Pilot-Scale Testing of In Situ Vitrification of Arnold Engineering Development Center Site 10 Contaminated Soils

Process verification testing using in situ vitrification (ISV) was successfully performed in a pilot-scale test using soils containing fuel oils and heavy metals from Site 10 Installation Restoration Program (IRP) at the Arnold Engineering Development Center (AEDC) located in the southern portion of middle Tennessee. This effort was directed through the U.S. Department of Energy ' s Hazardous Waste Remedial Action Program (HAZWRAP) Office managed by Martin Marietta Energy Systems. In situ vitrification is a thermal treatment process that converts contaminated soils and wastes into a durable product containing glass and crystalline phases. During processing, heavy metals or other inorganic constituents are retained and immobilized in the glass structure; organic constituents are typically destroyed or removed and captured by the off-gas treatment system. The objective of this test is to verify the applicability of the ISV process for stabilization of the contaminated soil at Site 10 . The pilotscale ISV testing results, reported herein, indicate that the AEDC Site 10 Fire Training Area may be successfully processed by ISV. Site 10 is a fire training pit that is contaminated with fuel oils and heavy metals from fire training exercises. Actual site material was processed by ISV to verify its feasible application to those soils . Initial feasibility bench-scale testing and analyses of the soils determined that a lower-melting, electrically conductive fluxing additive (such as sodium carbonate) is required as an additive to the soil for ISV processing to work effecti vely. The actual Site 10 soils showed a larger degree of compositional variation than the soil used for the bench-scale test . This variation dictates that each vitrification setting should be analyzed to determine the composition as. a function of depth and location . This data will dictate the amount (if any) of fluxing add itives of sodium and calci um to bring the melt composition to the recommended quantity of 5 wt% sodium and 5 wt% calcium oxide. Each variable additive adjustment would result in a vitrification melt composition of 5 wt% calcium and sodium oxide content . The pilot -scale operation created a vitrified block weighing 15 metric t onnes (t) and measuring 1.5 m (5 ft) deep and 2.4 m (8 ft) on each side. The quantity of fluxing additives and the method of placing the fluxing additives in the surface cover soil limited the operating electrical system providing power to the ISV melt. The power limitation created enhanced lateral growth of the block and resulted in a shallower depth . This method of adding fluxes demonstrated that ISV operating efficiency would be greatly improved if the fluxes were injected or mixed with the entire designated vitrification volume. However, the volume vitrified contained a sufficient quantity of hazardous contaminants to allow for an effective verification evaluation of ISV processing of the AEDC Site 10. Analytical efforts for this project were directed towards evaluating the organic destruction and thermal transport effects of ISV processing on the Site 10 contaminated soil. No thermal transport of hydrocarbon contaminants to the surrounding soil were detected. These results continue to confirm the organic destruction and nontransport mechanisms presented in this report . Off-gas releases of the hydrocarbons indicated an 89 wt% destruction efficiency by the ISV process exclusive of off-gas treatment. The destruction and removal efficiency of the overall ISV system was 99.85 wt%. Leach testing using extraction procedure (EP) toxicity and toxic characteristics leach procedure (TCLP) showed that all metals of concern were below leach testing release limits, indicating that the ISV process produces a nonhazardous product . These favorable results indicate that ISV can be used to effectively treat and remediate the contaminated soils at the AEDC Site 10