Transport and dissolution of microscale Composition B detonation residues in porous media.

The deposition of military explosive residues on training ranges has resulted in extensive contamination of land and water resources. Experiments were performed to examine the transport and dissolution of mm-sized and microscale Composition B (Comp B) residues applied to the top of sand columns under unsaturated flow conditions. Under a continuous application of artificial rainwater, greater dissolved effluent concentrations of TNT and RDX (5- and 10-fold, respectively) were observed for the columns amended with microscale residues than for the columns amended with the mm-sized residues. This difference between microscale and mm-sized residues likely was due, in part, to dissolution of microscale particles entrapped in the sand column. Elution of particulate Comp B from the columns, based on the difference between total and dissolved explosives concentrations in column effluent, indicated higher and more frequent detections of particulate explosives in the columns amended with microscale Comp B than the columns amended with mm-sized Comp B. Examination of the vertical profiles of explosives in sand indicated that particulate residues had migrated into the sand, with a greater particulate mass observed in the columns which had received the microscale Comp B compared to those which received the mm-sized Comp B. These results indicate that both mm-sized and microscale detonation residues can contribute to the undissolved (e.g., particulate) Comp B transport into to the subsurface. This particulate transport increases the effective contact time between residues and infiltrating rainwater, leading to overall increases in the dissolved mass contaminant flux.