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Limited Groundwater Investigation 3 Sacramento Valley as stretching from Red Bluff to the north to approximately the Lodi area (the Sacramento-San Joaquin Delta), to the east by the Siena Nevada, and the Coast Ranges to the west. The San Joaquin Valley is bounded by the Delta on the north and the Coast Ranges and the Tehachapi Mountains to the south. The sites are located in the San Joaquin Valley. The facilities and surrounding areas are located within the San Joaquin Hydrologic Basin (DWR, Bulletin 118),which straddles the portions of both Sacramento and San Joaquin Valleys. Sediments of the San Joaquin Valley consist of interlayered gravel, sand, silt, and clay derived from the adjacent mountains and deposited in alluvial-fan, floodplain, flood-basin, lacustrine, and marsh environments. Hydrogeologic units in the San Joaquin Basin include both consolidated rocks and unconsolidated deposits. The consolidated rocks include the Victor Formation, the Laguna Formation, and the Mehrten Formation. The unconsolidated deposits include continental deposits, lacustrine and marsh deposits, older alluvium,younger alluvium, and flood-basin deposits. The continental deposits and older alluvium are the main water-yielding units in the unconsolidated deposits. Regional groundwater flow in this area has been reported to the north, northwest, and northeast (San Joaquin County Flood Control and Water Conservation District, 1999). 2.2 Local Geology and Hydrogeology Shallow soils encountered at the Lathrop facility in the upper 10 to 15 feet consist primarily of interbedded unconsolidated fine-grained sands (silty sand, clayey sand, and poorly graded sand). Trace thin layers (< 1-foot thick) of fine to medium-grained sands were observed at approximately 4.5 feet below grade level (bgl) at sampling location LP-G1. A sandy clay layer was observed in locations LP-G1 and LP-G3 at 11 and 9.6 feet bgl,respectively. Difficult drilling conditions were encountered between approximately 12 to 16 feet bgl at sample locations LP-G1 and LP-G2 due to a hard pan layer. The outer casing (EC-5) of the sampling unit was unable to be advanced through the hard pan layer,with refusal occurring at 15 feet bgl. As a result, soil samples were not collected below 15 feet bgl at sample location LP-G1. To facilitate sampling activities and to obtain a groundwater sample, soil samples were not collected below 10 feet bgl at the remaining four sampling locations (LP-G2 through LP-G5).At these locations, the inner rod (EC-2) of the sampling unit was advance ahead of the outer casing at approximately 10 feet bgl to the anticipated depth of first groundwater. On May 7, 2001, groundwater was encountered at approximately 21 feet bgl at the five sampling locations (LP-G1 through LP-G5) at the Lathrop facility. Static groundwater levels measured at each sample location ranged between 18.01 and 19.45 feet bgl. At the French Camp facility, soils within the upper 31 to 37 feet consist of interbedded unconsolidated fine-grained sands (silty sands, clayey sands, and/or poorly graded sands), silts, and sandy clay. On May 8, 2001, first groundwater was encountered at approximately 29 feet bgl at the five sampling locations (FC-Gl through FC-G5) advanced at the French Camp facility. Static groundwater levels measured at each sample location ranged between 26.58 and 28.80 feet bgl. The boring logs for these sample locations are presented in Appendix A. p:\Wp\jobs\20587\LP FCGN['.doc—DCN 102300 June 2001