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.
“It’s a good approach if you want to use the site while you’re doing remediation and have less-complicated waste,” said David Liu, a director at environmental firm Tetra Tech Inc. who specializes in determining which cleanup methods are appropriate for which sites. “The advantage is that you can use the site. The disadvantage is that it takes a longer time to complete. And it could leave ‘hot spots’ the results might not be uniform.”
As an alternative to the “pump-and-treat” method, the past few years have brought advances in a treatment that cleans groundwater by creating an underground wall made of reactive chemicals or biological material. As water flows through this filter-type system, the reactive materials break down the contaminants and the water comes out essentially clean on the other side of the wall.
It will likely take some time before any of these techniques are employed on a regular basis. The federal government, which gives research grants for the development of new cleanup methods, is currently testing the use of plants and organisms to clean up some contaminated sites. But because commercial cleanup projects can be so expensive and time-consuming, many decision-makers prefer to stick with tried-and-true methods of cleanup instead of testing out newer, riskier ideas.
“(The new methods) have got to prove themselves first,” Petrilli said. “You don’t know what you’re really dealing with. Do they work? Do they give the performance you want? Sometimes in the lab it works fine, but in the field it doesn’t work at all. The time it takes to try a new technology, get regulatory approval, see if it works, tweak it a bit, is a couple of years.”
Many companies don’t want to wait all that extra time to clean a site, because they can’t begin developing the land until the cleanup is completed. “The whole idea is to clean the site up and turn it over for somebody to use it,” Petrilli said.
Yet there is little question that the new methods, if they work, are cheaper than the old ones. Bioremediation can cost anywhere from $20 to $70 per cubic yard of treatment, compared to as much as $115 per cubic yard to hire dump trucks to dig out the contaminated area and haul the refuse to a hazardous materials dumping site.
Some other groundbreaking environmental engineering developments aren’t used for the actual cleanup itself, though they are considered instrumental for the overall cleanup process. Locating the source of the contamination, and identifying the contaminants, are fields of research in and of themselves.
Toxic underground “pools” that contaminate groundwater sources can, in most cases, be cleaned. But finding those underground pools takes extensive research. The civil and environmental engineering department at UCLA, for one, is developing extremely complex mathematical models to trace contaminated water back to its source.
