Water Well Journal

March 2015

Water Well Journal

Issue link: https://read.dmtmag.com/i/465664

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Page 28 of 73

Bentonite for Geosynthetic Liners Bentonite for Geosynthetic Liners The use of geosynthetic liners began in Europe in the 1970s. By Heather Otell and Eric Frantz The use of geosynthetic liners began in Europe in the 1970s. By Heather Otell and Eric Frantz A s the global human population grows, so does our waste output. Landfills across the world continue to expand and cover more acreage each year. Surface water, groundwater, and aquifers exist beneath these landfills. A large part of freshwater for drinking and regular day-to-day life exchanges comes from these environments. But what happens when the waste that overlies these underground water sources contaminates them? Increasing technology has also increased the toxicity of waste, as well as our ability to handle these contaminants. Although several industries create these challenges with contaminant output, typically only the environmental industry is responsible for controlling them. Fortunately, the environmental industry has grown and ex- panded its technology to meet the new needs for contaminant or waste leachate control. One of the most effective advances in waste leachate control is the use of geosynthetic clay liners—in which a granular bentonite is incorporated into a plastic or fabric liner. The use of geosynthetic liners began in Europe in the 1970s. They are typically used for landfills, water contain- ment, shoreline protection, dewatering structures, and hydraulic marine structures. In landfill applications, polymer-amended bentonites help to contain leachate contaminants such as heavy metals and various hydrocarbons including methane, gasoline, benzene, and other hazardous compounds that must be isolated from the water beneath. This technique has also been used in the United States since the 1980s. This article focuses on the use of plastic lin- ers alone vs. the use of geosynthetic liners to protect natural groundwater. It also explains the benefits of using Wyoming sodium bentonite vs. other clay types in a geosynthetic clay liner. Clay Liners vs. Plastic Liners Among the first strategies for containing runoff waste and leachate was simply laying a plastic sheet or tarp on the ground. This method can work for simple applications, such as temporarily containing water. Plastic liners are temporary at best because the plastic becomes brittle and cracks over time, enabling the contained substances to leak and penetrate the ground below. From that point, any contaminants can be introduced into groundwater environments. Another issue with plastic is it is not absorptive, which enables accumulation of contaminants under the rubbish in a landfill. An accumulation of toxic contaminants can create harmful gases as well as detrimental effects to groundwater if an accidental discharge occurs from a ruptured liner. Some contaminants will increase the rate of degradation of the liner and compromise the water barrier. Bentonite can be used as a liner and can be applied in vari- ous ways. One way, which is the typical pond sealing applica- tion, is to mix the clay with the native soil before a pond is filled, or to spread it on top of the native soil. Both methods depend on the geology type, and the concentration is matched with the native soil to meet the required permeability. A sample of high quality sodium bentonite ore in its native laminar form. WWJ March 2015 25 Twitter @WaterWellJournl BENTONITE continues on page 26

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