Abstract

This study provides experimental evidence for the analytic model of oscillatory transport in soils, in which a vapor or solute in an oscillating mobile gas or liquid undergoes rate-limited equilibration with an immobile phase. During a field test of passive soil vapor extraction, the concentrations of volatile organic compounds in the produced gas were monitored at 90-min intervals. The data were compared with the results of numerical simulations based on the mobile–immobile model of oscillatory transport. A dual-porosity simulation matched the data when the simulated time for equilibration between the mobile vapor and the immobile phases was one-third day and the flow was restricted to only 5% of the air-filled porosity. A purely diffusion calculation without flow, utilizing the exchange diffusivity derived from the mobile–immobile model, predicted total production of extracted vapor during a 1-yr interval in agreement with the simulation. This illustrates the utility of the exchange diffusivity as an evaluation tool for passive soil vapor extraction.

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