Does it make sense to keep pouring billions of dollars into efforts to remediate groundwater at complex contaminated sites when the chances that the water will ever achieve drinking water standards are remote?

That’s the question the U.S. Department of Defense put to the National Research Council (NRC).  While the NRC did not exactly respond, “No, it does not,” it did recommend that a different approach be taken at sites where continuing expenditures bring little or no contaminant reduction.

126,000 sites

The NRC addresses this important issue in a new report, Alternatives for Managing the Nation's Complex Contaminated Groundwater Sites.  According to the NRC, documentation shows that there are at least 126,000 sites across the country (and likely many more) with residual contamination at levels preventing them from reaching closure.  About 10 percent of these are considered complex from a geological and contaminant perspective.  The complete removal of contaminants at many of these sites is unlikely, according to Michael Kavanaugh, chair of the NRC committee that produced the report.

“At many of these complex sites, a point of diminishing returns will often occur as contaminants in groundwater remain stalled at levels above drinking water standards despite continued active remedial efforts,” said Kavanaugh.  “We are recommending a formal evaluation be made at the appropriate time in the life cycle of a site to decide whether to transition the sites to active or passive long-term management.”

Transition assessment

The NRC committee calls this evaluation a transition assessment.  This process would determine if the effectiveness of active site remediation has reached a point of diminishing returns before reaching cleanup goals.  The assessment would determine if a transition to monitored natural attenuation or some other active or passive management is appropriate. 

At complex sites, such decisions should be made with an understanding of the geology and potential distribution of contaminants along with the biogeochemical dynamics associated with both the source area and the downgradient plume.  The NRC report therefore points to the need for emerging technologies that have yet to receive field testing.  Among these are improved spatial-temporal monitoring of groundwater contamination through better application of conventional monitoring techniques, the use of proxy measurements, development of sensors, and application of emerging diagnostic and modeling tools. 

Public misunderstanding

Also addressed is consideration of public perceptions in hazardous site remediations.  The NRC committee notes inconsistency in the use of nomenclature by public and private entities to describe phases of site cleanup.  For example, many sites described as “closed” and considered “successes” still hold contaminants and require oversight and funding for decades and, in some cases, hundreds of years to be protective.  One source of confusion is that Superfund and other federal and state programs have remediated sites to levels that prevent exposures in water or air, but contamination above drinking water standards still exists throughout affected aquifers.  More consistent and transparent terminology that simply and clearly explains the different stages of cleanup and progress would improve communication with the public, states the NRC.

The DOD sites constitute only 3.4 percent of active remediation sites, but many of these sites are complex and present the most daunting long-term challenges.  Over the last 30 years, “successful” remediations have occurred and sites have been closed, but remediations at DOD sites that result in meeting drinking water standards are rare.  The DOD has spent over $30 billion in addressing legacy contamination.

Click here for information on the NRC report.