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r 1 <br /> 21 October 1997 <br /> AGE-NC Project No 95-0121 <br />' Page 4 of 5 <br /> a <br /> t Concentrations of MTBE detected in the sample from well MW-5 were below the Central <br /> Valley Regional Water Quality Control Board (CVRWQCB) recommended 35 ppb closure <br /> limit However, due to increased dilution factors (detection limits), it is possible that MTBE <br /> F <br />' could be present at wells MW-1 through MW-4, but may be masked by the increased <br /> detection limits resulting from the overall high hydrocarbon concentrations <br /> • The top of the saturated zone was approximately 3 5 to 12 5 feet above the tops of the <br />' screened intervals in monitoring wells MW-1 through MW-9 Because screened intervals are <br /> significantly below the ground water table, analytical results from samples collected in these <br /> wells may not be representative of ground water conditions in the shallow saturated zone <br /> F 5.0. RECOMMENDATIONS <br /> Based upon data collected from the site, AGE recommends the following <br /> r • Based on the consistently high concentrations of petroleum hydrocarbons in MW-7 and the <br /> prevailing ground water flow direction, at least one additional ground water monitoring well <br /> is needed west of MW-7 to fully assess the dissolved petroleum hydrocarbon plume <br /> • Due to the detection of petroleum hydrocarbons in MW-4 and the current screen-interval <br />' being approximately eleven feet beneath the top of the saturated zone (a drowned well), at <br /> least one additional ground water monitoring well is needed northeast of MW-4 to fully <br /> assess_the dissolved petroleum hydrocarbon plume <br />�rr ` <br /> The wells should be dual completed with one deeper completion to test the ground water <br /> interval currently monitored by MW-1 through MW-4, and one completion at the current <br /> n saturated/unsaturated zone interface, with allowance for additional rise of ground water <br /> Upon the UST Cleanup Fund approval, installation of an active remediation system should <br /> commence <br /> The next quartet ly monitoring should be scheduled for November 1997 <br /> 6 0. LIMITATIONS <br /> Our professional services were performed using that degree of care and skill ordinarily exercised by <br /> environmental consultants practicing in this,or similar localities The findings were based upon <br /> analytical results provided by an independent laboratory Evaluation of the hydrogeologic conditions <br /> at the site for the purpose of this investigation was made from a limited number of available data <br /> Advanced GeoEntronmental,Inc <br /> r ' <br />