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23 September 1997 <br /> AGE-NC Project No 95-0184 <br /> Page 7 of 8 <br /> • Petroleum hydrocarbons were detected in each well sampled, at concentrations as high as <br /> 190,000 ppb The lateral extent of hydrocarbons in ground water has not been determined <br /> Additional monitoring wells will be necessary to delineate the horizontal extent of <br /> Ihydrocarbon-impacted ground water <br /> • Ground water flow was determined to be easterly for each monitoring event <br /> • Due to the rise of ground water elevation at the site, ground water is currently approximately <br /> seventeen feet above the screened interval in monitoring wells MW-1 through MW-3, six <br /> feet above the screened interval in MW-4 and one foot above the screened interval in MW-7 <br /> These wells recharge rapidly, possibly preventing significant drawdown in wells MW-1 <br /> through MW-3 during purging The hydrocarbon concentrations detected in these `drowned' <br /> wells may not be representative of shallower ground water where the maximum hydrocarbon <br /> impact would be expected <br /> • Ground water is currently within the screened interval in four vapor wells The data collected <br /> from these wells should be representative of shallow ground water conditions <br /> • The data is suggestive of two plumes of impacted ground water, one plume centered near <br /> Tank A and partially defined by wells VW-2, VW-3, and VW-5, the second plume centered <br /> near former Tanks B and C and partially defined by well MW-4 The area of well MW-7 <br /> may be in an area of co-mingling of the plumes <br /> • Petroleum hydrocarbons were detected in soil samples collected from each boring advanced <br /> at the site The lateral extent of hydrocarbon-impacted soil at the site has not been defined <br /> I The San Joaquin County PHS/EHD is anticipated to require additional assessment to <br /> determine the extent of impacted soil <br /> I _ <br /> 6 0. RECOMMENDATIONS <br /> Based upon data collected from the site, AGE recommends the following <br /> r <br /> • Additional monitoring wells should be installed to define the horizontal extent of <br /> hydrocarbon-impacted ground water We recommend the installation of monitoring wells in <br /> the sidewalk approximately 80 feet east of MW-4, southeast of MW-4 across Miner Avenue <br /> and inside the building at 825 Miner Avenue, approximately 80 feet north of MW-4 These <br /> wells will help delineate the eastern, down-gradient margin of the ground water plume(s) <br /> • A soil vapor extraction/in-situ air sparging pilot test should be conducted to examine <br /> remediation options at the site Findings of the vapor extraction/air sparging test can be used <br /> to determine the spacings of potential additional vapor and sparging wells <br /> Advanced GeoEnriron mental,Inc <br />