[CPEO-MEF] RDX Attenuation at Cornhusker AAP

[Lenny Siegel <lsiegel@cpeo.org>]

Last week we posted excerpts from an article, in the Grand Island
Independent (January 26, 2001), about an RDX (Royal Demolition
Explosive) groundwater plume emanating from the Cornhusker Army
Ammunition Plant, near Grand Island Nebraska. Because the article
reported that a planned off-site treatment system would not be built,
due to the natural attenuation of contaminants, I decided to explore
further.

Cornhusker, a 12,000-acre former ammunition manufacturing facility, was
placed on the "Superfund" National Priorities List in 1987. Even before
that date, the Army had funded the extension of water lines to more than
250 residences believed impacted by the presence of explosive compounds
in the groundwater. The Army and its regulators, U.S. EPA and the
Nebraska Department of Environmental Quality, agreed upon a groundwater
remedy in September, 1994, in the form of an Interim Action Record of
Decision. The remedy would include extraction wells both on- and
off-post. In late 1998, the on-post system began full operations, and in
March, 2000, the Army added another extraction well near the facility
boundary.

In December, the three agencies put forward an amendment to the Record
of Decision. They proposed to rely upon Monitored Natural Attenuation,
instead of the planned off-post pump-and-treat system, and they are
working with both the City of Grand Island and Hall County to outlaw the
construction or use of residential water wells above the plume. The
amended cleanup will save the Army at leas $4 million in capital costs.

I am not aware of any other facility where monitored natural attenuation
has been accepted as a remedy for groundwater polluted with RDX and
other explosive compounds, so I approached the Cornhusker proposal with
skepticism. These chemicals are increasingly being found on ranges and
other military properties, and it's important not to set an unprotective
precedent.

However, it appears that the parties are following U.S. EPA's policy on
Monitored Natural Attenuation. Not only are contaminant concentrations
falling appreciably in the off-post plume, but the Army is demonstrating
with multiple lines of evidence that biodegradation is in fact
occurring. Its consultant told me that they believe that the compounds
will continue breaking down until they form carbon dioxide and water.

I asked about the immediate breakdown products of RDX - MNX, DNX, and
TNX. These also are believed to be toxic and persistent, but the studies
thus far show low concentrations in the plume, suggesting that they too
are breaking down. Since there are apparently no standard methods of
testing for these chemicals, the Army and its consultant have relied
upon an innovative analytical method developed by the University of
Nebraska.

Does this mean that RDX plumes around the country will quickly attenuate
naturally? Probably not. Cornhusker has a unique feature. Fortuitously,
the plume, as it moves off base, travels directly beneath a huge cattle
feed lot. Apparently, bacteria  and nutrients from that lot have leached
down into the aquifer, stimulating the biodegradation (dinitrification)
of RDX and other chemicals. According to the consultant, it's a perfect
reducing environment.

In fact, one might argue that "natural attenuation" is not an accurate
description of what's happening to Cornhusker's off-post plume. It's in
situ biodegradation, but the Army's not controlling the injection of
microbes and other substances. Perhaps at other sites with RDX plumes,
the solution will be to construct cattle feed lots - if they can just
ensure that there's no danger of mad cow disease.

-- 


Lenny Siegel
Director, Center for Public Environmental Oversight
c/o PSC, 222B View St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/968-1126
lsiegel@cpeo.org
http://www.cpeo.org


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