Use of Wyoming Bentonite As a Soil Sealant From The
Impoundment of Highly Contaminated Industrial
Wastewater
JOHN HUGHES, Manager
Industrial Sales Division
American Colloid Company
Skokie, Illinois 60067
INTRODUCTION
In the designing of industrial waste pollution control systems there is frequently a
necessity for the storage of substantial quantities of the waste before, during, or after the
treatment process.
Traditionally, large diameter steel tanks or concrete structures have been used for such
impoundments.
However, due to the cost of these storage methods and the potentially damaging effect
of the stored liquids on the containers themselves, the use of earthern structures for the
containment of liquid wastes is becoming increasingly popular. These earthern structures
are referred to as retention lagoons, storage lagoons, or surge lagoons.
Clearly, it is necessary that the liquids should not seep out of the storage lagoons, into
the ground water table, or into neighboring containment areas. If one is fortunate enough to
locate the lagoon in a natural clay bed seepage may not be a problem, but here the benefits
may be more apparent than real, and I will refer later to the problems that can be
experienced with impoundment of contaminated waste in natural clay areas. However, in
cases where there is natural soil seepage, a lagoon lining system must be utilized for seepage
control.
Plastics and rubber liners of various kinds have been used for such applications, but
their use in the future is most likely limited by: I) The increased cost of these
petrochemically related products, and 2) The fact that a lagoon once installed with a specific
synthetic liner may in the future prove a constraint of the operation, since a change in the
operation resulting in the production of an effluent containing certain products
incompatible with those liners will cause a breakdown of the liner.
BENTONITE CLAY AS A SEALANT
One of the oldest means of sealing lagoons is with the use of bentonite clay, a material
found in the South Dakota and Wyoming areas of the United States. The use of this product
is enjoying a resurgence due to a recognition of its favorable economics and versatility.
This clay, found exclusively in Wyoming, South Dakota and Montana, is known for its
high swelling properties when contacted with water. Swelling of 10 times its original volume
is fairly common, but published data often reveals this refers to an average swelling of 13.8
times its original volume.
For ease of discussion in the balance of this paper, I shall consider that the bentonite
will swell to 10 times its original volume when contacted with water.
This swelling is important, since the entire swollen mass — that is clay and water —
behave as if it were clay. If, for example, one was seeking a soil with 50% natural clay, and
since bentonite will swell to 10 times its original volume, clearly one would need only 5% of
bentonite which, when fully swollen, would behave in the same fashion as a soil containing
148