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amec— <br /> area <br /> (Burow et al., 2004; AMEC, 2009), and therefore the natural in situ abiotic destruction of <br /> TCE may be an important intrinsic remediation process. Indirect evidence on the importance of <br /> this process could be obtained by characterizing the magnetite content of soil cores and/or <br /> conducting laboratory studies with aquifer sediments. <br /> 3.3 COMPOUND SPECIFIC ISOTOPE ANALYSIS (CSIA) <br /> Recent technological advances in analytical equipment have resulted in the application of <br /> CSIA towards environmental forensics and intrinsic remediation studies. CSIA is a powerful <br /> tool for intrinsic remediation studies because it can provide an "unequivocal indication of <br /> natural biodegradation (Wilson, 2010)."A recent guidance document has been prepared by <br /> the U. S. EPA that describes and promotes the application of CSIA towards studies of intrinsic <br /> remediation (EPA, 2008). Because CSIA is a relatively new approach, a basic overview of <br /> CSIA is provided in Section 3.3.1, and the results and interpretation are provided in Section <br /> 3.3.2. <br /> 3.3.1 Overview of CSIA <br /> The application of CSIA, which is a highly specialized type of analysis, is described in this <br /> section, as a series of questions and answers. <br /> What is CSIA? <br /> CSIA, stands for Compound Specific Stable Isotope Analysis. The term "compound-specific" <br /> means that the stable isotope ratio of a particular atom (e.g. carbon, hydrogen, chlorine, etc.) <br /> of a specific compound, such as TCE, is the target of the analysis. By analyzing stable isotope <br /> ratios, information on COC sources and COC degradation can be obtained that couldn't be <br /> obtained from traditional groundwater analytical methods. This method has seen increasing <br /> application towards biodegradation studies over the past decade. There currently are at least <br /> two commercial laboratories that offer this service. <br /> What are stable isotopes? <br /> Stable isotopes comprise the non-radiogenic nuclides of an element and are naturally <br /> occurring throughout the biosphere, hydrosphere and lithosphere. In other words, compounds <br /> containing elements such as carbon (12C), hydrogen (1H) and oxygen (160) invariably contain a <br /> lesser amount of the stable isotopes of each element (e.g. 13C, and 2H or D for deuterium). <br /> This is true for all organic matter including petroleum, plants, animals and industrial chemicals, <br /> and all inorganic matter (rocks, minerals, water, etc.). <br /> Usually, the less common stable isotopes have one or more extra neutrons in their nucleus <br /> which results in a higher atomic mass compared to the most common isotope. For example, <br /> 13C is the less common stable isotope of carbon with a mass of 13 grams per mole (g/mol), <br /> compared to 12C (12 g/mol) and is present as approximately 1% of all forms of carbon on earth <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 134-9 <br />