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.     

Water sorption in poly(ethylene furanoate) compared to poly(ethylene terephthalate). Part 1: Equilibrium sorption

Equilibrium water sorption properties of amorphous poly(ethylene furanoate) (PEF) and amorphous poly(ethylene terephthalate) (PET) were studied at 35 °C over the entire water activity range. PEF exhibits a largely increased equilibrium water sorption capacity of ∼1.8× averaged over the entire concentration range compared to PET, resulting from substitution of the non-polar phenyl ring in PET with the polar furan ring in PEF. Both polyesters exhibit dual-mode sorption up to ∼0.6 activity, after which the onset of swelling produces a noticeable upturn in concentration vs. activity for both polyesters. Excellent agreement was observed between three independent sorption measurement techniques, thereby providing a consistency check for the reported data. Sorption measurements performed at 15, 25, 35, and 45 °C allowed estimation of the effective enthalpy of water sorption for both polyesters, which were similar to the enthalpy of condensation for pure water. The current work demonstrates the importance of structure on sorption and transport properties in these two important polyesters.     

Findings of Case Histories on the Long-Term Performance of Seepage Barriers in Dams

In a vast majority of cases, seepage barriers increase the reliability of dams. However, it is important to recognize that seepage barriers often drastically increase hydraulic gradients around the boundaries of the barrier, and through any windows or defects in the barrier. The result is increased water pressures and hydraulic gradients behind and around the barrier. These increased pressures and gradients have potential to provide the catalyst for initiation of several modes of internal erosion that were either unlikely or less likely without the seepage barrier. As a consequence, seepage barriers give rise to the potential for additional mechanisms of internal erosion and piping in the dam and the foundation. A compendium of 30 case histories of dams that have had seepage barriers in place for over 10 years has been assembled, and observations and insights garnered from these case studies were compiled. Finite-element seepage and deformation analyses have been performed to provide better understanding of the performance of seepage barriers and the mechanisms that affect their performance. This paper presents a summary of our findings from the case histories and the analyses performed.     

Quantitative effects of drivers and barriers on networking strategies in public construction projects

Past studies have found that network strategies can contribute to better company and project performance. The adoption of network strategies is motivated by a set of factors (i.e., drivers), but also faces numerous challenges (i.e., barriers). The appreciation of the factors motivating and deterring networking strategies is beneficial to the successful implementation of network strategies. In the context of public construction projects, this study aims to examine the quantitative effect of drivers and barriers on three network strategies (i.e., trust, information sharing and joint problem solving). The results of a questionnaire-survey of 104 public projects show that the adoption of network strategies in public construction is mainly cost-driven. The results indicate that four barriers impede network strategies in public projects: (i) a lack of continuity and (ii) ethos of public services are harmful to trust; (iii) institutional constraints hinder information sharing; and (iv) a lack of capability is a hurdle to information sharing and trust. It is also found that one barrier (i.e., ethos of public services) has a positive influence on trust between clients and consultants. Recommendations on enhancing network strategies through the appreciation of drivers and barriers are provided.     

Analytical Models for the Design of Iron-Based Permeable Reactive Barriers

The preliminary design of iron-based permeable reactive barriers is often accomplished using analytic expressions for one-dimensional groundwater flow and contaminant transport. Typically, one or more of the governing processes is simplified or neglected to facilitate development of a tractable solution. This paper presents a set of improved design equations that include the effects of dispersion, finite domain boundary, sequential decay, and production processes, and increased flow through high conductivity barriers. When applied to realistic example problems, application of the expanded design equations typically results in the specification of a larger permeable reactive barrier thickness than obtained using conventional approaches.     

Chloride Interactions with Iron Surfaces: Implications for Perchlorate and Nitrate Remediation Using Permeable Reactive Barriers

Perchlorate (ClO4?) can be reduced by iron surfaces, suggesting that permeable reactive barriers may represent a useful groundwater remediation strategy. However, chloride produced by the reaction inhibits further perchlorate removal. Adsorption of chloride on iron filings was investigated as a potential mechanism of chloride interference. The effect of chloride on the removal of nitrate, another oxyanion reactive at iron surfaces, was also investigated to draw more general conclusions about anion competition when target compounds adsorb electrostatically. A triple layer adsorption model was used to describe chloride sorption isotherms on the iron filings using magnetite as the model surface and defining a single type of surface hydroxyl sorption site. The model considered electrostatic attraction, specific sorption, and the effect of adsorbed Fe2+ on chloride sorption. Experimental and modeling results indicate that chloride competition is probably not of concern for nitrate reduction in permeable reactive barriers. However, perchlorate reduction is significantly inhibited by chloride in both buffered and unbuffered solutions, possibly because the reactive sorbed Fe2+ sites may be preferentially occupied by chloride.     

A planar single facility location and border crossing problem

In this study, we tackle the problem of locating a facility in a region where a fixed line barrier divides the region into two. The resulting subregions communicate with each other through a number of passage points located on the line barrier. Our contribution is threefold. First, we formulate the problem as a Mixed Integer Nonlinear Programming (MINLP) model and provide an optimal solution methodology based on an Outer Approximation (OA) algorithm. Second, we discuss the minimax version of this problem for locating an emergency facility and use the OA algorithm to solve the problem. We then provide simple example problems and extensive computational results for both problems. Finally, we propose a one-infinity approximation approach for the latter problem which yields a linear model. Practical uses of the models have been discussed in the border crossing context.     

Deck-Mounted Steel Post Barrier System

An existing mountable safety barrier system, previously crash tested successfully on a wood bridge deck, was evaluated for use on a fiber reinforced plastic (FRP) bridge deck. In an attempt to avoid expensive full-scale crash testing, components of the existing system were evaluated using worst case conditions on two dynamic bogie crash tests and a series of computer simulations using nonlinear finite-element analysis. Simulation results closely approximated the physical results, with both displaying similar deformation, damage, and force levels. Both testing and simulation demonstrated that the barrier should function sufficiently if used on the FRP deck system. Further, the development of an accurate model makes it possible to evaluate the potential success of the existing system for use on other bridge decks. As an example, a more rigid bridge deck, similar to reinforced concrete, was evaluated. Results showed that due to the stiffer deck, more of the impact energy must be absorbed by the posts and attachment hardware, resulting in significantly more deformation than when used on the flexible FRP deck.     

Predicting Swelling Characteristics of Bentonites

Bentonite is currently planned for use as a buffer and backfill material for repositories of high-level nuclear waste because these materials must have swelling characteristics to seal the waste. However, it is necessary to choose the appropriate bentonite from among many kinds of bentonite in the design of buffer and backfill materials. To do this, the writers have proposed a new prediction method for swelling characteristics of bentonite-based buffer material. This prediction method comprises some equations that were previously developed for repulsive and attractive forces between two montmorillonite layers; others included in the method are the writers’ previously proposed equations for (1) the swelling volumetric strain of montmorillonite (Komine and Ogata 1999), and (2) the influence of pore water chemistry and specific surface of bentonite (Komine and Ogata 1996a). However, the applicability of this prediction method to swelling characteristics of some bentonites remains unclarified. This study clarifies the applicability of the prediction method by comparing predicted results with experimental data for five kinds of bentonite produced in Japan and the United States.     

Analytical and Numerical Modeling Assessment of Capillary Barrier Performance Degradation due to Contaminant-Induced Surface Tension Reduction

Analytical and numerical models of capillary barrier performance commonly use hydraulic characteristics measured using pure water. However, the potential exists for an infiltrating solution to have a surface tension lower than that of pure water due to the presence of surface-active contaminants (surfactants). A lower surface tension solution may impact capillary barrier performance due to the dependence of capillarity on surface tension. An existing analytical solution for capillary diversion length (L) was modified to include the effect of surface tension reduction on steady-state capillary barrier performance during uniform and constant infiltration. The L for a surfactant-contaminated system was found to be less than for a pure water system and equal to L for a pure water system multiplied by the relative surface tension. Numerical modeling using HYDRUS-2D also showed that diversion was less in the surfactant-contaminated system and that the difference in the performance of the two systems was due to the fact that the fine layer in the capillary barrier retains less liquid when wetted with surfactant solution.