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Permeability changes in layered sediments: impact of particle release
Theresa Blume1, Noam Weisbrod, John S Selker
1Department of Bioengineering, Oregon State University, Corvallis, USA.
Ground Water
|September 19, 2002
Summary
Freshwater flushing of saline-affected porous media can cause particle release, leading to significant permeability reduction. This phenomenon is particularly concerning in layered natural systems, impacting hydraulic conductivity.
Area of Science:
- Geosciences
- Environmental Science
- Hydrogeology
Background:
- Particle release from porous media can occur when fluid salinity drops below a critical threshold.
- This release can alter hydraulic conductivity through pore clogging or enlargement.
- Layered sediment structures are common in natural environments.
Purpose of the Study:
- To investigate permeability changes in porous media due to particle detachment.
- To understand the impact of salinity changes on sediment transport and pore structure.
Main Methods:
- Column experiments using Hanford Formation sediments (coarse and fine).
- Simulated salinity changes using saline (NaNO3) and freshwater pulses.
- Monitoring of outflow rates, hydraulic head, electrical conductivity, and pH.
Main Results:
- No permeability decrease observed in coarse matrix alone.
- Layered systems (fine sediment within coarse) showed irreversible permeability loss (10-20% of initial).
- Particle detachment and clogging in the fine layer were identified as the primary cause of permeability reduction.
- A sudden increase in outflow pH was observed during freshwater shock.
Conclusions:
- Alteration between saline and freshwater solutions can induce particle release and reduce matrix permeability in layered systems.
- The findings highlight the risk of permeability impairment in natural settings mimicking Hanford site conditions.
- In situ pH generation during freshwater flushing may play a role in particle detachment dynamics.