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L <br /> EXECUTIVE SUMMARY <br /> In accordance with Upgradient Environmental Consultants proposal 98006, which was <br /> preapproved by the State UST Cleanup Fund on February 25, 1998, Upgradient <br /> performed monitoring activities at the former Conrady Service Station in Stockton, <br /> California in September, 1998 <br /> Monitoring took place on September 24 Water depths and dissolved oxygen <br /> concentrations in the groundwater were measured and groundwater samples were <br /> collected Water was present in all wells The natural gradient is to the northeast, bu <br /> asphalt pavement in Yosemite Street to the west of the site appears to alter the gradient <br /> along the property boundary by limiting downard infiltration of surface water and <br /> lowering the water table beneath the street This forms a groundwater trough (low shot) <br /> along the property line There has been a drop in the water table of approximately 4 feet <br /> since monitoring began in April <br /> In contrast to the previous quarter, no wells had detectable concentrations of dissoly-.d <br /> oxygen The monitoring equipment appeared to be in good working order, so it appears <br /> that oxygen is no longer being released into the groundwater from the Oxygen Release <br /> Compound injection borings This may indicate that the added oxygen has been dep eted <br /> through microbial or chemical processes and is not available for further remediation of <br /> the contaminants <br /> All ten water samples were analyzed for TPH-gasoline, BTEX, and gasoline oxygenates, <br /> as directed by EHD and approved by the UST Fund As in the previouw two quarter3, no <br /> oxygenates were detected, it is clear that oxygenates were not in general use prior to the <br /> 1980 removal of the USTs, and oxygenates are not a concern at this site <br /> Unfortunately, the September samples indicate that neither gasoline nor BTEX <br /> concentrations have significantly declined since the remedial actions were performed in <br /> April After a slight decrease in the second quarter, TPH-g concentrations have again <br /> risen in MW-1, MW-2, MW-4, and SW-2 and fallen in MW-5 and SW-1 The highest <br /> concentration (54,900 ppb) was again detected in SW-I Benzene concentrations <br /> increased in MW-2 and SW-2 and decreased in MW-1, MW-5,VE-2, and SW-1 Th,,- <br /> highest concentration (235 ppb) was detected in MW-2 <br /> 1 <br />