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4.0 SUBSURFACE INVESTIGATION Treadwell& Rollo prepared a 23 December 2003 workplan for the Site to advance up to five borings to collect soil and groundwater samples in the vicinity of the former UST location. 4.1 Sample Collection Between 13 and 20 January2004, six borings (16B-6b through 16B-11)were advanced and soil and groundwater samples were collected for laboratory analyses. Figure 2 shows the boring locations. A boring permit was obtained from the SJCEHD, and an SJCEHD inspector visited the Site. Prior to conducting the subsurface investigations, we notified Underground Services Alert and contracted with a private utility locator to clear proposed boring locations for potential underground utilities. All soil, groundwater, and decontamination water generated during this scope of work were stored on site in drums pending analytical results. All borings were closed by pressure grouting in accordance with San Joaquin County requirements. Continuous soil cores were collected from each boring using a direct push method with a cased hole. Precision Sampling Inc. was the drilling contractor and used their proprietary direct push Enviro-Core sampling equipment. The Enviro-Core system consists of a 3.5-inch diameter drive casing and an inner sample barrel. Continuous soil cores are collected inside the sample barrel. After being advanced approximately 3 feet, the full sample barrel is retrieved while the drive casing is left in place to prevent the hole from collapsing. The direct push method produces minimal cuttings at the surface during the sampling process and allows grout to be pumped through the casing to close the borings. The borings were advanced from 18.5 to 31 bgs. To facilitate grab groundwater sample collection, the boring casing was pulled up to approximately just above the groundwater 4 25971014.DGD 7 April 2004