What Additional Value Can Compound Specific Isotope Analysis (CSIA) Bring to the Assessment of Organic Contaminants in Groundwater?
Over the last three decades, compound-specific isotope analysis (CSIA) has evolved from the state of laboratory studies to a recognized, highly-sensitive field assessment tool. For this reason, the tool has been deployed on numerous contaminated sites to gain key information on released organic compounds (such as petroleum hydrocarbons and chlorinated solvents) that traditional concentration measurements are unable to reveal. For instance, CSIA has proven its reliability and robustness in demonstrating the biological destruction of organic compounds in groundwater, thus becoming an indicated tool for use in the framework of a Monitored Natural Attenuation program. CSIA greatly enhances the quality of information derived from the dataset collected over time, strengthens the conclusions drawn on the fate of organic contaminants in groundwater, and reinforces the Regulator’s decision to approve on-site application of the natural attenuation remedial strategy. Furthermore, the tool has been used to differentiate sources of the same contaminant present in the subsurface for forensic purposes, or to better understand source architecture on complex sites having the potential for multiple release episodes. More recently, the application of the tool has reached another milestone, when it was applied in the framework of in situ remediation treatments to assess whether the intended contaminant mass reduction was initiated as anticipated. More specifically, CSIA was proven reliable in determining whether the contaminant mass reduction observed was attributed to dilution or destruction, or which co-occurring physical, chemical or biological process was the dominant mass-reduction process. In such cases, application of CSIA supports field practitioner’s decision to modify the treatment in real time, which leads to cost-effective remediation treatments. This talk aims to briefly explain the fundamentals of the CSIA method, followed by examples of field applications.