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CLEARWATE subsurface material indicates that liquid injection under positive pressure would be similarly effective, although with a reduced radius of influence. In the CAP addendum, dated December 31, 2003, in-situ oxygen curtain technology was the recommended choice for the remediation of soil and groundwater at the site based on regulatory directives and lower costs. Long-term effectiveness of the technology for sorbed-phase contamination was not well documented at the time, but after the pilot study, was shown to be effective as a treatment for groundwater impacts. It is now known that oxygen infusion system technology, although effective for groundwater remediation, is not effective for remediation of saturated soils with significant sorbed hydrocarbons. In the December 31 , 2003 correspondence from Clearwater to SJCPHS-EHD, oxygen infusion system technology was recommended as a more affordable alternative to costly air sparging, soil y vapor extraction, and other extraction type electrically powered systems. The oxygen infusion system did work effectively at reducing concentrations of TPH-g and benzene, toluene, ethylbenzene, and xylenes (BTEX) in groundwater, but was not as effective at reducing sorbed- phase concentrations of these COCs in soil. Therefore, an effective alternative must be applied for the purpose of reducing COC concentrations in soil so that case closure can be achieved for this site. i As it is now known that oxygen infusion system tools, operating to reduce concentrations in groundwater, remove the desorbing contaminants while leaving the mass intact, calculations of dissolved hydrocarbon mass from groundwater levels would not be an accurate representation, since the dissolved mass is currently being reduced by in-situ oxygen curtain tools operating at the site. Remediation of TPH-g in groundwater has been performed and is currently being performed using the oxygen infusion system, but the continued presence of the sorbed-phase source intiI provides a source of contamman�the groundwater over un'a-There ore, on the basis of the 2009 SCM in conjunction with the results of the recent Third Quarter 2009 Rebound Evaluation and Groundwater Monitoring Report, an updated remedial technology should be evaluated. UPDATED RECOMMENDED REMEDIATION TECHNOLOGY The most effective option for soil remediation at this time is in-situ chemical oxidation (ISCO) injected in a dewatered contaminated zone. In terms of successfully moving liquids under positive pressure through the subsurface and having an adequate radius of influence, the evidence of the 2002 feasibility study using air sparging indicates that liquid chemical injection has promise. ISCO can be performed with a variety of different possible chemical oxidizing agents: hydrogen peroxide with an iron catalyst and pH adjustment (classic Fenton's Reagent), sodium persulfste activated with ironM sodium ethylenediaminetriacetatomonoacetic acid (EDTA) or ozone gas catalyzed with hydrogen peroxide. The objective of ISCO is to contact hydrocarbon-affected soils in the saturated zone, desorbing hydrocarbons from silt and clay in the process. The liquid or gas-phase chemical oxidants are delivered through narrow-diameter (less than approximately 1-inch) injection ports set with delivery points at specific depths within Floyd Bames 3 Updated CAP ZB 178 Update to CAP March 2010