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• fining trend In TT-3, upward-fining orange sand is present from approximately 55 to 45 feet Unit 7--Unit 7 consists of several feet of sandy silt This unit is moderately consolidated and its color ranges through various shades of brown, indicating that it has undergone less extensive weathering and oxidation than the overlying sand of unit 6 Unit 8--Saturated, gray to orange-brown, very-coarse-grained, well-sorted sand underlies unit 7 at depths of 70 to 75 feet At the present time, this is the principal water-beanng zone at the site 4.2 Groundwater Gradient and Flow Direction The data in Table 1 were used to calculate the elevation of the piezometnc surface and determine the groundwater flow direction (Figure 6) The data indicate that the water table slopes eastward at a gradient of 0013 ft/ft This gradient is oriented perpendicular to the southward gradient reported by PHS/EHD prior to placement of the monitoring wells 4.3 Extent of Soil Contamination Twenty-five soil samples were analyzed for Total Petroleum Hydrocarbons as gasoline and diesel and for volatile aromatic hydrocarbons (BTEX and MTBE) (Table 2) Only one sample contained any of these contaminants at concentrations above the required reporting limits Concentrations of 170 mg/kg (parts per million) gasoline, 0 21 ppm toluene, 0 78 ppm ethylbenzene, and 7 1 ppm xylene were detected in boring TT-HP-1 at a depth of 25 feet The laboratory reported that diesel may be present but masked by gasoline, although it could not be detected above a concentration of 10 ppm No MTBE is present } The laboratory results can be used to outline an elliptical area of residual soil contamination(Figure 7) Gasoline and/or diesel is present at a depth of 25 feet (samples OE-1, OE-2, and TT-HP-1-25') Although sample TT-HP-1-30' was not analyzed, the low PID reading (I 6 ppm) from this sample implies that it is unlikely that the laboratory would have detected contamination above reporting limits, because none was detected in sample TT-HP-1-40', which had a PID reading of 58 ppm Therefore, we conclude that the zone of residual contammation is less than 5 feet thick We estimate that a maximum volume of 275 cubic yards of contaminated soil remains in place In the three samples collected from the contaminated zone, TPH concentrations range from 170 mg/kg (TT-HP-1-25') to 6,900 mg/kg (OE-2) The mean value of the three samples, although probably a poor approximation of the entire contaminated zone, is 3,376 mg/kg No benzene has been detected in any of the samples collected at this site, including those collected from the stockpiled soil 6