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i S ECOR Groundwater Flow and Gradient Shallow- Northeast @ 0 006 ft/ft - -- -- --- -- -- - - - - - -- Deep_Northeast X004-ft/ft DISCUSSION: Total petroleum hydrocarbons as gasoline (TPHg) were reported in six of the 20 wells sampled this quarter at concentrations ranging from 220 ppb (MW-2) to 39,000 ppb (EW-4) Elevated detection limits for TPHg was reported in seven samples Benzene was reported in four of the 20 wells at concentrations of 0 51 ppb (DMW-2) and 2,200 ppb (DMW-2) Elevated detection limits for benzene was reported in seven samples Methyl tert-butyl ether (MtBE), analyzed using EPA Method 8260B, was reported in 15 of the 20 wells at concentrations ranging from 2 2 ppb (DMW-1) to 150,000 ppb (EW-7) 1,2-Dichloroethane (1,2-DCA) was reported in nine of the wells at concentrations ranging from 0 71 ppb (DMW-2) to 78 ppb(MW-4) Chemical concentrations were generally consistent with historical data Groundwater flow within the shallow water-bearing zone was to the northeast at an approximate gradient of 0 006 ft/ft Groundwater flow within the deeper water-bearing zone was to the northeast at an approximate gradient of 0 004 ft/ft The groundwater flow direction and hydraulic gradient reported for the shallow and deeper water-bearing zones during the first quarter 2004 are also consistent with historical data Groundwater extraction, soil vapor extraction and weekly batch extraction of offsite wells continues at the site Offsite groundwater extraction well EW-7 was connected to the extraction system in June 2004 A remedial performance summary of site remediation activities is included in Attachment A Field and laboratory procedures are included in Attachment B Certified laboratory analytical reports, chain-of-custody documentation, and field data sheets are included as Attachment C Groundwater monitoring and sampling was coordinated with activities performed at former 76 Service Station No 4409, located northeast of the site Attachment D contains a report prepared by TRC, which includes groundwater elevations and analytical data for groundwater monitoring wells at the former 76 Service Station site This report presents our understanding of existing conditions at the subject site The conclusions contained herein are based on the analytical results, and professional judgment in accordance with current standards of professional practice, no other warranty is expressed or implied SECOR assumes no responsibility for exploratory borings or data reported by other consultants or contractors ATTACHMENTS: • Table 1 --Groundwater Elevation and Analytical Data • Table 2-Fuel Oxygenates Analytical Data • Table 3-Groundwater Gradient Data • Table 4-Batch Extraction Removal Data • Figure 1 -Groundwater Elevation Contour Map-Shallow Water Bearing Zone • Figure 2-Groundwater Elevation Contour Map-Deep Water Bearing Zone • Figure 3-Groundwater Chemical Concentration Map • Figure 4-MtBE Isoconcentration Contour Map-Shallow Water Bearing Zone • Figure 5-MtBE Isoconcentration Contour Map-Deep Water Bearing Zone • Attachment A-Remedial System Performance Evaluation • Attachment B-Field and Laboratory Procedures • Attachment C-Certified Laboratory Analytical Report, Chain-of-Custody Documentation, and • Field Data Sheets (ARCO) • Attachment D-Groundwater Monitoring and Sampling Report for Former 76 Service Station No 4409 (TRC) 11ARC0149321Q1V1Rs1200412QMR04 doc