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tank removal activities, at a depth of 8 feet below grade. Laboratory analysis of these samples indicated the presence of 17 parts per million (ppm) diesel, 12 ppm toluene, and 4.9 ppm ethylbenzene in the eastern end of the excavation. The transmission fluid tank was underlain by an underground concrete pad, which was not removed during excavation. Groundwater was observed in the excavation at a depth of approximately 6 feet below surface during the December 1989 tank removal activity. PACIFIC installed groundwater Monitoring Wells U-1 through U-3 on October 24 and 25, 1990. Selected soil samples were analyzed for total petroleum hydrocarbons (TPH-gasoline and TPH-diesel), halogenated volatile organics (EPA 8010), and benzene, toluene, ethylbenzene, and total xylenes (BTEX compounds). The hydrocarbon concentrations ranged from none detected to 1,800 ppm TPH-gasoline, and from none detected to 710 ppm TPH-diesel at the 5 to 6-1/2 foot interval. The concentrations attenuate to none detected at the 10 to 11-1/2 foot interval with the exception of 3.2 and 5.2 ppm TPH-diesel in Borings U-1 and U-3, respectively. Detectable concentrations of halogenated volatile organics were not discovered in the soil samples submitted for analysis. Details of the first phase of PACIFIC's site investigation are described in a Soil and Groundwater Investigation Report dated February 13, 1991. Static groundwater occurred at a depth of approximately 9-1/2 feet below grade in November 1990 with a calculated northerly flow direction at a gradient of 0.006. Groundwater samples were analyzed for TPH-gasoline, TPH-diesel, BTEX compounds, and halogenated volatile organics (EPA 624) during the November 1990 sampling event. Samples obtained from Wells U-1 and U-2 contained 140 ppb and 670 ppb TPH-gasoline, respectively. Maximum concentrations of 19 ppb benzene and 2.4 ppb ethylbenzene were detected in groundwater from Well U-1. The groundwater sample from Well U-2 contained the maximum xylene concentration of 99 ppb. Wells U-3 and WSW-1 contained no detectable concentrations of any of the analyzed compounds. Diesel was not detected in any of the wells sampled. PACIFIC installed groundwater Monitoring Wells U-4 through U-6, and Exploratory Soil Borings U A through U-C, on May 9, 1991. Selected soil samples were analyzed for TPH-gasoline, TPH-diesel, and BTEX compounds. The hydrocarbon concentrations ranged from none detected to 1,700 ppm TPH-g Zn to 4,900 ppm TPH-diesel, and none detected to 3.9 none detected 9 ppm benzene, with the higher concentrations occurring above the 9-1/2 foot depth. Details of this investigation are described in PACIFIC's Soil and Groundwater Investigation Report dated ,— September 30, 1991. .r- 3100103/REPORTS 2 June 11, 1992