Compound specific isotope analysis (CSIA) is an analytical method that measures the ratio of stable isotopes (13C/12C, 2H/1H, or 37Cl/35Cl) of a contaminant. CSIA results can provide conclusive proof of contaminant degradation, insight into degradation mechanisms, rate estimations, and contaminant source distinction/delineation.
CSIA can provide conclusive evidence of degradation of many common contaminants including PCE, TCE, DCE, and vinyl chloride. During degradation of the contaminant, the ratios of stable isotopes (e.g, 13C/12C) change in predictable ways. Conversely, physical processes like dilution, adsorption, and volatilization do not appreciably impact isotopic ratios.
CSIA is applicable to many contaminants (chlorinated ethenes, ethanes and methanes) and degradation mechanisms (biotic and abiotic). Furthermore, CSIA has many applications in environmental remediation and forensics including determining if degradation has occurred, identification of multiple sources, and assessment of vapor intrusion.
δ13C values for common contaminants are determined with a high degree of precision (within +/-0.5‰). With the high precision of the analysis, site managers and all stakeholders can be confident in the conclusions drawn from CSIA.
CSIA data can provide an estimate of the extent of degradation and an independent evaluation of biodegradation rates used in site models.
The MI CSIA Database is a one stop resource to help with CSIA interpretation. The Database has custom graphing capabilities (Dual Isotope, Modified Kuder Plots) and all the manufactured ranges and enrichment factors from the literature compiled into easy to use tables.
CSIA is inexpensive and ultimately saves money by allowing site managers to make more informed decisions.
HOW TO USE CSIA:
Along with chemical, geochemical, and microbial analyses, compound specific isotope analysis can provide a strong line of evidence when evaluating contaminant degradation, treatment options, remedy performance, and investigating the potential for multiple contamination sources.
Use CSIA to help answer…
- Is degradation occurring?
- Collect samples from the source area and along the centerline of the plume.
- Compare δ13C values of all compounds including daughter products to the parent compound baseline (most negative δ13C value of the parent compound).
- δ13C values more than 2‰ greater than baseline are conclusive proof of degradation.
- Are there multiple contaminant sources (source distinction/delineation)?
- Sample all possible sources areas and at least three locations along the flow paths between sources and the plume.
- Prepare a Dual Isotope Plot (δ13C and δ37Cl) in Excel or using the MI CSIA Database.
- Look for linear trends in the results from the source along the flow path to the plume.
CSIA and MI CSIA Database – Multiple Sources
– Stakeholders at a TCE-impacted site required conclusive evidence of TCE degradation and suspected that multiple sources of TCE may exist at the site. CSIA conclusively demonstrated that TCE degradation had occurred at several locations at the site.
CSIA for Performance Evaluation
– CSIA was performed to conclusively demonstrate that TCE, cis-DCE and vinyl chloride degradation had occurred at several locations at the site giving the client confidence in the selected treatment strategy.
CSIA: Are TCE and Daughter Products Degrading
– Stakeholders at a TCE-impacted site were concerned about elevated cis-DCE and vinyl chloride concentrations relative to ethene. CSIA was performed to make conclusive determination.
CSIA: Actionable Data for Site Assessment and Performance Monitoring
• During site assessment of a TCE site, compound specific isotope analysis (CSIA) did not demonstrate TCE or cis-DCE degradation, consistent with CENSUS qPCR results indicating low concentrations of Dehalococcoides (DHC).
• Multiple lines of evidence increased stakeholder confidence in full-scale treatment.