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r) } Atlantic Richfield Company • • 2 ARCO Station #595 6100 North Highway 99,Stockton CA February 15 2002 . 0 110 mg/kg to 6 47 mg/kg Tert-butyl alcohol (TBA), di-isopropyl ether(RIPE), Ethyl tert-butyl ether(EtBE), tert-amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and ethylene dibromide (EDB) were reported as nondetectable in the samples From June 1 to June 6, 2000, four groundwater monitoring wells (MW-1 through MW-4) and three soil borings (B--1, B-2, and B-3) were completed at the site by West Hazmat Drilling of Rancho Cordova, California, under the direction of SECOR staff Site assessment activities showed that petroleum hydrocarbons had impacted the soil and groundwater beneath the site From July 17 to July 24, 2001, three offsite groundwater monitoring wells (MW-5 through MW-7) and two soil borings (PSB-1 and PSB-2) were completed Groundwater monitoring wells MW-5, MW-6, and MW-7 were set at 70 feet below ground surface (bgs) and screened from 50 to 70 feet bgs Borings PSB-1 and PSB-2 were drilled to a total depth of 100 feet bgs, and backfilled with grout upon completion TPHg, BTEX, MtBE, and fuel oxygenates were reported as nondetectable in soil samples with the exception of trace detections of benzene, toluene, and xylenes in MW-5 at depths of 15, 25, and 55 feet bgs Depth discrete groundwater "grab" samples were collected from boring PSB-1 at depths of 75 and 90 feet bgs, and from PSB-2 at depths of 64, 75, and 95 feet bgs Dissolved • concentrations of MtBE and 1,2-DCA were reported in the grab water samples collected from PSB-1 at depths of 75 feet bgs and 90 feet bgs Grab water sample PSB-1 collected at 90 feet bgs contained 39 ppb MtBE and 10 ppb 1,2-DCA MtBE and 1,2-DCA were reported in PSB-2 at depths of 64 feet bgs and 95 feet bgs MtBE and 1,2-DCA concentrations in the sample collected at 95 feet bgs were 2 7 ppb and 4 2 ppb, respectively Additionally, the groundwater sample from PSB-2 at 95 feet bgs contained minor detections of toluene (1 0 ppb), ethyl-benzene (0 54 ppb), and xylenes (3 0 ppb) Groundwater samples were collected from wells MW-5 through MW-7 on August 1, 2001 MtBE was reported at concentrations of 2 6 ppb (MW-5) and 94 ppb (MW-7) 1,2-DCA was reported at concentrations of 3 2 ppb (MW-5) and 23 ppb (MW-7) All other analytes in the new wells were reported as nondetectable Quarterly groundwater monitoring is currently ongoing Since June 2000, groundwater flow direction is generally to the west and northwest Subsurface Conditions Soil encountered during drilling activities generally consisted of interbedded layers of sands, silts, and clays (Figure 3 and 4) The most prominent soil types beneath the site appear to be sandy silts and silty sands First groundwater was encountered at approximately 50 to 64 feet bgs Groundwater levels stabilized at approximately 60 feet bgs The groundwater encountered at the site appears to be unconfined • WPLAN595-2-15-2002