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2 4 Excavation 1 On May 10 and 11, 1993, approximately 500 cubic yards of contaminated soil were removed from tank pit #1 Soil was removed from the excavation to a depth of 35 feet at the ' southern end of the excavation Field screening with a photo-ionization detector (PID) detected organic vapors at the floor of the enlarged excavation In subsequent verbal communication, the PHS/EHD notified Pacific Gas that, due to seasonal high groundwater ' of approximately 45 feet, a groundwater investigation involving the installation of three monitoring wells would be required 2.5 Backfilling On May 12 and 13, 1993, the excavation was partially backfilled Crushed rock and pea gravel were used to backfill the southern portion of the excavation The entire excavation was then backfilled and compacted to a depth of 5 feet below surface grade This would to allow for drilling within the former tank cavity, if necessary 3.0 PROCEDURES 3.1 Drilling and Sampling From November 3 to 5, 1993, five soil borings were drilled at the site Borings B-10 and B- 11 were placed in the excavation (approximately 5 feet below surface level) and advanced to depths of 75 and 70 feet respectively Three other borings were advanced to 88 feet and completed as groundwater monitoring wells MW-1, MW-2 and MW-3 Auger returns were placed on plastic sheeting and stored on-site The boring and monitoring well locations are illustrated in Figure 2 ' The borings were drilled using a truck-mounted B-61 HDX drill rig The drill rig and two- man crew were supplied by V & W Drilling During drilling, auger returns were monitored for the pi esence of organic vapors using a photo-ionization detector (PID Thermo Environmental 580A, 100 eV, calibrated to isobutylene) Discrete soil samples were ' collected ahead of the drill bit using a split-tube sampler loaded with three pre-cleaned 2- inch by 6-inch brass sleeves The samples were collected at five-foot intervals, using a 140 pound hammer to advance the sampler 18 inches The number of blows required to advance the sampler in 6-inch increments was recorded on the boring logs To avoid cross contamination, the sampling equipment was washed in a tri-sodium phosphate (TSP) solution and rinsed twice with water prior to each sampling run ' For each sample, both ends of the lead tube were covered with aluminum sheets, capped and sealed with tape The samples were then stored on ice and transported under chain of ' custody to McCampbell Analytical Inc in Pacheco, California Gro1o1&—1 Audd Sere— I.. 4 Pauls Qaart2 16J;V651 5