Energetic compounds, such as 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and their degradation products can act as a source of contamination for soil on Department of Defense (DoD) testing and training ranges. Base hydrolysis degrades nitroaromatics and nitramines, and the potential effectiveness of lime to induce this reaction has been demonstrated at the laboratory scale.
The objective of this project was to further examine both basic and applied aspects of alkaline application for reducing source-zone contamination on military ranges.
Bench-scale microcosms were used to examine basic conditions that could affect the alkaline hydrolysis reaction, such as soil organic matter content, lime concentration, soil type, and contamination type. Larger-scale experiments, conducted in vessels packed with approximately 55 kg of soil, were used to investigate topical versus well-mixed applications of three alkaline materials (hydrated lime, quicklime and Class C fly ash).
Results from experiments using soil from a variety of ammunition production facilities and training ranges, in general, support the use of explosive contaminant treatment by alkaline material in well-mixed systems. RDX in crystalline form was more resistant to treatment, possibly due to limitations associated with the dissolution of the RDX from the crystal to the aqueous phase. In the larger-scale experiments, TNT, RDX and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in the mixed system were removed quickly from both the leachate and soil. However, results from experiments with topical applications of alkali material indicated that the aqueous transport of hydroxide ion was not sufficient to overcome the buffering capacity of the soil. Consequently, the soil pH was not raised to the extent necessary for alkaline treatment of explosive compounds. This result is fundamentally related to the cation exchange capacity properties of the soil.
This research provided preliminary knowledge of the efficacy of treating soils contaminated with energetics by topically applying lime to the ground surface. Although it would be site-specific, topical application of alkali material could be an inexpensive and easily applied in situ treatment technique for energetic compounds on ranges.