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At toxic cleanup sites across the country, environmental agencies have allowed groundwater contamination to go untreated and slowly diminish over time—a strategy that saves money for polluters but could cost taxpayers dearly and jeopardize drinking water supplies.

The strategy is called monitored natural attenuation, or MNA. With little public awareness or debate, it has come into increasing use nationally since the 1990s as a way to cope with the enormous cost of some groundwater cleanups.

Despite the imposing bureaucratic name, it basically means keeping a watchful eye while natural processes purge groundwater of chemical pollution. According to Environmental Protection Agency guidelines, it’s an acceptable approach under some circumstances. That includes when contaminants are expected to degrade in years rather than centuries, and where there is no risk of polluted water seeping into, and spoiling, fresh water supplies. MNA can be effective with contaminants such as petroleum hydrocarbons that are eaten by microbes in the soil and groundwater.

But some advocates and experts say MNA sometimes has been approved in violation of EPA guidelines. Because it is usually much simpler and cheaper than active cleanup methods—such as pumping water out of the ground and treating it—they say that MNA is being aggressively pushed by polluters at many contaminated sites, often with too little pushback from regulators.

“I have a very sour attitude towards this concept of monitored natural attenuation,” said Robert Alvarez, a senior scholar with the Institute for Policy Studies, a Washington-based think tank, and a senior adviser to the energy secretary during the Clinton administration. “It’s a very big concern, especially for very contaminated sites.”

There are obvious risks in leaving toxic contaminants in groundwater for any length of time. If the pollutants aren’t correctly monitored, they could continue to spread and contaminate nearby aquifers.

With wide areas of the U.S. already facing dwindling water resources due to drought and population growth, particularly in Western states, any widespread reliance on MNA threatens to eliminate more water from public use. And if the land atop polluted groundwater is subsequently sold, or if those responsible for the pollution go out of business, taxpayers could be left holding the bill.

Alvarez is particularly critical of the use of MNA at radioactive waste sites around the country, where it’s estimated that certain radionuclides will take millions of years to naturally degrade to safe levels. The most dramatic example is the Hanford Nuclear Reservation in southern Washington State, the site of the nation’s biggest nuclear cleanup, where part of the problem is being handled with MNA.

Despite multiple requests over a period of months, the EPA refused to grant an interview about the use of MNA. The agency, in one of the responses it provided via email, said that under its Superfund toxic waste site program “cleanup remedies are selected to be protective of human health and the environment. EPA has developed numerous technical and policy guidance documents that present a logical technical approach to deciding whether MNA is a viable remedy and for assessing MNA’s effectiveness. These MNA decisions are made with the same rigor as all Superfund remedial decisions.”

Heavy use at military sites

FairWarning has been unable to determine a reliable estimate of the number of sites around the country where MNA has been applied, as there appears to be no comprehensive count. But according to data from the EPA, MNA is in use at 85 of 141 U.S. military sites that are classified as Superfund sites. That includes Camp Lejeune in North Carolina, where from the 1950s into the 1980s hundreds of thousands of people may have been exposed to tainted drinking water. A separate assessment shows that in 2011, the most recent year tracked, 31 percent of EPA groundwater cleanup decisions involved some use of MNA.

It appears that most state environmental agencies, which supervise many cleanups, do not keep data on MNA use over the years. Still, experts agree that MNA has been pushed more aggressively in recent years.

The issue does not appear to be on the radar of most major environmental groups, although Geoffrey Fettus, a senior attorney with the Natural Resources Defense Council, said his group has “significant concerns about natural attenuation as a cleanup method.”

MNA has come under attack by some regional officials and residents near polluted sites. For example, water quality authorities in California have been locked in a protracted tug-of-war with the Air Force about its proposed use of MNA to treat contamination at George Air Force Base on the edge of the Mojave Desert in California, where a federal cleanup has gone on since the early 1990s.

At George and many other military bases, chemicals and jet fuel were leaked or haphazardly disposed of for many years, polluting hundreds of acres of groundwater. Trichloroethylene, a cancer-causing solvent, has contaminated two aquifers and threatens a third aquifer as well as the Mojave River. It also has tainted monitoring wells at a nearby wastewater reclamation plant, forcing workers there to drink bottled water as a precaution.

“Their only source of drinking water is groundwater”

More than $100 million already has been spent on an active cleanup of the pollution over the years. But contaminants are continuing to spread, and the Lahontan Regional Water Quality Control Board, the agency overseeing the cleanup, claims that they won’t reach safe levels for up to 500 years if MNA is applied as proposed by the Air Force. This, in a region where water is already scarce, and where the nearby towns of Adelanto, Victorville and Hesperia continue to expand.

“The Mojave Desert is the Mojave Desert. Their only source of drinking water is groundwater,” said Patty Kouyoumdjian, executive officer of the Lahontan water board.

If the polluted aquifers become critically needed by the growing communities, the cleanup could be shifted to California taxpayers, said Kouyoumdjian. “It’s a long-term problem … because some of that pollution isn’t going to magically disappear.”

That’s why the water board is pushing for a return to active treatment, such as pumping and cleansing the water and then returning it to the ground. But the Air Force disputes the water board’s dim assessment of MNA for the site. In an email, the Air Force said it remains “in discussions” with the agency to “reach a common understanding of the nature and extent of the contamination.”

Such tensions are commonplace, but they raise a question: Why can’t the EPA and state environmental regulators simply demand an active cleanup when they think MNA is the wrong choice? It largely comes down to money. The cleanup of Defense and Energy department sites depends on Congressional appropriations, and the amount of available funding is limited. That narrows options and leads regulators to compromise. Largely for that reason, the Defense and Energy departments wield “a lot of influence,” said Mike Barden, a former state regulator in Wisconsin and now an environmental consultant.

When the polluter is a small private company, money also often is a problem. Philip Chandler, a senior geologist with the California Department of Toxic Substances Control, said “cash-strapped” companies commonly struggle with the costs of installing, maintaining, and sampling monitoring wells. Chandler – emphasizing that he was speaking not for his department, but as a “concerned citizen” – said he has come across cases of regulators in his agency letting polluters get away with doing things like not putting in enough wells to adequately track the movement of polluted water.

Sometimes, Chandler said, “we effectively look the other way on the basic requirements of MNA.” The department, in an email response, said that, on its cleanups, “a rigorous evaluation process is followed to ensure the most appropriate technology for the site is chosen. All DTSC Cleanup staff follow the same process in evaluating the best solution for a particular site.”

“Such a big issue”

Lenny Siegel, director of the Center for Public Environmental Oversight, a nonprofit advocacy group based in Mountain View, Calif., believes that more and more polluters are proposing MNA instead of trying “newer and better” remedies. “My argument is that you have to try alternatives before you just go in and use Monitored Natural Attenuation,” he said. “Particularly at sites where there’s a chance of human exposure to these contaminants.”

MNA came into use in the 1990s. The Air Force, frustrated with escalating costs and the slow pace of cleanups at a number of bases, took the lead in studying whether nature could do the job more quickly and cheaply than technology can. Officials at an array of agencies, however, struggled to figure out how to regulate MNA, prompting the Environmental Protection Agency to issue an MNA directive in 1999.

That directive, and the EPA’s updated guidelines, state that MNA shouldn’t be applied when, among other things, the source of pollutants isn’t yet under control, when the tainted groundwater still is spreading and when the contaminants won’t break down to safe levels within a “reasonable” period.

“The notion of reasonable timeframe has been such a big issue,” said Peter Strauss, of PM Strauss & Associates, an environmental consulting firm. For many experts, a rough rule of thumb is 30 years. For Strauss, MNA should work as quickly as proven active remedies. “Ideally, you should be looking to get as much done as possible without burdening future generations,” he said.

Many of the nation’s most complex toxic cleanups are on the EPA’s Superfund list. At some Superfund sites, critics say, MNA has been applied in circumstances that clearly violate the agency’s guidelines. As an example, these critics point to Hill Air Force Base in Northern Utah. It’s the second largest U.S. Air Force Base in size and personnel, and the site of a cleanup that has continued for about 20 years.

“Right away it does not meet the EPA’s MNA criteria”

Perhaps the greatest concern among local residents and environmentalists is a contaminated area straddling the northern boundary of the base, uphill from an elementary school in the City of South Weber. It is polluted with an array of highly toxic contaminants, including the carcinogens arsenic and benzene.

For nearly 25 years, John Carter was employed as an environmental consultant by the South Weber Coalition, a local residents group. Carter says the Air Force has put out a “false image” of MNA as safe, given that contaminated water is seeping downhill and underneath homes in the city. “And so, right away it does not meet the EPA’s MNA criteria of no potential for movement of contamination,” he said.

In addition, Carter said, some of the contaminants won’t break down naturally within a reasonable period. And, “in the case of arsenic, because it’s an element on the periodic table, it simply cannot degrade,” Carter said. Perhaps most crucially, inadequate monitoring means that the full reach of the contamination has never been accurately mapped, he said. The result, according to Carter, is that South Weber residents are at risk of toxic exposure through indoor vapor intrusion, meaning that noxious gases can seep into homes through the floor, often undetected.

Air Force officials said an estimated 5 percent to 10 percent of homes in a voluntary monitoring program had contaminants in their indoor air exceeding accepted levels from a sewer containing groundwater with the cancer-causing solvent trichloroethylene. The officials said that, over the years, the Air Force has put air cleanup systems in 123 homes to suck vapors from beneath their floors, and that there is no “unacceptable risk of exposure” to residents from contaminants. But many potentially at-risk residences have yet to be tested because the program is voluntary, said Brent Poll, a member of the South Weber Coalition.

“The only thing you can say that’s good about [MNA] is that it’s very cheap,” said Poll. “It’s just not a realistic remediation choice, and anybody who says that it is, is either foolish or a liar.”

Monitoring Failures

Barden, the environmental consultant, said a frequent problem with MNA is the failure to properly monitor contaminated sites. “I’ve seen scenarios where the monitoring just gets lost in the process. They’re not monitoring for the right things. They’re not monitoring at the right frequency,” he said. At times, he said, there is no sampling for certain contaminants or there aren’t enough wells to track the movement of groundwater.

Among sites where the monitoring has come under criticism is Camp Minden, formerly known as the Louisiana Army Ammunitions Plant, near Shreveport. Chemical explosives like TNT and RDX are among some of the most toxic contaminants in the groundwater there, as well as carcinogens like benzene. MNA has been applied there since 2007.

National Guard Bureau spokesperson Lieutenant Colonel Dianna Lebedev wrote in an email that “to the best of our knowledge today,” the contamination plumes “are not migrating or expanding.” Yet records and interviews suggest military officials lack the evidence to prove that.

A report last year conducted for a local citizens advisory group and funded by the EPA found numerous holes in the groundwater monitoring data going back more than two decades. According to Wilma Subra, a technical adviser to the citizens group, the monitoring system in place probably needs “a lot more” wells to accurately map the extent of the contamination. In response to the criticism, the military is planning to test private drinking water wells near the base that might be polluted.

While EPA guidelines call for MNA only where pollution will degrade to safe levels within a reasonable period, it is one of the techniques being used at the Hanford Nuclear Reservation in southwestern Washington State along the Columbia River. Nuclear weapons development there, which began as part of the Manhattan Project during World War II, left radioactive residues not expected to reach safe levels for millions of years if left to break down naturally. Taking all of the nation’s water pollution threats into account, nuclear wastes such as those at the site are “the most dangerous stuff,” said Alvarez, of the Institute for Policy Studies.

“We’re not going to do anything because it costs too much money”

The effort at the site began in 1989. According to an assessment two years ago, it has already cost more than $19 billion. It is dealing with contaminants that have leached into the Columbia River and that, the EPA has found, contaminate fish.

Probably the most controversial use of MNA at Hanford is for treating a nearly 23-square-mile plume of radioactive iodine-129. The half-life for iodine-129, which has been linked to thyroid cancer, is 15.7 million years. Cheryl Whalen, an official regulating the cleanup for the Washington State Department of Ecology’s Nuclear Waste Program, downplayed environmental concerns about the plume. She said it won’t reach the Columbia River for at least 30 years and, at that point, the outflow will be better than federal drinking water standards. Whalen said measures taken at the site are “working well” to stop contamination from spreading.

Others disagree. Dale Engstrom, natural resources specialist with the Oregon Department of Energy, which participates in the cleanup, said that contamination in excess of drinking water levels could reach the Columbia River within five years. In addition, Engstrom and local critics of the cleanup, including Susan Leckband, who sits on a Hanford citizens advisory panel, are skeptical about Whalen’s assertion that MNA is the only technically feasible way to handle the iodine-129. Leckband said MNA is being applied at Hanford by “default,” without enough consideration given to active remediation methods. “Monitored Natural Attenuation says, ‘we’re not going to do anything because it costs too much money,’” she said.

For MNA critics, waiting for nature to purge radioactive waste at Hanford is a dramatic example of the risks posed at sites employing the technique around the country.

“It’s an ongoing problem,” said Strauss, the environmental consultant. “If in 30 years you have to go in and say, ‘oh, Monitored Natural Attenuation isn’t working,’ who’s paying for that? That’s our children – it’s a possible shifting of a tax burden to future generations.”

About FairWarning

This story was reported by FairWarning (, a nonprofit news organization based in Pasadena, Calif., that focuses on public health, safety and environmental issues.