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The depth to groundwater in the Riverbank Formation had been monitored in GT-1, GT-2, and GT-3 . on seven occasions prior to the current drilling phase (Table 1) These data were used to map the piezometric surface and determine the groundwater gradient and flow direction In all but one instance, flow appeared to be southward As described in section 3 3 1, a southward gradient was confirmed when GT-5 and GT-6 were drilled in August, 1996 However, the gradient of 0 011 ft/ft was more than twice as steep as previously calculated when only three wells were available for measurement, implying that groundwater flow is more rapid than was assumed Groundwater monitoring after GT-9 was drilled in October further complicates the interpretation of the groundwater flow direction (Figure 9) Although the southward gradient from GT-5 toward GT-3 is confirmed, the gradient does not continue in this direction from GT-3 to GT-9 The elevation of the piezometric surface in GT-9 is 0 04 R higher than would be expected if the southward gradient continued This is a small amount, but it forces the conclusion that the flow direction turns sharply from south to southwestward near the Gillies-Barbot property line, creating a narrow trough in the surface of the water table This probably indicates that water flow is deflected along a high-permeability axis within the Riverbank aquifer between GT-3 and GT-9 4.4 Soil Chemistry and Bacterial Activity In response to a request from PHS/E D, several soil samples were submitted for analysis of their ability to support natural biodegradation of the contaminants Samples were analyzed for bulk density, moisture content, Total Organic Carbon (TOC), nitrate, phosphate, potassium, Ph, and bacterial abundance Laboratory reports for these analyses are included in Appendix E The results are discussed briefly below As shown in Table 2, the samples that were analyzed for hydraulic conductivity were also analyzed for bulk density and moisture content, parameters that may be used in the future if a nsk assessment is performed Density ranges from 86 to 108 pounds per cubic foot Density is not related to gram size or moisture content Except for GT-4-45', (which was collected at the top of the saturated zone), all have sufficient moisture to sustain bacterial growth Two samples from the Modesto aquifer in GT4 were analyzed for TOC Both samples came from the lower part of the aquifer, where high diesel concentrations are present, and both samples yielded significant TOC values (Table 3) Samples from uncontaminated zones have TOC concentrations that range from less than 50 mg/kg to at least 170 mg/kg Two samples were submitted for analysis of the bacterial nutrients (nitrate, phosphate, and potassium) and Ph One sample was from the silt bed in the middle of the Modesto Formation (GT-8-30'), and one was from the upper part of the Riverbank Formation (GT-5-65') Nutrient concentrations in both samples are quite low, below what would be considered sufficient for healthy plant growth (Table 3) Both samples are slightly alkaline, with Ph values above 7 0 9