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Atlantic Richfield C'nmpanv 4 Forster ARCO l 4413.205 N' Cenlei Street.Stuckton.CA Sep(cinha j.2000 • Benzene, cis-1, 2-dichloroethene, and trichloroethene (TCE) were reported in well MW-5 at concentrations of 2.75 ppb, 5.46 ppb and 20.2 ppb, respectively. Benzene, MtBE, cis- 1, 2-dichloroethene, and TCE were reported in groundwater samples from well MW-6 at concentrations of 1.87 ppb, 171 ppb, 17.6 ppb, and 3.28 ppb, respectively. Well MW-7 was non detect for all constituents analyzed. Groundwater analytical data is presented in Tables 2, 3, and 4 and is shown on Figure 2. Field and laboratory procedures are presented as Attachment E. Groundwater sampling parameters are included on the field sheets in Attachment G. All wells were surveyed relative to mean sea level by Tom Morrow Surveying a California licensed surveyor. Attachment H contains the surveyor's site plan showing the locations and elevations of the wells. Groundwater Flow Direction Depth to groundwater at the site ranged from 1 1.63 to 13.81 feet bgs Based on monitoring data collected on June 16, 2000, groundwater flow was to east with a gradient of 0.006 ft/ft (Figure 3), consistent with historical data. Stockpiled Soil Approximately 2 cubic yards of soil generated during the drilling of borings and installation of the wells was stockpiled onsite. One composite sample (4 sleeves to 1 sample) was collected from the stockpiled soil and analyzed for TPHg, BTEX, MtBE, and total lead. Soil was disposed of at Vasco Road Landfill in Livermore, California. Stockpiled soil analytical data is presented in Table 5. SUMMARY OF FINDINGS • Shallow groundwater was encountered within a silty sand to sand at depths of approximately 13 to 16 feet bgs in the four borings drilled. A lower permeability zone was encountered at depths of 33 to 43 feet bgs. A potential confining layer was encountered in deep boring B-1 at approximately 56 feet bgs to the bottom of the boring at 60 feet bgs. • TPHg was detected in soil sample B-1 @25' at a concentration of 47 9 tng/kg. MtBE was reported in soil sample B-I @ 16' at a concentration of 0.254 rnglkg. • TPHg, benzene, and MtBE were detected in all three groundwater "grab" samples collected from boring B-1. Concentrations of TPHg, benzene, and MtBE at 60 feet bgs were 663 ppb, 56.5 ppb, and 28.8 ppb, respectively. • Benzene, cis-1, 2-dichloroethene, and TCE were reported in groundwater samples from well MW-5 at concentrations of 2.75 ppb, 5.46 ppb, and 20.2 ppb, respectively. Benzene, MtBE, cis-1, 2- dichloroethene, and TCE were reported in groundwater samples from 1177.41258:,;30rwoll rnatall2.duc