TRANSPORT OF 2,4,6-TRINITROTOLUENE AND HEXAHYDRO-1,3,5-TRINITRO-1,3,5-TRIAZINE IN SOILS

We investigated the fate and transport of explosives in soils. Transport experiments were conducted to describe the mobility of 2, 4, 6-trinitrotoluene (TNT) and hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) in a SWy-1 reference clay (bentonite mixed with sand) and two selected soils (Norwood and Kolin). Miscible displacement experiments in packed soil columns under steady flow were used. For the bentonite/sand column, TNT was highly mobile and fully reversible when methanol was used as the background solution. In contrast, with 0.005 M Ca(NO3)(2) as the background solution, the TNT pulse was strongly retarded with as much as 50% of that applied remaining within the bentonite/sand, Norwood, or Kolin columns. Products of the transformation of TNT to 4-Am-DNT and other compound were identified in the effluent solution. A 7-day flow interruption during the TNT pulse application resulted in decreased TNT levels in the effluent solution. This decrease corresponded to a sudden increase in the 4-Am-DNT concentration in the effluent, with peak concentrations of 0.60 mg ml(-1). For RDX, only limited retention as observed in all columns. These findings are consistent with results from adsorption-desorption batch experiments. The TNT and RDX transport results were successfully described by a nonlinear multireaction and transport model (MRTM), which accounted for equilibrium and kinetic (reversible and irreversible) retention mechanisms. However, efforts to describe RDX transport were more successful than efforts to describe TNT when independently determined (batch) parameters were used. The mobility of TNT, RDX, and other compounds from a contaminated soil obtained from a Louisiana Army Ammunition Plant (AAP) site was also investigated. A gradual release and subsequent movement of various contaminants, including HMX, TNT, RDX, TNB, 2-Am-DNT, and 4-Am-DNT, was observed. The leaching patterns were consistent with results from uncontaminated Kolin soil columns and reflected the affinity of contaminants during leaching in the AAP soil.