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Revised Work Plan For Soil and Groundwater Assessment 3 Ranch Market 23569 South Santa Fe Road Riverbank California April 25,2000 UST Removal and Confirmation Soil Sampling On May 20, 1991, the following underground storage tanks (UST)were removed from a common tank pit: #1 1,000-gallon premium-leaded gasoline tank; 92 1,000-gallon regular-leaded gasoline tank; and #3 500-gallon unleaded gasoline tank. The approximate location of the former tank pit is shown on Figure 2. Strong hydrocarbon odors and discolored soil was observed by SJCEHD in the tank pit following removal of the tanks. Following UST removal, a total of six soil samples were collected from the tank pit floor at depths ranging from 9.5 to 11 feet below grade surface(bgs). As shown on Table 1 in Attachment 3, the six samples were analyzed for benzene,toluene, ethylbenzene and xylenes (BTEX) and total petroleum hydrocarbons-as-gasoline (TPHg) using U. S. Environmental Protection Agency(EPA) method 8020/8015 modified, ethylene dibromide (EDB), and total lead using EPA method 7420. All six samples contained reportable concentrations of TPHg (Table 1). No reportable concentrations of EDB or total lead were detected. Soil Assessment In January 1998 soil boring B-1 was advanced into the former tank pit to a depth of 30 feet bgs. Analyses of soil samples collected at depths of 20, 25, and 30 feet bgs show a decline in TPHg concentrations from a high of 4,140 mg/kg at 20 feet to 6 mg/kg at 30 feet(Table 1). The sample collected at 20 feet bgs was also analyzed for and did not contain reportable concentrations of tertiary butanol(TBA), methyl-tert butyl ether(MtBE), di-isopropyl ether (RIPE), ethyl-tertiary-butyl ether(ETBE), and tertiary-amyl-methyl ether(TAME). In November 1998, three groundwater monitoring wells were installed at the Site: MW-1 in the former tank pit and MW-2, MW-3, and MW-4 center around the former tank pit(Figure 2). Samples collected from MW-2, MW-3, and MW-4 at depths of 15, 20, 31, and 35 bgs were analyzed for BTEX and TPHg and the samples collected at 20 feet bgs were analyzed for MtBE, TBA, DIPE, ETBE, and TAME using EPA method 8260. Maximum concentration of TPHg were reported in sample collected be 20 and 30 feet bgs (Table 1). MtBE was reported samples MW-2 at 20 feet at 0.27 mg/kg and in MW-4 at 30 feet at 0.0079 mg/kg. Fik"-GeoPrabr&Wdliul.W