Dissolution and Transport of TNT and RDX from Explosive Composition B in Unsaturated Soils.
Katerina Dontsova1, Judith Pennington1, Jirka Simunek2, Charolett Hayes1, and Clint Williford3. (1) US Army Research & Development Ctr, CEERD-EP-P, 3909 Halls Ferry Road, Vicksburg, MS 39180, (2) Univ of California, Riverside, Environmental Science Dept, Bourns Hall A135, Riverside, CA 92521, (3) Univ of Mississippi, Dept of Chemical Engineering, Anderson Hall, Room 134, P.O. Box 1848, University, MS 38677-1848
Unexploded rounds present a possible water-quality problem for military installations and surrounding areas. This study was conducted to estimate dissolution, adsorption and transport of explosives in their pure form and as components of explosive formulation. Pure dissolved 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5- trinitro-1,3,5-triazine (RDX), dissolved Composition B (an explosive formulation containing RDX, HMX and TNT) and solid Composition B residue from low-order detonations were applied to two unsaturated soils, Adler silt loam (coarse-silty, mixed, superactive, thermic Fluvaquentic Eutrudepts) from Vicksburg, MS and Plymouth loamy sand (mesic, coated Typic Quartzipsamments) from Camp Edwards, MA. Interrupted flow experiments were conducted to evaluate contribution of non-equilibrium processes to explosive adsorption and transport. Breakthrough of explosives was analyzed using HYDRUS-1D code for simulating the one-dimensional movement of water, heat and multiple solutes in variably saturated porous media. Results of these experiments indicated that TNT and RDX had similar retardation under saturated and unsaturated conditions. Unsaturated columns that had lower flow rates exhibited less chemical nonequilibrium than saturated columns. Smaller flow rate and longer residence time under unsaturated conditions also resulted in less TNT and fewer degradation products in outflow. This study allowed to model behavior of explosives when present on soil surface as solid particles and indicated that dissolution was controlling explosive transport.