The effect of spontaneous gas expansion and mobilization on the aqueous-phase concentrations above a dense non-aqueous phase liquid pool |
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Authors: | Kevin G Mumford James E Smith Sarah E Dickson |
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Institution: | 1. Department of Civil Engineering, McMaster University, Hamilton, ON, Canada L8S 4L7;2. School of Geography and Earth Sciences, McMaster University, Hamilton, ON, Canada L8S 4L7 |
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Abstract: | The spontaneous expansion and mobilization of discontinuous gas above dense non-aqueous-phase liquid (DNAPL) pools can affect the aqueous-phase concentrations of the DNAPL constituents above the pool. The results of an intermediate-scale, two-dimensional flow cell experiment showed that the discontinuous gas flow produced by spontaneous expansion, driven by the partitioning of 1,1,1-TCA from the surface of a DNAPL pool, resulted in detectable aqueous-phase concentrations of 1,1,1-TCA well above the pool surface. In comparison to a conventional model for DNAPL pool dissolution in the absence of a discontinuous gas phase, these concentrations were greater than expected, and were present at greater than expected elevations. Additionally, this study showed that the discontinuous gas flow produced transient behavior in the aqueous-phase concentrations, where the elevated concentrations occurred as short-term, pulse-like events. These results suggest that the spontaneous expansion and mobilization of discontinuous gas in DNAPL source zones could lead to the misdiagnosis of source zone architecture using aqueous concentration data, and that the transient nature of the elevated concentrations could further complicate the difficult task of source zone characterization. |
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Keywords: | Groundwater NAPL dissolution Spontaneous gas expansion Unstable gas flow 1 1 1-Trichloroethane Multi-component gas phase Invasion percolation Source characterization |
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