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ELECTROKINETICALLY ENHANCED DENSE
NON-AQUEOUS PHASE
LIQUID (DNAPL) REMOVAL

Student’s name, Dr. Parvinder S. Sethi, and Dr. Laura L. Sanders*

M.S. Program in Earth Science

Past and present industrialization and waste disposal practices have released a variety of harmful compounds into surface soils, subsurface soils, and the groundwater regime. Of the organic chemical contaminants detected, dense non-aqueous phase liquids (DNAPLs) are the most frequently encountered and pose considerable challenges to remediate.

This paper presents the testing of the hypothesis that electrokinetics (electrolytic removal or migration of contaminants), applied in situ to site soils and bedrock, will increase the volume of DNAPLs removed and decrease the time it takes to remove them as compared to passive DNAPL removal methods. Electrokinetics creates multiple mechanisms for the migration and transport of water, inorganic analytes, and organic compounds in the subsurface. Cations transport their hydrated sheath (surface coating of water or contaminant) toward the cathode, also imparting a dragging force on the water or contaminant molecules around them. Cations already free in the pore water are driven toward the cathode. In addition, an acid front develops at the anode and migrates toward the cathode, desorbing ions or organic compounds adhering to soil particles and rendering them into solution to be driven toward the cathode.

Three different geologic scenarios were constructed for the study: a sandy silt overlying a glacial till, sand and gravel overlying a glacial till, and sand and gravel overlying a limestone bedrock. The primary objective of the study was to determine if application of electrokinetics to soils and bedrock increases the volume of DNAPLs removed as compared to passive removal of DNAPLs (using only an extraction well and gravity). Additional objectives included comparing initial and final tar chemistries, and monitoring development and migration of the acid front in different geologic scenarios.

The results of this study showed that electrokinetics can significantly enhance the removal of pure phase coal tar DNAPLs below the water table from a geologic environment consisting of cohesive materials. Electrokinetics did not appear to enhance DNAPL removal from a geologic environment consisting of granular or bedrock materials. A possible reason for this may be that an artificial groundwater flow system was not part of the laboratory apparatus. This fact may have reduced or eliminated any effects associated with electroosmosis.