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EXECUTIVE SUMMARY In accordance with Upgradient Environmental Consultants proposal 96006, which was preapproved by the State UST Cleanup Fund on February 25, 1998, Upgradient performed site remediation activities at the former Conrady Service Station in Stockton, California in April and May, 1998 Prior to initiation of field work, Upgradient submitted a work plan detailing the proposed corrective action to San Joaquin County Environmental • Health and received verbal approval and a drilling permit on April 7 On April 24, a direct-push Geoprobe drilling rig was used to drill seven soil borings to depths of 20, 30, or 35 feet, for a total of 210 feet The borings were located within the 100 parts-per-billion isocontour of benzene as mapped by the previous consultant, and were spaced at distances of 4 to 8 feet apart A slurry of Oxygen Releasing Compound (ORC) was infected under pressure into a 10-foot interval of each boring to facilitate the breakdown of gasoline hydrocarbons by increasing the concentration of oxygen dissolved in the groundwater Oxygen is normally a limiting factor in the breakdown of hydrocarbons but is a necessary component of the destruction process A total of 500 • pounds of dry ORC (approximately 270 gallons of slurry) was injected, as approved by the UST Fund Site monitoring took place on April 24 and May 8 The site was remapped on April 24 to correct errors in the location of some of the wells on the existing maps, and all 10 wells were surveyed (including four wells that had not been previously surveyed) on May 8 Water depths and dissolved oxygen concentrations in the groundwater were measured on both days, and groundwater samples were collected on April 24 Water was present in all wells, and gradient maps were prepared for both days The natural gradient is to the northeast, but asphalt pavement in Yosemite Street to the west of the site appears to alter • the gradient along the property boundary by limiting downard infiltration of surface water and lowering the water table beneath the street Dissolved oxygen concentrations were generally low and decreased during purging as i fresh, undegraded groundwater entered the wells when the standing water was purged No correlation between well location and DO concentration was evident, but after ORC injection a signficant increase in DO concentration was observed in one well that is located within 3 feet of an injection boring Water samples were analyzed for TPH-gasoline, BTEX, and gasoline oxygenates, as • directed by EHD and approved by the UST Fund No oxygenates were detected, but gasoline was detected in all but one sample and at least one BTEX compound was detected in every sample TPH-g concentrations ranged from 860 ppb to 37,000 ppb, and benzene concentrations ranged from 0 824 to 379 ppb •