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ATTACHMENT D:MAP AND CROSS SECTIONS OF USDWS east(City of Lodi,2006).As a result, groundwater in the vicinity of the STIG-LEC facility flows generally from west to east (Figure D-5). The higher groundwater use to the east of the STIG-LEC facility is evident by the higher number of wells to the east of 1-5,as shown in Figure D-6. Groundwater elevations in the vicinity of the STIG-LEC facility project site fluctuate seasonally and in response to annual precipitation variation(City of Lodi,2006). Groundwater fluctuations are lower to the west of the LEC project site because the Delta is subject to less groundwater pumping and provides more uniform recharge throughout the year.Groundwater elevations at production wells in the vicinity of the LEC project site typically fluctuate by up to approximately 10 feet annually (City of Lodi,2006) and are also affected by local groundwater pumping(see Figure D-4). Figure D-6 shows the identified wells within the 2 mile AOR of the STIG-LEC project site. The primary uses of groundwater in the area are for agricultural and domestic supply. Source of groundwater recharge in the vicinity of the STIG-LEC facility,in addition to precipitation, include irrigation of Delta lands and seepage from related Delta waterways to the west, surface-water-irrigated lands to the north and east,percolation from WPCF storage ponds, and recharge from WPCF land application areas (City of Lodi,2006). Potable Aquifers The Tertiary and Quaternary deposits that comprise the local potable aquifers are,from oldest to youngest, the Valley Springs,Mehrten,Laguna,Turlock Lake (formerly referred to as the Victor Formation),Riverbank, and Modesto formations. These alluvial and fluvial sediments were associated with tectonic uplift of the Sierra Nevada and were deposited into the subsiding structural trough of the Central Valley. Saline water occurs within the Late Cretaceous to Eocene sediments and rock (City of Lodi, 2006). Regionally or locally extensive confining layers do not occur between or within these units in the STIG-LEC facility, and consequently, these aquifers are unconfined. Figure D-7 shows a cross-section of the potable aquifers in the Stockton area. Several groundwater investigations have occurred near the White Slough WPCF to assess the impacts of the facility's percolation ponds on underlying shallow groundwater (City of Lodi,2006). A network of 22 monitoring wells has been installed to support this investigation. Two groundwater investigations are also occurring at the Highway 12/1-5 commercial area,referred to informally as Flag City. Groundwater levels near the facilities occur at depths that are less than 10 feet bgs. Underground Sources of Drinking Water USDW are defined (40 CFR 144.3) as any aquifer capable of supplying a public water system with water of less than 10,000 milligrams per liter (mg/L) total dissolved solids (TDS). Local studies evaluating the USDW underlying the STIG-LEC facility were not identified. However,two studies assessing the base of the fresh water aquifer, defined as water having a TDS value of 3,000 mg/L or less,have been conducted for the area. This information is presented here because it is the general depth targeted for well plug installation during SACI3713221082550018(ATTACHMENT-D.DOC) D-3