Laboratory Evaluation of Low-Temperature Thermally-Enhanced Soil Vapor Extraction

The goal of this study is to understand the conditions in which heat collected from soil-borehole thermal energy storage (SBTES) systems can be used for thermally enhanced vapor extraction. Although thermal enhancement of soil-vapor extraction (SVE) has been investigated in several studies, they typically involved temperatures in the range of 50-400 degrees C. The soil in SBTES systems typically only reaches temperatures of 40-60 degrees C, which is not significant but is from a renewable source and can be applied for a long duration at low cost. The approach used in this study involves column tests in which a vacuum is used to draw air through an unsaturated soil layer that has a uniform initial diesel distribution. Three tests were performed in which the soil was heated to 20, 40, and 60 degrees C and a vacuum was imposed to cause upward air flow through the soil column. The amount of diesel removed from the soil increased with temperature. Although up to 90% of the pore water was removed in the 60 degrees C test, only a small fraction of the free-phase diesel was removed due to its low volatility. Nonetheless, the results indicate that combining SBTES systems with remediation strategies for volatile NAPLs may have a positive long-term impact on the reuse of contaminated sites.