Environmental Hydrogeology
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Chemically and electrically coupled transport in clayey soils and sediments
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Researchers: drs. S. Bader, dr. R.J. Schotting
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Collaboration with: University of Utrecht,
Vrije Universiteit Amsterdam,
Transport of water and solutes in clayey soils and sediments plays a crucial role in management of groundwater
quantity and quality. In nearly all existing water transport models, water movement is driven by differences
in hydraulic potential and solution density only. However, for well compacted clayey materials other driving
forces can induce water transport as well. Theoretical formulations exist to describe water transport in these
media induced by gradients in salt concentration (chemical osmosis) and electrical potential (electro-osmosis).
Any of these gradients can in turn induce one or more of the other gradients. A well known example of this is the
electrical ("streaming") potential induced by hydraulic water transport. Thus a clay layer can act as transport
membrane for chemical and electro-osmosis. The ideality of clay as transport membrane depends on its surface
charge, cation occupation and degree of compaction. Chemically and electrically driven water transport in
porous earth materials is significant at hydraulic conductivities below 10e-9 m/s.
To this date, chemical- and
electro-osmosis are absent in groundwater models and experimental and fields studies of these processes hardly
exist. Moreover, transport of water by osmotic potential gradients is unjustly neglected in several practical
situations, for instance:
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in assessment of seepage, drainage capacity, salt water intrusion and groundwater extraction in holocene coastal areas, where clay layers are subject to large gradients in salt concentration.
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in assessment of contaminant leakage from disposal sites of waste of high salt concentration with clay as impermeable liner.
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in assessments of contaminant emissions from contaminated clay in regions of large salt concentrations, e.g. storage sites of harbour sludge in coastal areas.
In this part of the project, chemical and electro-osmosis are incorporated in an existing groundwater model
and the behaviour of this model will be studied numerically as well as analytically.
This project is a cooperation with the Vrije Universiteit Amsterdam, where a Ph.D. will be performing
field studies for validation of osmotic transport, and the University of Utrecht, where a third Ph.D. will
be doing laboratory studies of transport by chemical and electro-osmotic coupling.
