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0 <br />4.4.2 Regional H dro eolo <br />9 Y 9 9Y <br />Regional hydrogeology is described in 1988 Geologic and Hydrogeologic Report (Appendix C). <br />4.4.3 Hydraulic Conductivity <br />Insitu hydraulic conductivity tests were performed at the landfill using slug tests in a groundwater <br />well and falling head testing in two permeameters. The estimated hydraulic conductivity in the <br />groundwater well ranged from 8.3x10-3 to 9.7 x10-3 cm/sec depending upon the assumed depth of <br />penetration of the groundwater well into the aquifer. Permeameter tests yielded hydraulic <br />conductivities ranging from 2x10-7 to 3x10' cm/sec. Laboratory hydraulic conductivity on <br />remolded samples ranged from 1x10-4 cm/sec (silty sand) to 2x10-8 cm/sec (very clayey fine <br />sand) (Appendix C). <br />4.4.4 Groundwater Flow <br />I* The first encountered groundwater at the site is approximately 145 to 157 feet below the native <br />ground surface. Groundwater elevations range from 30 feet below mean sea level (MSL) to <br />42 feet below MSL. Groundwater flow direction for the landfill is to the west-southwest (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 was less than five feet and the minimum difference in <br />depth between the proposed base of landfill excavations and the groundwater table is greater <br />than 90 feet (see Appendix C). <br />North County RC&SL Page 19 of 69 Public Works/Solid Waste <br />Joint Technical Document County of San Joaquin — February 10, 2010 <br />