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S E C O R 7-Eleven Store#14117 Field Test for Evaluation of Oxidation Capacity of Groundwater July 22, 2004 Page 3 On October 30, 2001, three groundwater monitoring wells (MW-5, MW-6, and MW-7) were advanced to 20 feet bgs TPHg, BTEX, and MtBE in soil were not detected above laboratory reporting limits, except for 0 006 mg/kg total xylenes (MW-7@20') (Table 1) Selected halocarbons also reported in the soil samples indicated possible dry cleaner plume contributions (IT Corporation, 1999) An active USA Gasoline (former Exxon) service station is located east of the site On August 14, 2003 SECOR oversaw the installation of one monitoring well (MW-8) and one soil boring (SB-1) (Figure 2) Soil samples collected from MW-8 indicated that the vertical limits of TPHg, benzene, and MtBE in soil have been defined south of the pump islands (Figure 2 and Table 1) The presence of benzene, TPHg, and MtBE in grab groundwater samples collected from MW-8 and SB-1 indicate that the vertical limit of dissolved hydrocarbons is not defined onsite south and east of the pump island (Table 2) On February 27, 2004 SECOR submitted the Additional Stte Assessment Report and Fate and Transport Model, which included the results of the August 2003 well installation and the results of Fate and Transport modeling using Flowpath 2 Historical groundwater flow direction data indicated a time-dependent variability in groundwater flow direction, which appeared to result in a net zero gradient over an extended period of time Four models were run with varying results Results of the first and second modeling runs were very similar and indicate that MtBE will mtgrate approximately 120 to 180 feet from the source area to the northeast Results of the third and fourth modeling runs represented a near- "flat" hydraulic gradient and indicated that the MtBE contamination would remain in the immediate vicinity of the UST area and concentrations will decrease with time due to dispersion and natural decay Overall, it was determined that it is difficult to accurately model the migration of contaminate plumes at this site because of the relatively flat groundwater table and the highly variable groundwater flow direction in the area OXYGEN INJECTION WELL INSTALLATION SECOR proposes the installation of one injection well that will be used to conduct oxygen injection (Figure 3) Oxygen injection is used to stimulate the biodegradation of gasoline- range petroleum hydrocarbons and oxygenates dissolved in groundwater Past studies on subsurface bacterial colonies (Site Conceptual Model, Shaw Group, June 20, 2002) indicate indigenous populations of bacteria are present in-situ at the site, and are capable of intrinsic biodegradation The injection well will be placed within five feet of MW-1 for use as an observation well within the radius of influence of oxygen injection Site Health and Safety As required by the Occupational Health and Safety Administration (OSHA) Standard "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910 120), and by California Occupational Health and Safety Administration (Cal-OSHA) "Hazardous Waste Operations and Emergency Response" guidelines (CCR Title 8, Section 5192), SECOR will prepare a Site-Specific Health and Safety Plan prior to the commencement of 14117 Field Test Oxidation Capacity doc SECOR international Incorporated