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r PHASE VII SUBSURFACE INVESTIGATION San Joaquin County Montgomery Ward Auto Service Center Public Health Services Department 5400 Pacific Avenue Stockton CA Site Code 2163 r 2.3.5 Phase V Investigation ' In February 1993, three borings (borings B-11, MW-1 and MW-2) were drilled on the Montgomery Ward site Two of the borings (borings MW-1 and MW-2) were converted into ground water monitoring wells MW-1 and MW-2 (see Figure 2) rThe analytical testing results of the soil samples obtained from borings drilled as part of this investigation show that TPH-G concentrations ranging from 6 9 to 3,110 ppm were encountered The highest concentrations of TPH-G were detected in samples collected from boring location MW-2 at depths ranging between 20 and 60 feet bgs (see Table 5) Elevated hydrocarbon concentrations also were detected in the samples collected from boring B-11 between 40 and 50 feet bgs TPH-G were detected only in one sample (MW-1 @ 45 feet) ' collected from boxing MW-1 BTEX were detected in many samples Several chlorinated hydrocarbons not associated with gasoline also were detected at selected sample locations, e g , tetrachloroethene (PCE), trichloroethane (TCE), and 1,1,1-trichloroethane (1,1,1-TCA) (see Table 5) The source of these chlorinated hydrocarbons is unknown (see EAI, 1993) 2.3.6 Phase VI Investigation In January 1995, four ground water monitoring wells (MW-3 through MW-6) were drilled, installed, and sampled (see Figure 2) TPH-G and BTEX were identified in borings MW-3 and MW-4 near the top of the water table, at depths ranging from 45 to 50 feet bgs (see Table 6) TPH-G ranged in concentration from 72 to 670 ppm and BTEX ranged in concentration from 0 0095 to 3 ppm Toluene at a concentration ranging from 0 0052 to 0 0062 ppm was identified in both borings No other TPH-G or BTEX were identified in soils obtained from borings MW-3 or MW-4 No TPH-G or BTEX were detected in any soil sample obtained from borings MW-5 or MW-6 with the exception of sample number MW-6 @ 49-50 5' which contained toluene at a concentration of 0 0052 ppm (see EAI, 1995B) 2.3.7 Ground Water Testing Results Table 7 contains the results of quarterly ground water sampling completed at the Montgomery Ward site between March 1993 (the first time ground water samples were collected from the I site) and December 1995 TPH-G, BTEX, and 1,2-dichloroethane (1,2-DCA) have been detected in all wells associated with the Montgomery Ward site 3.0 FIELD WORK � 7 7Y�771Ya riT]L7l+Y7T0 J.>L 11 l 1Jll t lJ1I t.11L'J On January 31, 1996, four drive point borings (hydropunches) (HP-1 through HP-4) were advanced at the Montgomery Ward site (see Figure 2) Prior to drilling, permits to drill and sample the hydropunches were obtained from the County (see Appendix A) At the time the hydropunches were advanced, the depth to ground water was approximately 50 feet bgs However, recoverable amounts of water did not enter the hydropunch water sample chamber until a depth of approximately 64 feet bgs was reached on each hydropunch Project No 1232 - 4 - ENVIRONMENTAL AUDIT, INC