Quantifying the transport of energetic materials in unsaturated sediments from cracked unexploded ordnance

Dissolved explosive species have been found in the groundwater under military training areas. These explosives are thought to originate from munitions although the mechanism of transport to the groundwater is poorly understood. This study was conducted to determine whether ruptured unexploded ordnance may be a viable source term for these explosives. The rupturing effect of one 81 mm-mortar exploding in close proximity to another 81-mm mortar was observed and the resulting contaminants were collected. These contaminants were then subjected to leaching experiments on repacked, jack drill compacted unsaturated sediment columns in a climate controlled laboratory. The mortars which were exposed to nearby explosions were shown to be susceptible to rupturing rather than sympathetically detonating under certain conditions. The ruptured mortars released up to 166+/-2 g of pulverized explosive residues (largely Composition B) and the results from the subsequent leaching tests showed that this explosive residue is highly mobile in unsaturated sandy soil. Up to 4.45+/-1.00 g of dissolved explosive contamination was transported through the unsaturated soil columns during the first year of infiltration. The results indicate the mass of transported explosive residue dissolved in the leachate was primarily caused by the preferential dissolution of explosive contaminants having a grain size under 0.125 mm. Surface or near-surface unexploded ordnance (UXO) on live fire ranges may therefore be significant sources of explosive environmental contamination after they have been exposed to other rounds which explode nearby.