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<br /> <br />Foothill Sanitary Landfill Page 14 of 52 San Joaquin County DPW - Solid Waste <br />Joint Technical Document Revised 12/04/2025 <br /> <br />Investigation groundwater levels were measured in three domestic wells located within a 1-mile <br />radius of the landfill. Groundwater elevations ranged from 64 to 110 feet MSL (Appendix D). <br /> <br />4.10.2. Site Hydrogeology <br />4.10.2.1. Hydraulic Conductivity <br />During the 1985 Geologic Investigation, six borings were advanced to depths ranging <br />from 70 to 100 feet in the central area of the site (Appendix D). Approximately two-thirds of the <br />soils encountered in the six borings consisted of moderately cemented clay/claystone and <br />cemented silt/siltstone with in-place hydraulic conductivities on the order of 10-6 to 10-7 cm/sec. <br />These same soils had remolded hydraulic conductivities as low as 10-9 cm/sec. The remaining <br />soils consisted of cemented silty sand/silty sandstone with in-place hydraulic conductivities on <br />the order of 10-3 cm/sec and remolded hydraulic conductivities between 10-4 to 10-5 cm/sec <br />(Appendix D). <br /> <br />During a Geologic Investigation (Kleinfelder 1990), seven soil borings (B-1 through B-7) <br />were advanced to depths ranging from 30 to 65 feet in the east, southeast, and southern areas <br />of the site. The soils encountered in the seven borings consisted of cemented clay/claystone, <br />cemented silt/siltstone, and cemented sand/sandstone with in-place hydraulic conductivities <br />ranging from 10-3 to 10-5 cm/sec. Remolded soils had hydraulic conductivities ranging from 10- <br />4 to 10-6 cm/sec. The results of the laboratory testing are tabulated in a report dated January 2, <br />1991 (Appendix E). <br /> <br />4.10.2.2. Groundwater <br />First encountered groundwater at the site varies from about 200 to 300 feet below <br />ground surface. Groundwater elevations generally range from about 36 feet MSL on the <br />southern side of the site to about 61 feet MSL on the northern side of the site +/- 1 foot of <br />seasonal variation. The average groundwater elevation at the site is about 45 feet MSL (2015 <br />WDR). Groundwater flow velocity is approximately 90 feet per year based on a hydraulic <br />gradient of 0.0027 foot per foot (Figure 12). <br /> <br />4.10.2.3. Surface Waters