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{ <br /> i <br /> Mr. Bob Fratto <br /> July 27. 1993 <br /> Page 4 <br /> SITE GEOLOGY., O OGY AND HYDROGEOLOGY <br /> Geology <br /> The lithology beneath the site generally consists of primarily silts and clays. Silty sands, <br /> clayey sands, and clean sands were encountered in thin beds in TWL TW2 and SB10. The <br /> sand layer thickens to the south as interpreted by a 10-foot thick sand layer in TW4 and <br /> 15-foot thick sand layer in TW3. Pebbles identified in the sands in TW3 may indicate the toe <br /> of a gravel bar in a former stream channel. Finer grained sediments, such as the silts and <br /> clays, were probably deposited as flood plain or shallow, low-energy stream deposits. Much <br /> of the fine grained sediments is fractured and riddled with root traces. Some sands are locally <br /> cemented. Figure 1 shows the location of two cross-section lines, A-A' and B-B'. The cross- <br /> sections illustrate simple geological interpretation of the subsurface based on borehole logs. <br /> The cross sections are shown on Figures 2 and 3, respectively. <br /> G <br /> Hydrogeology <br /> Groundwater was encountered ata approximately 76 to 78 feet below round surface during <br /> pp Y g g <br /> drilling. Water level measurements from TWI, TW2, and TW3 were used in estimating the } <br /> groundwater flow direction and the estimated hydraulic gradient. Data from TW4 was not I <br /> E; used because of the increased error induced by possible movement of the borehole off the <br /> j targeted 30 degrees. The estimated groundwater flow direction is to the southwest. The <br /> hydraulic gradient of 0.001 was calculated using estimated distances between wells. Figure 4 <br /> shows relative groundwater level elevations and estimated groundwater flow direction at the <br /> � site. i <br /> ANALYTICAL RESULTS 1 <br /> All laboratory results are attached as Appendix B. ' <br /> Soil Results <br /> COnly one soil sample contained detectable levels of hydrocarbon constituents analyzed for. <br /> Sample TW I-15-15.5 contained benzene at a level of 0.0071 milligrams per kilogram(mg/kg). <br /> Analytical results for soil samples are summarized in Table 2. <br /> t <br /> Groundwater Results <br /> iGroundwater collected from TW4 contained detectable levels of ethylbenzene (0.78 <br /> micrograms per liter (ug/l)), total xylenes (0.5 µg/1), and TPH as gasoline (66 pg/l)). <br /> fi L Groundwater collected from TW I, TW2, and TW3 did not contain any detectable levels of <br />` Brown and Caldwell <br /> �OriSLi:i r'.l5 7603\C'0RRFSPA7603-01.L-1 <br />