The Data Don’t Lie: Has MNA Science Outpaced Site Decision-Making?

Posted on July 26, 2016 by Charles Efflandt

The importance of a thorough technical evaluation of monitored natural attenuation (MNA) at chlorinated solvent and other groundwater-contamination sites cannot be overestimated. Regulatory acceptance of MNA as a preferred remedial alternative can save millions of dollars in response costs compared to common presumptive remedies. Because “active” remediation technologies rarely achieve complete contaminant treatment or removal, MNA is an implicit, if not specifically evaluated, component of most groundwater remedial actions. A proposal to use MNA as the primary cleanup mechanism, however, is often met with resistance from regulators, notwithstanding years of supportive data.  Such resistance may be attributable to antiquated agency policies or, perhaps, an inadequate evaluation of evolving MNA science.

The use of MNA at groundwater sites has typically required a showing of a stable or shrinking plume, source control, sustainable natural attenuation conditions, and acceptable risk to health and the environment. Today, mathematical and modeling tools can systematically establish data trends demonstrating that remedial action objectives will be achieved through natural attenuation in a reasonable time frame.

Unfortunately, even if confronted with irrefutable data, many state regulators will reject meaningful consideration of MNA unless the attenuation mechanism can be pigeon-holed into  policies that focus on the demonstration and scoring of anaerobic biodegradation conditions at a site.  That is because after almost two decades, EPA’s 1998 Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water remains the framework for MNA evaluations and decision-making in many states. Because the 1998 Protocol presumed that the primary effective mechanism for natural attenuation was anaerobic biodegradation, the Protocol has unduly restricted state policies for screening and approval of MNA remedial action.

Numerous studies since the publication of  the 1998 Protocol, however,  have shown that a viable MNA remedial strategy can be supported by attenuation mechanisms other than anaerobic biodegradation These studies have documented other viable contaminant-destructive attenuation mechanisms and evaluation tools, such as aerobic cometabolism enzyme degradation, magnetic susceptibility, compound specific isotope analysis, and improved sampling and modeling techniques. Greater awareness of these scientific developments by regulators and environmental professionals will result in MNA being an increasingly important remedial tool at many groundwater sites.

We have learned the hard way that it’s much more difficult and expensive to clean up sites using default remedies than first thought. Fortunately, it is becoming increasingly apparent that nature has an ability to degrade various chemicals more quickly and effectively than previously believed.   Regulatory acceptance should not, and need not, include unreasonable technical hurdles, such as imposing  attenuation “causation” requirements that are neither feasible nor necessary to support what cannot be disputed. That a proposed MNA remedy does not neatly fit into the traditional anaerobic degradation box, and cannot with precision be attributed to one or more alternative degradation mechanisms potentially active at a site should not be determinative. At the end of the day, the data don’t lie. The MNA determination ought to begin with, and remain focused on, the empirical data and data trends.

EPA’s Draft Groundwater Remedy Completion Strategy: Focusing on the Procedures or the Problems?

Posted on December 9, 2013 by Charles Efflandt

EPA is seeking stakeholder input on its draft Groundwater Remedy Completion Strategy.   Released on October 29, 2013, the strategy is advertised as a guide for evaluating remedy performance and improving decision-making to more effectively and expeditiously move groundwater sites to completion. Having experienced the problems associated with the “set it and forget it” approach to groundwater remedial action, my interest was piqued by the prospect of a new EPA strategy incorporating more flexibility in evaluating remedial action objectives, remedy performance and systematic risk assessment.

The potential impact of EPA’s remedy completion strategy is arguably diminished, however, by a lack of clarity as to its scope and purpose. The stated objective of documenting a uniform approach to efficiently completing groundwater remedial actions is qualified by an ambiguous disclaimer that the strategy does not change other guidance or policy, is not intended to alter the way the agency develops remedial objectives and cleanup goals and is not intended to interfere with the federal or state site decision-making process. So, what exactly does EPA hope to accomplish in proposing this new strategy?

The elements of the strategy consist of understanding site conditions, designing a site-specific remedy evaluation process, developing performance metrics, conducting remedy evaluations and making appropriate site management decisions. The focus of EPA’s strategy as presented is largely procedural. The strategy does not address common site impediments to achieving an effective and expeditious groundwater exit strategy. To that extent, it is primarily a restatement of a remedy evaluation process that has been the subject of numerous articles and that, in fact, has historically been implemented at many sites.

But perhaps my initial reading is too narrow. The strategy hints at more substantive remedy completion issues, such as addressing site remedial action objectives that become impracticable and unnecessary for the protection of health and the environment, as well as the need to more consistently evaluate remedy change at mature groundwater sites.

From the perspective of focusing on site groundwater scenarios that often delay remedy completion, I suggest that the draft strategy falls short of the goal line. Rather than simply allude to the remedy completion obstacles that presumably inspired the agency’s effort, EPA might better achieve its stated purpose if it revises its strategy to include more discussion of how the strategy may apply to common groundwater completion impediments. For example, it would be useful for the strategy to address the cost and inefficiencies of continuing to operate and maintain asymptotic pump and treat systems at low-threat sites, how to better incorporate plume stability trend information in the evaluation of remedy change, changes in exposure pathway risks and the impact of natural attenuation mechanisms, institutional controls and land use on remedy modification and remedy completion decision-making.

What I had hoped to see in the draft strategy was EPA’s blessing of a more flexible and common sense approach to specific groundwater remedy completion obstacles. My first reading of the draft strategy suggested to me that it was essentially a redundant procedural roadmap for remedy evaluation.  But upon reflection, I think it could be more.  Indeed, it could also be – and I hope, after consideration of stakeholder comments, will be – a tool for encouraging more consistent regulatory acceptance of remedy change and evolving risk assessments to overcome the inertia of inflexible remedial action objectives and remedy selection impacting many groundwater sites.