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19 October 1998 AGE-ITC Project No. 97-0439 Page 2 of 4 2.3. SITE ASSESSMENT On 20 and 23 December 1996, four soil probe borings were advanced at the site by The Twining Laboratory Inc. (Twining). Three soil borings were established vertically (SP-1, SP-IA and SP-2), while one additional soil probe boring (SP-3) was established at 30-degree angle from vertical and projected under the structure on the site. - Soil samples were collected continuously from the probe borings. Soil samples from specific depths were analyzed for TPH-d and BTEX with methyl tertiary butyl ether(MTBE) in accordance with EPA Methods 8015m and 8020, respectively (Table 1). Additionally, a grab water sample was collected from a depth of 48 feet bsg from probe boring SP- IA. The grab water sample was analyzed for TPH-d and BTEX with MTBE in accordance with EPA Methods 8015 and 8020, respectively. Soil analysis indicated that limited soil contamination was present in the southern portion of the UST area. TPH-d was detected in the probe samples at concentrations up to 4,100 parts per million: ppm. The greatest depth for the detection of TPH-d was 16 feet bsg in sample SP-1 A at a concentration 11 ppm. Samples collected from depths of 20 and 26 feet bsg did not have detectable concentrations of TPH-d. Ground water beneath the site has contained low concentrations of TPH-d, toluene and xylene. The analytical results of the soil samples are summarized on Table 1. The lateral extent of the - hydrocarbon-impacted soil is depicted on Figure 2. The vertical distribution of impacted soil is depicted in Figure 3. Analytical data for the UST removal and site assessment are included in Appendix A. An estimated 32 cubic yards of TPH-d impacted soil remain at the site (Appendix B). However, apparently twenty feet of clean soil lies between the Iowest depth of detectable TPH-d impacted soil and the water level at the time of the sampling. Ground water has risen to a level that is still below the depth of TPH-d impacted soil. Approximately, 20 to 25 feet of non-hydrocarbon impacted soils remain above the estimated static ground water level at the site. 2.4. REGIONAL GEOLOGIC SETTING The site is located in the central portion of the Great Valley geomorphic province of California. The - valley is a nearly flat,elongate trough trending northwest and southeast for approximately 450 miles. The valley is enclosed by the granitic Sierra Nevada on the east and the sedimentary and — Advanced GeoEnvironmental,Inc.