ARCHIVED REPORTS_2003 FEASABILITY STUDY REPORT AND SITE ASSESSMENT WORK PLAN

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S E C O R r2003 Feasibility Study Report and Site Assessment Work Plan July 18, 2003 Page 6 Two soil samples were collected from the former pump island area. Groundwater was observed in the tank excavation at approximately 8 feet bgs. (PEG, 1995). • In May 1995, Pacific Environmental Group submitted a Problem Assessment Report, dated May 15, 1995 (PEG, 1995). The principal findings of the PAR are listed below: 1. The lateral and vertical extent of dissolved hydrocarbons in the lower water bearing zones was adequately defined. 2. Continued operation of the containment system, including the pumping of groundwater from the extraction wells maintained the shallow groundwater plume on site. 3. Continued SPH recovery and extraction of dissolved-phase hydrocarbons from three wells within the SPH plume on site reduced hydrocarbon mass in groundwater. • On March 25, 1996, a dual extraction system (DE) system began continuous operation. The DE system was comprised of 14 DE wells (MW-1, MW-2, MW-7, MW-8, MW-14, MW-15, MW-16, and DE-1 through DE-7), a water knockout tank, an oil/water separator, four granular activated carbon vessels arranged in series, and a thermal oxidizer. In May of 1997, site data suggested the onsite SPH plume had been substantially diminished by the DE system. In addition, groundwater influent concentrations of TPHd had declined from 69,000 micrograms per liter (,ug/L) to 5,300 and influent vapor concentrations had declined from 300 parts per million by volume (ppmv) to 21 ppmv (SECOR, 1997). The DE system was shut down in June of 1997. Temporary shutdown of the DE system was approved by Ms. Gail Wiggett of the RWQCB during a meeting on June 2, 1997. • From September of 2001 through April of 2002, SECOR conducted a six-month ISO-GEN TM pilot test/feasibility study for groundwater treatment. The pilot test included the installation of six four-inch test wells (TW-1 through TW-6) and nine two-inch ISO-GEN TM monitoring wells (MW-24A through MW-32A). The groundwater monitoring wells and ISO-GENTm remediation wells have screen intervals of approximately 15 to 30 feet bgs and 5 to 30 feet bgs, respectively. The ISO-GENTM treatment system appeared to have limited impact on the increase of dissolved oxygen (DO) concentrations and the reduction of methyl tertiary butyl ether (MtBE) concentrations. However, the ISO-GENTM system did reduce TPHd concentrations in well MW-26A and MtBE concentrations in wells MW-28A and MW-32A (SECOR, 2003e). The results of the ISO-GENTM Pilot Study indicated the following biological activity is occurring at the Banta Fuel Terminal: 1 Nitrate (NO3) and sulfate (SO4) are present throughout the site, with the exception of the area around MW-26A. Nitrates and sulfate in this area are depleted due to natural biodegradation. 2. Surface water infiltration from the agricultural drainage trench is high in nitrates and sulfates. This situation creates a biodegradation-barrier to contaminant migration. 3. The mass flux of TPHd and MtBE along the down-gradient margin of the Banta Fuel Terminal is three orders in magnitude lower than the concentrations of available I:\Chevron\1001621\REPORTS\2003\2003FS\FS 2003 revD.doc