March 31, 2002
Natural cleanups picking up steam
By PAUL M. KRAWZAK
Copley News Service
WASHINGTON — Natural attenuation, the main component in plans to clean up the Industrial Excess Landfill, is a new term for an ancient process.
At least since the days of the American colonists, people have segregated hazardous wastes in holding ponds where they break
down into less harmful substances.
“Natural system technology is an old concept,” said Carl Tammi, a wetlands biologist for ENSR International, an environmental
consulting firm in Westford, Mass. “But it’s only recently been re-evaluated for things beyond domestic and municipal waste water.”
In the last decade or so, the deployment of natural processes to deal with closed landfills has become increasingly popular. The
method is much cheaper than clay or synthetic caps; pumping and treating ground water; or excavating and transporting toxic
According to authorities, probably several dozen waste sites across the nation are using some natural remediation. They include toxic waste sites supervised by the U.S. Departments of Energy and Defense, the Environmental Protection Agency, and state and local governments.
“Natural attenuation” describes the processes by which bacteria break down many types of contaminants in ground water or soil. It typically occurs without human intervention and may take years or decades.
Sometimes, the breaking down gets a boost from planted trees, whose roots deliver air and other substances to accelerate the
Roots “oxygenate the soil, promoting microbial degradations,” Tammi explained.
Natural cleanup techniques have “really gathered steam in the last five years,” said Craig H. Benson, a geo-environmental engineer at the University of Wisconsin-Madison. “There are lots of landfills considering them.”
Benson is among the investigators in a U.S. EPA evaluation of the effectiveness of vegetative caps in blocking water infiltration at U.S. landfills.
Vegetative caps, vegetative covers and phytoremediation are different forms of natural remediation.
Phytoremediation refers to the use of trees or plants to draw contaminants from the soil or ground water, absorb and break them down into harmless components, and even release them into the air through leaves.
Vegetative caps serve the same function as clay or synthetic caps, which prevent rainwater from percolating down into buried
wastes, picking up contaminants and transporting them to the ground water below.
The natural caps are built by covering a landfill with several feet of soil and planting vegetation. The soil and plants soak up water and release it into the air before it reaches buried waste.
The cover proposed for the Industrial Excess Landfill near Uniontown will stop some, but not all, surface water from penetrating. It is not designed as a true cap, state and federal authorities say. The cover’s fundamental purpose is to accelerate the breakdown of contaminants.