Some four centuries ago, Sir Walter Raleigh happened upon asphalt from Pitch Lake in La Brea, Trinidad, and used the substance to caulk his ships, calling it "Most Excellent Goode." Over the years many engineers who've turned to asphalt for roofing, paving and other projects have echoed his praise. Now John Bowders and Erik Loehr of the University of Missouri have come across another promising asphalt application: using it to make liners to seal off potentially hazardous landfills. The idea is now being field-tested at a site 180 by 50 feet near Blue Springs, Mo., and the researchers are presenting construction recommendations at this November's GeoEng2000 Conference in Australia.
Just as Raleigh found that asphalt could prevent leaking in his ships, Bowders and his colleagues say it will help contain waste in landfills far better than current liners, which typically consist of two feet of compacted soil and 1.5-millimeter-thick plastic membranes. The hydraulic conductivity of the asphalt liner--a measure of how readily liquid flows through it--is 100 to 1,000 times less than that for soil counterparts; the flow rate, too, is dramatically decreased. Also, the asphalt liner is more flexible, thus less liable to crack, and impervious to punctures. Finally, it takes up less space, costs the same amount to install and should prove more lasting than traditional liners. It's not for all landfills. Petroleum wastes, hydrocarbon wastes and organic solvents can degrade the new liner. But Bowders says it could be applied to 90 percent of all landfills in the U.S.