Artillery range firing point
Results from analysis of the 48 surface soil samples from the artillery firing
point for Guns 1 and 2 at Fort Lewis (Tables 5 and 6, respectively) show the
following major propellant-related compounds: dinitrotoluenes (2,4DNT,
2,6DNT, 2,5DNT, and 3,4DNT); the two isomeric environmental transformation
products of 2,4DNT, 4A2NT and 2A4NT; and 2,4,6TNT, presumably a
manufacturing impurity in dinitrotoluene. Of these compounds 2,4DNT was
present at the highest concentration in all samples from both guns.
Concentrations of 2,4DNT varied from 982 to 175,000 :g kg-1 (median value =
31,500 :g kg-1) for surface samples collected in front of Gun 1 and from 1,030 to
237,000 :g kg-1 (median value = 40,900 :g kg-1) in front of Gun 2. While these
numbers appear quite large, they are in :g kg-1, or parts per billion, and the guns
had fired approximately 610 rounds from the same position over the previous
several months.
The propellant-related compounds detected at the next highest concentrations
were 4A2NT and 2A4NT. These two compounds ranged in concentration for
surface soil from below detectable limits <d to 3,000 :g kg-1 and from <d to
1,340, :g kg,-1 respectively. Concentrations in the surface soil were typically
about two orders of magnitude lower than concentrations of 2,4DNT.
Concentrations of 2,6DNT, 3,4DNT, and 2,4,6TNT were also at least two orders
of magnitude lower than 2,4DNT; concentrations of 2,5DNT were generally
three orders of magnitude lower than 2,4DNT.
Gun 1. The distribution of 2,4DNT in the soil samples collected in front of
Gun 1 is shown in Figure 15. All but two of these samples were collected from
surface soil. Samples were collected as far as 10 m beyond the muzzle of the gun.
The mean concentration of the three samples at 10 m was 19,500 :g kg-1. A
seven-sample set of surface soils was collected in a wheel pattern in front of
Gun 1, 2 m from the muzzle. This was done to assess the short-range spatial
heterogeneity of analytes in the surface. Results indicated that concentrations of
2,4DNT ranged from 4,400 to 99,200 :g kg-1 (Figure 15). Thus as found
elsewhere, the distribution of munitions-related analytes was spatially very
heterogeneous, even over short distances. Only two subsurface soil samples were
collected in the area in front of Gun 1. These samples were collected on the
center line, 2 m in front of the gun, below the center of the samples collected in
the wheel pattern. The concentrations of 2,4DNT in the surface soil, in the soil
segment from 0.5 to 5 cm, and from 5 cm to 9 cm were 66,900, 955, and 458 :g
kg-1, respectively. Therefore, some downward migration of 2,4DNT is possible,
but cannot be confirmed with only one set of samples.
Gun 2. The distribution of 2,4DNT in the soil in front of Gun 2 is shown in
Figure 16. Concentrations of 2,4DNT, the two amino transformation products of
2,4DNT, 2,4,6TNT, and the other isomers of DNT were very similar to those
found for samples collected in front of Gun 1. For Gun 2, samples were collected
at distances as far as 20 m from the muzzle of the gun on the center line and 3 m
to the left and right of the center line. A chromatogram for the extract of one of
the samples collected 20 m from the muzzle is shown in Figure 17. Even at this
range, the mean concentration was 4,060 :g kg-1. Thus propellant residues were
32
Chapter 2 Characterization of Explosives Contamination at Military Firing Ranges
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