Oct. 17, 2000 COLUMBIA, Mo. -- There are certain neighbors no one likes having: the barking dog, the railroad track and, perhaps the most notorious of all, the landfill. More than 200 million tons of trash are produced annually in the United States, and environmental safety and landfill space are always of concern. Therefore, researchers at the University of Missouri-Columbia are developing a new type of landfill liner that improves safety while increasing capacity.
"Since 1993, the Environmental Protection Agency has required that landfills are lined with at least a two-foot layer of compacted soil and a 1.5-millimeter plastic membrane," said John Bowders, an associate professor of civil engineering. "For an alternative liner to be used, it must meet or exceed current standards, and an asphalt liner can do just that."
The asphalt landfill liner has a number of advantages, the most important of which is increased environmental safety. The asphalt liner can have a hydraulic conductivity that is 100 to 1,000 times lower than traditional compacted soil liners. Hydraulic conductivity describes how a liquid flows through a material, and is important when preventing leakage from landfills.
"Landfills with traditional soil liners may have a flow rate of about 140 gallons per acre per day," said Bowders, who works with Civil Engineering Assistant Professor Erik Loehr to evaluate the new liner. "With asphalt alone, the flow rate decreases to about nine gallons per acre per day. When you complete the liner with a layer of sprayed asphalt and a geosynthetic fabric on top, the flow is almost unmeasurable."
Another environmental safety advantage of the asphalt liner is that it is more flexible and pliable than traditional soil liners. This allows it to handle deformations without cracking, which sometime happens with traditional soil liners. In addition, the layer of sprayed asphalt on the liner's surface has the ability to seal itself against punctures, a feature traditional plastic membranes do not possess.
Asphalt landfill liners also take up less space. Traditional soil liners are more than two feet thick, but asphalt liners are between four and six inches thick. Because the liner takes up less space, the landfill can hold more trash.
"Although it doesn't sound like much, the additional volume that the asphalt liner provides is substantial," Bowders said. "If you installed a four-inch-thick asphalt liner on a 30 acre landfill, you would gain 70,000 cubic yards of volume. This would mean that the landfill could hold about 50,000 more tons of trash."
Bowders said that asphalt liners could be used to line about 90 percent of landfills in the United States. Landfills that hold petroleum wastes, hydrocarbon wastes or organic solvents could not use asphalt because these wastes could degrade the liner. He added that installation costs are comparable between asphalt and traditional liners.
Produced from a variation of the same materials that are used in road construction, the development of the asphalt landfill liner is based on the knowledge that natural asphalt formations are known to remain intact for between 3,000 and 6,000 years.
"Today's compacted soil/plastic membrane liners can last up to 700 years, but more permanent systems are in demand," Bowders said. "Using asphalt, we can build liners that could last for 1,000 years and beyond."
A 180-by-50-foot test pad has been built near Blue Springs, Mo., to study the properties of asphalt landfill liners. Laboratory and field testing have produced a number of results, prompting Bowders' research team to develop a set of construction recommendations.
These recommendations will be outlined in the paper, "Asphalt Barriers for Waste Isolation," that will be presented at the GeoEng2000 Conference in Melbourne, Australia, from Nov. 19 through 24. The conference brings together members of a number of international organizations including the International Society for Soil Mechanics and Geotechnical Engineering, the International Society for Rock Mechanics, and the International Association of Engineering Geology and the Environment.
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