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Using Stable Isotopes to Understand Degradation of Organic Contaminants in Ground Water
Citation:
WILSON, J. T. Using Stable Isotopes to Understand Degradation of Organic Contaminants in Ground Water. Presented at The 2010 Restoration and Technology Transfer Workshop, San Antonio, TX, April 06 - 09, 2010.
Impact/Purpose:
Using stable isotopes as a tool to understand biodegradation.
Description:
Stable isotopes are a powerful tool to understand biodegradation. However, there are two interactions that can substantially confuse the interpretation of CSIR data: heterogeneity in flow paths in the aquifer and proximity to NAPL or other source of contamination to ground water. The real attenuation in concentrations at the site was substantially greater than would be expected from the prediction of C/Co based on the analysis of stable carbon isotopes. There are two primary causes for this underestimation of the true extent of degradation. Heterogeneity produces blended samples with contribution form flow paths that experienced degradation and flow paths that did not. Because of the exponential relationship between the shift in isotopic ratio and the predicted fraction remaining, the blended samples underestimate the true extent of degradation. These two interactions have important consequences for design of a sampling strategy for CSIA. Samples should be evenly balanced between high concentrations, intermediate concentrations, and low concentrations. Putting a heavy emphasis on wells with low concentrations of organic contaminants may seriously underestimate the true contribution of degradation processes at a site. The absence of fractionation in particular wells, particularly in wells with low concentrations of contaminant, should not be taken as evidence for there is no degradation in the plume.