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• A layer of fine- to coarse-grained sand underlies the silt bed. In most borings, the sand becomes coarser grained downward. Rock fragments and various dark minerals are common in the sand, and the layer is generally medium to dark gray in color. Samples from this layer in GP-1, GP-2, and GP- 3 exhibited slight hydrocarbon odors. The sand bed is underlain by dense, massive, blue clay at a depth of 30.to 33 feet. This bed is somewhat plastic in consistency. No gasoline odors were detected in this bed. 5.2 Soil Analytical Results 5.2.1 Hydrocarbons Fourteen soil samples were analyzed by Sequoia Analytical using EPA methods 8015m for Total Purgeable Hydrocarbons (gasoline) and Methanol, 8020 for volatile aromatics (BTEX), and 8260 for gasoline oxygenates. The laboratory report is included in Appendix C and the results are summarized in Table 2. No contaminants were detected in the samples from either GP-4 or GP-5, and only very minor contamination was detected in the other borings. Hydrocarbons are rather randomly dispersed in the other borings: seven samples contained only one hydrocarbon, two samples contained two hydrocarbons, and only one sample (GP-2-15-16') contained more than two hydrocarbons. The . results are somewhat difficult to interpret, but the uniformly low concentrations of all analytes are several orders of magnitude less than the concentrations that were detected in the tank removal samples, and imply that the magnitude of soil contamination is much Iower than was expected_ Benzene and TPH concentrations were plotted on Figures 3 and 4 and contoured to illustrate the interpreted lateral and vertical extent of soil contamination. The data were also plotted on the site chap and contoured to illustrate the lateral extent in plan view in the depth range from 15 to approximately 20 feet (Figure 5). The cross sections show that TPH is primarily Iimited to the upper silty clay bed above a depth of 20 feet and that benzene extends to the base of the underlying sand bed directly beneath the UST cavity. Laterally, both TPH and benzene are limited to within a distance of 10-20 feet from the edges of the cavity. 5.2.2 Total Organic Carbon Sequoia also analyzed three samples for Total Organic Carbon. This analysis was performed in order to provide data regarding the availability of food sources for naturally occurring soil bacteria, as well as to provide data that may be used later if a health risk assessment is performed. Two of the samples were collected from the sand layer, and one was collected from the underlying clay bed. Neither of the sand samples contained organic carbon above the detection limit of 50 mg/kg (Appendix C). In the clay sample, the laboratory reported a concentration of 200 mg/kg 5 .