Cynthia B. Price

Abiotic transformation of TNT in montmorillonite and soil suspensions under reducing conditions

Abstract Abiotic reduction of nitrobenzenes by Fe +2 adsorbed to various surfaces has been demonstrated by others. The objective of this study was to describe abiotic TNT transformation as a function of pH and confirm the possibility of an abiotic Fe +2 reduction pathway in reduced soils.Effects of pH on abiotic transformations of TNT were examined in buffered batch tests with montmorillonite and Fe +2 . Results indicated that TNT was rapidly reduced under abiotic conditions, with the rate of reduction highest at pH 8. Mass balance experiments indicated that unextractable or unknown transformation products were produced. Suppression of the abiotic Fe +2 reduction mechanism in anaerobic soil by complexing Fe +2 with EDTA demonstrated the presence of the pathway in a soil.

Aquifer Soil Cation Substitution and Adsorption of TNT, RDX, and HMX

1U.S. Army Engineering Research and Development Center, Environmental Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180; 2DynTel Corporation, 350 Manor Dr., Vicksburg, MS 39180 these contaminants in aquifer soils and groundwater. The objective of this laboratory study was to determine the effects of changing composition of simulated groundwater on TNT, RDX, and HMX adsorption in low carbon aquifer soils. Batch shake tests using homo-ionic aquifer soils and clay minerals were used to determine the effects of cation composition on sorption. Results of batch shake tests showed that simulated groundwater cation composition substantially affected the sorption of TNT in aquifer soils. Saturation of the cation exchange sites with K+ and NH4 resulted in increased TNT sorption to the aquifer soils by up to 9780%. TNT adsorption by biionic K+:Ca++ aquifer soil increased until 40% saturation of the exchange sites was attained. Past this point, pronounced increases in adsorption were not observed until 100% saturation with K+ was reached. Changing the cation substitution on aquifer soils by saturation with either K+ or NH4 did not consistently increase the adsorption of RDX and HMX. TNT shows great potential for treatment using cation substitution, while this is not the case for nitramines. The production of 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-hexahydrotriazine (RDX), and octahydro-1,3,57-tetranitro1,3,5,7-tetrazocine (HMX) has resulted in significant contamination of soil and groundwater at ammunition plants. The development of remediation and risk management strategies requires an understanding of the environmental fate and transport processes affecting TNT, RDX, and HMX. The transformation and soil sorption are key process descriptors that must be quantified to effectively evaluate the environmental fate of

Volatilization of Contaminants from Suspended Sediment in a Water Column during Dredging

Abstract Remedial dredging of contaminated bed sediments in rivers and lakes results in the suspension of sediment solids in the water column, which can potentially be a source for evaporation of hydrophobic organic compounds (HOCs) associated with the sediment solids. Laboratory experiments were conducted in an oscillating grid chamber to simulate the suspension of contaminated sediments and flux to air from the surface of the water column. A contaminated field sediment from Indiana Harbor Canal (IHC) and a laboratory-inoculated University Lake (UL) sediment, Baton Rouge, LA, were used in the experiments, where water and solids concentration and particle size distribution were measured in addition to contaminant fluxes to air. A transient model that takes into account contaminant desorption from sediment to water and evaporation from the water column was used to simulate water and sediment concentrations and air fluxes from the solids suspension. In experiments with both sediments, the total suspended solids (TSS) concentration and the average particle diameter of the suspended solids decreased with time. As expected, the evaporative losses were higher for compounds with higher vapor pressure and lower hydrophobicity. For the laboratory-inoculated sediment (UL), the water concentrations and air fluxes were high initially and decreased steadily implying that contaminant release to the water column from the suspended solids was rapid, followed by evaporative decay. For the field sediments (IHC), the fluxes and water concentrations increased initially and subsequently decreased steadily. This implied that the initial desorption to water was slow and that perhaps the presence of oil and grease and aging influenced the contaminant release. Comparison of the model and experimental data suggested that a realistic determination of the TSS concentration that can be input into the model was the most critical parameter for predicting air emission rates.

Vapor-Phase Transport of Explosives from Buried Sources in Soils

Abstract The fate and transport of explosives in the soil pore vapor spaces affects both the potential detection of buried ordnance by chemical sensors and vadose zone transport of explosives residues. The efficacy of chemical sensors and their potential usefulness for detecting buried unex-ploded ordnance (UXO) is difficult to determine without understanding how its chemical signatures are transported through soil. The objectives of this study were to quantify chemical signature transport through soils under various environmental conditions in unsaturated soils and to develop a model for the same. Flux chambers, large soil containers, and batch tests were used to determine explosives signature movement and process descriptors for model development. Low signatures were observed for explosives (2,4-dinitrotoluene, 2,6-dinitrotoluene, and 1,3-dinitrobenzene) under all environmental conditions. A diffusion model was used to describe the chemical transport mechanism in the soil pore air. The soil-air partition constant was treated as a fit parameter in the model owing to the uncertainty in its a priori estimation. The model predictions of the trends in experimental fluxes and the soil concentration were only marginal at best. It was concluded that better estimates of the partition constant are required for more accurate estimation of the chemical concentration at the soil-air interface. Chemical sensors will need to be very sensitive because of low signatures. However, this may result in many false alarms because of explosives residues not associated with UXO on firing ranges. Low explosives signatures also should result in insignificant air environmental exposures.