ARCHIVED REPORTS_2003 FEASABILITY STUDY REPORT AND SITE ASSESSMENT WORK PLAN

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S E C O R 2003 Feasibility Study Report and Site Assessment Work Plan July 18, 2003 Page 16 4.6 Conclusions Results of the fate and transport modeling of the COCs present in the groundwater beneath and offsite of the Site indicates the CDCs would not migrate beyond wells MW-57 and MW-59 at concentrations above current levels of concern. 5.0 REMEDIAL OBJECTIVES The remedial objective is to select the most appropriate remedial technology for the site that protects off-site groundwater, achieves compliance with the WQOs (per CAO) and minimizes impacts to short-and long-term terminal operations. 6.0 REMEDIAL ALTERNATIVES The remedial alternatives identified to meet these remedial objectives for groundwater consist of 1. groundwater barrier, 2. hydraulic control line, 3. combination groundwater barrier and hydraulic control line), and, 4. groundwater oxygenation system. iA description of each of these remedial alternatives is presented below. 6.1 Groundwater Barrier This alternative consists of a subsurface, low-permeability, wall used to function as a groundwater barrier along the down-gradient terminal property line (Figure 2). The barrier wall would be approximately 1,000 feet long, 30 feet deep and 12 inches wide. The barrier would extend from the northwest property line (near well MW-47A), continue around the northern-most property corner (near well MW-50B) and end along the northeast property line (near well MW-51 A). Installation of the barrier wall could be accomplished using a long-reach excavator equipped with a 12-inch wide bucket, bentonite slurry, and miscellaneous hoses and pumps. The excavator would remove native soil to form a trench and create the barrier mold. The excavated trench forming the barrier mold would then be backfilled with bentonite slurry to create the low-permeability groundwater barrier. The low-permeability wall is expected to reduce groundwater velocity down-gradient and off- site, and reduce future concentrations of hydrocarbons to below WQO's. The effectiveness of the barrier could be evaluated through semi-annual off-site groundwater sampling. The analytical test results of these samples could be evaluated with respect to the Basin Plan's WQOs. 6.2 Hydraulic Control Line This alternative consists of installing pumping wells used to function as a hydraulic control line along • the down-gradient terminal property line (Figure 2). The hydraulic control line would be approximately 800 feet long and extend from the northwest property line (near well MW-47A), I:\Chevron\1001621\REPORTS\2003\2003FS\FS 2003 revD.doc