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! q Additional Assessment Report 6 • Chevron USA Products Company 2405 Airport Way, Stockton California September 23, 1994 4 0 RESULTS OF ADDITIONAL ASSESSMENT 41 Hydrogeology The site is located in the northern part of the San Joaquin Valley at an elevation of approximately 18 feet above sea level The valley fill consists of late Mesozoic through Eocene marine deposits overlain by late Tertiary and Quaternary non-marine deposits which usually contain fresh water In the Stockton area, late Cenozoic deposits are approximately 3,000 feet thick and generally consist of alluvial gravel, sand, sift, and clay Groundwater in these alluvial deposits is unconfined to semiconfined The materials logged to a depth of 65 feet during drilling at the site are interbedded clayey silts and silty clays with lenses of sand Groundwater was encountered during drilling of MW-5 at a depth of approximately 59 feet BGS, and was measured at 54 29 feet below top of casing (54 55 feet BGS) on August 22, 1994 Groundwater flow on July 8, 1994 was estimated to be to the northeast at a gradient of 0 001 (Figure 3) On July 22, 1994 the flow was toward the center of the site at a gradient of 0 002 (Figure 4) • 42 Results of Soil Sample Analyses Results of all soil sample analyses from MW-5 are summarized in Table 2 No BTEX or TPH-G was detected in any of the analyzed soil samples Copies of the laboratory analyses reports and chain-of- custody manifests are included in Appendix E 42 Results of Groundwater Sample Analyses Results of groundwater samples collected on July 8, and August 22, 1994 are summarized in Table 3 No dissolved BTEX or TPH-G was detected in any of the groundwater monitoring wells sampled Copies of the laboratory analytical reports and chain-of-custody manifests are included in Appendix E • 5038suM RPT C� GROLIND"IATE;R TECHNOLOGY