Influence of the presence of clay and water on the efficiency of soil vapor extraction in sand laboratory columns

Soil vapor extraction (SVE) has been one of the most widely used technologies for remediating sites contaminated with volatile organic compounds. This technique consists of creating a depression in the soil and inducing a controlled flow of air which will entrain the volatile contaminants in the extracted gas phase. To learn the influencing factors that affect the effectiveness of removal of contaminants by the SVE method, an experimental study was performed to provide a comprehensive analysis of the SVE by tracking outgoing gases as well as the hydrodynamics of the flows. Two soil models were used: 100% sand (Soil 1) and sand mixed with 5% of Kaolin (Soil 2). Hydrodynamic tests were carried out using three mass water contents in each soil. It was shown that the quantity of mobile water is largely affected by soil composition. Experiments on soils contaminated by two tested contaminants (decane and toluene) were carried out with samples in dry and wet conditions. Results show that the SVE presented yields of 80.00% and 87.07% of the n-decane and toluene, respectively, injected into Soil 1 against 79.88% and 86.11% of n-decane and toluene, respectively, injected into Soil 2. The decrease of water soil saturation due to the extraction and the influence of the presence of water on the performance of the SVE were highlighted. Lower removal rates were observed for the contaminant with the lower vapor pressure (n-decane).