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Draft Supplemental Environmental Impact Report Page IV.G-9 Forward Inc. Landfill 2018 Expansion Project project area are generally to the north, sometimes with a northeast component in response to pumping of agricultural and municipal wells east of Stockton. Figure IV.G-1 shows the most recent groundwater (elevation)contours,published in 2018,which illustrate the generally northward groundwater flow direction,with a local southeasterly gradient beneath the southern half of the Forward Unit,potentially associated with agricultural pumping on adjacent properties (GLA 2018a). The Water Quality Control Plan (Basin Plan)for the Sacramento River and San Joaquin River Basins indicate the site is located in the Duck-LittleJohns Hydrologic Area of the San Joaquin River Basin. The San Joaquin Hydrologic Basin is a major regional aquifer system and groundwater in the basin is used for industrial, domestic, and agricultural purposes. The first encountered groundwater in the site area ranges from about 60 to 80 feet bgs and the depths to water fluctuate by as much as 15 feet between wet and dry seasons. No regionally continuous fine-grained layers have been identified in the older alluvial formations and groundwater is largely unconfined. However, due to the fluvial depositional environment, laterally discontinuous layers of fine-grained soil are present and local areas of groundwater confinement are known to occur (DWR 2003; GLA 2017a, 2018a,2018b). The area surrounding the landfill is primarily agricultural and there are numerous supply wells and irrigation distribution tanks with piping networks to discharge pumped groundwater to the crops in the area. Most of the production wells are constructed to depths on the order of 500 feet or more and produce water from the Laguna Formation. Groundwater at the Forward Landfill is monitored by 50 groundwater monitoring wells,three domestic wells, and five piezometers. The monitoring wells are used to collect water level elevations as well as water quality data. In addition, the current Corrective Action Program (CAP)includes four active groundwater extraction wells. Data from these wells and piezometers indicate uppermost groundwater beneath the landfill occurs at depths that range from about 50 to 80 feet bgs in the younger alluvium and is unconfined. Groundwater gradient (the steepness of the slope of the groundwater flow)varies seasonally, being reflective of the weather cycles and pumping,with a steeper,north-trending gradient in dry years and a more gentle,northeast gradient in wet years. Data collected by GLA between 2003 and 2018 indicate that, groundwater generally flows to the north and northeasterly at a gradient between 0.001 and 0.003ft/ft. Locally, a southeast gradient has been noted in the southern area of the Original Forward Landfill beginning in May 2011 that is believed to result from adjacent agricultural pumping. Pump testing performed for extraction wells EW-1 and EW-2 at the Forward Landfill resulted in an estimated hydraulic conductivity of about 250 feet per day (ft/day)for the uppermost aquifer beneath the landfill (CDM, 1999). Assuming an effective porosity of 0.35,the groundwater flow rate is estimated to be about 0.7 to 2.1 ft/day. Depth to water measurements in shallow and deeper well pairs in the Evaluation Monitoring Program(EMP)wells for the Austin Road Unit(ARU)indicate there is no appreciable vertical hydraulic gradient below the Forward Landfill.