Appendix K - Tungsten Information - STATES

56
CONCLUSIONS
ERDC/CRREL TR-07 -xx
Tungsten is present in the surface soils of three small arms ranges at Camp Edwards. The level
of tungsten in subsurface soils (generally less than 1 mg/kg) is significantly less than surface
soils and decreases with depth. Soil pore-water in the unsaturated zone beneath the bullet
pockets and trough areas has tungsten at levels that appear to correspond to the surface soil
concentrations and range usage. Tungsten is present in one monitoring well located
downgradient of the berm on B Range. Field and laboratory results indicate that the tungsten
from the tungsten/nylon bullets is rapidly dissolved with solubility levels approaching several
hundred mg/L. As tungsten metal is insoluble, we hypothesize that the small particles of
tungsten in the bullets have oxidized and that we are dissolving tungsten oxides. Relatively high
levels of tungsten (up to 400 mg/L) in the unsaturated zone pore water at depths up to 65 cm
indicates tungsten is mobile through these sandy, acidic, aerobic soils. The presence of
tungsten in groundwater at Camp Edwards indicates relatively rapid migration through the
unsaturated zone. Results from nanopore sieving tests and HPLC GC tests suggest that the
mobile form of tungsten is a tungstate anion, however, we cannot yet rule out a polytungstate
form. Rapid migration indicates that the tungsten carried in the pore water is not retarded by
sorption possibly because the clay content of Camp Edwards soils is low. Ground water impacts
are possible for those installations with shallow depth to ground water and sandy soils. Surface
water impacts are possible in temperate environments where surface water drains off the small
arms range. Migration of tungsten from small arms ranges can be expected from sites with
significant amounts of precipitation such as the Eastern United States or coastal regions of the
Western United States with delayed impacts in arid environments.
RECOMMENDATIONS
As outlined in the Final Proposal Addressing Tungsten Fate and Transport at Camp Edwards
dated May 25, 2006 additional studies are recommended to assess the fate and transport of
tungsten at Camp Edwards. This additional work has been funded and will be focused on
mapping the extent of tungsten in ground water at B Range, experimental work quantifying the
dissolution rate and adsorption/desorption kinetics of tungsten on Camp Edwards soil,
unsaturated and saturated zone modeling to assess the transport rates, and tungsten speciation
studies to identify the aqueous form present in the environment.
For the dissolution experiments, the next step is to standardize the experimental methods and
run a series of tests using different soil:solution ratios. A test using aqueous sodium tungstate
standard solution also is necessary to test whether tungsten is lost during sample preparation.
One activity planned as part of the second phase of the tungsten study at Camp Edwards is to
more rigorously establish the background level of tungsten in the soil pore-water and
groundwater. We plan to install several additionallysimeters in remote locations to ascertain the
background level of tungsten. In addition, we plan to sample up to a dozen additional
background monitoring wells (to be identified in cooperation with the IAGWSP) to determine the
natural background level of tungsten in the environment.