Influence of Water Content on SVE in a Silt Loam Soil

The performance of soil vapor extraction systems in the field commonly is less than optimum and is difficult to predict. The factors that cause deteriorating performance are not well understood or quantified. To gain a better understanding, the venting behavior of a single compound (toluene) and a binary mixture (toluene and m-xylene) from a silt loam soil was investigated in a series of multiple column experiments. The contaminants were present initially as non-aqueous-phase liquids. The venting experiments were conducted at three water contents of air-dry, 16 and 22 wt%. The vapor extraction was influenced strongly by the soil's water content. Equilibrium conditions predominated for the air-dry and 16% water content experiments. At a water content of 22%, venting became mass transfer limited. This mass transfer limitation developed early in the venting process with the non-aqueous-phase liquid still present.