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to perform a subsurface investigation Two bonngs were drilled (TB-1 and TB-2), and TB-1 was completed as a groundwater monitoring well, with a screened interval from 75 to 100 feet below surface grade Soil and water samples were collected for analysis Upgradient Environmental later renamed the monitoring well GT-3 (Figure 2) Gasoline and/or diesel were detected to the bottom (70 feet) of TB-2 and to a depth of 85 feet in GT-3 Gasoline and diesel were also detected in the groundwater sample from the well As directed by San Joaquin County PHS/EHD, monitoring wells GT-I and GT-2 were installed in September 1994 under Upgradient's supervision Both wells were screened from 75 to 100 feet Five soil samples from GT-1 were selected for laboratory analysis, and all five contained both diesel and gasoline-range hydrocarbons Total Petroleum Hydrocarbon (TPH) concentrations (gasoline plus diesel) decreased downward from 7050 mg/kg at 35 feet to 104 mg/kg at 55 feet Three samples were selected from GT-2 for analysis A TPH concentration of 288 mg/kg was reported at a depth of 55 feet, no contamination was detected at 50 feet or 60 feet Diesel was detected in the groundwater sample from both wells, and gasoline was also detected in the sample from GT-2 Monitoring well GT-3 was also sampled, but no hydrocarbons were detected in the sample from that well Upgradient continued to monitor groundwater conditions, and hydrocarbons were detected in all three wells in January 1995 Due to the wet winter of 1994-95, the groundwater level began to rise until it reached a depth of approximately 64 feet in late I995 Because groundwater was several feet above the screened interval in all three wells, samples were not collected after July 1995 Hence, San Joaquin County PHS/EHD requested Gillies Trucking to drill additional wells and complete them at shallower depths so that groundwater samples could be collected Upgradient submitted a work plan to drill five new borings (including three monitoring wells) in February 1996 However, drilling was postponed until the third quarter of the year until access to the adjacent property south of Gillies Trucking could be obtained The activities performed during the third quarter of 1996 are described in the next section 3.0 DRILLING AND SAMPLING PROCEDURES 3.1 Drilling and Sampling--First Phase On August 16 and 19, 1996, V & W Drilling of Rio Vista drilled three soil borings on the Gillies property Beginning at a depth of either 10 or 15 feet, soil samples were collected from each boring at 5-foot intervals using a split-spoon sample barrel loaded with clean brass sample tubes Organic vapor readings and other observations were noted on the boring logs (Appendix A), and selected samples were capped, sealed, labeled, and placed in a cooled ice chest for laboratory analysis The first boring (GT4) was drilled on August 16 near the estimated northern edge of the soil contaminant plume When saturated sand was encountered at 46 feet, a hydropunch was driven to a depth of 48 feet to collect a water sample However, water entered the sampler very slowly, and after 2