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't 3;S 26 April 2011 ;c l AGE-NC Project No. 95-0104 Page 2 of 12 i A UST Unauthorized Release (Leak)/Contamination Site Report (UAR) was filed by San Joaquin County Environmental Health Department (EHD) on 05 April 1988; petroleum impact was confirmed in soil samples collected beneath the UST in March 1988. The responsible party listed on the 1988 UAR is Melvin Marlowe. As a result, the EHD directed that a subsurface investigation be performed beneath the former UST area. A copy of the 3 1988 UAR report is included in Appendix B. 2.1. REGIONAL GEOLOGICIHYDROGEOLOGIC SETTING According to Geologic Map of California, published in 1977 by the State of California Department of Mines and Geology, the site area is!l�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�jto 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 derivedfrom 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 of the property is the Mokolumne River, located approximately 1/2-mile north of the site. R k Based on the United States Department of Agriculture ;IiNatural Resources Conservation Service's Web Soil Survey map, surface sediment at the site area is classified as urban land, Galt clay, Hollenbeck silty clay, and Vignolo silty clay loam. The Galt Series consists of moderately deep, moderately well drained soils that formed in fine textured alluvium from mixed but dominantly granitic rock sources; gait soils are on low terraces, basins, and basin rims. The Hollenbeck series consists of deep to,duripan, moderately well drained soils that formed in alluvium from mixed rock sources; Hollenbeck soils are on basin rims and interfan basins. The Vignolo series consists of moderately deep to hardpan, �l ,C Advanced GeoEnvironmental,Inc. I E ii