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Satnam Singh - 3 - October 26, 2011 <br /> General Site Conditions <br /> • Geology and Hydrogeology: The Site is underlain by interbedded and intermixed sand, <br /> silt and clay. The depth to groundwater is approximately 6 feet bgs and the groundwater <br /> gradient is northwest at approximately 0.004 feet/foot. <br /> • Estimate of Hydrocarbon Mass in Soil: Prior to remediation, Aqua Science Engineers <br /> estimated that approximately 7,384 pounds of TPG in soil and 43 pounds of TPHg was <br /> dissolved in groundwater <br /> • Groundwater Trends: There are more than 11 years of groundwater monitoring data for <br /> this Site. MTBE trends are shown below, source area (MW-2) <br /> METHYL-TERT-BUTYL ETHER(MTBE)Results for MW-2 <br /> 1400 <br /> 1200 <br /> 1000 <br /> } t <br /> zoo <br /> —--METHYL-TERT-BUTYL ETHER(MTBE) --- Tr—d <br /> Risk Evaluation <br /> There are no water supply wells or surface water receptors present within 400 feet of the Site. <br /> Recommendation <br /> May 2008, the Fund made the following recommendation: The Fund concurs with the San <br /> Joaquin County LOP that ozone sparging continue and to maximize the treatment system as <br /> necessary to achieve Water Quality Objectives in a timely manner. The Fund will review the <br /> site next year to track progress. <br /> UPDATED, May 2009, the Fund recommends that the San Joaquin County LOP consider <br /> reviewing this site for closure. <br /> UPDATED, May 2010, the Fund continues to recommend that the San Joaquin County LOP <br /> consider this site for closure. Further investigation at this site is unlikely to benefit the people of <br /> California. <br /> UPDATED, October 2011, source area monitoring well MW-2 has consistently had elevated <br /> concentrations of residual hydrocarbons in groundwater. However, after 11 years of monitoring <br /> and active remediation, the groundwater plume is shrinking in size and concentration. <br /> Groundwater within the source area will likely remain above WQOs for years. The Fund <br /> recommends that the San Joaquin County LOP review this site for closure. <br /> 61 <br /> Kirk Carson, P.G. Date RoberfTrommer C.H.G. Date f l� <br /> Engineering Geologist Senior Engineering Geologist <br /> Technical Review Unit Chief, Technical Review Unit <br /> (916) 341-5663 (916) 341-5684 <br />