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Chevron Products Company . • Chevron Service Station #9.2033. 508 West Charter Way, Stockton, California January 18 2001 The most recent groundwater monitoring results for the site, from 2nd quarter 2000, reported groundwater levels approximately 18 to 19 feet bgs calculated to flow east to northeast under a hydraulic gradient of 0.005 feet/foot. ASSESSMENT ACTIVITIES AND FINDINGS' On August 30 and 31, 2000, SECOR supervised Precision Sampling (Precision) of Richmond, California as they advanced three soil borings. Soil boring SB -2 was drilled using hollow stem augers and sampled at 5 -foot intervals to 85 feet bgs. Cone penetration tests, SB-3/CPT-01 and SB-4/CPT-02, were monitored continuously for soil behavior and pore pressure to approximately 94 feet bgs. Boring logs and CP tests are included as Attachment A. Field and laboratory procedures are presented as Attachment B. Certified analytical reports and chain -of -custody documentation are presented as Attachment C. The findings of this assessment are summarized below: Subsurface Conditions. Review of the boring logs and CP profiles suggests silt mixtures with sand and/or clay to approximately 25 to 30 feet bgs. These strata were underlain by sand to approximately 30 to 40 feet bgs and another thick clay / silt stratum to approximately 45 feet bgs. Water bearing silty sand with some silt and clay interbedding was the encountered to approximately 50 feet bgs. This water bearing layer may not be laterally continuous. It was underlain by silt and clay to approximately 55 feet bgs, where a water bearing sand with some fine-grained interbeds were encountered to about 65 feet bgs. This was underlain by silt and clay to approximately 70 feet bgs. Relatively thin layers, 5 to 10 feet thick, of alternating fine grained materials and sands comprised the remaining strata to total depth of 95 feet bgs. Cross sections for strata encountered during this investigation and prior investigations are presented as Figures 2 and 3. Pore water pressure data in the two CP profiles suggest an upper water bearing zone approximately 20 to 30 -feet thick. Relatively equal pore pressure, i.e. 10 to 20 pounds per square (psi), was encountered in both SB-3/CPT-1 and SB- 4/CPT-2 suggesting minimal horizontal pressure differential between the two profiles. CP data suggest a second groundwater zone in both test profiles from approximately 55- to 60 -feet bgs. Relatively thin sandy layers 3- to 5 -feet thick may constitute a tertiary water bearing zone at depth of approximately 78- to 88 -feet bgs. In soil boring SB -2 groundwater was encountered at approximately 45 -feet bgs and appeared to stabilize at 20 feet bgs. 077.41991.0181:\Chevron\92033\REPORTS\92033 PhaselISA RevA.doc