18    LONG-TERM COMPATIBILITY STUDY OF A TREATED
BENTONITE/SOIL LINER WITH A HEAVY METAL
SLUDGE
James T. Olsta, Manager
Environmental Products Division
American Colloid Company
Arlington Heights, Illinois 60004
INTRODUCTION
American Colloid Company is a specialty mineral manufacturer that supplies a wide array of
industrial markets. The Environmental Products Division evolved to serve a growing need by industry, municipalities and commercial entities to control seepage from containment structures such as
ponds, lagoons, landfills and tank farms.
In 1975, a large chemical company in the Northeast United States chose American Colloid Company's contaminant-resistant treated bentonite as part of a double liner system for their proposed
industrial landfill. The chemical company requested that American Colloid Company set up a laboratory permeability column to simulate the landfill. The column was to be maintained for the active life
of the landfill. A column was set up with the actual industrial waste sludge and has been tested for
over ten years.
Since the start-up of this laboratory column, legislation has come into effect which regulates
hazardous waste disposal. The Resource Conservation and Recovery Act (RCRA) of 1976 and its
revision, the Hazardous Solid Waste Act (HSWA) of 1984, provide that soils may be used as a
component of the liner system of a hazardous waste disposal facility. U.S. Environmental Protection
Agency regulations specify liner permeability as a major performance design standard for soil liners.
Additionally, the liner shall prevent migration through itself during the life of the facility.
Fixed-wall permeability measurements have been cited as the most sensitive geotechnical laboratory
method available to measure liner/leachate compatibility and determine the acceptability of a liner
with respect to U.S. EPA criteria.1
The applicability of short-term compatibility testing to the long-term effectiveness of various types
of liner systems comes into question. Only one long-term laboratory study has been reported that
examined the compatibility of a soil liner with actual industrial waste.2 The purpose of this chapter is
to illustrate the long-term effectiveness of a contaminant-resistant treated bentonite/soil liner with an
actual industrial waste as shown by the change in hydraulic conductivity over time.
BACKGROUND
The ability of a native soil to serve as a hydraulic barrier is directly related to the particle size
distribution of the soil. If the clay content is high, the soil will normally have a relatively low
permeability. If the gravel/sand/silt content is high the soil will usually exhibit unacceptably high
permeability characteristics. If sufficient quality soil is not available in the immediate vicinity of a
waste containment project, then admixtures may be considered. The most widely used admixture is
sodium bentonite.
The sodium form of bentonite is mined and processed in the Western United States with the bulk of
proven reserves being located in the states of Wyoming and South Dakota. Bentonite is a clay
comprised primarily of the three-layer alumina silicate mineral called montmorillonite. The characteristic that makes sodium bentonite advantageous as an admixture is its ability to swell many times its
original volume when hydrated. When sodium bentonite is admixed into a soil and wetted, the sodium
bentonite swells and occupies void spaces. The ability of water to pass through the bentonite/soil
admixture is greatly impeded resulting in lower permeabilities.
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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