Application of six-phase soil heating technology for groundwater remediation

Abstract

A treatability study for implementation of a thermally enhanced environmental remediation technique has recently been completed at a Department of Energy uranium enrichment facility in Paducah, KY. The contaminated groundwater plume beneath the site, containing primarily trichloroethylene (TCE) and technetium-99, is one of the largest-ever documented plumes, encompassing some quarter of a billion m 3 of contaminated water (10 billion gal). Various remediation technologies have been applied at the plant site over the past 15 years with moderate degrees of success. The presence of dense nonaqueous phase liquids (DNAPLs) in the groundwater are believed to be one of the major sources of TCE feeding the contaminated plume. Recovery/remediation of these DNAPLs was attempted in a small-scale study with a soil-heating technique called six-phase soil heating. This technology uses buried resistive heating probes to heat the soil and associated liquids upward to 125° C to literally vaporize the TCE solvent. Vacuum recovery wells are used to direct solvent/water vapor flow to the surface for recovery. At the end of the test period, soil and groundwater samples were compared to baseline (pretreatment) samples. This comparison indicated an average TCE concentration reduction in soil of 98% and greater than 99% reduction in TCE concentrations in groundwater within the test cell. Two- and 4-week posttreatment groundwater samples within the test cell have shown a slight fluctuating increase from end-of-test results, but all samples collected at various well depths indicate greater than 98% reduction in TCE concentration. Monitoring well data indicates six-phase soil heating technology was effective in extracting solvent DNAPLs rather than merely relocating them. Results of this treatability study were judged to be favorable and a full-scale implementation at the site has been recommended. © 2004 American Institute of Chemical Engineers Environ Prog.