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were placed in areas known to contain TPH to determine the vertical extent of impacted soils The remaining seven soil borings were placed around the perimeter of the excavation to provide a preliminary assessment of the horizontal extent of petroleum hydrocarbon- impacted soil The locations of the ten soil borings are shown on FIGURE 2-2 Soil samples were obtained at different depths and analyzed for TPH using EPA Method 8015M. Analytical results from the soil samples indicate TPHd concentrations up to 7,400 ppm Except for B-6 and B-9, petroleum hydrocarbon-impacted soil was confined to a zone around the bottom of the former excavation Impacted soil was detected at an approximate depth of 35 feet in boring B-6 and 26 feet in boring B-9 Except for B-6, results of the deepest sample analyzed from each boring were non-detect Boring B-6 was terminated at a depth of 35 feet in order to avoid possible contamination of groundwater, which at the time was believed to be between 35 and 40 feet bgs Sample depths and analytical results are presented in TABLE 2-2 During a preliminary groundwater investigation conducted by ERM-West in January 1991 (to be discussed in detail in Section 2 3 2), three monitoring wells were installed around the former tank locations Soil samples were obtained from each well borehole (SFW-1-1, SFW-2-1, and SFW-3-1) near the groundwater level The soil samples were analyzed for TPHd and gasoline using EPA Method 8015M and BTEX using EPA Method 8020 None of the soil samples had any detectable concentrations of TPH or BTEX Sample depths and analytical results are presented in TABLE 2-3. Based on the soil investigations conducted by ERM-West, it appears that impacted soils have generally been detected between a depth of 5 feet and just below the bottom of the former tank pit (approximate 15 feet bgs) The soil data suggest that hydrocarbon-impacted soils were probably backfilled into the tank pit In May, 1991, ERM-West conducted further investigations in the vicinity of the former tanks to supplement the information gathered during the August 1989 and January 1991 soil sampling activity. Three soil borings (B-11, B-12, and B-13) were drilled to depths of 40, 30, and 25 feet The location of boring B-11 was chosen to collect a sample where the highest concentrations of TPH had previously been detected in August 1989 and to determine the deepest occurrence of impacted soil The locations of borings B-12 and B-13 were chosen to deternune the Iateral extent of petroleum hydrocarbon impacted soil beyond borings B-7 and B-10 FIGURE 2-2 shows the locations of the three soil borings Four soil Z=717WM4TAn FNL%I..W m 93 2-6 cb x.r 190