Monday,
March 8, 2010
6:00 - 7:30 pm
Pellissippi
State Technical Community College
10915 Hardin
Valley Road, Knoxville
J.L. Goins Administration Building, Cafeteria Annex
MARCH PRESENTATION
Transport of Dissolved
and Particulate Explosives Compounds
in Saturated Flow Column Experiments
by
Beth Lavoie
Dept. of Earth and Planetary Sciences
University of Tennessee, Knoxville, Tennessee
Contamination of surface soils with explosives residues (ER) is a
common phenomenon on military operational ranges. However, at
some sites (e.g. Camp Edwards, MA), plumes of munition
constituents in groundwater have also been observed. The exact
mechanism of ER transport through the vadose zone to underlying
aquifers is poorly understood. To date, most research and
modeling work was based on the assumption that ER transport
occurs exclusively in the dissolved phase. The failure of such
models to predict the extent and concentration of ER in
groundwater suggests other forms of transport may be occurring.
This study presents results from experiments designed to
investigate the potential for ER particulates to be transported
through the vadose zone, especially during infiltration of storm
flow, and then to dissolve in underlying aquifers.
A series of column experiments were conducted in repacked soils
utilizing both dissolved and particulate explosives compounds. In
separate experiments, latex microspheres (0.5, 1,0 and 2.0 um)
and fine grained (<250 um) 2,6- Dinitrotoluene (DNT) particles
were applied to columns, both in suspension and mixed with the
first centimeter (cm) of soil to mimic near-surface soil
contamination. The columns were pre-scored in one cm sections for
easy post-experiment segmentation enabling high resolution
analyses of the spatial distribution of explosives
particulates/microspheres entrained in the porous media. A novel
combination of detection methods, including chemical staining,
flow cytometry, and quantitative microscopic analysis, was used
to analyze column effluent and soil samples.
In each of the microsphere experiments, the 0.5 µm size
particles accounted for the majority of particles detected in the
effluent. However, in the suspended flow experiment the 1.0 µm
spheres were also transported and comprised almost 30% of the
spheres in effluent, compared to < 5% in the surface
application experiment. Concentrations differences in filtered
and unfiltered samples from both DNT experiments, indicates that
particulate transport accounts for a measurable fraction of the
DNT detected in the effluent. Our preliminary results suggest
that mobilization of colloid-sized ER plays a significant role in
the transport of explosive contaminants under steady-state flow
conditions.
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