PI/Co-PI: Jim Smart, PhD and David Atwood PhD (University of Kentucky)

Keywords: soil resistance heating, environmental remediation, TCE

In the closing years of the 20 th Century, de facto technology standards for environmental remediation of groundwater and soil was pump-and-treat and ex-situ incineration/disposal, respectively. Since then, new in-situ technologies are being developed and refined, including electoosmosis, permeable treatment zones, and ohmic heating. Six-phase heating is an in-situ resistive heating technique that literally heats up the soil and groundwater with use of electrodes, inserted to depths of 30 m. Over a period of months as the entire soil and water mass achieve elevated temperatures, objectionable contaminants such as volatile organic compounds (VOCs) reach their boiling point. These vaporized contaminants are coaxed out of the soil and water and are pulled out of the vadose and saturated zones with a vapor extraction system. The vapors are collected and condensed at ground level for disposal or further treatment.

Even though basic operational principles of ohmic heating technology are successfully applied in the field environment, possible reaction mechanisms and consequences associated with heating organic compounds to elevated temperatures (125 o C) over a period of months are not well understood. Transformation reactions of VOCs can occur through numerous abiotic and biotic methods, including biodegradation, photolysis, hydrolysis, oxidation, and reduction. Most of the organic contaminants vaporized in an actual ohmic heating remediation campaign are collected and condensed in tact. However, there are degradative reactions occurring in the remediation process and some residual daughter products may remain behind in the vadose or saturated zones of the environment. It would be desirable to study possible pathways and kinetic rates associated with generation of these transformative reactions. In this manner, predictions about their generation and subsequent minimization may be possible.

Abiotic transformations of trichloroethene (TCE) are not well understood, even under ambient conditions. In the past thirty years, investigators have been studying individual abiotic transformation pathways of TCE, including hydrolysis, aqueous oxidation, and reductive dehalogenation. This proposal intends to assemble all previous kinetic rate studies at conditions corresponding to six-phase heating and combine them with new laboratory results of reductive chlorination by key metals found in soils. In this manner, predictive rates of TCE transformation pathways under ohmic heating conditions can be described. These predictions will be compared to further measurements of TCE transformation in more complex soil/groundwater matrices.

Currently, a six-phase heating remediation event of TCE contaminated soil and groundwater is planned at a Department of Energy uranium enrichment site at Paducah, Kentucky later this year. It would be possible to collect soil and groundwater samples during the actual remediation event and study transformation reactions of TCE