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• • • Draft Supplemental Environmental Impact Report Page IV.G-8 • Forward Inc. Landfill 2018 Expansion Project Since before the early 1960s, the San Joaquin hydrologic basin has experienced overdraft as a result of heavy pumping. In the Central San Joaquin Irrigation District, which encompasses Forward Landfill, water levels have dropped approximately 70 feet in the past 40 years. Beyond • the trend of historical over-drafting (removing more groundwater than is naturally recharged) • from the aquifer, the San Joaquin Valley's groundwater basins have the tendency for water levels to show seasonally variations. Seasonal fluctuations reflect the rainy and dry seasons. Rainy season infiltration raises the water table, and dry season pumping lowers the water table. Seasonal fluctuations in the project area are on the order of 5 to 10 feet due to a distinct rainy • season and dry season. During the rainy season infiltration raises the water table and during the • dry season drawdown by water well users lowers the water table. The declining water levels throughout the Stockton area have induced the eastward movement of poor-quality water from the delta sediments. Migration of these saline waters had already impacted the utility of • groundwater as far east as Stockton at the time of a 1981 study by the U.S. Geological Survey • (USGS) (SJCFCWCD, 1990). The San Joaquin County Flood Control and Water Conservation District has documented a decline in water quality for the Stockton area due to a general increase in chlorides. The regional water quality in the area around Forward Landfill meets the State's Drinking Water Standard. The water is a calcium-magnesium/bicarbonate water type, with TDS concentrations under 500 mg/1. Groundwater Uses and SUUI)ly The designated beneficial use of the groundwater in the landfill area, as specified in the Basin Plan, are domestic and municipal supply, agricultural supply, industrial service supply, and industrial process supply. Groundwater wells in the area are used primarily to supply water for agricultural and domestic purposes. 0 Groundwater within 1 mile of the project site is pumped by several existing irrigation and 0 domestic wells and the most recent sampling at the domestic wells show exceedance of the 0 drinking water standards. 0 Water supply (non-potable) to the landfill is provided by three onsite wells. The water is used 0 for dust control, compaction, and irrigation. One well, located near the main entrance facility for 0 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 0 approximately eight times per hour. Another well is located south of the South Branch of South Littlejohn Creek, and has a capacity of 500 gpm.The third well is located along the northern • 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. i These wells are unaffected by the proposed changes. 0 • Site H,1 drog_eoloa 0 The local geology consists of unconsolidated stream channel deposits (younger alluvium) 0 comprised of clay, silt, sands, and gravels that extend from the ground surface up to 100 feet lie0 is 0