Abstract

Laboratory visualization experiments in fine- to very fine-grained sands (grain diameter <0.21 mm) re- veal a previously unrecognized air-flow geometry. This air-flow geometry is termed and is char- acterized by: (1) a significant horizontal component, (2) pervasive air-flow coverage within a region demarcated by a distinct, irregular boundary, and (3) the presence of predominantly vertical inlet and outlet channels. The at- tributes of chamber flow differ significantly from chan- nelized flow and pervasive/bubbly flow, which occur at larger grain sizes and have been described in the litera- ture by several researchers. Previous research, which in- dicates a dramatic increase in contaminant removal time in sediments <0.2 mm, indirectly corroborates the phe- nomena observed in this study. The extent of sediment column affected by chamber flow of sparge air ranges from 4-54% on an area basis, and is approximately 28% on a volume basis. These values indicate that chamber air flow has the potential to affect a much larger percent- age of the sediment column than either channelized or pervasive/bubbly flow. Because of the irregularity of air- flow chambers, in terms of both form and frequency, a detailed knowledge of stratigraphy is important to maxi- mize air-sparging efficiency at sites where chamber flow is likely to occur. Resume Des experiences de visualisation en laboratoire dans des sables a grains fins a tres fins (diametre des grains inferieur a 0,21 mm) ont mis en evidence une geo- metrie des ecoulements d'air non reconnue auparavant. Cette geometrie des ecoulements d'air est nommee «ecoulement en cavite» et est caracterisee par (1) une

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