Environmental engineers have come a long way since the days when contaminated sites were cleaned up simply by scooping out the toxic waste and hauling it away.

Complex purification plants and soil-treating methods are now practically old hat. And researchers are fine-tuning more sophisticated cleanup methods, including toxin-absorbing plants and chemical-neutralizing organisms, that are expected to lower costs and decrease cleanup time in the future though experts say it could take several years before they're used on a widespread basis.

"People want to talk about innovative technologies, but I think sometimes everyone's more comfortable about getting back to basics, because they work," said Joe Petrilli, director of federal programs for Jacobs Engineering Group Inc., an environmental firm in Pasadena.

Many engineers currently clean up contaminated groundwater using a method called "pump and treat," which essentially removes the affected water and then purifies it in a costly and time-consuming process.

For surface soil contamination, many environmental firms use heat to loosen contaminants from ordinary dirt. Engineers might insert electric rods, beam microwaves or pump steam into the soil to heat the ground. Once it's sufficiently heated, the contaminant basically turns into a vapor that can be sucked out with a vacuum. But this technique is not without problems.

"Soil doesn't like to be heated. In fact, it's a great insulator," said Tom Harmon, an associate professor in UCLA's civil and environmental engineering department with expertise in groundwater and soil cleanup methods. "(These heating methods) all work to some extent, but it's hard to get the temperature sufficient throughout the whole soil, so there's always little bits left over."

Even some of the cutting-edge solutions currently in development have limitations.

Researchers are testing ways to use plants to extract contaminants from soil. That method, called phytoremediation, uses a plant's natural ability to extract nutrients from soil through its roots. Scientists are working to find, and in some cases engineer, plants that can survive the absorption of the metals found in many contaminants.

"That has the obvious problem that you can only clean down to where the roots will go," Harmon said. "Plants and phytoremediation are really good for 'brownfield' cleanup, where there's dirty soil near the surface."

("Brownfield" is the industry term for a contaminated site that may be feasible for cleanup and redevelopment.)

Perhaps one of the most exciting new fields of contaminated-site cleanup is bioremediation, or the use of living organisms to remove toxins. Some researchers are testing the potential of certain existing organisms or bacteria to break down the contaminants, while others are genetically engineering organisms to do the job. Bioremediation can be used at the surface soil level, and for deeper groundwater problems.


For reprint and licensing requests for this article, CLICK HERE.