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Appendix A Site Closure Request July 2,2010 Speedy Foods-Stockton Page 4 of 13 2.0 Site Geology and Hydrogeology 2.1 Regional Information The subject site is located in the southern portion of the Sacramento Basin, a part of the northern section of the Great Valley. The Great Valley consists of marine sediments deposited during the Cretaceous Period. These deposits are overlain by sands, silts, and gravels of the Tertiary Period, and Quaternary alluvium, derived from the Sierra Nevada. The Great Valley extends from Red Bluff in the north to the Transverse Ranges to the south. The topography of the area is relatively flat. The ground surface in the vicinity of the site generally slopes gently to the west. The elevation is approximately thirty-two feet above mean sea level (USGS 7.5 minute topographic quadrangle, Lodi South). The nearest surface water body is an unnamed ditch located approximately 30 feet south of the site. The Mokolumne Aqueduct is located approximately 2,000 feet west of the site and the Calaveras River is located 7,000 feet to the south. 2.2 Site Specific Information Soils encountered at the site consisted of primarily silt and clay, with some sand. The soil stratigraphy is dominated by silt and clay from the ground surface to approximately 30 feet bgs, with the exception of minor sand lenses at approximately 15 feet bgs. The interval between approximately 30 feet bgs and 43 feet bgs consists primarily of a laterally continuous layer of well graded silty-sand. This silty- sand unit was underlain by clay and silt to approximately 55 feet bgs. A water bearing sand unit was encountered from approximately 55 to 63 feet b s. Soil from approximately 63 feet bgs to 300 feet bgs consists primarily of clay and silt wt in several mor sand lenses. Groundwater elevation has been monitored onsite since October 1999. During this time, depth to water has fluctuated between approximately 56 and 76 feet bgs. Groundwater flow direction has varied on the site from north-northeast to east. However, the predominant direction of flow has been to the northeast. Groundwater gradient has ranged from 0.001 ft/ft to 0.01 ft/ft with the usual gradient approximately 0.003-0.008 ft/ft. 3.0 Sensitive Potential Receptors Ground Zero contacted the Department of Water Resources (DWR)to obtain information on any wells within 2,000 feet of the subject site. No log of the on-site water supply well was available from DWR. All wells for which a log was received from DWR were plotted on a street snap to give an indication of the spatial distribution of water supply wells within 2,000 feet of the site. A map showing the locations of wells, as determined from DWR well logs, is shown on Figure 2. A summary of well construction details for wells found dining the DWR review is presented in Table 1.