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M IT CORPORATION sample with the highest LEL reading was retained in a brass liner, capped and refrigerated for laboratory analyses. Soils were classified in accordance with the Unified Soil Classification System, presented on Plate I. Soils and LEL measurements taken during drilling are described and recorded in the borehole logs an Plates 2 through 12. 2.2 EARTH MATERIALS Earth materials encountered during the drilling phase of this investi- gation were alluvial deposits consisting of interlayered sands (SM and SP), silts (ML), and clays (CL). As is characteristic of alluvial depo. sits, the various soil types are laterally discontinuous. and individual lenses cannot be correlated between boreholes, as shown on cross-section A -A' (Figure 2.2). The location of cross-section A -A' is shown in Figure 2.3. 2.3 FIELD HYDROCARBON DETECTIONS Hydrocarbons were detected in several of the soil samples using the technique described in Attachment 1. In general, hydrocarbons were detected in the upper 20 feet in wells DH -1, MW -1, and MW -2, which are located near the three underground product tanks. In wells MW -6 and MW -7, hydrocarbons were detected at depths greater than 40 feet. Field hydrocarbon testing results are shown in Table 2.1. 2.4 VOLUME OF CONTAMINATED SOIL An estimate of the volume of contaminated soil was made from data derived from LEL readings at five-foot increments. The LEL readings are presented in Figures 2.4 through 2.12. If an LEL reading was detected, an assumption was made that the entire five-foot increment was contami- nated. A simple model of the estimated volume of contaminated soil is shown in Table 2.2. The model indicates that there is approximately 2,672 cubic yards of contaminated soil under the station, with the -__-_-_majority _of -this _material --at_a-depth-of-35- feet -or- greater- ---Three soil ---- - - -- ---- samples were analyzed in the laboratory for benzene, toluene, and xylene t�.