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Nestle USA, Inc.—Ripon, CA January 28, 2011 <br /> 2011 Revised Feasibility Study <br /> periods of time in the subsurface compared to many highly reactive <br /> chemicals such as strong oxidants. This allows for greater deliverability of <br /> organic substrates compared to many other in-situ reagents. <br /> • Long-term implementation: because naturally occurring microbes mediate <br /> the destruction process, and these microbes appear to be ubiquitous, a <br /> long timeframe for in-situ passive treatment can be sustained due to <br /> residual organic substrates and reduced minerals within the treatment <br /> zone, following active treatment. <br /> The major disadvantage of this technology is the potential impact to groundwater <br /> quality due to increases in dissolved metal concentrations in groundwater (e.g., <br /> iron, manganese and arsenic). In addition, elevated TDS concentrations (as a <br /> result of increases in dissolved metals, alkalinity and organic carbon) are also an <br /> observed and significant drawback to the application of in-situ enhanced <br /> reductive dechlorination technologies. A detailed assessment of in-situ <br /> chemical/biological treatment (or bioaugmentation), and its feasibility within the <br /> Study Area, is included in Attachment B.2. <br /> 9.3.2.1.1 Effectiveness <br /> In order to be cost effective, in-situ reductive dechlorination treatment typically <br /> targets areas with COC concentrations in the range of thousands of parts per <br /> billion. Groundwater modeling results (Attachment C) indicate that removing or <br /> reducing the high COC concentrations at the Site will significantly reduce the <br /> plume size emanating from the Site. <br /> Some processes can reduce TCE and cis-1,2-DCE, but reductive dechlorination <br /> may stall at cis-1,2-DCE and VC instead of degrading further to ethene, if <br /> conditions are not favorable for substantial further transformation. Under these <br /> conditions, the injection of engineered microbial cultures can promote complete <br /> degradation. This is called bioaugmentation and is discussed in greater detail in <br /> Attachment B.2. The likelihood of complete dechlorination to low toxicity end- <br /> points, or the potential generation of incomplete and higher toxicity intermediates, <br /> such as vinyl chloride, is a critical consideration in assessing the effectives of an <br /> in-situ treatment approach. This technology may be effective in reducing the <br /> COC concentrations within the Study Area. <br /> 9.3.2.1.2 Implementability <br /> The implementability of in-situ technologies requires access to the Site for <br /> installation of wells and other infrastructure. There are no surface or subsurface <br /> barriers that will prevent physical implementation of in-situ chemical/biological <br /> treatment. However, complex geology may present challenges for delivery of <br /> chemical or biological reagents, reducing overall efficacy. For the application of <br /> enhanced biological approaches, the use of recirculation wells may solve these <br /> challenges. However, recirculation wells may be less effective for chemical <br /> oxidation due to the short life of the chemical reagents; distribution of injected <br /> microbes using injection wells is examined in further detail in Attachment B.2. <br /> 33 <br />