Abstract

Air sparging (AS) laboratory experiments were performed to assess the effects of grain-size heterogeneity and sediment stratification on air-flow geometry and area of impact. Results were interpreted in terms of the three air-flow geometries described in the literature: chamber flow, channelized flow, and pervasive/bubbly flow. Compared to sparging experiments in monostratigraphic layers, AS of coarsening-upward sequences can increase the extent of the sediment column affected by air because of changes in air-flow geometry and/or sparge angle at strata transition boundaries. AS of fining-upward sequences can also increase the extent of sediment affected in an overlying unit in which channelized flow occurs by generating multiple air-source points. Laboratory simulations of the AS injection interval, representative grain size, and stratified saturated zone of a field site were also performed. These experiments indicated the potential occurrence of chamber flow at the site and revealed the effect of pulsed AS. The effect is to fill in areas of the sedimentary column between air-flow chambers that otherwise would not be affected by air during continuous sparging. This phenomenon, observed in the laboratory, is a likely explanation for remediation performance at the site.

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