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Well Installation Report August 17,2001 ARCO Facility No. 5469 Stockton,California • Page 4 with three clean 2.0- by 6-inch stainless-steel sleeves, into undisturbed soil using a 140-pound slide hammer falling 30 inches (blow count). The lowermost intact sample was retained for analysis. The sample ends were covered with TeflonFM sheets and plastic caps and samples were placed in an ice-chilled cooler. Each sample was appropriately labeled and identified on a chain of custody form. Additional sleeves of soil collected at each sampling interval were field screened for volatile organic compounds using a photoionization detector(PID). The soil was also classified using the Unified Soil Classification System. Soil classifications, field screening results, blow counts, and other pertinent data are presented on the boring logs in Appendix B. The newly installed monitoring wells were developed on June 25, 2001 using a surge block and groundwater pumping. On June 28, 2001, Delta returned to the site to measure water levels and collect purge groundwater samples. Field data sheets from well development and groundwater sampling are presented in Appendix C. Monitoring wells MW-7 through MW-10 will be incorporated into the quarterly monitoring program. Morrow Surveying, Inc. of West Sacramento, a California licensed professional land surveyor, established tap-of-well-casing elevations for the newly installed wells in June 2001. Well casing • elevations were established to the nearest 0.01-foot, referenced to City of Stockton Benchmark 992, elevation 16.64 feet mean sea level. Site plans provided by Morrow Surveying Inc. in July 2000 and July 2001 are presented in Appendix D. Site Geology and Hydrogeology The soils encountered at the site from 0 to 60 feet bgs are primarily silt, with clayey silt, sandy silt, and thin, discontinuous lenses of silty sand. Fine to coarse grained sand was encountered from approximately 40 to 55 feet bgs at boring MW-10. Sand with interbedded silt was encountered in boring MW-10 from 60 to 73 feet bgs. Silt was encountered in boring MW-10 from 60 to 73 feet bgs, with silty sand present at 71 feet bgs. Cross section A to A' illustrates interpreted geologic relationships along the eastern portion of the site. The surface trace of cross section A to A' is shown on Figure 2. Depth to groundwater measurements in the monitoring wells have ranged from approximately 36.5 to 38.5 feet bgs since monitoring was initiated in June 2000. The groundwater flow direction at the site has consistently been calculated to be towards the southeast at a low gradient (0.002 ft/ft average gradient) during four previous monitoring events. A northeast groundwater flow direction at a low gradient (0.001 ft/ft average gradient) in the northern portion of the site was also observed at the time of the second and fourth quarter 2000 sampling events. Depth to water measurements for wells MW-1 through MW-10 were collected and used to construct a igroundwater elevation contour map (Figure 4). The groundwater flow direction at the site for C:1ARC0154691R8P0RTS15469Wcll Installation 0601.doc