In Situ Mixed Region Vapor Stripping in Low-Permeability Media. 2. Full-Scale Field Experiments

Abstract

This paper is the second in a three-part series that describes mixed region vapor stripping (MRVS) for in situ treatment of fine-grained soils contaminated by volatile organic compounds (VOCs) including trichloroethene (TCE), 1,1,1-trichloroethane (TCA), and related halocarbons. As described in this paper, MRVS processes were studied during full-scale field experiments wherein ambient or heated air was injected at high volumetric flow rates during in situ soil mixing, and VOCs were volatilized and advectively removed from the subsurface, captured in a shroud covering the mixed region, and then treated on-site. The field test was conducted at an inactive land disposal site in southern Ohio where dense silty clay soils were contaminated by VOCs at concentrations in the 10-500 mg kg -1 range. During the field studies, seven columns, each 3.0 m diameter and 4.6 or 6.7 m deep, were treated with ambient air (∼15-25°C) or heated air (∼120-130°C) injected at flow rates of 28-40 m 3 min -1 . Intensive monitoring and measurement activities defined contaminant behavior and key MRVS operation and performance parameters. The field testing revealed that MRVS could rapidly reduce the concentrations of VOCs (i.e., TCE, TCA,...) in dense silty clay soil by 88-98%. The rate and extent of reduction was somewhat higher with the injection of heated air as compared to ambient air. Regardless of injection air temperature, as treatment progressed, the rate of VOC removal became increasingly mass transfer limited.