Energetic Residues and Crater Geometries from the Firing of 120-mm High-Explosive Mortar Projectiles into Eagle River Flats, June 2007

Abstract : Fourteen 120-mm high-explosive mortar projectiles were fired into the Eagle River Flats (ERF) impact area in June 2007 to determine physical disturbance of the mudflat when it is not covered by ice. Currently, ERF is used only when it is covered by ice that prevents disturbance of the underlying sediment. Thirteen of the projectiles functioned normally and produced high-order detonations. The high order detonation craters averaged 2.7 m in diameter and 0.7 m in depth, and no high-explosives residues from the Comp B filler were detected in the sediments in and around the craters. One projectile partially detonated. The crater was 1.7 m in diameter and 0.7 m in depth. Residues of TNT, RDX, and HMX were detected at tens of parts per million concentrations on the day of the detonation. None of the detonations exposed white-phosphorus-contaminated sediments or unexploded ordnance. Water draining off the mudflats immediately adjacent to areas with explosives residues on the surface had detectable concentrations of RDX, but water within the gully system had energetic concentrations of < 0.06 g/L. At the firing points, the propellant residue expelled from the mortar consisted of partially consumed grains that had nearly the same proportion of nitroglycerin as in the unfired propellant. Surface soils at the firing points had NG concentrations (around 10 g/g) similar to those observed during previous sampling events.