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amec— <br /> TECHNICAL <br /> ATTACHMENT 13.4 <br /> Intrinsic Remediation Assessment <br /> Nestle USA, Inc.- Ripon, CA <br /> 1.0 INTRODUCTION <br /> On behalf of Nestle USA Inc. (Nestle), AMEC, in conjunction with ECM, has conducted this <br /> intrinsic remediation assessment for groundwater affected by chlorinated volatile organic <br /> compounds (VOCs) associated with the historical discharge of untreated industrial wastewater <br /> at the City of Ripon Wastewater Treatment Plant (WWTP), which is approximately one half <br /> mile south of the former Nestle facility at 230 Industrial Avenue (the site, Figure B.4.1). These <br /> VOCs are constituents of concern (COCs) to be addressed by the remedial alternatives <br /> outlined in the Revised Feasibility Study submitted to the California Regional Water Quality <br /> Control Board, Central Valley Region (Water Board), on January 28, 2011 (FS). The selected <br /> alternatives described in the FS include onsite groundwater extraction, intrinsic remediation <br /> and institutional controls. Intrinsic remediation is a major component of the alternative for the <br /> WWTP area because it has been determined that other active remedial technologies would <br /> not be effective or implementable in this area. Because intrinsic remediation is a central part of <br /> the recommended alternative for groundwater treatment, direct evidence supporting the <br /> feasibility of this remedial technology prior to selection of the alternative was requested by <br /> Water Board staff. <br /> 1.1 BACKGROUND AND PURPOSE <br /> Groundwater monitoring data from wells near the WWTP indicate that COC concentrations <br /> have been generally stable or decreasing (ECM, 2010a). Groundwater monitoring results for <br /> wells near the WWTP showing clearly that biotransformation from the parent compound <br /> (trichloroethene; TCE) to lower chlorinated degradation products (cis-1,2-dichloroethene <br /> [cDCE] and vinyl chloride) is occurring naturally (AMEC, 2009). Although these trends are <br /> promising, the application of intrinsic remediation as a final remedy is contingent on confirming <br /> that the biotransformation of chlorinated VOCs includes the transformation through vinyl <br /> chloride to environmentally benign end-products. Confirmation of the complete degradation <br /> pathway often is accomplished by measuring the concentration of ethene in groundwater <br /> samples. Although ethene is an environmentally benign end-product of reductive <br /> dechlorination, biodegradation of chlorinated VOCs to non-specific mineralization products <br /> such as carbon dioxide and methane also may be substantial. Therefore relying on ethene <br /> accumulation alone can greatly underestimate the extent of degradation (Bradley and <br /> Chapelle, 2010). Using indirect evidence to evaluate the progress of reductive degradation <br /> (e.g., concentration trends and geochemical conditions) provides additional support helpful for <br /> establishing the effectiveness of intrinsic remediation. Because additional direct evidence for <br /> AMEC Geomatrix, Inc. <br /> \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.4\Attach B-4.docx 134-1 <br />