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07 August 1998 AGE-NC Project No. 97-0327 Page 2 of 5 Xylenes were detected at 0.026 parts per million(ppm)in a single sample collected from a depth of 27 feet bsg; MtBE was detected at concentrations of 0.13 ppm and 0.28 ppm in samples collected from depths of 23 feet bsg and 27 feet bsg, respectively. A summary of the investigation was included in AGE's Preliminary Site Assessment Report - May 1997 dated 06 .lune 1997. 2.3. UNDERGROUND STORAGE TANK REMOVAL It is our understanding that one waste oil underground storage tank (USTs) was removed from the site in April 1996. One soil sample was submitted to a state-certified laboratory for analysis and detected only residual petroleum hydrocarbons. On 27 July 1998, one 10,000-gallon UST and two 6,000-gallon USTs were removed from the site. Soil samples collected from beneath the USTs were submitted to a state certified laboratory for analysis of TPH-g, TPH-d, BTE&X, total lead and oxygenating compounds including MtBE, di- isopropyl ether (DIPS), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME) and tert-butanol (TBA). Laboratory analysis reported that TPH-g was detected in soil samples collected beneath all three USTs at concentrations as high as 3,000 ppm; TPH-d was detected as high as 1,000 ppm; BTE&X as high as 290 ppm; MtBE as high as 0.80 ppm; TBA as high as 0.420 ppm; and total lead as high as 19 ppm. Beneath the former product piping area, TPH-g was detected at concentrations as high as 110 ppm; TPH-d was detected at concentrations as high as 2,000 ppm; BTE&X as high as 2.8 ppni; MtBE as high as 0.0065 ppm; TBA as high as 0.028 ppm; and total lead as high as 12 ppm. Analytical results from UST removal activities are summarized in Table 1. 2.4. REGIONAL GEOLOGIC SETTING According to the Geologic Hap of California, published in 1977 by the State of California Department of Mines and Geology, the site area is within the Great Valley Geomorphic Province of California, a large, elongate, northwest trending structural trough. The Great Valley 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 ill the south to the Klamath Mountains in the north. The western and eastern boundaries of tills province are comprised of the California Coast Range and the Sierra Nevada, respectively. The Great Valley Province is subdivided into two maior divisions designated the Sacramento and San Joaquin Valleys. Based on the General Soil Map from the San Joaquin County Soil Survey, published by the United Advanced GeoEnvironmental,Inc.