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MNA for Chlorinated Solvents and Fuel Oxygenates: Why It Occurs, How It Evolved, and Using Stable Carbon Isotopes to Predict Plume Behavior
Citation:
WILSON, J. T. MNA for Chlorinated Solvents and Fuel Oxygenates: Why It Occurs, How It Evolved, and Using Stable Carbon Isotopes to Predict Plume Behavior . Presented at Advanced Tools for In-situ Remediation Workshop, Albany, NY, April 16, 2009.
Impact/Purpose:
The objective is to use stable carbon isotopes to predict plume behavior.
Description:
The organisms that degrade MtBE under anaerobic conditions are evolved to acquire energy for growth by using molecular hydrogen and carbonate ion to cleave methyl ether bonds. Methyl ether bonds are common in nature and the bond also occurs in MTBE. MTBE in contaminated ground water will be degraded under anaerobic conditions if adequate concentrations of molecular hydrogen are available, usually from the methane fermentation of BTEX compounds. Anaerobic biodegradation of MtBE produces strong fractionation of stable carbon isotopes. This makes is possible to estimate the extent of biodegradation of MTBE from the shift in the ratio of 13C to 12C in MtBE in the contaminated ground water. The shift in the ratio can be used to estimate the extent of biodegradation along a flowpath in the aquifer. The extent of biodegradation can be used to estimate the rate of biodegradation in the aquifer. The rate of biodegradation can be used to calibrate a transport and fate model to support an exposure assessment of impact to receptors down gradient of the spill. In like manner, chlorinated organic compounds such as PCE, TCE, cis-DCE and vinyl chloride are fractionated during sequential reductive dechlorination carried out by microorganisms or through abiotic reactions, or degradation during abiotic elimination reactions. If the parent compound is entirely consumed, the further degradation of a daughter product can be recognized by comparing the ratio of 13C to 12C in the daughter product to the ratio the original parent compound.
