problems alluded to above. We attempted to limit sol-
The question of whether the contamination recov-
vent penetration of casing materials by using methanol
ered by this method is truly limited to the surface was
instead of more invasive solvents. Methanol is adequate
addressed. One of each of the four mine types was
for dissolving small amounts of explosives but not
sampled five times in rapid succession (i.e., within min-
nearly as invasive of paints and plastics as acetone. No
utes) at two locations on the surface. The two disks
rubbing or wiping was done as before; the filter papers
were composited to form each sample and placed in 1
were simply emplaced, then removed with as little dis-
mL of acetonitrile for analysis, as before. The data are
turbance as possible. In view of the spatial heterogene-
shown in Figure 1. Surface concentration measurements
ity of individual swabs observed in the 1992 study, we
are clearly subject to experimental randomness but gen-
composited multiple disks to obtain a larger sample
erally decreased with repeated sampling of the same
from each mine. This would give a better estimate of
spot. However, they don't go to "zero," which means
the total contamination present on each mine, while sac-
that either the contamination is being replaced or it is
rificing information on smaller-scale distribution of con-
not being efficiently recovered.
tamination.
Environmental conditions at the time of sampling
undoubtedly affect surface concentrations. The air in-
side the CRREL bunker was calm and the ambient tem-
perature approximately 28C. The conditions at Fort
RESULTS AND DISCUSSION
Leonard Wood were windy, and the ambient tempera-
One mine of each type was tested concurrently at
ture was variable but generally higher. Surface samples
CRREL for reproducibility of surface sampling. To do
were also taken at CRREL on a set of 12 mines at four
this, we placed several sets of disks on each mine and
carefully controlled temperatures ranging from 3 to
34C, in conjunction with flux measurements. These
analyzed the replicate groups separately. Table 3 gives
the means and standard deviations of replicate samples
data are scattered but suggest a rising trend in surface
for the three major signature compounds using the above
concentration with increasing temperature for all con-
procedure. This would be a measure of the intra-mine/
taminants (Fig. 2). Wind might be expected to deplete
inter-sample variability. Generally, this produced num-
surface concentrations relative to still air. According to
bers within about 10% of the means. For DNB and TNT
mass transport theory, resistance to mass transfer de-
on the TMM1, sampling variability was more than 60%,
creases with wind speed, which means a higher flux
however.
from the surface with increasing wind speed
Data for all the individual mines sampled at Fort
(Thibodeaux 1979). Whether this causes depletion of
Leonard Wood are not presented here, but may be made
surface concentrations, however, hasn't been deter-
available at the discretion of the sponsor. Ranges, mean,
mined. That would depend on the permeability of the
and median surface concentrations of major signature
material relative to the rate of desorption from the ma-
components from this data set are given in Table 4. The
terial.
frequency distributions expressed as percentage of
Under stagnant conditions in air, surface and bulk
mines with a given surface concentration are shown in
concentrations in the plastic may be near saturation
Appendix B, Figures B1B4. For a given mine type,
(solubility). This is presumably the initial state of mines
the means and medians were generally similar, though
that have been boxed and stored in bunkers for many
the frequency distributions do not appear Gaussian in
years prior to deployment and may persist when mines
every case. RDX was found only on the PMA2 and is a
are deployed initially in dry soil. However, when liq-
component of the booster charge in this mine.
uid water comes in contact with a mine surface, these
Table 3. Mean concentrations (and standard deviations) of
major surface contaminants found on mines sampled in the
CRREL bunker at 28C (ng/cm2).
1,3-DNB
2,4-DNT
TNT
PMA1A
2.92 (0.17)
1.87 (0.19)
1.55 (0.38)
PMA2
0.57 (0.02)
0.66 (0.03)
0.15 (0.07)
TMA5
1.50 (0.16)
8.01 (1.42)
6.25 (0.58)
TMM1
4.77 (2.99)
31.8 (2.75)
16.2 (11.0)
3
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