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1 ' Site Characterization In 1996, The Twining Laboratories, Inc. conducted a site investigation to assess the lateral extent of petroleum h drocarbon impacts to soil and ground water at the site. The site characterization Y P activities consisted of the advancement of seven soil probes (S13-1 through SB-7) and the collection ' of soil and in-situ ground water samples for laboratory analysis (Figure 2). Laboratory analysis of soil samples detected BTEX, TPH-d, TPH-g and methyl tertiary-butyl ether ' (MTBE)for samples collected from soil probe boring SB-5. In addition,relatively low concentrations of petroleum hydrocarbon compounds were detected for soil samples collected from SB-4 and SB-7. The analytical results of ground water samples collected from the soil probe borings suggested that ' ground water has been extensively impacted by BTEX, TPH-d, TPH-g and MTBE. The greatest petroleum hydrocarbon impacts to ground water were reported for soil probe boring locations SB-5 and S13-7 located north of the former diesel UST location. Laboratory analysis of ground water samples collected from soil probe S13-5 detected benzene (6,500 ppb), toluene (35,000 ppb), ethylbenzene (4,500 ppb), total xylenes (25,000 ppb), TPH-d(320,000 ppb), TPH-g (93,000 ppb), and MTBE (560 ppb). In April 1999, five soil borings (B-1 through B-5) were advanced, B--4 and B-5 were subsequently completed as monitoring wells MW-4 and MW-5, respectively, at locations down gradient (north) ' of previous soil probe boring SB-7 and the former UST locations, and soil boring B-1 was advanced at a location up gradient(south) of the former UST locations. Soil boring B-2 was advanced east of '• the former UST area to evaluate previously reported anomalous ground water analytical results in the vicinity of monitoring well MW-1 and soil probe boring SB-1. Soil borings B-3 was completed west of previous soil probe boring SB-6 and the former UST area. Soil borings B-1 through B-3 were advanced to a total depth of 15 feet bsg. Soil borings MW-4 and MW-5 were advanced to depths of 21 feet bsg and 17 feet bsg,respectively. During the soil boring activities,ground water samples were collected fi•om soil borings B-1 through B-3 for laboratory analysis. There were no reported detections of BTEX, TPH-g, or TPH-d in soil samples collected from the five soil borings. Fuel oxygenating compound MTBE was detected at concentrations of 65 µg/mg ' and 110 µg/mg in soil samples collected from soil boring MW-4 at 17.5 and 20 feet bsg,respectively. Concentrations of TPH-d were detected in two of the eight ground water samples analyzed TPH-d was reported in samples B-2 and B-3 at concentrations of 570 µg/l and 130 µg/1, respectively. 1 On 18, 20 and 23 February and 08 March 2002, the soil borings (B8, B9 and B 10) were advanced at the site. Boring B8 and B9 were sampled for the collection of discrete ground water. A ' HydroPunch water sampling assembly was advanced to a depth of 60 feet bsg in boring 138, also to a depth of 65 feet bsg in boring B8 without yielding water, and finally to a depth of 71 feet in boring ' B8 for collection of a grab ground water sample. A hydropunch water sampling assembly was also advanced to a depth of 60 feet bsg in boring B9 and finally to a depth of 70 feet in boring B9 for collection of a deeper grab ground water sample. Soil boring B9 was single-completed as ground ' water monitoring well MW-9 screened from 70 to 75 feet bsg. Soil boring B 10 was single-completed as ground water monitoring well MW-10 screened from 55 to 60 feet bsg. • Advanced Geo Environmvital,inc. i 1