Sally L. Yost

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

Air emission flux from contaminated dredged materials stored in a pilot-scale confined disposal facility.

ABSTRACT A pilot-scale field simulation was conducted to estimate the air emissions from contaminated dredged material stored in a confined disposal facility (CDF). Contaminated dredged material with a variety of organic chemicals, obtained from Indiana Harbor Canal, was used in the study. It was placed in an outdoor CDF simulator (i.e., a lysi-meter of dimensions 4 ft x 4 ft x 2 ft). A portable, dynamic flux chamber was used to periodically measure emissions of various polynuclear aromatic hydrocarbons (PAHs). A weather station was set up to monitor and record the meteorological conditions during the experiment. The fluxes of several PAHs were monitored over time for 61/2 months. Initial 6-hr average fluxes varied from 2 to 20 ng/cm2/hr for six different PAHs. The flux values declined rapidly for all compounds soon after placement of the dredged material in the CDF. Chemical concentrations derived from flux values were generally of low magnitude compared with ambient standards. Data obtained from the experiment were compared against those predicted using models for air emissions. Model simulations showed that initially the flux was largely from exposed pore water from saturated (wet) sediment, whereas the long-term flux was controlled by diffusion through the pore air of the unsaturated sediment. Model predictions generally overestimated the measured emissions. A rainfall event was simulated, and the dredged material was reworked to simulate that typical of a CDF operation. Increased flux was observed upon reworking the dredged material.

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.

Evaporation of Hydrophobic Organic Compounds from Suspended Sediment Solids during Dredging

The advent of new screening technologies has dramatically reduced the high cost of dioxin/furan analyses (i.e., nearly an order of magnitude). The P450 HRGS assay (EPA method 4425) represents a screening tool that uses a transgenic human liver cancer cell (101L) to assay extracts of sediments for carcinogenic chemicals (CYP1A1 inducers). Results of assays for dioxins/furans are expressed as an HRGS Toxicity Equivalent Quotient (TEQ) and responses to PAHs are normalized to benzo-[a]-pyrene (as B [a] P equivalents). Because of the potential cost savings much attention has focused on the application of the method for dioxin analysis. The purpose of this study was to demonstrate the utility of the HRGS assay as a cost-effective analytical tool for the evaluation of both dioxin/dioxin-like compounds and PAHs. Fifteen surficial sediment samples were collected from selected sites in a designated area of Long Beach Harbor for initial evaluation by HRGS to identify response ranges for both dioxins/furans and PAHs. Based on these results a smaller subset (5 samples) was selected for subsequent confirmatory analysis by conventional analytical techniques (EPA 8290). Additional sub-samples of these 5 were sent to the USACE ERDC lab in Vicksburg, MS for analysis using the same cell line. Results are discussed in terms of the correlation between the P450HRGS method and conventional analyses, inter-laboratory variability, and the application of the method as a low cost screening tool for the evaluation of potentially contaminated harbor sediments.