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The formations are generally overlain by residual soil or recent <br /> alluvial deposits except where exposed by the current landfill <br /> operations. <br /> 8 .2 SOILS <br /> Six exploratory borings were drilled and sampled for this <br /> investigation. The depth of the borings varied from 70 to 100 feet <br /> (see Plate II of Appendix E) . The borings confirmed the regional <br /> and site conditions outlined above. The soil boring locations are <br /> shown on Plate II of Appendix E. <br /> Laboratory tests were performed on selected samples from the soil <br /> borings including moisture content and dry density, gradation <br /> analysis, Atterberg limits, and permeability. The results of the <br /> tests are shown on Plate XII of Appendix E. <br /> 8.3 GROUNDWATER <br /> Most water in the eastern part of San Joaquin County is drawn from <br /> the Arroyo Seco, Laguna, and Mehrten Formations. The groundwater <br /> obtained from these formations is continually being recharged by <br /> percolation surface waters which originate in the Sierra Nevada or <br /> adjacent foothills. <br /> In addition to the existing well on-site, there are 5 wells within <br /> a one mile radius of the site (Figure 9) . Attempts were made to <br /> measure depth to water in all of these wells. However, it was not <br /> possible to measure the depth to water in most of the wells due to <br /> the necessary removal of equipment within the well casing. The <br /> most detailed data was obtained from the Hatler well. Depth to <br /> groundwater measurements have been made on this well continuously <br /> since 1959. Records indicate approximately a 13 foot drop from <br /> 1959 to 1985. <br /> Depth to groundwater in the monitoring wells ranges between 195' <br /> and 2501 . Groundwater level ranges between 55' and 61' above mean <br /> sea level (MSL) . The groundwater gradient is 0. 20 to the south- <br /> southwest. <br /> 9. 0 SURFACE AND SUBSURFACE DRAINAGE <br /> The drainage facilities are shown on drawing 2 of the Preliminary <br /> Closure Plan (Appendix A) . Surface runoff will drain to a <br /> perimeter ditch system which drains to several siltation/detention <br /> basins around the perimeter. Water will eventually flow off-site <br /> from the west or southeast discharge points. The water remaining <br /> in the detention basins will be kept until it evaporates or <br /> infiltrates. Run-on from adjacent areas is controlled by <br /> constructing perimeter berms to direct water away from active <br /> disposal areas. The design for the landfill's drainage is based on <br /> 25 <br />