Improving the Sweeping Efficiency of Permanganate into Low Permeable Zones To Treat TCE: Experimental Results and Model Development

The residual buildup and treatment of dissolved contaminants in low permeable zones (LPZs) is a particularly challenging issue for injection-based remedial treatments. Our objective was to improve the sweeping efficiency of permanganate into LPZs to treat dissolved-phase TCE. This was accomplished by conducting transport experiments that quantified the ability of xanthan-MnO₄^– solutions to penetrate and cover (i.e., sweep) an LPZ that was surrounded by transmissive sands. By incorporating the non-Newtonian fluid xanthan with MnO₄^–, penetration of MnO₄^– into the LPZ improved dramatically and sweeping efficiency reached 100% in fewer pore volumes. To quantify how xanthan improved TCE removal, we spiked the LPZ and surrounding sands with ¹⁴C-lableled TCE and used a multistep flooding procedure that quantified the mass of ¹⁴C-TCE oxidized and bypassed during treatment. Results showed that TCE mass removal was 1.4 times greater in experiments where xanthan was employed. Combining xanthan with MnO₄^– also reduced the mass of TCE in the LPZ that was potentially available for rebound. By coupling a multiple species reactive transport model with the Brinkman equation for non-Newtonian flow, the simulated amount of ¹⁴C-TCE oxidized during transport matched experimental results. These observations support the use of xanthan as a means of enhancing MnO₄^– delivery into LPZs for the treatment of dissolved-phase TCE