Contaminant Mass Transfer During Boiling in Fractured Geologic Media

摘要

The DoD is responsible for cleanup of groundwater that is contaminated with chlorinated volatile organic compounds (CVOC) at thousands of sites. Many of these sites are underlain by fractured rocks or soils with significant matrix porosity. As dissolved CVOC and dense nonaqueous phase liquids (DNAPL) move through fracture networks, the CVOC diffuse into the lower permeability matrix materials, where they can remain for hundreds of years. Remediation options for treating fractured geologic media are extremely limited because the low matrix permeability, and unknown fracture locations make any type of fluid or chemical delivery difficult or impossible. Thermal methods hold promise for remediation of fractured media, because heat can be efficiently transferred without any fluid flow by the mechanisms of thermal conduction and electrical resistance heating. Once a fractured rock or soil is heated above the water boiling point, subsequent depressurization of the fracture network by vacuum extraction may induce boiling in the matrix, leading to large gas phase pressure gradients, and a steam stripping effect that can remove the contaminants from the matrix.