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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 2 transient and, following cessation of oxygen injection, the groundwater and aquifer lithologies would return to the initial pre-injection equilibrium state, i e , oxidation reaction products would tend to revert back to the unoxidized species present in the aquifer at equilibrium A carefully planned and executed oxygen injection field test, conducted on a very limited scale in lieu of bench scale testing, will provide data to (1) evaluate potential use of oxygen injection as a viable remedial approach, and (2) assess potential detrimental changes to groundwater chemistry from oxidation reactions and products as the injection events are completed A groundwater sampling and analysis program can monitor potential changes in groundwater chemistry due to injection of oxygen As such, the oxidation capacity of the groundwater would be evaluated based on analysis of those species most sensitive to changes in oxidation-reduction conditions, i e , multi-valent species, and which in higher oxidation states pose a health hazard or impact aquifer characteristics The specific methods for conducting and monitoring the limited field test program are described in the following sections BACKGROUND On July 17, 1998, three 10,000-gallon single-walled USTs were removed from the site The UST excavation was extended to the east, and two new 10,000-gallon double-walled steel USTs were installed (Figure 2) The new tanks were installed in a tank pit located east of the original UST locations One ten-inch diameter Schedule 40 PVC conductor casing was installed in the new UST pit between the new tanks for future installation of well MW-2 On September 29 and October 2, 1998, Fluor-Daniel GTI advanced six offsite (OSGP-1 through OSGP-6) and 11 onsite (GP-7 through GP-17) Geoprobe soil borings (Table 1) The offsite borings did not contain total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and total xylenes (BTEX), or methyl-tert-butyl ether (MtBE) in soil above laboratory reporting limits (Table 1), except for one detection of total xylenes in the shallow sample (4 foot below ground surface) in OSGP-2 (Table 1) The onsite borings reported benzene, TPHg, and MtBE at maximum concentrations of 12 5 milligrams per kilogram (mg/kg) (GP-17@20'), 42,900 mg/kg (GP-15@15'), and 234 mg/kg (GP-14@10'), respectively (Fluor Daniel GTI, 1998) TBA was detected at two samples at a concentration of 166 mg/kg (GP-14@10') and 23 4 mglkg (GP-17@15') On May 13 and 14, 1999, four groundwater monitoring wells (MW-1 through MW-4) were advanced to 51 feet below ground surface (bgs) Benzene, TPHg, and MtBE in soil were reported at maximum concentrations of 2 89 mg/kg (MW-3-15'), 429 mg/kg (MW-3-15'), and 1 95 mg/kg (MW-3-15', Method 8020), respectively (IT Corporation, 1999) (Table 1) 14117 Field Test Oxidation Capacity doc SECOR International Incorporated