title: Analysis of sources of bulk conductivity change in saturated silica sand after unbuffered TCE oxidation by permanganate.
abstract: Time lapse resistivity surveys could potentially improve monitoring of permanganate-based in situ chemical oxidation (ISCO) of organic contaminants such as trichloroethene (TCE) by tracking changes in subsurface conductivity that result from injection of permanganate and oxidation of the contaminant. Bulk conductivity and pore fluid conductivity changes during unbuffered TCE oxidation using permanganate are examined through laboratory measurements and conductivity modeling using PHREEQC in fluid samples and porous media samples containing silica sand. In fluid samples, oxidation of one TCE molecule produces three chloride ions and one proton, resulting in an increase in fluid electrical conductivity despite the loss of two permanganate ions in the reaction. However, in saturated sand samples in which up to 8mM TCE was oxidized, at least 94% of the fluid conductivity associated with the presence of protons was removed within 3h of sand contact, most likely through protonation of silanol groups found on the surface of the sand grains. Minor conductivity effects most likely associated with pH-dependent reductive dissolution of manganese dioxide were also observed but not accounted for in pore-fluid conductivity modeling. Unaccounted conductivity effects resulted in an under-calculation of post-reaction pore fluid conductivity of 2.1% to 5.5%. Although small increases in the porous media formation factor resulting from precipitation of manganese dioxide were detected (about 3%), these increases could not be confirmed to be statistically significant. Both injection of permanganate and oxidation of TCE cause increases in bulk conductivity that would be detectable through time-lapse resistivity surveys in field conditions.
authors: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO, USA. Electronic address: rhort@mines.edu.
authors: Ryan D
authors: RD
authors: Hort
authors: Department of Geophysics, Colorado School of Mines, Golden, CO, USA; ISTerre, CNRS, UMR CNRS 5275, Université de Savoie, 73376 cedex, Le Bourget du Lac, France. Electronic address: arevil@mines.edu.
authors: André
authors: A
authors: Revil
authors: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO, USA. Electronic address: junko@mines.edu.
authors: Junko
authors: J
authors: Munakata-Marr
mesh_terms: D060587:Groundwater / Q000737:chemistry*; D017895:Manganese Compounds / Q000737:chemistry*; D008962:Models, Theoretical; D010087:Oxides / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D014054:Tomography; D014241:Trichloroethylene / Q000737:chemistry*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D017895:Manganese Compounds; D010087:Oxides; D014874:Water Pollutants, Chemical; C048856:permanganic acid; D014241:Trichloroethylene; D012822:Silicon Dioxide
keywords: Electrical resistivity tomography (ERT); In situ chemical oxidation (ISCO); Permanganate; Protonation; Trichloroethene (TCE)