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Nestle USA, Inc.—Ripon, CA January 28, 2011 <br /> 2011 Revised Feasibility Study <br /> water quality if not carefully controlled. The use of environmentally benign <br /> alkanes (such as propane) as co-metabolic inducers has shown some success <br /> recently, and may be a more desirable option when considering groundwater <br /> remediation using aerobic co-metabolism. <br /> The implementability of in-situ co-metabolic degradation relies on the ability to <br /> accurately mix dissolved oxygen and the co-metabolic inducer within the targeted <br /> treatment zone. Because both oxygen and propane are gases, a "biosparge" <br /> type of system would have to be employed. In general, sparging applications <br /> typically do not result in a uniform distribution of air bubbles around the injection <br /> point, but rather in a limited number of air channels that are heterogeneously <br /> distributed and difficult to predict. This channeling effect allows injected gas to <br /> bypass a significant portion of the subsurface targeted for treatmentx1v"', xl'X, 1. A <br /> study conducted by Braida and Ong in 2001 indicated that VOC concentrations <br /> just outside the air channel remained relatively constant, suggesting that the <br /> mass transfer zone is limited to the immediate vicinity of the air channel during <br /> sparging applications, limiting the effective distribution of amendments'. Further <br /> discussion of the infeasibility of biosparging is provided in Attachment B.1. <br /> Another significant complication in sparging applications is the groundwater <br /> permeability reduction created by entrapped air and air channelsxlv"'. The <br /> permeability of a porous media to groundwater flow (hydraulic conductivity) is <br /> inversely proportional to the amount of air occupying the pore space. As more <br /> air occupies the pore space, the pore space available for groundwater flow <br /> decreases, resulting in an overall reduction in the hydraulic conductivity. This <br /> permeability reduction can potentially lead to contaminated groundwater <br /> bypassing the treatment area', thereby limiting the contact of injected gas with <br /> COCs and greatly impairing treatment performance. <br /> Based on the research summarized above, it is clear that sparge points must be <br /> very closely spaced, and even under these circumstances, sparging may not be <br /> effective. For example, the biosparge barrier system at Port Hueneme, <br /> California, was constructed with sparge wells at 2-foot and 8-foot centers to treat <br /> shallow groundwater impacted by methyl tertiary butyl ether (MTBE). Assuming <br /> a biosparge barrier were to be installed near the Stanislaus River to guard <br /> against the potential southward movement of COC-impacted groundwater, the <br /> barrier would have to be at least 4,500 feet in length (from M-31 C to M-32C) and <br /> approximately 120 feet deep (Attachment 113.1). This is a very large undertaking <br /> for a system that has a low likelihood of success. <br /> As described in Attachment B.1, a large biosparge system does not appear to <br /> be implementable. <br /> 9.3.2.5 Relative Cost <br /> The costs for implementing co-metabolic treatment in the area of the Site are not <br /> included because it would likely not be effective for treating current TCE <br /> 35 <br />