Performance Monitoring of Embankments Containing Tire Chips: Case Study

Tire chips (or shredded tires) have been successfully used as a filler material in a number of embankments, but this use has also led to problems such as spontaneous combustion, settlement, and so on. To ensure proper construction and to avoid such problems, the Texas Department of Transportation sponsored a study to monitor the performance of embankments constructed of tire shred fill material in El Paso, Texas. Three embankments, consisting of (1) a mixture of soil and shredded tires; (2) shredded tires wrapped in a geotextile; and (3) a reference embankment built with conventional soil, were instrumented and monitored. The performance of the embankments in terms of vertical settlement, temperature change, and air and water constituency changes were monitored. The performance of these three embankments has shown that there is little potential for environmental impacts in a climate like that of El Paso, and that the construction techniques employed limited the settlements in comparison with some previous experiences.     

Sorptive and Reactive Scavenger-Containing Sandwich Membranes as Contaminant Barriers

The barrier properties of composite membranes containing either zero-valent iron nanoparticles or powdered activated carbon mixed into an aqueous clay suspension and sandwiched between two sheets of high-density polyethylene were measured using carbon tetrachloride and trichloroethylene as model contaminants. The lag time to trichloroethylene breakthrough increased 17-fold when 24?wt?% powdered activated carbon was mixed into the 400-μm-thick center layer of the composite. Zero-valent iron was successful in extending the lag time for carbon tetrachloride but not for trichloroethylene, presumably because the latter reaction with zero-valent iron is slow relative to diffusion. Approximately 30% of the total iron in the composite membrane was consumed before carbon tetrachloride breakthrough, a major improvement over the 2–3% reported previously for single-layer high-density polyethylene membranes containing iron nanoparticles. Simplified multilayer membrane models used to describe contaminant breakthrough are consistent with the experimental results.     

Optimal Design of a Compacted Soil Liner Containing Sorptive Amendments

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.     

Characterizing Polyurethane Foam as a Sink for or Source of Volatile Organic Compounds in Indoor Air

Polyurethane foam (PUF) is widely used in indoor consumer products. Despite strong potential interactions with volatile organic compounds (VOCs), the effect of PUF on indoor concentrations of VOCs has not been examined. This study determines the behavior of PUF as a potential sink for or source of VOCs in indoor air. A flexible polyether-type foam and eight aromatic VOCs ranging in molecular weight from naphthalene to benzene were studied. Rapid determinations of PUF–air partition coefficient (K) and PUF–phase diffusion coefficient (D) were achieved using a dynamic microbalance procedure. A diffusion model was applied to interpret the experimental data. The PUF sample was assumed to conform to semi-infinite cylindrical geometry with solid-phase diffusion being the rate limiting step. The results indicate that sorption of VOCs by PUF is fully reversible. For the VOCs studied, K can be correlated with vapor pressure and D with molecular free surface area. Humidity appears to reduce the extent of sorption and slow the sorption kinetics. These findings should facilitate the prediction of the source/sink behavior of PUF and the related impact on VOC concentrations in the indoor environment.     

Removal of Toluene Vapor with Dispersed Activated Carbon

This work considers the mechanisms of mass transfer in a process of dispersed sorbent injection. During experiments, an air supply was dosed with toluene vapor, at partial pressures between 4 and 15 Pa. Powdered activated carbon (PAC) was added to remove the toluene from the air, and the resulting mixture was passed through a 3-m-long, tubular, aluminum test section. Toluene concentrations were measured at seven axial locations within the test section. Comparing the measurements with mathematical models indicated the importance of adsorption kinetics. At reduced toluene inlet concentrations the PAC removed a slightly bigger fraction of toluene from the air stream. This fraction increased with PAC concentration. The effect on removal of varying the air temperature between 25 and 85°C was small. Alternative models incorporating either pore diffusion or surface diffusion were fitted to the results. The quality of the fits was fair only, but sufficient to show that the pore diffusivity that gave the best fit was far larger than would be expected from the Knudsen diffusivity in the pores. That is, surface diffusion was an important part of the intraparticle mass transfer.