EPSCoR: Investigating NAPL Source Removal From Low Permeable Silt Layers

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

0229147 Hayden The overall focus of this research is to investigate the behavior, and enhanced removal of a nonaqueous phase liquid (NAPL) contamination from low permeable silt layers under unsaturated conditions. Low temperature heating will also be employed in the silt layer and the effect of this on contaminant removal will be determined. A comprehensive approach to investigating this problem including laboratory experiments, field data and mathematical modeling will be used. A unique large-scale (10'x14'x 8') state-of-the-art physical groundwater will be used for pilot-scale experiments. Column experiments will be used for measuring thermal conductivity as a function of moisture content. Existing temperature data from our doctoral student's field site will be modeled and used to size the power requirements for the large-scale tank experiments. Finally, mathematical modeling of heat and mass transfer will be performed and applied to the laboratory data in order to better understand the processes involved. NAPL contamination in low permeable porous media is still a significant long-term source of groundwater contamination that continues to defy current remediation strategies. In the unsaturated zone, soil vapor extraction (SVE) is a common in-situ remediation technique, but it is energy intensive, expensive and less effective for sites where the NAPL contamination is residing in low permeable layers. Passive SVE is a relatively new, innovative remediation technology that utilizes changes in barometric pressure to pump gas from the soil and does not rely on electricity. This low cost technique is useful at sites where rates of mass transfer are low, such as in low permeable media, and where health and environmental risk are not imminent. Low temperature heating using renewable technologies offers a low cost, and more sustainable solution to the idea of heating the subsurface than other heating technologies. The idea is to heat the subsurface such that mass transfer from the low permeable layers to more permeable layers is enhanced. In combination with another low cost method, such as passive SVE, this technique could greatly enhance the removal of the contaminants. Low temperature heating could also greatly enhance the biological activity in the heated layer thereby enhancing the degradation of the contaminants. Heating using renewable energy sources provides intermittent heating, which may be advantageous in that it will result in less drying of the soil. Drying the soil may defeat the purpose if enhancing biological degradation is the aim. The intellectual merit of the experimental and modeling research proposed is that it will lead to a better understanding of NAPL source removal and NAPL mass transfer from silt layers. In addition, heat transfer through silt media at different water saturations will also be determined. The application of renewable technologies to site remediation is an intriguing possibility that needs to be explored further.