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Workplan for Vertical Groundwater Investigation And Bench Test for In-Situ Oxidation 7835 Thornton Road, Stockton, CA Sft.lf Page 7 of 8 ISOTEC will perform a bench-scale laboratory treatability study to evaluate the effectiveness of the modified Fenton's reagent process on representative site-specific soil and groundwater samples, to evaluate the potential generation of toxic interim daughter products, and to determine the amount of catalyst/oxidant reagent required to oxidize site contaminants. ISOTEC's protocol for conducting the bench-scale laboratory treatability study is included in Attachment 3. In addition to the standard analyses outlined in ISOTEC's protocol, untreated and treated samples will also be analyzed for CAM17 metals, chromium VI, bromide, and bromate. The experimental control samples, which are set up to document reduction in contaminant concentrations due to sample dilution and/or volatilization,will not be analyzed for these additional constituents. Representative soil samples will be collected from the intended treatment zone (---40-56 feet bgs) during drilling of the proposed deep well discussed previously in this report. A sufficient volume of soil will be collected and transported to ISOTEC for the bench-scale test. Groundwater necessary for the test will be collected from well MWS following Ground Zero's general quarterly sampling protocol. FuII-Scale Remediation by In-Situ Oxidation A specific stoichiometry will be determined through the bench-scale laboratory study, with preliminary treatment quantities calculated. Assuming the bench-scale study determines that no toxic daughter products will be generated, a full-scale remediation plan will be proposed. Based upon initial evaluation of site data, ISOTEC has prepared a conceptual remedy for the site as follows: • Injection of reagent over an approximate 9,000 square foot area, roughly equivalent to the footprint of the previous excavation and that part of the plume greater than or equal to 10 ppb benzene, based upon the November 2005 analytical data; • Injection points at 20-paint centers within the target area, based upon an anticipated 10-foot reagent distribution radius; • Injection interval of 40-56 feet bgs, based upon site lithology. The normal screened interval is for injection is 8 feet, so injection through the broader depth interval will be accomplished through twinned borings at each location, one boring with a target interval of 40-48 feet bgs and the second with a target interval of 48-56 feet bgs. • Injection of approximately 200 pounds of reagent per injection point, or approximately 400 pounds of reagent per location. • Based upon follow-up sampling of well MW5, additional applications will be scheduled as necessary. ISOTEC will utilize direct-push technology (DPT) to introduce reagent at the site. Reagents will be injected through direct-push injection screens installed by the DPT subcontractor. Each injection screen will be 8 feet long and deployed through 1.25-inch or 1.5-inch direct push rod. G:IGROUNDZE\KNO WLES.HAM\REPORTS\WKPLAN_deepwell_bench1doc