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In August 2004,the County collected two bulk samples, at the locations shown on Plate 9. Soil was being excavated from this area for use as daily cover material at Module 1. The samples were collected at a depth of approximately 15 feet below original grade in a cut-slope where the landfill was being modified for placement of waste. The soil was a cemented silt/siltstone, gray brown, hard, moderately cemented, moderately weathered, moderately soft, and contained the characteristic black andesite detrital grains found in the Mehrten Formation. This unit extended to the base of the cut, indicating the unit was at least 10 feet in thickness at this location. The samples were collected to evaluate soil properties, which included, but was not limited to, hydraulic conductivity at 80, 85, and 90 percent compaction by ASTM method D5084 C. The samples produced hydraulic conductivities on the order of 10-4 cm/sec (Appendix G). 5.4.2.2. Groundwater Flow Recent groundwater data from the third quarter 2003 through second quarter 2004 monitoring events show the depth to groundwater was approximately 205 feet below ground surface (bgs) in MW-1, 255 feet bgs in MW-2R, and 270 feet bgs in MW-3. Well construction details are shown in Table 4. For a given monitoring event, groundwater elevations were approximately 49 feet above mean sea level (MSL) in the up-gradient well MW-1, 42 feet above MSL in down- gradient well MW-2R, and to 46 feet MSL in down-gradient well MW-3. Groundwater elevations fluctuated seasonally less than one foot. For each event the groundwater gradient direction was to the south-southwest with and average gradient of approximately 0.002 foot per foot. The first semester 2005 groundwater elevation contour map is shown on Plate 13. 5.4.2.3. Capillary Rise Capillary rise is dependent upon the pore size of the soil. Capillary rise is greatest in fine grained soils such as clay. Clays can have a capillary rise of 80 centimeters up to several meters. Coarser materials such as silts or sandy silts can have a capillary rise of up to a meter. Clean sands may have a capillary rise of only 20 to 50 centimeters. Currently, the static groundwater at the landfill varies from approximately 40 to 50 feet msl. Gravel and sand/sandstone are the predominant soil types at that elevation (Plate 11). The sandstone is described as weakly or moderately cemented so the pore size would be smaller than that of clean sand, but likely not as small as the pore size of clay. Foothill Sanitary Landfill Page 26 of 62 Public Works/Solid Waste JTD County of San Joaquin—Revised 10/6/05