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PRELIMINARY REPORT AND TANK CLOSURE REPORT Tracy Boulevard Shell 3725 Tracy Boulevard,Tracy,California Delta Project No.40-89.012 Page 6 Depths to ground water were measured and recorded in the new monitoring wells on August 28, 1990. Ground water was observed between 9 and 11 feet below ground surface. Field measurements are presented in Table 2. The direction zf ground water now was calculated using the ground water table elevations and determined to be from the southwest to the northeast at a gradient of 0.001. A ground water table contour map for August 28, 1990,was generated and is presented in Figure 7. Hydraulic conductivity of the water-bearing materials was estimated by performing slug testa on the three monitoring,,wells(MSV-1,MW-2,and MW-3),and by grain size analysis of soil samples collected from soil boring SB-8 at depths of 16 and 20 feet within the water-bearing material. The slug test data were evaluated in accordance with methods presented in Bower and Rice, 1976. 'Che grain size data were analyzed using equations developed by Hazen(Freeze and Cherry, 1977,and Krumbein and Monk, 1943). Analysis of the I slug test data indicated hydraulic conductivity for the sandy to clayey silts,which were observed at the water table,average 23.2 feet per day(Table 3). soil samples were collected from soil boring 58-8 at depths of 16 and 20 feet. The soils were taken from below the water table and were classified as silty sand and sandy silt, respectively. The soils were sent to the laboratory for sieve analysis to determine grain size distribution(Appendix D). Grain size distribution was analyzed by equations developed by Hazen,and Krumbein and Monk to estimate hydraulic conductivity. lected at a depth of 16 feet averaged 5.2 feet per day, The k�draulic conductivity of the silty sands col T whereas,the sandy silt collected at a depth of 20 feet averaged 1.4 feet per day(Table 4). 3 3 Maniiorin Well Installation and Abandonment Three 4-inch-diameter monitoring wells were installed at the site (MW-1, MW-2, and MW-3) on September 15, 1989. Monitoring well locations are shown in Figures 2 and 3. The wells were constructed with Schedule 40 PVC riser pipe, 0.010 slot-size screen, #3 Monterey sand filter pack, and sealed with bentonite pellets and a cement bentonite grout. The three monitoring wells were screened from 7 to 22 feet below the surface. Construction details are presented in Appendix C -- — Monitoring w-elis MW-1, MW-2, and MW-3 were damaged beyond repair during station reconstruction -- activities in May and June 1990. Delta supervised the abandonment of these wells on July 5.1990. The well. casings,screens, filter packs,and annular seals were removed with the aid of a hollow-stem auger drill rig and a backhoe. The borehole was scaled by lowering a tremie tube to the bottom and pressure grouting to "" the surface with grout consisting of Portland cement and 5 percent bentonite.