Traditional performance monitoring techniques for in situ chemical oxidation (ISCO) applications rely on layers of costly and often misleading performance data to demonstrate contaminant destruction. This is because definitively attributing contaminant concentration decreases to oxidant application can not be efficiently performed using concentration data alone. Compound-specific isotope analysis (CSIA), which has recently become commercially available (Microseeps, Inc., Pittsburgh Pennsylvania), when combined with concentration data can provide an almost definitive indication discerning contaminant destruction from non-destructive physical processes such as dilution and displacement that can be associated with ISCO.
CSIA distinguishes destructive reactions from non-destructive processes by tracking the naturally occurring stable carbon isotopes 13C and 12C in organic chemicals (e.g., common petroleum constituents and chlorinated solvents) present in groundwater. The majority of all carbon is present as the 12C isotope but a small percentage of carbon is naturally present as the stable (i.e., not radioactive) 13C isotope (natural abundance approximately 1 percent of all carbon). Chemical bonds involving the 13C isotope are slightly stronger than those of the 12C isotope and as a result react slower in bond breaking reactions including chemical oxidation and biodegradation. The slower reaction rate leads to an accumulation of the 13C isotope in the residual contaminant. The physical mechanisms of natural attenuation (e.g., dilution and sorption) and mechanisms associated with amendment fluid application (e.g., displacement) do not significantly affect the isotopic signature of residual contaminant as they can with simple chemical concentration data.