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amec�9 <br /> vinyl chloride cannot be calculated from the isotope data because the constituents are <br /> intermediate degradation products that are produced and degraded in situ (Wilson, 2010). <br /> Additional data and modeling studies could be conducted during the implementation of the <br /> intrinsic remediation program to help assess the cDCE and vinyl chloride degradation rates in <br /> a more quantitative manner. <br /> Extent of COC Destruction to Date <br /> Equation 2 can be rearranged to calculate the extent of TCE biotransformation and the net <br /> COC destruction (removal of TCE, cDCE and vinyl chloride) to date at each CSIA sampling <br /> location using the calculated s of-4.5%o, estimated initial 613Co value of-31.8%o and 613Cbu,k <br /> values for each CSIA sample. These calculations are summarized in Table B.4-6, where the <br /> fraction remaining (f) after degradation is calculated for TCE and also for net COCs. Percent <br /> degradation can be calculated from f as follows: <br /> Percent degradation = (1-t) x 100% Equation 5 <br /> The calculated percent degradation for TCE ranges from 82% to 99.8% as shown in Table <br /> B.4-6. This calculation is based on the estimated s of-4.5%o, estimated initial 613Co value for <br /> TCE of-31.8%o and 613CTCE values for each CSIA sample, and therefore does not account for <br /> cDCE and vinyl chloride degradation. The calculated percent net removal of COCs ranges <br /> from 0% to 99.8%. This calculation does account for degradation of TCE, cDCE and vinyl <br /> chloride because the calculation is based on the 613CbUlk values for each CSIA sample, an <br /> estimated s of-4.5%o, estimated initial 613Co value for TCE of-31.8%o. For this reason, percent <br /> TCE degradation is generally greater than or similar to the percent net COC removal. In some <br /> cases, calculated percent net COC removal is greater than percent degradation of TCE (M-6A, <br /> M-6C1, M-6C2 and M-49A; Table B.4-6). The discrepancy between these values is generally <br /> small (1% to 7%) and may be the result of: 1) the enrichment factor for cDCE and vinyl <br /> chloride may be larger (more negative) than -4.5%o, 2) TCE from a different source such as a <br /> conduit well, soil gas, etc. could be commingled with COCs originating at the WWTP, and 3) <br /> these values may be an artifact of applying simplistic calculations towards a complex site. <br /> The E of-4.5%o used in the calculation of percent net COC removal is assumed to apply for <br /> cDCE and vinyl chloride, however, the accuracy of this estimation is not known. Nonetheless, <br /> the value of the enrichment factors for cDCE and vinyl chloride may not be important in these <br /> calculations when: 1) the concentration of these intermediate degradation products are much <br /> less than TCE, or 2) net loss of cDCE and vinyl chloride is negligible compared to production <br /> from the reduction of TCE. Therefore, the calculations presented in Table B.4-6 appear to be <br /> reasonable estimations based on the available dataset. <br /> COC Destruction Rate by Intrinsic Remediation <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 134-16 <br />