research by Chris Neuzil - US Geological Survey

Chris Neuzil's research at the USGS mainly focusses on the hydrologic behavior of Cretaceous Shales. The nature of groundwater flow in these low permeability settings is poorly understood firstly due to historic inattention to non-aquifer/reservoir rock units and secondly due to inherent difficulties, related to time and size scales, of observing the phenomena of interest. Nonetheless, low-permeability units are of great importance because they mediate aquifer/reservoir behavior, have important roles in the evolution of hydrologic systems and geologic processes over geologic time and can confine toxic materials for long periods. Cretaceous shales in the US midcontinent offer the opportunity of studying, at relatively accessible depths, thick and extensive bodies of low-permeability media. Objectives of this project are to develop, through theoretical studies coupled with study of the flow systems in midcontinental Cretaceous shales, a better understanding of the significant flow processes in low-permeability environments. This information can then be exploited to extract information about flow history retained in the current conditions because of long response times and also will permit long-term prediction of flow behavior. An overview of the publications on this topic can be found hereIcon_External_Link.

Chis recently published a well written publication wich shows that recent experimental data points to a greater role for osmotic pressures in the subsurface. The complete article can be found via the
download page or at the website of the USGSIcon_External_Link. A short on-line summary can be found at the Water Resources ResearchIcon_External_Link website of the AGUIcon_External_Link.

follow-up on my research

My research on chemical osmosis in natural clayey material formed the basis the research project Chemically and electrically coupled transport in clayey soils and sediments funded by the TRIAS-program, which stands for TRIpartite Approach on Soil System processes, managed by NWOIcon_External_Link. The project was an interdisciplinary research involving laboratory work, field investigation and numerical modelling. The results of this research project are compiled in three Ph.D.-theses. Katje Heister at Utrecht University focused on the performance of laboratory experiments to quantify the effect of induced electrical potentials on the transport of water and ions in clays. Ana Maria Garavito at the Free University of Amsterdam worked on the field investigation of osmotic phenomena. Finally, Sam Bader at the Technical University of Delft worked on the development of a continuous transport model that takes into account chemical osmosis and electro-osmosis. On this page a short introduction of these studies is given together with links where more information can be found. The full text of all three Ph.D.-thesis are also available via the download page.

by Katja Heister - Utrecht University

The research focused on the determination of the ideality of selected clayey materials as semipermeable membranes for chemical and electro osmosis. Chemical and electro osmosis belong to the coupled flow phenomena. They can be described with coupled flow equations of irreversible thermodynamics. The contribution of these coupled flow phenomena to solute and water transport are not negligible in materials with a low hydraulic conductivity, although they are not taken into account in existing water transport models yet. In this context induced electrokinetic phenomena due to water transport such as streaming potentials and membrane potentials were measured by means of laboratory experiments. Sample materials include commercially available bentonite and clay samples associated with field experiments performed by Ana Maria Garavito at the Free University of Amsterdam, for example the Boom Clay. The results were used to predict the osmotic water transport when electrical gradients are applied across a sample.

Katja defended her Ph.D.-thesis titled
Coupled transport in clayey materials with emphasis on induced electrokinetic phenomena on May 30th, 2005.

Links to more information on the work Kaja did can be found on these sites:

Katja Heister currently holds a position at the Lehrstuhl für BodenkundeIcon_External_Link, Technische Universität MünchenIcon_External_Link, Freising, Germany.

by Ana Maria Garavito - Free University of Amsterdam

The object of this project is to quantify the role of chemically and electrically coupled transport in clayey soils and sediments and to try to establish its relevance for the distribution and emission of contaminants and water. The focus of this Ph.D.-research wa on field investigation of osmotic phenomena. The objective of the work, as formulated at the start of the project, was to provide field evidence for osmotic phenomena of clayey sediments and to quantify membrane properties from in-situ tests. Additionally, numerical modelling was initially proposed to assess the significance of the inferred membrane properties for flow and transport in groundwater systems. Of these two objectives, the first has received far more attention than the second. The main topic of the research and thus the Ph.D.-manuscript is, therefore, field experiments and in-situ measurement of membrane behavior and membrane properties of clays. Both shallow, unconsolidated clays and deep, strongly consolidated clays have been investigated. The focus is on natural clays and chemical osmosis phenomena. Numerical modelling has also been primarily applied in the context of field experiments.

Ana Maria defended her Ph.D.-thesis with the title
Chemical osmosis in clayey sediments on February 6th, 2006.

Links to more information on the work Ana Maria did can be found on these sites:
  • full textIcon_External_Link (3.6 Mb pdf-file) of her Ph.D.-thesis

by Sam Bader - Technical University of Delft

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 or 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:
  • 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.
  • in the assessment of contaminant leakage from disposal sites of waste of high salt concentration with clay as impermeable liner.
  • in the 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 research 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.

Sam defended his Ph.D.-thesis with the title
Osmosis in groundwater: chemical and electrical extensions to Darcy's Law on October 4th, 2005.

Links to more information on the work Sam did can be found on these sites:

Sam Bader is currently working at the Laboratory for Radiation Research at the National Institute for Public Health and Environment, RIVMIcon_External_Link, Bilthoven, the Netherlands.