MTBE Fate in Unsaturated Zone

Volatilization and biodegradation near the water table are two processes that can contribute significantly to the natural attenuation of volatile organic compounds (VOCs) in shallow ground water. A model developed by the USGS (R-UNSAT) is currently being applied to quantify the rates of mass transfer of methyl tert-butyl ether (MTBE) and BTEX from ground water to the unsaturated zone due to volatilization and diffusive transport at the Laurel Bay research site in South Carolina. Calibration of R-UNSAT to unsaturated-zone gas-concentration data indicates that thevolatilization rate of MTBE from the water table source to the unsaturated zone is similar to the volatilization rate of BTEX. This finding is critical to the evaluation of natural?attenuation remediation, because rates of natural attenuation in the interior of a ground-water-solute plume are smaller for MTBE than for BTEX.

• Galloway, NJ web page
• U.S. Geological Survey Fact Sheet FS-019-98

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