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t24 September 1999 ' AGE-NC Project No. 96-0232 Page 3 of 12 ' fuel oxygenated compounds. However, dissolved TPH-d was detected in the initial ground water samples collected from MW-5,MW-6A and MW-613 at concentrations ranging as high ' as 280µg/1;dissolved MTBE was detected in the initial ground water samples collected from MW-6A, MW-6B and MW-7 at concentrations as high as 14 µg/1. Analytical results are summarized in Tables 3 and 5. ' • Between July 1996 and June 1999, eight ground water monitoring and sampling events were performed at the site. TPH-g has been detected from ground water samples collected from ' MW-1 at concentrations ranging as high as 480 µg/1; TPH-d has been detected in samples collected from wells MW-1 through MW-7 at concentrations ranging as high as 1,500 µg/l. Ethylbenzene was detected in a sample collected from well MW-6B at a concentration of ' 0.51 µg/1. MTBE was detected in samples collected from wells MW-1 through MW-7 at concentrations ranging as high as 1,600µg/l. Analytical results are summarized in Table 5. • In February,April and June 1999, MTBE was detected in water samples collected from the ' Rocky's Restaurant domestic drinking water well at concentrations ranging as high as 14 µg/1. Analytical results are summarized in Table 5. 1 Additional background information prepared by AGE is summarized in Closure Summary Report (30 April 1997) and submitted to the PHS-EHD. ' 2.3. REGIONAL GEOLOGIC SETTING According to a Geologic Map of California, published in 1966 by the California Department of ' Conservation Division of Mines and Geology, the site area is within the Great Valley Syncline (GVS), a large, elongate, northwest trending structural trough. The GVS is subdivided into two major divisions designated the Sacramento and San Joaquin Valleys, which have been filled to the ' 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 western and eastern boundaries of this province are ' comprised of the California Coast Range and the Sierra Nevada, respectively. Based on a General Soil Map from the San Joaquin County Soil Survey, published by the United tStates Department of Agriculture Soil Conservation Service in 1992, the site area is within the Guard-Devries-Riblancho (GDR) association. The GDR soils are located within basin rims along ' the eastern edge of the Sacramento-San Joaquin Delta area, and generally consist of poorly drained, fine to coarse textured soils. The GDR soils generally formed in alluvium from mixed rock sources. The Modesto, Riverbank, Turlock Lake Formations and overlying recent alluvium are the principal Advanced GcoEnviron mental,Inc.