW-5). <br /> Source Area Well <br /> Benzene Trend for MW-5 <br /> 70000 <br /> 60000 <br /> 3 50000 <br /> 40000 <br /> v <br /> c <br /> $ 30000 <br /> c <br /> a <br /> 00 20000 <br /> 10000 <br /> 0 <br /> 8/22/2008 8/22/2009 8/22/2010 8/22/2011 8/22/2012 <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: Undefined. <br /> • Plume Stable or Decreasing: Unknown. <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 extent of groundwater contamination is undefined east (downgradient) of <br /> the Site. <br /> • Indoor Vapor Risk from Residual Petroleum Hydrocarbons: This case meets Policy Criterion <br /> 2b. Although no document titled "Risk Assessment' was found in the files reviewed, a <br /> professional assessment of site-specific risk from potential exposure to petroleum constituents <br /> as a result of vapor intrusion found there to be no significant risk of petroleum vapors adversely <br /> affecting human health. The onsite building is an active facility with multiple rollup doors that <br /> would prevent the accumulation of soil vapors in the building. In addition, excavation was <br /> conducted to depth of 15 feet and nearly 8,258 pounds of TPHg was pulled from the <br /> subsurface by soil vapor extraction. Rebound test showed soil vapor extraction had reached <br /> asymptotic levels. <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 /> Page 8 of 10 <br />