BREAKTHROUGH OF BRINE THROUGH
COMPACTED FINE GRAINED SOILS
Kevin J. D. Ridley, Research Assistant
J. K. Bewtra, Professor
Department of Civil Engineering
University of Windsor
Windsor, Ontario
Canada N9B 3P4
INTRODUCTION
Compacted Fine grained soil is used as a barrier to contain domestic and industrial wastewaters,
some of which may be extremely hazardous. Often the assumption is made that the soil material composing the liner will be sufficiently thick and impermeable to prevent the stored liquid from seeping
into the natural environment. However, compacted fine grained soil has a finite hydraulic conductivity and ultimately, over long periods of time, a breakthrough will occur depending on the type and
amount of compaction, amount of moulding water used, use of additives, and the amount and type of
clay minerals present. The breakthrough phenomena is inevitable, even if the stored fluid or generated
leachate is nonreactive with the soil.
Motivation for this study was to demonstrate: (1) the breakthrough phenomenon; and (2) that the
breakthrough of an anionic pollutant, CI " , from a compacted fine grained soil mass occurs much
faster than the rate that simple seepage theory predicts.
A 30% NaCl brine was used as the permeant. Brine was selected for this study because compacted
fine grained soils are currently being used as a containment barrier for storing brine in surface reservoirs. The brine is used as a displacement medium for petroleum by-products stored beneath the
ground, as a dust-inhibiting compound on country roads, and as a medium for entrapment of solar
energy.
LITERATURE REVIEW
Displacement studies have become important in predicting the movement of dissolved chemical
substances or solutes through soil. Studies of this nature can provide valuable information about the
porous medium and the behavior of a chemical in that medium. The work which has been done to
date is reviewed and well documented [1-3].
The mass transport of solutes by the bulk motion of the flowing fluid can be approximated by
Darcy's law in a macroscopic sense. This process is known as convection. Nonreactive solutes are carried at the average linear velocity of the permeant with no compensation for the distribution of fluid
velocities within the pores. Thus, convective flow is often referred to as plug or piston-type flow.
However, the solute displays a tendency to deviate and spread out from the path predicted by the convective hydraulics of the flow system causing dilution of the solute. This phenomenon is referred to as
hydrodynamic dispersion and occurs because of the combined effects of mechanical mixing that
causes disperson and molecular diffusion. The following definitions by Simpson [4] are used to define
diffusion and dispersion.
Diffusion-the spreading of particles, molecules, atoms or ions in a vacuum, a fluid or a fluid-filled (or a fluid-
and-gas-filled) porous medium, in a direction tending to equalize concentrations in all parts of the system. It
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