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22 October 2009 AGE-NC Project No. 00-0697 Page 2 of 10 A UST Unauthorized Release(Leak)/Contamination Site Report(UAR)was fled by Harlin Knoll of the San Joaquin County Environmental Health Department(EHD)on 30 June 1988;as a result, the EHD directed that a subsurface investigation be performed beneath the UST area.A copy of the UAR is included in Appendix B. 2.1. REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING According to Geologic Map of California,published in 1977 by the State of California Department of Mines and Geology, the site area is located within the Great Valley Geomorphic Province of California.The Great Valley Province is a nearly flat,elongated structural trough trending northwest and southeast for approximately 450 miles;it is bounded on the east by the Sierra Nevada mountains and on the west by the Coast Ranges. The Province has been filled to its present elevation with thick sequences of sediment ranging in age from Jurassic to present day,creating a nearly flat-lying alluvial plain extending from the Tehachapi Mountains in the south to the Klamath Mountains in the north. The surficial and upper several hundred feet of subsurface layers consists of a great thickness of predominantly unconsolidated alluvial and flood plain deposits (primarily sands, silts, and clays) of Quaternary age, which are derived from the granitic mountains of the Sierra Nevada. Beneath the upper sedimentary deposits lies a thick sequence of marine deposits of Mesozoic age. These marine deposits are further underlain by a pre-Jurassic complex of igneous and metamorphic basement rock. The Province is subdivided into two major divisions,designated the Sacramento and San Joaquin Valleys. The San Joaquin Valley is drained primarily by the San Joaquin River, and the Modesto, Riverbank,and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22).The nearest surface water feature in the vicinity ofthe property is an irrigation drainage ditch,located approximately 120 feet south ofTerminous Market,and the Mokelumne River,located approximately 2,500 feet west of the site. Based on the United States Department of Agriculture-Natural Resources Conservation Service's Web Soil Survey map, surface sediment at the site area is classified as Kingile muck. The Kingile series consists of very deep,very poorly drained soils formed in highly decomposed organic material underlain by fine textured alluvium from mixed sources.The Kingile soils formed from hydrophytic plant remains and mixed mineral alluvium in fresh water marshes, deltas,and old river channels. Based on quarterly ground water monitoring events conducted at the site between November 2004 and October 2008,depth to ground water has ranged between 2.56 feet and 6.82 feet below the tops of the well casings(btoc).Between November 2004 and October 2008,ground water flow directions AAawced CeoEoviromextd,Inc.