Got toxics in the earth? Try 'steam cleaning' it
Method may revolutionize Superfund cleanups
Engineer Craig Eaker's boots crunch on gravel that covers toxic ground. He's surrounded by pipes, huge boilers, and electronic sensors that reach deep into the ground. For a Superfund site, it is remarkably clean.
Eaker is monitoring a field test of a "steam cleaning" method that promises to radically speed up the recovery of sites contaminated with gasoline, solvents, or creosote - a coal-tar preservative used here in the first half of the century to coat wooden utility poles.
Officials at Southern California Edison, the corporate owner of this site 175 miles north of Los Angeles, say cleaning up the land with established technology would take 1,000 years. But based on the success of the new method, Mr. Eaker says the project will be complete in two to five years.
Lawrence Livermore National Laboratory (LLNL), located near San Francisco, cleaned up an underground gasoline spill with steam injection in 1993. Now it is licensing private companies to use the technology. Six other sites are scheduled to use the method so far, and it could potentially take care of 25 percent of America's 1,300 Superfund sites - areas whose contamination has been deemed serious enough by the government to require stringent cleanup rules.
The process - heating up the earth with steam and forcing toxic compounds to migrate to wells where they can be removed - has resulted in a rate of extraction at the Visalia site that is dumbfounding environmental scientists.
"You get gasps," says Roger Aines, an LLNL geochemist and co-developer of the project. Environmental scientists have "seen mason jars full of this material in the past, but they've never seen big, blue, 20,000-gallon tanks completely filled with contaminants."
Each day, 250 gallons are removed, Eaker says. And in 16 months, according to Edison statistics, the company has pulled out 900,000 gallons of creosote. Compare that with just one gallon a day from a method known as "pump and treat," used frequently at contaminated sites.
Visalia was a sleepy agricultural town back in 1923 when Southern California Edison set up its site to make utility poles. Over the years, barrels of creosote leaked, contaminating the earth as deep as 110 feet. When employees complained of tasting creosote in the water in 1965, "our first environmental reaction was just to go on the city water system," Eaker says.
But more was clearly required. Large pumps were built to push water into the ground, flush out some creosote, bring the mixture to the surface, filter it, and then return the water to the ground.
This pump-and-treat approach "was going to go on for centuries," at Visalia, Eaker says. So the speed of LLNL's method - called dynamic underground stripping (DUS) - got Edison's attention.
The Environmental Protection Agency (EPA), which has been monitoring the test of DUS in Visalia, is enthusiastic. "I don't know anything else that could have removed so much so fast," says EPA scientist Eva Davis.
DUS technology advances a method long used by the oil industry to extract petroleum not accessible from regular oil wells. In Visalia, huge boilers inject steam through 11 wells drilled to encircle the contaminated area. The heat forces the toxics to migrate toward seven extractor wells located in the middle of the four-acre site. Creosote compounds are then pumped to the surface. They either burn off as a vapor, or the liquid filters through the previously existing treatment facility.
LLNL geophysicist Robin Newmark, a co-developer of the project, says getting the creosote out is like washing a dirty shirt. If washed "in cold water, it doesn't wash as cleanly," she says. "Heat it up, the dirt goes into solution" and the contaminant can be easily removed.
Some environmentalists, while supportive of the new technology, remain cautious. So far, outside scientists have not conducted independent tests at Visalia, notes Peter Strauss, a consultant for the peace and environmental group Tri-Valley CARES. Mr. Strauss has evaluated data provided by LLNL about its 1993 cleanup of the gasoline spill.
Strauss warns that misapplication of the steam could actually drive the contaminants deeper. He'd like to see further testing of DUS. "There have to be people to watchdog the process before it's fully commercialized," he says.
Newmark agrees that careful oversight is needed. But she says the Visalia field test shows DUS works and is ready to be used elsewhere.
Some companies interested in DUS are discouraged by the high, initial cost. Edison, for example, estimates it will cost $22 million before the Visalia pole yard is cleaned up, much of it spent in the first year. But the utility had budgeted $45 million for 30 years of "pump and treat," fully expecting to spend more. So if owners want to sell or otherwise make quick use of the land, Ms. Newmark says, shifting to steam injection makes sense.