as In-Situ Tracers for Monitoring the
Natural Attenuation of Explosives
PAUL H. MIYARES, C. MICHAEL REYNOLDS, JUDITH C. PENNINGTON,
RICHARD B. COFFIN, THOMAS F. JENKINS,
AND LUIS CIFUENTES
the ever rising cost of energy, the price of pump
INTRODUCTION
and treat remediation for the Army is significant
and increasing.
Background
One of the most serious environmental problems
Natural attenuation has been proposed as an
facing the U.S. Army is the contamination of the
alternative remedial action at sites contaminated
soil and groundwater with secondary explosives
with explosives (Watson 1995). Precedence for this
at many of its installations. Explosives contami-
proposal was set by the widely implemented pro-
nation is the result of the manufacture of explo-
tocol for natural attenuation of fuels developed
sives, production of ordnance, and the disposal of
by the Air Force Center for Environmental Excel-
off-specification and out-of-date material. Con-
lence (AFCEE) (Weidermeier 1994). Natural
taminants include the explosives, manufacturing
attenuation is defined as allowing the natural
impurities and by-products, and environmental
physical, chemical, and biological processes at a
degradation and transformation products (Walsh
given site to reduce the levels of contaminants in
et al. 1993). One of the unique characteristics of
the environment enough that they are no longer
these compounds is their mobility through soil,
considered a health threat. Attenuation may
resulting in contaminated groundwater plumes,
occur through mineralization, transformation, or
often miles in length (Kayser and Burlinson 1982,
fixation (adsorption or chemical binding). Natu-
Pugh 1982, Rosenblatt 1986, Maskarinec et al. 1986,
ral attenuation has the advantages of being non-
Spaulding and Fulton 1988).
intrusive and significantly less expensive than the
The remediation efforts at these sites are cur-
currently used pump and treat systems, includ-
rently twofold: source removal and groundwater
ing monitoring.
treatment. The soils at the contamination sources
Many organic compounds attenuate naturally
are excavated, then either incinerated or treated
in soils and sediments by microbiological miner-
by composting or anaerobic slurry digestion. The
alization to CO2, biotic and abiotic transformation
groundwater plumes are remediated almost
to other compounds, irreversible sorption, incor-
exclusively using pump and treat systems.
poration by chemically bonding into organic mac-
Although a number of research efforts are in
romolecules such as humic and fulvic acids, trans-
progress to develop innovative treatment schemes,
port, and volatilization (Marvin-Sillema and
the principal method is passing the water through
deBont 1994, McGrath 1995, Pennington et al. 1995,
Pennington 1996). These processes are not neces-
activated carbon. Remediation by pump and treat
is slow, requiring years and perhaps decades to
sarily exclusive and can occur both simultaneously
reach target concentrations. It is also expensive.
and sequentially. Understanding the relative con-
tribution of these cycles to the reduction of the lev-
With many new remediation efforts starting and
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