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i <br /> I <br /> Working to Restore Nature <br /> 5.0 SITE CONDITIONS <br /> 5`1 Site Geolaa <br /> Based on an extrapolation of a geological map prepared by Marchand and Atwater (1977), <br /> sediments beneath the site consist of Quaternary alluvial deposits of the Modesto <br /> Formation Specifically, sediments underlying the site from ground surface to approximately <br /> 66 feet bsg consist primarily of clayey silt with silty sand and fine- to coarse-grained sand <br /> lenses From 66 feet to approximately 78 feet bsg, the sediments consist predominantly of <br /> fine- to coarse-grained sand, with some layers of silt The interpreted subsurface conditions <br /> are shown on geologic cross-sections A-A', B-B', and C-C' (Plates 5 through 7) The traces <br /> of the geologic cross-sections are included on Plate 2 <br /> 5_2 Site Hydrogeolog� <br /> During drilling, groundwater was encountered at approximately 61 to 68 5 feet bsg in <br /> sediment consisting of sand under unconfined conditions From October 1991 to November <br /> 1993, static water levels have fluctuated from approximately 60 to 66 feet bsg The rise and <br /> fall of water in the wells during 1992 appears to be due to seasonal fluctuations Depth to <br /> water measurements are shown on Table 4 <br /> Using the groundwater elevations from January 1992 through November 1993, we evaluated <br /> the groundwater gradient and direction of groundwater flow The direction of groundwater <br /> flow has fluctuated from the northeast to southeast with a gradient ranging from 0 001 to <br /> 0 03 Plates 8 and 9 depict previous groundwater flow directions and gradients <br /> S30003-7 8 <br />