around the rim of the crater. Concentrations of RDX ranged from trace to
5.0 :g kg-1, 4ADNT from 5.4 to 20.6 :g kg-1, and 2ADNT from 2.6 to
15.2 :g kg-1. TNT was also detected in four of the six samples with
concentrations ranging from 1.3 to 6.0 :g kg-1. 2,4DNT was observed in two
samples at 6.9 and 15.3 :g kg-1. While detectable, the concentrations in all of
these residues were very low, and would not have been detectable using SW-846
Method 8330. The main charge for 155-mm rounds generally contains TNT, not
Composition B. Therefore, the RDX found in these samples may have originated
from a source other than the 155-mm detonation.
The sixth area was a series of background samples collected in a wheel
pattern within the range, but not close to any visual crater (Table 7, samples 97 to
103). Low levels of RDX, 4ADNT, 2ADNT, and TNT were observed in these
samples, but concentrations were always below 30 :g kg-1. These results indicate
that low concentrations of explosives residues are distributed in some places over
fairly large areas even when no craters are observable, but identification of a
specific source is not possible.
A series of six craters were sampled that could be identified as recent
105-mm craters, probably formed from detonations within a week of sample
collection (Table 7, samples 113-118). Composite samples from the inside walls
of all six of these craters were similar in that TNT, 4ADNT, and 2ADNT were
the residues at highest concentrations. TNT concentrations ranged from 59.2 to
1750 :g kg-1 in these samples; concentrations of 4ADNT and 2ADNT ranged
from 13.5 to 140 :g kg-1 and 5.4 to 145 :g kg-1, respectively. RDX was observed
in only two of these samples, and the concentrations were low, 4.8 and
charge, either RDX has preferentially leached out of these craters, or the residues
were deposited from a TNT-containing round instead and were not associated
with the 105-mm rounds that made the craters. The preferential leaching of RDX
from these craters would be somewhat surprising, since RDX dissolves more
dissolved, soils have much less tendency to adsorb RDX than TNT.
TNT, 4ADNT, and 2ADNT were detected in two composite samples col-
lected in a 1-year-old crater probably formed by detonation of a 60-mm mortar
(Table 7, samples 119 and 120). Lack of RDX in this crater was surprising since
the main charge in 60-mm mortar rounds is 0.43 kg of Composition B.
The next series of samples were collected at various points throughout the
range (Table 7, samples 58-61, 86 and 87, and 105 and 106). Samples 58 and 59
were taken a short distance from an unidentified crater and contained no
measurable residue. Likewise, samples 60 and 61 were taken near two very old
craters and no residues were detectable. Samples 86 and 87 were collected next
to more recent craters, and low concentrations of RDX, 4ADNT, and 2ADNT
were found in each. Samples 105 and 106 were taken from an area that had
recently burned due to an illumination round, and again concentrations of RDX,
4ADNT and 2ADNT were detectable.
1
P. H. Miyares and T. F. Jenkins, 1999, unpublished data.
41
Chapter 2 Characterization of Explosives Contamination at Military Firing Ranges
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