ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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amec— chlorinated VOC destruction, particularly, vinyl chloride destruction, has not been obtained prior to conducting this study, Nestle requested AMEC and ECM to jointly conduct an expedited intrinsic remediation assessment in 2010 to provide additional information on the feasibility of intrinsic remediation, and specifically to seek direct evidence on whether COC destruction by intrinsic remediation is occurring. The objectives, scope, results and conclusions of the assessment are summarized herein. This assessment provides a strong technical basis for selecting intrinsic remediation as a central remedial technology for treating COC-affected groundwater for the study area including the area in the vicinity of the WWTP. 1.2 OBJECTIVES AND APPROACH For the purposes of the FS, intrinsic remediation is defined as the natural abiotic and/or biological destruction of COCs in situ, without engineered process enhancements. Intrinsic remediation can also be described as the component of natural attenuation that involves the destruction of COC mass, as opposed to a reduction in COC concentration or mobility. The objectives of this assessment and corresponding technical approach are as follows: 1. Characterize the hydrochemistry of groundwater samples from monitoring wells within the intrinsic remediation area shown in Figure B.4-1 to further understand spatial variability in groundwater flow and geochemical conditions. Efforts to evaluate the major and minor ion composition of groundwater using samples from selected B-, A-, C- and D-zone monitoring wells (Section 3.1) was an important aspect of this work. 2. Assess the feasibility of intrinsic remediation based on geochemical conditions. This was accomplished in part by classifying ambient geochemical conditions as oxidizing or reducing (i.e. redox conditions) relative to TCE, cDCE and vinyl chloride to assess whether such conditions could be favorable to support the abiotic or biological destruction of COCs by one or more of the well-documented redox-based pathways (Section 3.2). This was conducted to provide indirect evidence for the feasibility of intrinsic remediation. 3. Seek direct evidence for COC destruction. This was accomplished using compound specific isotope analysis (CSIA) as described in Section 3.3. 4. Estimate a reasonable and conservative timeframe for COC removal by intrinsic remediation. The extent of COC destruction to date was estimated from CSIA and used to approximate a range of bulk COC destruction rates (Section 3.3), and 5. Summarize the key conclusions of this work (Section 4). 2.0 GROUNDWATER SAMPLE COLLECTION AND ANALYSIS Groundwater samples were collected by ECM during the second and third quarterly groundwater monitoring events (Q2 and Q3, respectively; ECM, 2010b and ECM, 2010c) as AMEC Geomatrix, Inc. \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTS Assessment_Apx B_012711\Attachment B.4\Attach B-4.docx 134-2