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i PROBU M ASSESSMENT REPORT 1605 SOplrh El Dorado Str"t Stockton California 3.0 INVESTIGATION RESULTS I 3 1 Soil Boring and Sampling I Soil borings MW-4 through MW-6 were drilled to 60 feet bs, boring MW-7 to 55 feet g 9 bs, VEW-1 to 15 feet bs, and VEW-2 to 45 feet bs at the locations shown on ' Figure 2 Soil borings MW-4 through MW-7 were completed as 4-inch-diameter groundwater monitoring wells, and VEW-1 and VEW-2 were completed as 4-inch- diameter vapor extraction wells Wells MW-6 and MW-7 were drilled off site, upgradient and downgradient, respectively The borings were drilled with 10 25-Inch hollow-stem augers by Woodward Drilling Company of Rio Vista, California, under the I direction of an Aegis geologist During drilling, subsurface sods were logged in the field using split-spoon samples collected at 5-foot intervals and significant lithology changes The samples were inspected in the field for evidence of petroleum hydrocarbons by sight, odor, and with a portable photoionization detector (PID) Soil boring logs are included as Appendix C Figure 2 shows cross-section location A-A'(Figure 4) The generalized cross-section included as Figure 4 indicates the sods beneath the site consist mostly of silty clay and clayey silts, with a relatively continuous, 5- to 10-foot thick silty to clayey sand layer extending from approximately 25-30 to 35 feet bs Some silty sands were also noted below the water table 3 2 Analytical Results Soil A total of 14 soil samples were analyzed by Pace Inc of Novato, California, for concentrations of a) TPH, as gasoline, by GC/FID Method 5030), and b) BTEX by EPA Method 8240) The soil sample analytical results are summarized in Table 4 The laboratory report and chain-of-custody forms are included in Appendix D Detectable petroleum hydrocarbon concentrations were found only In soil samples collected between 10 5 and 35 5 bs in boring VEW-2, within the former UST basin (Table 4) 3_3 Well Installation, Development, and Surveym4 IFour-inch-diameter groundwater monitoring wells were installed in borings MW-4 through MW-7 and 4-inch-diameter vapor extraction wells were Installed in borings VEW-1 and VEW-2 (Figure 2) Groundwater monitoring and vapor extraction well construction details are included on the boring logs in Appendix C The wells were constructed according to the standards found in California Code of Regulations, Tale 23, Section 2647 and 2648, and the California Department of Water Resources Bulletin 74-81 91 044A PAR 6