Live-fire training is an essential element in maintaining the readiness of armed forces. Propellants, commonly tested on live-fire ranges, are known as low explosives because of their reaction speed; unlike high explosives, which detonate, propellants deflagrate, or burn rapidly. This rapid burning produces large quantities of gas that propels the projectile out of the barrel of the weapon system. The most common propellants used by the U.S. and Canadian military are nitrocellulose (NC) based. Nitrocellulose is a polymeric material that has a very low solubility in water. Energetic compounds typically alloyed to NC include 2,4-dinitrotoluene (2,4-DNT), nitroglycerin (NG), and nitroguanidine (NQ).
The low solubility of these compounds in the NC polymer matrix poses specific challenges to sample homogenization and extractions. Consequently, methods to overcome these analytical challenges are needed. While transport process descriptors have been developed for all of the principal high explosives, their transformation products, and their formulations, similar data for propellant constituents and formulations crucial to transport predictions and risk assessment is lacking.
The objective of this project was to develop an improved understanding of the distribution and fate of propellant residues, develop the environmental data to characterize potential releases and fate of gun and rocket propellants as they occur on training and testing ranges, and to characterize residues from gun propellants and leaching rates of contaminants bound in these materials.
Field studies were conducted to estimate the propellant residue mass deposited per round fired from various munitions as well as residues from the field disposal of excess propellants. Experiments also were performed to measure the rate of release of energetic compounds after deposition. Training ranges were then examined to determine the mass and distribution of residue accumulation, and profile sampling was conducted to document the depth to which these residues had penetrated the ground. Column studies were carried out with propellants to document transport rates for solution-phase propellant constituents and to develop process descriptors for use in models to enable prediction of fate and transport for constituents of concern and testing of propellant burn structures was initiated.
A list of the propellant formulations used in the major Army and Marine Corps weapon systems was developed and prioritized such that efforts focused on the most widely used munitions, with emphasis on those containing the most mobile constituents. Field experiments were conducted during live-fire training to delineate the footprint of deposition and the mass deposited as a function of distance from the firing position. Representative soil samples collected at Army and Marine Corps firing points and propellant burn areas helped to determine the accumulation rate of propellant residues for the different weapon systems and laboratory column experiments were used to define transport process descriptors suitable for use in environmental transport models or in environmental and human health risk assessments. Selected propellant constituents and solid phase propellant formulations were tested under different flow regimes and in different soils. Additionally, shallow subsurface soil samples and water samples from tension lysimeters installed in the field were collected to investigate downward transport through the vadose zone.
Lead nano particles were present in some of the gaseous emissions filters of small-arms weapons systems, pointing to a potential immediate health risk. Two shoulder-fired rocket systems were tested for propellant residues and one deposited 0.1% of the original NG load, while the other deposited 14% of the original NG load. Tests on U.S. AT4 rockets confirmed high unburned propellant dispersion rates, with over 70% of the NG recovered following the firing of six rockets. Larger rocket systems were found to be quite efficient, with little or no energetic compounds or perchlorate from the propellants detected after firing. Tank firing tests showed deposition of only 0.0023% of original DNT load and preliminary results from the firing of British triple-based 155-mm munitions indicated no detectable energetics residues following the firing of 78 rounds utilizing various propellant loads.
Characterization work conducted on a former shoulder-fired rocket range, at small arms ranges, and on demolition ranges, indicated heavy energetics contamination that will be a long-term issue for range managers. Surface water contaminated with energetics also was found at one range. A 57-mm naval gun tested for residues yielded no detectable energetics residues following the firing of 10 rounds; however, a former training site for the weapon system contained detectable levels of DNT in the soil, so these tests were considered preliminary.
Soil column fate and transport studies conducted on M9 and M30 propellants indicated slow dissolution rates from raw propellant grains but high mobility in soils of compounds such as NQ.
Results from this project provided information on the long- and short-term environmental impacts of training on military ranges. Additionally, strategies to minimize or eliminate off-site migration of propellants promote environmental stewardship while protecting the readiness mission.
Adoption of sampling and sample processing methods developed through this project and its predecessor Distribution and Fate of Energetics on DoD Test and Training Ranges (ER-1155) is accelerating, with many NATO countries already utilizing the protocols. As a result, both Canadian and U.S. participants that worked on this project have been asked to participate in the NATO AVT-ET-108 work group “Munitions Related Contamination–Source Characterization, Fate and Transport.”