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3 <br /> 2.0 SUMMARY OF REGIONAL GEOLOGY AND SITE CONDITIONS <br /> L This section presents a discussion of the regional geologic setting and Site conditions. This <br /> discussion is based on a review of subsurface findings developed from the limited field <br /> investigation conducted at the former UST in 1991, and the Tenera Associates, Inc (Tenera) <br /> monitoring well installation report dated September 20, 1993 [(Tenera, 1993)]. <br /> a <br /> 2.1 REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING <br /> In June 1993, VFO installed three shallow groundwater-monitoring wells around the former <br /> VFO discharge pond, which is located at the north end of the former Dole property (Figure 1). <br /> a As described in the 1993 Tenera report, the regional subsurface hydrogeologic framework <br /> consists of medium dense fine-grained silty sands, which are underlain by dense medium-grained <br /> clayey sands and gravely sands. These deposits were encountered from the surface to the <br /> maximum depth of 80 feet below ground surface (bgs). Based on annual groundwater-level <br /> measurements in the on-site monitoring wells, shallow groundwater in the Site vicinity typically <br /> occurs at depths ranging from approximately 55 to 75 feet below the wellhead measuring point. <br /> No other information is available regarding regional depths to groundwater. <br /> L <br /> 2.2 SOIL BORINGS AND SITE HYDROGEOLOGY <br /> Shallow depth deposits were penetrated and recovered during the Site investigation fieldwork. <br /> The drilling assessment involved the collection of soil samples at two locations for purposes of <br /> ' evaluating the presence of BTEX and MTBE compounds in soil at the former VFO UST <br /> (Figure 3). The rationale for siting the two borings was described in the Work Plan. <br /> The nature of the upper 20 feet of Site soil ranges from silty sand to silty clay deposits_ Soil <br /> Boring B-1, which was installed in the center of the former UST excavation, penetrated loose <br /> medium-grained silty sands. Minor amounts of pea gravel (likely excavation backfill)were <br /> observed in drill cuttings recovered from the first 10 feet. Observed soil characteristics were <br /> relatively unchanged from the surface to the total depth of approximately 21 feet bgs. <br /> Soil Boring B-2 was installed approximately 10 feet west of the edge of the former UST <br /> excavation (Figure 3). The soils encountered from below the asphalt pavement to approximately <br /> 15 feet bgs consisted of dark-brown silty sand with minor amounts of silt, clay, and loam_ No <br /> L. pea gravel was encountered in the drill cuttings returned to the surface_ Soil samples collected <br /> from 15 feet bgs to the total boring depth of 21.5 feet bgs increased in silt and clay content with <br /> lw <br /> ` DF100101.S1CPHS.ARSC.062000 3 <br />