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5.4.2 Regional Hydrogeology Regional hydrogeology is described in 1988 Geologic and Hydrogeologic Report found in Appendix D. 5.4.3 Hydraulic Conductivity Insitu hydraulic conductivity tests were performed at the landfill using slug tests in a groundwater well and falling head testing in two permeameters. The estimated hydraulic conductivity in the groundwater well ranged from 8.3E-3 to 9.7E-3 cm/sec depending upon the assumed depth of penetration of the groundwater well into the aquifer. Permeameter tests yielded hydraulic conductivities ranging from 2E-7 to 3E-7 cm/sec. Laboratory hydraulic conductivity on remolded samples ranged from 1E-4 cm/sec (silty sand) to 2E-8 cm/sec (very clayey fine sand). These data can be found in the report contained in Appendix D. 5.4.4 Groundwater Flow The first encountered groundwater at the site is approximately 145 to 157 feet below the native ground surface. Groundwater elevations range from —30 feet mean sea level (MSL) to --42 feet MSL. The most recent (April 2004) groundwater elevation contour map (Plate 12) for the landfill shows the groundwater flow direction is to the west-southwest with a hydraulic gradient of 0.00035 foot per foot. Typically, groundwater underlying the site occurs under unconfined conditions within gravelly or silty sands. Seasonal groundwater elevation generally fluctuates 6 feet. 5.4.5 Capillary Rise All landfill units are designed, constructed, and operated to ensure that wastes will be placed a minimum of five feet above the highest anticipated elevation of underlying groundwater. The estimated capillary rise for the site was less than 5 feet and the minimum difference in depth between the proposed base of landfill excavations and the groundwater table is greater than 90 feet(see Appendix D.) North County RC&SL Page 22 of 48 Public Works/Solid Waste JTD County of San Joaquin—November 30,2004