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Draft Supplemental Environmental Impact Report Page IV.G-8 Forward Inc. Landfill 2018 Expansion Project Groundwater within 1 mile of the project site is pumped by several existing irrigation and domestic wells and the most recent sampling at the domestic wells show exceedance of the drinking water standards in some wells. Water supply (non-potable)to the landfill is provided by three onsite wells. The water is used for dust control, compaction, and irrigation. One well, located near the main entrance facility for the Forward Landfill, was drilled to a depth of approximately 135 feet and encounters groundwater at a depth of approximately 70 feet.The well was likely installed before the opening of the landfill, having been previously used for agricultural purposes. It is pumped at a rate of approximately 1,500 gallons per minute (gpm)at a maximum frequency of approximately eight times per hour. Another well is located south of the South Branch of South Littlejohns Creek, and has a capacity of 500 gpm. The third well is located along the northwestern boundary of the former Austin Road Landfill. This well was installed in 1972 and has a production of approximately 60 gpm. Bottled water is supplied for potable water at the landfill. These wells are unaffected by the proposed changes. Site Hydrogeology The local geology consists of unconsolidated stream channel deposits (younger alluvium) comprised of clay, silt, sands, and gravels that extend from the ground surface up to 100 feet below ground surface (bgs). Underlying the younger alluvium are older alluvial deposits (Victor Formation and the Laguna Formation)that consist of similar interbedded sandy silt, clayey silt and fine to medium-grained sand. Beginning at approximately 100 feet bgs, increasing coarse-grained sands and gravelly lenses have been noted in the boring logs for site monitoring wells. As stream channel deposits,these sedimentary units interfinger and are laterally discontinuous. The Victor Formation is underlain by the Laguna Formation of Plio- Pleistocene age (two million years ago). These older alluvial deposits thicken to about 650 feet in the Stockton area (DWR 2006). The main area of VOC groundwater plume impact from the combined landfill is associated with the northern section of the landfill in the area downgradient of what used to be the Austin landfill Unit,based on the unlined nature of that landfill unit and historical data of the late 1980s and early 1990's collected around the Austin Unit. These data showed significantly higher concentrations of such contaminants of concern (CDCs)primarily VOCs found associated with the downgradient(southern)Forward Unit. The deeper water bearing units north of the landfill are likely affected by inputs from both units (GLA 2017a,b,c; GRA 2018a). As the groundwater cleanup and monitoring are regulated for the Forward Landfill, the source of the contamination does not affect the evaluation of whether the proposed landfill expansion addressed in this EIR would contribute additional impacts to groundwater or require additional mitigation measures. In general, any incremental additional potential impact to groundwater from this relatively small expansion—compared with the overall landfill—would be small. Hydrogeologic conditions at the site are measured by a series of monitoring wells, as depicted on Figure IV.G-1. Historically high groundwater in the vicinity of the Landfill occurred in 1974 with groundwater being at an elevation of-2 to-5 feet amsl. As discussed in the regional hydrology, and confirmed in quarterly monitoring reports, groundwater flows in the northern