Determination of Chlorinated Solvent Sorption by Porous Material—Application to Trichloroethene Vapor on Cement Mortar

Abstract

Experiments have been performed to investigate the sorption of trichloroethene (TCE) vapor by concrete material or, more specifically, the cement mortar component. Gas-flow experiments were conducted using columns packed with small pieces of cement mortar obtained from the grinding of typical concrete material. Transport and retardation of TCE at high vapor concentrations (500 mg L−1) was compared to that of a non-reactive gas tracer (Sulfur Hexafluoride, SF6). The results show a large magnitude of retardation (retardation factor = 23) and sorption (sorption coefficient = 10.6 cm3 g−1) for TCE, compared to negligible sorption for SF6. This magnitude of sorption obtained with pollutant vapor is much bigger than the one obtained for aqueous-flow experiments conducted for water-saturated systems. The considerable sorption exhibited for TCE under vapor-flow conditions is attributed to some combination of accumulation at the air-water interface and vapor-phase adsorption, both of which are anticipated to be significant for this system given the large surface area associated with the cement mortar. Transport of both SF6 and TCE was simulated successfully with a two-region physical non-equilibrium model, consistent with the dual-medium structure of the crushed cement mortar. This work emphasizes the importance of taking into account sorption phenomena when modeling transport of volatile organic compounds through concrete material, especially in regard to assessing vapor intrusion.

Field Study of Soil Vapor Extraction for Reducing Off‐Site Vapor Intrusion

“…A likely explanation is the placement of subslab probes in locations with good slab integrity spaced away from cracks or other potential openings where VI occurs. As suggested by the persistence of indoor air concentrations and rapid rebound in subslab probes, the concrete slab itself could also be a reservoir of contaminants that were released and became available to discrete building entry points (Musielak et al ). Very low flow in and around these small, discrete slab openings during SVE would be undetected by conventional field instruments in nearby probes but would have a significant impact on indoor air concentrations (U.S. EPA ).…”