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4.4.2 Regional Hydrogeology <br />Regional hydrogeology is described in 1988 Geologic and Hydrogeologic Report (Appendix C). <br />4.4.3 Hydraulic Conductivity <br />In situ hydraulic conductivity tests were performed at the landfill using slug tests in a groundwater <br />well and falling head testing in two permeameters. Based on these tests, the hydraulic <br />conductivity in the groundwater well is estimated to be between 8.3x10"3 and 9.7 x10"3 cm/sec, <br />depending upon the assumed depth of penetration of the groundwater well into the aquifer. <br />Permeameter tests yielded hydraulic conductivities ranging from 2x10-7 to 3x10-7 cm/sec. <br />Laboratory hydraulic conductivity on remolded samples ranged from 1x10 cm/sec (silty sand) to <br />2x10-$ cm/sec (very clayey fine sand) (Appendix C). <br />4.4.4 Groundwater Flow <br />IPThe first encountered groundwater at the site is approximately 145 to 160 feet below the native <br />ground surface. In 2014, Groundwater elevations range from 47 to 49 feet below mean sea level <br />(MSL). Groundwater flow direction is apparently affected by off-site water withdrawal east of the <br />landfill (Plate 14). <br />Typically, groundwater underlying the site occurs under unconfined conditions within gravelly or <br />silty sands. Groundwater elevation generally fluctuates six feet seasonally. <br />4.4.5 Capillary Rise <br />Title 27 of the CCR requires that landfill units are designed, constructed, and operated to ensure <br />that wastes will be placed a minimum of five feet above the highest anticipated elevation of <br />underlying groundwater. <br />The estimated capillary rise for the site is less than five feet and the minimum difference in depth <br />between the proposed base of landfill excavations and the groundwater table is greater than 90 <br />feet (see Appendix C). <br />North County RC&SL Page 19 of 68 Public Works/Solid Waste <br />Joint Technical Document County of San Joaquin — October 10, 2014 <br />