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17 November 1997 AGE-NC Project No. 95-0152 Page 2 of 5 toluene, ethyl benzene and xylene: BTE&X) and total lead. TPH-g and BTE&X were present in soil samples collected from beneath the former gasoline UST;no petroleum hydrocarbons were detected beneath the diesel UST. On 21 September 1995, approximately 40 cubic yards of hydrocarbon-impacted soil was excavated from the former gasoline UST area. Soil samples were collected from the sidewalls and floor of the excavation. Laboratory analysis of the soil samples detected TPH-g at concentrations ranging from 770 ppm (floor of excavation)to 3,500 ppm(west wall of excavation). Toluene, ethyl benzene and xylenes were detected in soil samples at concentrations up to 360 ppm. Benzene was not detected in any of the excavation soil samples. 2.3. PRELIMINARY SITE ASSESSMENT On 13 and 14 December 1995, four soil probings (P1 through P4) were advanced near the former UST area to maximum depths of 40 feet below site grade (bsg). A total of ten soil samples from probe borings P1 through P4 were submitted for analysis. Toluene was detected from P1 at depths of 15 feet bsg and 40 feet bsg at concentrations up to 0.013 ppm (parts per million). Ethyl benzene and xylenes were detected from PI at 15 feet bsg at concentrations up to 0.039 ppm. Logs of probe borings P1 through P4 are attached. 2.4. REGIONAL GEOLOGIC SETTING According to the Geologic Map 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 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. The Great Valley Province is subdivided into two major 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 States Department of Agriculture Soil Conservation Service in 1992, the site area is within the Tokay-Acampo (TA) association. The TA soils are located on low terraces near the Mokelumne River, and generally consist of well drained coarse textured soils that derived from granitic rock sources. Advanced GeoEnrironmental,Inc.