Showing papers by "Shannon L. Bartelt-Hunt published in 2006"

Fate of chemical warfare agents and toxic industrial chemicals in landfills.

Abstract: One component of preparedness for a chemical attack is planning for the disposal of contaminated debris. To assess the feasibility of contaminated debris disposal in municipal solid waste (MSW) landfills, the fate of selected chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) in MSW landfills was predicted with a mathematical model. Five blister agents [sulfur mustard (HD), nitrogen mustard (HN-2), lewisite (L), ethyldichloroarsine (ED), and phosgene oxime (CX)], eight nerve agents [tabun (GA), sarin (GB), soman (GD), GE, GF, VX, VG, and VM], one riot-control agent [CS], and two TICs [furan and carbon disulfide] were studied. The effects of both infiltration (climate) and contaminant biodegradability on fate predictions were assessed. Model results showed that hydrolysis and gas-phase advection were the principal fate pathways for CWAs and TICs, respectively. Apart from CX and the TICs, none of the investigated compounds was predicted to persist in a landfill for more than 5 years. Climate had little impact on CWA/TIC fate, and biodegradability was only important for compounds with long hydrolysis half-lives. Monte Carlo simulations were performed to assess the influence of uncertainty in model input parameters on CWA/TIC fate predictions. Correlation analyses showed that uncertainty in hydrolysis rate constants was the primary contributor to variance of CWA fate predictions, while uncertainty in the Henry's Law constant and landfill gas-production rate accounted for most of the variance of TIC fate predictions. CWA hydrolysates were more persistent than the parent CWAs, but limited information is available on abiotic or biotic transformation rates for these chemicals.

Coupled mechanical and chemical behavior of bentonite engineered with a controlled organic phase

Abstract: This experimental investigation quantified the physical and chemical behavior of two organoclays, synthesized using the quaternary ammonium organic cations hexadecyltrimethylammonium bromide (HDTMA) and benzyltriethylammonium chloride (BTEA). The organic cations were exchanged onto montmorillonite at increasing percentages of the clay's cation exchange capacity in order to increase the packing density of the organic cations on the clay surfaces. Increasing the organic content of the organoclays, and the cation packing density, decreased the specific gravity, N 2 -BET surface area, liquid limit in water, and clay compressibility in the consolidation test for both organoclays. However, the liquid limit in methanol and sorptive capacity for benzene increased for HDTMA organoclay but decreased for BTEA organoclay as the density of organic cation packing was increased. Additionally, the measured friction angle for HDTMA organoclay decreased, while the friction angle for BTEA organoclay increased as a function of increasing organic cation packing density. The creation of an organic phase on the soil created a hydrophobic, rather than hydrophilic, clay that demonstrated reduced interaction with water. The nature of the organic phase in the long chain HDTMA was a fluid-like phase that demonstrated partitioning uptake of organic compounds, and reduced (lubricating) frictional interaction in the direct shear test. In contrast, the organic phase in the BTEA clay formed an adsorptive phase that interacted specifically with organic compounds (that is, not through dissolution), and increased the frictional interaction as the organic cation packing density was increased.

Application of heuristic optimization techniques and algorithm tuning to multilayered sorptive barrier design.

Abstract: Although heuristic optimization techniques are increasingly applied in environmental engineering applications, algorithm selection and configuration are often approached in an ad hoc fashion. In this study, the design of a multilayer sorptive barrier system served as a benchmark problem for evaluating several algorithm-tuning procedures, as applied to three global optimization techniques (genetic algorithms, simulated annealing, and particle swarm optimization). Each design problem was configured as a combinatorial optimization in which sorptive materials were selected for inclusion in a landfill liner to minimize the transport of three common organic contaminants. Relative to multilayer sorptive barrier design, study results indicate (i) the binary-coded genetic algorithm is highly efficient and requires minimal tuning, (ii) constraint violations must be carefully integrated to avoid poor algorithm convergence, and (iii) search algorithm performance is strongly influenced by the physical-chemical properties of the organic contaminants of concern. More generally, the results suggest that formal algorithm tuning, which has not been widely applied to environmental engineering optimization, can significantly improve algorithm performance and provide insight into the physical processes that control environmental systems.

Optimal design of a compacted soil liner containing sorptive amendments

Abstract: The design of a compacted soil liner that includes sorptive amendments is presented and evaluated as a combinatorial optimization problem. An objective function based on the materials costs, opportunity costs, and construction costs of the liner was used to evaluate the effect of incorporating four sorptive materials: benzyltriethylammnonium-bentonite, hexadecyltrimethylammonium-bentonite, shale, and granular activated carbon (GAC) into a compacted clay liner in order to mitigate transport of organic solutes through the liner. The results from this study indicate that the inclusion of sorptive amendments as a component in compacted soil liners can effectively retard the transport of organic contaminants through the liner without violating regulatory hydraulic conductivity requirements. In all cases when aqueous transport was considered as a constraint in the objective function formulation, the resulting liner always contained some amount of sorptive amendment. In general, shale and GAC were selected for use in the sorptive liner design for all organic solutes tested. The modeling framework presented in this study is general and could be used to evaluate other types of sorptive materials or additional constraints, and thus represents a flexible new tool for the design of compacted soil liners.