Hydraulic Conductivity Reductions Resulting from Clay Dispersion within
Alluvial Sediments Impacted by Sodium-rich Water
By Lance J. King and Harold W. Olsen, Colorado School of Mines, Golden, Colorado,
and George N. Breit, U.S. Geological Survey, Denver, Colorado.
ABSTRACT
Substantial reductions in hydraulic conductivity (HC) of soils and sediment
can result from dispersion of clay into flowing ground water. Smectitic clays
with high amounts of exchangeable sodium are particularly likely to disperse
into ground water if the ionic strength of the pore water substantially decreases.
Our experimental study evaluated the HC decrease possible due to clay dispersion
resulting from a sodium-rich leachate plume moving through smectite-containing
alluvium near the Norman Landfill, Oklahoma. Core samples of alluvium were
placed in a triaxial cell and flushed with background water, NaCl solutions
and distilled water. These tests detected substantial dispersion of clay that
was associated with decreases in HC of more than two orders of magnitude from
4.38 x 10-3 cm/sec to 2.05 x 10-5
cm/sec (centimeters per second) in sediments containing less than 5 percent
clay-sized particles. The change in HC attributable to clay dispersion can
change the distribution of hydraulic conductivity in an aquifer. Such changes
need to be considered in forecasting plume migration and developing remediation
strategies.