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f'� Draft Environmental Impact Report Page IVY-8 Forward Inc. Landfill Expansion along the northern boundary of the existing landfill. This well was installed in 1972 and has a production of approximately 60 gpm. The fact that groundwater flow near the existing Forward/Austin Landfill units is not modified by pumping from the landfill wells suggests that the well is drawing from a confined unit below the groundwater units that are monitored at the site. Bottled water is supplied for potable water at the landfill. Rl Site Hydrogeology Historically high groundwater in the vicinity of the Forward/Austin landfill occurred in 1974 with groundwater being at an elevation of-2 to-5 feet above msl. Considering the overdraft conditions within the San Joaquin basin since then those elevations are not likely to be attained again. The recommended bottom grade of the new landfill of 3 feet amsl (5 feet above the highest anticipated groundwater of-2 feet amsl) should be protective. Current elevations of groundwater across the section where the proposed landfill expansion would occur, based on the Q2-2008 elevations, are between-13 and-30 feet amsl. This translates to depth of about 47 to 64 feet below the ground surface. F, The sediments underlying the new expansion area are consistent with the regional geology, consisting of interlayered sand, silt, and clay with occasional beds of coarse sand and gravel. The interpretation of the hydrogeology in the various investigations completed since the 1989 Solid Waste Assessment Test (SWAT) investigation are consistent, and characterize the sediments as fluvial (river-borne) deposits (Kleinfelder, 1988;CDM, 1999a;JTD,2001;AEE, 2001b). Most of the northern exploratory bore data north of Austin Road Landfill was completed by the CDM study(1999a), HA, (2008a, 2008b). Figure IV.F-1 shows monitoring well locations and downgradient receptors. I F, The first major water-bearing unit beneath the landfill appears to be the intermediate interval of sand between approximately-40 and-80 feet msl. North of the landfill,the sand unit appears to thicken and is interbedded with silt beds (CDM, 1999a). The silt layers become thicker and more abundant north of ARL-1A where there appears to be three distinct sand units beneath- d 40 feet msl. The shallowest unit does not appear to be in direct hydraulic connection with the underlying intermediate sand unit in the immediate area because it pinches out between data points ARL-1C and MW-14 reported by CDM (1999a). This interpretation is supported by the absence of trichloroethene (TCE), tetrachloroethene (PCE),or other compounds detected in the sample from this unit(ARL-IA-GW-85). The only water quality data from the intermediate sand unit was collected from ARL-3A (sample ARL-3A-105). No organic compounds were detected in the one sample collected from the intermediate unit, though it is unclear if this is due to hydraulic isolation or distance from the source. The lowest unit has shown detectable TCE and PCE, suggesting it is in hydraulic connection with the upper unit. In May 2007 GeoLogic (2008a) collected geotechnical and hydrologic data form 15 exploratory bore placed on the main expansion area (the larger Brocchini parcel). The southwestern ore was completed as a monitoring well (MW-24)to provide future water quality data upgradient of the proposed landfill area. However, water quality data has not yet been collected at this well(D Litchfield, verbal communication, 2009). F �f i I r