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1 <br />' 30 November 1998 <br /> AGE-NC Project No 95-0104 <br /> 1 <br /> Page 4 of 5 <br />' slotted screen intervals In wells MW-2 through MW-6 Samples were not collected from <br /> wells MW-2, MW-3 and MW-4 as they are not likely to be representative of dissolved <br /> petroleum hydrocarbon concentrations In shallow ground water <br />' • From June 1998 to September 1998, dissolved petroleum hydrocarbon-concentrations <br /> Increased substantially in samples collected from well VW-I <br />' • A plot of TPH-g and benzene concentrations and ground water elevation versus time <br /> (Appendix C) suggests a negative correlation at well VW-1 from April 1996 to March 1998, <br />' however, the plot suggests a positive correlation at well VW-1 from March 1998 to <br /> September 1998 <br /> • Concentrations of benzene detected In a sample collected from well VW-1 were above the <br />' State of California Maximum Contaminant Level (MCL) for drinking water of 1 0 ppb <br /> • Concentrations of toluene were above the MCL of 150 ppb in well VW-1 <br />' • MTBE was detected In a water sample collected from MW-1 at a concentration of 1 /,zg/L <br /> • TBA was detected in a water sample collected from MW-5 at a concentration of 6 3 µg/L <br />' No other fuel oxygenating compounds were detected from analyzed water samples <br /> i <br /> • The elevated concentrations of petroleum hydrocarbons detected in samples collected from <br />' well VW-1 Indicates that this well is within or near the"core area"of the plume of dissolved <br /> petroleum hydrocarbons <br /> • Although MW-5 Is nearly 3-feet below the ground water table, the screened Intervals of <br />' MWA, VW-1 and MW-5 are adequate under the current ground water flow direction to <br /> constrain the upgradsent and downgradient extent of hydrocarbon-impacted ground water <br /> 1 <br /> 5.0. RECOMMENDATIONS <br />' Based upon the results of this investigation, AGE recommends <br />' • Initiation of a soil vapor extraction/air sparging pilot test upon approval of San Joaquin <br /> County Air Pollution Control District permit application <br />' • Continued quarterly monitoring and sampling of selected ground water monitoring wells <br /> The next sampling event is tentatively scheduled for December 1998 <br /> 1 <br /> 1 <br />' Advanced GeoEnviron mental,Inc <br />