Numerical Study of Volatile Organic Compound Removal in 3D Field-scale Thermal Treatment

ABSTRACT: Non-aqueous phase liquids (NAPLs) such as chlorinated solvents and petroleum products have the potential to contaminate soil and groundwater. NAPLs slowly dissolve into groundwater and can persist for centuries if not treated. In situ thermal treatment (ISTT) technologies, such as electrical resistance heating (ERH) and thermal conductive heating (TCH), can be effective in treating NAPL sources if implemented correctly and have the potential to achieve up to 99% mass recovery. ISTT technologies rely on increasing the temperature of the subsurface to increase the mobility of contaminants, particularly through vaporization, which enables subsequent extraction and treatment. However, failure to reach target temperature or capture contaminant vapors can result in incomplete NAPL mass removal and possible redistribution of contamination. To investigate the effectiveness of ISTT under different field conditions, a 3D field-scale model is developed to simulate the mass recovery of NAPL sources by TCH. The developed model couples a finite difference model that simulates variably saturated flow, heat transfer and phase change with a macroscopic invasion percolation (Macro-IP) model that simulates gas migration. This model will be used to simulate NAPL removal under different permeability distributions, boundary conditions, and heater and extractor configurations to investigate their correlations with mass recovery. The simulations can be used to examine the usefulness of indicators (i.e., temperature, mass recovery curve) for determining the progress of mass recovery. In addition, the model can serve as a tool to identify the factors that may cause incomplete removal of NAPL sources under different field conditions, such as insufficient heating due to high groundwater fluxes and escaped contaminant vapors outside the heated zone, which can be helpful for planning and decision-making in ISTT applications.