The Role of Bentonite in Soil Sealing Applications

Abstract

The use of bentonite as a natural soil sealant has experienced a phe­nomenal increase over the past 15 years. Swelling bentonites, which occur mainly in Wyoming, are exported all over the world for various uses, in­cluding the sealing of ponds, lagoons, and landfills and as a component of the slurry in slurry trenching. The natural swelling and adsorption capacity of bentonites are of tremendous value in the sealing off and containment of industrial waste sites. Landfills and lagoons are often constructed in areas where the natural soils have a permeability that is not consistent with safety standards. Admixing 5 to 15 percent bentonite into those soils will quickly reduce the natural permeability to the desired levels. All landfills require a cap once they are filled, to prevent the formation of a “bathtub” full of water and commensurate generation of excessive leachate. A cap consists of a 4 to 6 in. layer of soil-bentonite and two to three ft of natural soil, to allow for vegetation. Over the years, many hazardous waste sites have contaminated the ground water to such a degree that it is not fit for drinking. These sites can be encapsulated by constructing a slurry cut-off wall. These trenches are filled with a bentonite or cement-bentonite slurry during excavation and then backfilled with natural soil or a soil-bentonite mixture. The most important aspects of using bentonites as waste site sealants are the proper installation of the sealing systems and a knowledge of the limitations of bentonites regarding resistance to contamination. Types of bentonite, installation practices, and testing methods are discussed in this paper.