A study of trichloroethylene (TCE) release rate from Borden, Ont. aquifer sediments through intermittent purging
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The method of contaminant removal, "pump and treat," has been ineffective at fully remediating many sites that have been contaminated with chlorinated solvents due to aqueous-phase contaminant concentration tailing and rebound after cessation of pumping. Contaminant tailing observed during pore-water flushing is the result of long-term slow release of contaminant molecules from solid-phase aquifer material to mobile phase air or groundwater. This research will create an experimental methodology allowing for the measurement of contaminant desorption rates using characterized aquifer lithocomponents. The laboratory experiments employed grains sieved to three different grain size populations of 2.8-4.0mm (big grains), 2.0-2.8mm (medium grains) and 0.7-2.0mm (small grains). The grains were created from the Gull River Formation that is a source rock to the Borden aquifer, Ontario. The grains were pre-equilibrated with trichloroethylene (TCE), a volatile organic compound, at high (∼10 3 mg/L) and low (∼10 0 mg/L) concentration. The sealed rock and water systems were purged and analyzed by gas chromatography over a period of up to about 70 days for the small grains and 220 days for the big grains. The Gull River formation contains kerogen. It has been demonstrated by previous studies that hydrophobic organic compounds, such as TCE, sorb with nonlinear behavior to this sediment. The goal of this project is to demonstrate how this non-linear behavior affects the desorption rate. Experimentally and by numerical simulations we demonstrated that the long term desorption rate is controlled by a consistent mechanism based on retarded pore diffusion.