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Title: Does Water Content or Flow Rate Control Colloid Transport in Unsaturated Porous Media?

Mobile colloids can play an important role in contaminant transport in soils: many contaminants exist in colloidal form, and colloids can facilitate transport of otherwise immobile contaminants. In unsaturated soils, colloid transport is, among other factors, affected by water content and flow rate. Our objective was to determine whether water content or flow rate is more important for colloid transport. We passed negatively charged polystyrene colloids (220 nm diameter) through unsaturated sand-filled columns under steady-state flow at different water contents (effective water saturations Se ranging from 0.1 to 1.0, with Se = (? – ?r)/(?s – ?r)) and flow rates (pore water velocities v of 5 and 10 cm/min). Water content was the dominant factor in our experiments. Colloid transport decreased with decreasing water content, and below a critical water content (Se < 0.1), colloid transport was inhibited, and colloids were strained in water films. Pendular ring and water film thickness calculations indicated that colloids can move only when pendular rings are interconnected. The flow rate affected retention of colloids in the secondary energy minimum, with less colloids being trapped when the flow rate increased. These results confirm the importance of both water content and flow rate for colloid transportmore » in unsaturated porous media and highlight the dominant role of water content.« less
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Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0013--936X
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science and Technology; Journal Volume: 48; Journal Issue: 7
Research Org:
Idaho National Laboratory (INL)
Sponsoring Org:
Country of Publication:
United States
99 GENERAL AND MISCELLANEOUS colloid transport; water content