reduce the amounts of explosives residues contaminating surface soils at impact
ranges.
Summary and Conclusions
Three training areas were sampled at Fort Lewis, WA: an impact area within
the hand grenade range, a 105-mm howitzer firing point, and a portion of the
impact area within the heavy artillery and mortar ranges. A set of eleven water
samples from monitoring wells and seeps adjacent to the artillery impact area
were also analyzed. Soil samples were also collected at a hand grenade range at
Fort Richardson, AK.
RDX was detected in all 96 soil samples, both surface and shallow subsur-
face, at the two hand grenade ranges. Concentrations in surface soils ranged up
to 51,200 :g kg-1 at Fort Lewis, and 518 :g kg-1 at Fort Richardson. TNT and
HMX concentrations were also detectable in most soils from these two grenade
ranges. Whether these residues are a result of the large number of high-order
detonations of hand grenades or the much lower number of low-order detonations
is uncertain. Overall, concentrations of explosives-related contaminants were an
order of magnitude higher at the Fort Lewis than at the Fort Richardson hand
grenade range. This may be due to higher use at Fort Lewis. While RDX concen-
trations were moderate, removal of the contaminant to prevent potential ground-
water contamination would not be difficult because these ranges are relatively
small.
At the Fort Lewis artillery range where surface and near-surface soil samples
were collected at a 105-mm howitzer firing point, 24DNT, a component of the
single-based propellant, was found at concentrations as high as 237,000 :g kg-1.
Whether 2,4DNT is leaching deeper into the soil profile is uncertain, because
only two shallow subsurface samples were analyzed.
In the artillery range impact area at Fort Lewis, concentrations of explosives
residues associated with craters formed by high-order detonations were very low,
often below a detection limit of 1 :g kg-1 (1 part per billion). RDX, the analyte of
most concern for groundwater contamination, was always less than 100 g kg-1
(ppb) in these soil samples. Concentrations of TNT were extremely high
(1.5 percent) in the surface soil under a 155-mm round that had undergone a low-
order detonation, and remained substantial in soils collected beneath this round at
5- and 10-cm depths. Clearly the residues of explosives resulting from low-order
detonations are many orders of magnitude higher than those that result from
high-order detonations. Therefore, efforts should be made to locate and
eliminate the debris resulting from low-order detonations.
Results of analysis of water samples obtained from five monitoring wells and
five seeps that border the artillery range at Fort Lewis indicated a low level
(<1 ppb) of RDX contamination. The source of this contamination is uncertain.
Results from Fort Lewis and Fort Richardson suggest that very low
concentrations of explosives residues are widespread at testing and training
48
Chapter 2 Characterization of Explosives Contamination at Military Firing Ranges
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