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S ECOR _. Ms. Vicky McCartney September 15, 2003 Page 5 Though interim remediation via groundwater batch extraction appears to have effectively reduced concentrations of MtBE in the source area, MtBE and a significant amount TBA mass still remains within the source area;During interim groundwater batch extraction activities, concentrations of TBA have remained at elevated yet stable levels (Table 4).'Since MtBE levels appear to have reached asymptotic levels as a result of groundwater batch extraction activities (Figures 3 through 5) and elevated concentrations of TBA are present in source area wells MW-1R, MW-2R, and VW-1, SECOR proposes an alternate interim remedial action plan, which is presented below. REVISED TRAP To further expedite remediation of the dissolved plume beneath the site, SECOR recommends discontinuing interim remediation via groundwater batch extraction. To further enhance source removal and prevent the further off-site migration of MtBE and TBA, SECOR proposes the installation of an OS system for the removal of petroleum hydrocarbons and fuel oxygenates beneath and in the vicinity of the site. With subsurface soils consisting predominantly of mixtures of silt and sand within the upper portion of the saturated zone (approximately 12 to 14 feet bgs), the introduction of ozone through several OS points would directly destroy dissolved petroleum hydrocarbons, MtBE,-and-TRA, and stimulate in-sift a rr oobic biodegradation of dissolved petro eum hydrocarbons and petroleum hydrocarbons in the saturated zone by increasing su surface oxygen concentrations. Though concentrations may initially increase due to the desorption of petroleum hydrocarbons from soil .( f caused by the aggressive mechanical scrubbing action of the ozone- OS is capable of �✓ facilitating subsequent rapid degradation of the dissolvedplu em beneath th site. The installation of OS points along the eastern/northeastern property boundaryary would act as a barrier, inhibiting migration of dissolved petroleum hydrocarbons, MtBE, and TBA further downgradient of the site. Conceptual Design of the OS System ,�41, A total of 10 OS points (OS-1 through OS-10) are proposeZthe' area surrounding the USTs. The locations of the wells were selected based on an asssum�d$0-foot ozone radius of influence, in order to maximize the remedial coverage in the vicinity of the USTs and along the eastern/northeastern perimeter of the site. A work plan for.the installation of the OS points is included in the following section. Process Flow Ozone injection tubing (approximately 3/8-inch diameter), doubly-contained within PVC tubing, will connect each OS well to a 10-point panel, located in a small remediation compound behind the station building. The panel will be plumbed to a 10-point injection solenoid within the OS unit, allowing rotation of the injection lines between the 10 OS points at a rate of 6 standard cubic feet per minute (scfm). The OS unit will be equipped with a compressor rated to deliver 6 scfm at 10 pounds per square inch (psi). The proposed layout of the OS system is presented as Figure 7. Remediation System Permitting and Installation Following approval cif the TRAP, OS well construction permits will be obtained from San Joaquin County Environmental Health Division (SJCEHD). Construction of the remediation system will begin, following the approval of permits, and receipt of necessary equipment. 11ConocoPhillips%Tosco Marketing11I1931Reports\Revised TRAP&WP.doc