Center for Public Environmental Oversight
San Francisco Urban Institute, San Francisco State University
October, 1998

The National Stakeholders' Forum on Monitored Natural Attenuation, held near San Francisco August 31 and September 1, 1998, brought together nearly 250 scientists, activists, and government officials. Organized by the Center for Public Environmental Oversight (CPEO), with sponsorship from the Air Force, the Navy, U.S. EPA, and the Department of Energy, the Forum offered a balanced series of informative presentations on natural attenuation as a cleanup strategy, and it provided the public stakeholder participants with perhaps their only opportunity to influence national policy on natural attenuation.

The racially diverse community participants, many of whom live near federal facilities, represented communities from throughout the U.S. Most indicated their appreciation for the opportunity to gain a wider understanding of the science and policy of natural attenuation, as well as the chance to network with people from other areas of the country with similar problems. Participants from all constituencies recognized the value of the Forum's unique format: Large numbers of people representing federal responsible parties, regulators, consultants, academia, and the public nationally were able to exchange their views openly and respectfully.

To guide national policy development, organizers of the Forum laid out four questions for participants:

  1. What are the advantages and disadvantages of monitored natural attenuation as a remedy?

  2. When and where is monitored natural attenuation appropriate?

  3. How does one predict and verify the effectiveness of natural attenuation?

  4. What should be done if natural attenuation doesn't work as anticipated?

Forum planners did not seek consensus. There was no formal voting. Rather, the Forum provided opportunities for those present to express themselves, in breakout groups as well as plenary sessions, and CPEO recorded those points of view.

Panelists consisted of community activists, regulators, academics, and scientists in the employ of the Departments of Energy and Defense. They represented differing points of view, but each brought his or her own expertise to the podium. Community representatives, for example, not only stressed the importance of community concerns, but they showed how grassroots activists could, over time, achieve a serious level of technical competence.

Other speakers stressed the importance of factoring in all scientific aspects when considering natural attenuation as a remedy. They described how cleanup teams study contamination in the subsurface environment, pointing out how difficult it is to know exactly what's going on underground. Speakers agreed that natural attenuation, to some degree, always occurs at contamination sites. While project scientists must estimate the extent of natural attenuation processes, the question for decision-makers is whether such processes are sufficient to achieve cleanup goals. Finally, panelists explored the terminology used to describe natural processes. Though some found the term "natural attenuation" acceptable, others felt it confused degradation with other natural paths to reduce contaminant concentration.

Forum participants offered a wide range of comments on Monitored Natural Attenuation in general and specifically on EPA's interim policy, but the public stakeholders who spoke out tended to agree on key issues. Below is CPEO's summary of those comments.

The Importance of Trust

Public participants indicated widespread suspicion of Monitored Natural Attenuation as a cleanup strategy, but they did not challenge the science presented by its proponents. In fact, at first Forum organizers were frustrated by comments that centered on what seemed to be other issues, such as risk assessment, institutional controls, and the general absence of trust for government officials, particularly those working for agencies, such as the Departments of Defense and Energy, which have large contamination problems.

In reviewing the Forum record, however, that response stands out as the key lesson of the event: Decision-makers who believe monitored natural attenuation is the best remedial response at a site must win the trust of the public long before they propose it as a remedy.

Many traditional remedial strategies, such as "dig and haul" or "pump and treat," are superficially simple. Most people understand the basic concepts. They can see whether it's happening. The case for monitored natural attenuation, on the other hand, relies upon complex analysis before and after the fact. Before remedy selection, site characterization must show that natural attenuation is likely to achieve remedial objectives. Once natural attenuation is endorsed, long-term monitoring must continue until those objectives are reached. Both characterization and monitoring depend upon multiple lines of evidence, most of which involve variables that are difficult, at best, for the average person to understand.

Furthermore, at least one public participant pointed out that in practice decision-makers often rely upon only two lines of evidence, but use the term multiple to reinforce the perceived certainty that natural attenuation is proceeding with enough strength, speed, and stamina to complete the job.

Typically, when natural attenuation is under consideration, experts working for the responsible party present charts, graphs, and arguments designed to show that Monitored Natural Attenuation will achieve comparable results to other, more expensive remedial options. In fact, at the forum one Air Force scientist presented a graph showing that the rate of contaminant mass reduction in one major plume using natural attenuation wasn't much different than the estimated rate using conventional remedies. That graph demonstrated, he suggested, that Monitored Natural Attenuation was worth considering at that site.

However, from the public stakeholders' point of view, the only sure thing in the presentation was that natural attenuation would save the polluter -- in this case the Air Force -- a great deal of money. They had no way to independently test the Air Force's projection. And in fact, many were aware that even in the best of situations the Air Force comparison was fraught with technical uncertainty. As one speaker pointed out, "It's dark down there." That is, it's difficult to measure what's going on throughout the subsurface environment. Finally, they had no way to know whether there might be a third approach, with a better graph, waiting in the wings.

If, as many of the Forum participants indicated, people are already mistrustful of responsible parties -- and often regulators -- around issues they better understand, such as land use and health, they are unlikely to believe the promises of even the most knowledgeable, articulate experts. Natural attenuation is suspect, therefore, wherever the rest of the restoration program is suspect. It takes more than pretty pictures or sound science to win support where there is little trust.

On the other hand, at those facilities where the public believes that officials are both honest and willing to shape their decisions to meet public concerns, the public appears willing to evaluate the lines of evidence for natural attenuation, or any other remedy, on their merits.

Not surprisingly, public representatives at the forum underscored the importance of public participation in the screening and selection of remedial alternatives. The people who design and approve a natural attenuation strategy for a groundwater plume will be long gone by the date at which remedial objectives are expected to be reached, but most of the residents or their descendants will still have to live with the results. Public stakeholders also bring to the table local expertise and frequently an institutional memory that the scientific or regulatory experts lack. However, seeking public approval may present a "Catch 22" for the proponents of monitored natural attenuation. To win endorsement, they must increase the possibility of rejection.

To support such public participation, attendees called for a printed primer and more events like the Forum, to discuss the science and implications of natural attenuation. Though many of the participants said that they valued the technical presentations, some expressed frustration that speakers at the Forum were too technical, hard to follow, and difficult to understand.

Relationship to Other Remedies

Monitored natural attenuation seemed to be most acceptable to public stakeholders when regarded as just another tool in the remediation toolbox. As suggested in EPA's policy, natural attenuation may complement other remedies.

One participant, for example, argued that "enhanced" natural attenuation was more acceptable than the other kind, although he didn't provide a sharp line distinguishing the two. While some other participants, in their written comments, complained that too many people were focusing on the semantics of the term "monitored natural attenuation," it's clear that "natural attenuation" still carries with it the baggage with which it was first widely publicized, as a "do-nothing" remedy.

Another stakeholder proposed that monitored natural attenuation be approved as a remedy only in conjunction with other remedies, though she allowed that there might be exceptions. While some argued that other remedies were usually required for technical reasons, others echoed the perceptual importance of visibly "doing something" at a site. In other words, the presence of a visible physical or engineered remedy at a site demonstrates that action is actually being taken.

In particular, numerous people supported source removal as essential for natural attenuation to work. However, at the Forum this was not up for debate. All of the proponents of natural attenuation made the case for source removal. No one -- as others have elsewhere -- suggested letting natural processes deal with free product contaminants.

A number of speakers challenged the Defense Department's perceived policy of always considering monitored natural attenuation as a possible remedy for groundwater contamination. While an Air Force spokesman said that current guidance simply required that site characterization efforts collect the data necessary to evaluate the extent of natural attenuation, the critics felt that natural attenuation was almost a presumptive remedy, that budgets would be built and characterization would be biased on the assumption that natural attenuation was a front-running option. They argued that natural attenuation should be on a equal footing with other approaches.

Some participants expressed concern that reliance upon natural attenuation would undermine the development and use of innovative alternatives. In a site-specific evaluation of alternatives, monitored natural attenuation might look like it better satisfies remediation criteria -- such as the nine criteria of the National Contingency Plan -- than pump-and-treat, but there may be other, less well known options. A Cape Cod participant explained that residents in one neighborhood didn't want intrusive extraction systems in their yards, so they tended to support monitored natural attenuation as the local remedy. They were unaware of other options, such as horizontal wells, that might meet their needs while accelerating the removal of contaminants.

Some speakers raised the fear that natural attenuation might be approved at some sites now, because better alternatives are not yet proven. Then, when new technologies emerge that better satisfy remediation criteria, it's unlikely that the remedy will be reopened, even at five-year review. They asked: If monitored natural attenuation is approved as the best of a collection of uninspiring alternatives at a large number of sites, what incentive is there for anyone to invent better approaches? If new alternatives are developed, will there be any incentive to employ a new remedy at a monitored natural attenuation site?

At least, EPA's policy discusses the need for contingency remedies should monitoring demonstrate that natural attenuation is not working as expected. Participants liked that idea, but they showed concern that monitoring might not be good enough or soon enough to flag problems before they get out of hand. Because natural attenuation is frequently much less costly than other approaches, they expressed concern that budgets built on the assumption that natural attenuation will do the job may actually lock it in as a remedy, even when it doesn't work. One participant suggested a performance bond that would guarantee that money is available should it be necessary to call upon contingency remedies.

Destructive vs. Non-Destructive Remedies

Public stakeholders expressed strong preference for degradation as opposed to other forms of natural attenuation, such as dilution, dispersion, and volatilization. Many believed the non- destructive forms of attenuation should not be acceptable, and one tried to pin that down by asking what share of attenuation should be attributable to degradation for it to be considered the principal process. Another asked that the record of decision for each site specify the dominant attenuation process anticipated there.

Similarly, some participants were uncomfortable with the goal of "plume stabilization," considering it just another form of containment. They felt that treatment or removal, as currently required by regulations, was more desirable.

As a result of these preferences, some participants appeared more willing to accept monitored natural attenuation at petroleum sites, where degradation of the principal contaminants is more widespread and better documented, than at sites with volatile organic compounds. Few responded to the Department of Energy's description of the natural attenuation of inorganic substances - it was too new and too different. Those who did respond thought that metals should be dealt with in a separate policy, since degradation does not occur (except with radionuclides).

No matter what the principal contaminant, participants were concerned that remedies address all contaminants -- such as MTBE (methyl tertiary butyl ether) in gasoline or whatever sits in a landfill -- and that the persistent formation of toxic breakdown products, such as vinyl chloride, was an unacceptable result.

Land Use

Finally, a number of participants -- particularly from communities with closed and closing military bases -- expressed concern that natural attenuation, as a slow, uncertain remedy, could delay the transfer and/or reuse of contaminated properties. While long-term pump-and-treat as a groundwater remedy may be essentially as cumbersome as natural attenuation, "dig-and-haul" is a much faster way to deal with soils. And sometimes pump-and-treat can reduce or limit the size of a plume, making it easier to reuse or transfer property which does not lie over the contamination, even if the achievement of cleanup objectives remains a long way off. Some noted that any step in the remedial process that delays unrestricted use of property represents a real or potential economic loss to the community or property owner receiving the property.

Several participants felt the land and water use control as a component of remedial action is a significant area with many unresolved issues. They noted that the Defense Department, as evidenced by discussions at the most recent meeting of the Defense Environmental Response Task Force, is just beginning to grapple with complex issues surrounding institutional controls. Since monitored natural attenuation often depends upon the implementation of land and water use restrictions, participants from various constituencies urged the organization of a similar forum to discuss institutional controls.


On the whole, forum participants recognized that the adoption of monitored natural attenuation often requires more scientific review than conventional, engineered remedies. They expressed concern, however, that the open discussion of natural attenuation does not begin early enough in the remediation decision-making process. Many also felt that natural attenuation, as it is currently being defined, does not accurately depict the remedial strategy. For the most part, public stakeholders are willing to accept uncertainty when reviewing proposed remedies, but they are much less open to unconventional or complex remedies when they mistrust decision- makers.

That is, the uncertainty and technical complexity surrounding monitored natural attenuation magnify the mistrust found at many major contamination sites. To compensate for that uncertainty, the public wants contingency plans in place should monitored natural attenuation not perform as advertised. Community members want a clear mechanism for revisiting remedies if better alternatives are developed.

Researchers at the forum may have been disappointed that public participants chose not to focus on the scientific questions to which they devote their professional lives. They brought questions of their own to the table, instead. Until communities, responsible parties, and regulators better address the causes and consequences of mistrust, then proposals to rely upon monitored natural attenuation to address complex or significant contamination sites will be greeted, more often than not, with skepticism.