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1 <br /> events The results of the Weston assessment and monitoring are presented in <br /> Appendix A on Tables A-2 and A-3, and the sample locations are shown on Figure 3 <br /> 1 .4 Site Geology <br /> Based on soil boring logs from the additional assessment and previous <br /> investigations, the geology of the site consists of two sedimentary units The upper <br /> unit extends from the surface to approximately 10 to 15 feet below ground surface <br /> (bgs) and consists of clay and silty clay The lower unit extends from 10 feet bgs to <br /> approximately 25 feet bgs and consists of fine grained sand, silty sand, and sandy silt <br /> 1 .5 Site H dro eolo <br /> Y g 9Y <br /> The site is basically flat and at approximately 5 feet above mean sea level (msl) <br /> Surface water drains to the east Groundwater has been measured at approximately <br /> 10 to 12 feet bgs Groundwater elevations measured during the third quarter 1993 <br /> ' indicated that the groundwater gradient was 0 002 feet per foot (ft/ft) in the <br /> southwest direction This correlates to the groundwater flow direction (southwest and <br /> ' gradient (0 002 to 0 004 ft/ft) determined during the Kleinfelder assessment The <br /> May 3, 1991, Weston assessment reported groundwater gradients ranging from 0 0037 <br /> ft/ft to 0 0065 ft/ft and flow directions from nearly due west to southwest based on <br /> several three-point solutions within the seven well monitoring array Weston <br /> concluded that the groundwater potentiometric surface is not planar <br /> ' Quarterly monitoring conducted by Weston during the second and third <br /> quarters of 1992 and the first and second quarters of 1993 indicated a southwesterly <br /> ' groundwater flow direction for all quarters except the first quarter of 1993 An <br /> easterly flow direction was reported for this quarter The groundwater gradient and <br /> ' flow direction appear to be susceptible to seasonal fluctuations <br /> The regional groundwater is reported to flow towards the northwest Local <br /> pumping wells, recharge areas, or other artificial gradient influences may be the cause <br /> ' of local southwesterly flow direction <br /> The tidal fluctuations of the Stockton Deep Water Channel have a minor <br /> ' influence on the groundwater beneath the Stockton Service Center and appear to <br /> have no effect on the groundwater gradient or flow direction at the site <br /> 1 <br /> ' 931122 East Bay Municipal Utility Distract <br /> 40429500 asa 4 Stockton Svc Ctr -Site Assessment/Remedial Options <br />