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amec- <br /> 4.0 <br /> CONCLUSIONS <br /> This intrinsic remediation assessment involved the collection of groundwater samples for <br /> conventional geochemical characterization, redox parameters and CSIA to further understand <br /> the groundwater flow system and COC destruction processes. Based on this evaluation, the <br /> following conclusions are made: <br /> • groundwater appears to be impacted by sources of salinity in some areas, but the <br /> salinity impacts did not strongly correlate with VOC concentrations (specifically, <br /> groundwater samples from TH-10 and M-31 C, located southeast of the WWTP, did not <br /> appear to be impacted by anthropogenic sources of TDS such as industrial and <br /> municipal wastewater). <br /> • redox conditions near the WWTP were strongly reducing and favorable for TCE <br /> destruction by dehalorespi ration, where indigeneous microbes convert TCE to less <br /> chlorinated and eventually non-chlorinated degradation products. <br /> • farther away from the WWTP, the presence of nitrate in groundwater samples and <br /> absence of dissolved methane indicates that conditions become less reducing such <br /> that dehalorespi ration is not likely to be an important COC destruction process, <br /> therefore the production of vinyl chloride is not expected at distances farther from the <br /> WWTP. <br /> • As cDCE and vinyl chloride in groundwater move farther from the WWTP by advection, <br /> the shift toward more oxidizing conditions may drive the mineralization of these <br /> compounds to carbon dioxide and methane, which is difficult to detect using <br /> conventional groundwater monitoring methods. <br /> A new method called CSIA was used to provide direct evidence of COC destruction that could <br /> not be obtained previously. The CSIA data indicate that: <br /> • cDCE and vinyl chloride degradation occurs at higher rates farther from the WWTP, <br /> where conditions appear to be more oxidizing, and that greater than 90% destruction <br /> of CDCs has already occurred. <br /> • A half-life of approximately 0.5 years for COC removal by intrinsic remediation was <br /> calculated based on the CSIA data near the WWTP. <br /> Therefore, based on this assessment, intrinsic remediation appears to be a very promising <br /> remediation technology for groundwater impacted by the WWTP, and intrinsic remediation <br /> should play a central role in the overall Remedial Action for groundwater within the study area. <br /> 5.0 REFERENCES <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 134-18 <br />