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S E c o R Cumulative groundwater extracted 744,200 (GWE), 99,340 (Batch Extraction) Approximate Depth to Groundwater 31 49—37 01 ft� � � � y Groundwater Flow and Gradient Shallow— Radially Inward toward wells EW-1 and EW-7 Deep— Northeast @ 0 004 ft/ft DISCUSSION Total petroleum hydrocarbons as gasoline (TPHg) were reported in two of the 21 wells sampled this quarter at concentrations of 330 ppb (MW-3) and 3,100 ppb (MW-4) Benzene was reported in four of the 21 wells at concentrations of 2 0 ppb (MW-3), 19 ppb (MW-4), 98 ppb (EW-6), and 160 ppb (EW-1) Ten wells (MW-1, MW-2, MW-6, and EW-1 through EW-7) reported elevated detection limits for TPHg, while seven wells (MW-1, MW-2, MW-6, EW-2 through EW-5, EW-7) reported elevated detection limits for benzene Methyl tert-butyl ether (MtBE), which is analyzed using EPA Method 8260B, was reported in 16 of the 21 wells at concentrations ranging from 0 93 ppb (DMW-3) to 40,000 ppb (EW-4) 1,2-Dlchloroethane (1,2- DCA) was reported In seven of the wells at concentrations ranging from 0 56 ppb (DMW-2) to 100 ppb (MW-1) Groundwater flow within the shallow water-bearing zone was radially Inward toward extraction wells EW-1 and EW-7 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 third quarter 2004 are also consistent with historical data Chemical concentrations beneath and in the vicinity of the ARCO site were generally consistent with historical data, with the exception of MtBE in well EW-6, which was reported at a historical maximum concentration of 4,700 ppb Decreases in concentrations of petroleum hydrocarbons, MtBE and/or TBA continue to be observed in several of the site wells as a result of remedial system operation and ongoing groundwater batch extraction activities Groundwater extraction (GWE), soil vapor extraction (SVE), and weekly batch extraction of offsite wells continues at the site Off-site well EW-7 was connected to the GWEISVE system in June 2004 Remediation at the site will be expanded to Include the installation of an off-site ozone sparging system on the adjacent Taco Bell property Access to the property was recently obtained, and permits for the Installation of off-site ozone sparge wells were submitted during the third quarter 2004 SECOR will submit a permit for the Installation of the ozone sparge system during the fourth quarter 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 Solutions (TRC), which includes groundwater elevations and analytical data collected during the third quarter 2004 joint monitoring and sampling event 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 • 1 WRC0149321Q1V1Rs1200413Q1V1R04 doc ti