This SERDP-sponsored research project elucidated the principle mechanisms controlling the performance of Thermal Conduction Heating (TCH) for treatment of Dense Nonaqueous Phase Liquids (DNAPL) in aquitards. To improve understanding of heat transfer and remediation mechanisms, 2D and 3D experiments and numerical simulations were conducted. Tanks (volume 75 and 150 m~3; height 4.5 m) were filled with silt-sized material (aquitard layer, Ks = 10~(-6) to 10~(-7) m/s), above a sandy underlying aquifer layer, and beneath a sandy overlying vadose layer. The groundwater level was maintained at the top of the aquitard layer, which was contaminated in some experiments with perchloroethylene (PCE) and tracers. Thermal wells in the aquitard heated the pore water to steam temperatures and vaporized the contaminants for recovery by Soil Vapor Extraction (SVE). The groundwater flux was controlled, as were power consumption and SVE fluxes. Hundreds of sensors enabled determination of characteristic heat transport and multiphase flow parameters. The impact of different groundwater fluxes was quantified, as was the contaminant removal efficiency.
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