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A S S O C I A T E S I M C FI ElLHD UWESTTGATION To assess current subsurface conditions at the site, two soil borings were advanced to a depth of approximately 86 5 feet below ground surface (bgs) All field activities were performed in accordance with ATC Associates' Workplan for Subsurface Investigation at 6732 East Highway 88, Stockton, California, dated April 8, 1998 and subsequent work plan addendum dated April 16, 1998 The workplan was approved by San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) on April 20, 1998 Each boring was advanced until three consecutive soil samples contained no obvious physical evidence (odor, PID readings, etc) of petroleum hydrocarbons The total depth that was explored was approximately 86 5 feet bgs during this phase of the investigation One soil boring was advanced through the excavation area of the former 1,000-gallon UST, identified as Tank #3, near the approximate location where the 1986 soil sample was collected The second soil boring was placed between the former waste oil UST, identified as Tank #4, and the unleaded gasoline UST, identified as Tank#1 The boring locations are shown on Figure 2 • Soil Sample Collection On June 18, 1998, an ATC geologist supervised the advancement of two soil borings to 86 5 feet bgs A site plan showing the soil boring locations is included as Figure 2 Drilling was conducted by V&W Drilling (State C57 license no 720904) utilizing a hollow stem auger drill rig A field geologist logged all drill cuttings and cored soil samples utilizing the Unified Soil Classification System Cored soil samples were collected at five-foot intervals using a 2-inch diameter split- spoon sampler containing three brass tubes The cored samples and drill cuttings were characterized for soil type, moisture content, and visual evidence of petroleum contamination Descriptions of soil types encountered and sample collection intervals are presented on the bonng log contained in Attachment 1 Each soil sample was field screened with a Photoiomzation Detector (PID) for the presence of volatile organic compounds The measured PID readings ranged from 1,178 parts per million (ppm) at 25 5 feet bgs to 2 5 ppm at 5 5 bgs in soil boring SB 1 PID readings from soil samples collected from soil boring SB2 ranged 825 ppm at 15 5 feet bgs to 4 ppm at 5 5 feet bgs Upon retrieval, cored soil samples were immediately sealed in brass sample tubes at each end using Teflon tape and plastic end caps, labeled, and placed on ice Selected soil samples were kept on ice and delivered under chain-of-custody documentation to State-certified Sequoia Analytical laboratory (FLAP No 1210) for chemical analysis PID readings are presented on boring logs in Attachment 1 Field observations (i a PID measurements, odor, and discoloration) indicate petroleum hydrocarbons were generally limited to the upper 45 feet in SB 1 and upper 60 feet in SB2 w 11488SVepoAslsum dw 2