Contaminant Barrier Research Articles

Laboratory and In Situ Tests for Long-Term Hydraulic Conductivity of a Cement-Bentonite Cutoff Wall

Slurry trench cutoff walls, constructed using self-hardening slag-cement-bentonite (Slag-CB), are the most common form of in-ground vertical contaminant barrier in the U.K., Europe, and Japan, and are increasingly being used in the United States. This paper presents a case study of the hydraulic conductivity evaluation of an 11-year-old Slag-CB wall material at a sulfate-contaminated site, using different in situ techniques and laboratory tests. The laboratory results suggest that the hydraulic conductivity of the samples, which vary in age from 4 weeks to 11 years, decreases with time for the first 3 years but then remains constant. The results indicate that the long-term performance of these containment walls is influenced by various parameters such as aging, the type/duration of contaminant exposure, mixing of surrounding soil during construction, and wall depth. Piezocone tests, packer tests, and self-boring permeameter tests were carried out in the field to determine the suitability of different in s...

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 ...

Theoretical investigation of the effects of consolidation on contaminant transport through clay barriers

AbstractConsolidation of clayey contaminant barriers such as landfill liners has been postulated as a cause of early breakthrough of contaminants. In this paper we theoretically investigate this proposition. For this purpose a sophisticated one‐dimensional, large‐deformation model of coupled mechanical consolidation and solute transport is employed. This new model is a generalization of existing coupled consolidation and solute transport models described in the literature. It takes into account both non‐linearities in geometry as well as constitutive relations. The latter relate the compressibility, hydraulic conductivity and coefficient of effective diffusivity to the deformation of the soil. The model is applied to a case study of a clay liner and geomembrane system. Results obtained from numerical solution of the model equations are compared with those from various simplified models, including a ‘diffusion only’ (i.e. a rigid soil) model traditionally used in contaminant barrier design. For barriers incorporating low compressibility soils (as for many well compacted clays), there is little difference between contaminant transit (i.e. breakthrough) times predicted by the two models. However, for contaminant barriers incorporating more compressible soils, consolidation is shown to significantly accelerate transport. These results indicate the potential importance of accounting for the effects of soil consolidation and highlight the limitations of existing models when modelling solute transport through composite barriers utilizing soft soils. Based on these limited results, we suggest a possible way of taking into account soil consolidation using simplified models. Copyright © 2008 John Wiley & Sons, Ltd.

Stereological Analysis of Aggregate Distribution in Contaminant Barrier Concrete

The distribution of large aggregate particles in concrete is a significant determinant of concrete strength, durability and wave/fluid transmission characteristics. These characteristics are important with respect to the performance of concrete containment systems for interim storage of radioactive waste. Even distribution of aggregate particles within concrete matrix promotes spatial uniformity of concrete characteristics and minimizes the weakness that can develop in aggregate-deficient portions. The internal heterogeneity of concrete can be assessed destructively through standard load testing or indirectly through imaging and stereological analysis of obtained images. In this paper, an indexing methodology is developed and applied to the analysis of the areal and volumetric distribution of aggregates in samples extracted from hardened concrete grout for waste storage. Analyses of 301 mm mini-slices that were reconstructed into 4 full slices on the basis of a fixed aggregate diameter of 16.93 mm indicate a statistical goodness of fit χ2 value of 4, which is below the 5% significance level (18.3). This result indicates no significant unevenness in the spatial distribution of aggregate particles in the concrete grout. The results demonstrate that this stereologically based approach is useful in quality assurance assessments of emplaced concrete.

High-Density Polyethylene Membrane Containing Fe0 as a Contaminant Barrier

To improve the performance of polymer-based containment barriers with respect to the breakthrough of chlorinated solvents, a high-density polyethylene (HDPE) membrane containing zero-valent iron ( Fe0 ) nanoparticles was developed as a reactive barrier. The performance of the reactive membrane was evaluated by challenging it with carbon tetrachloride in a diaphragm cell apparatus. In a Fe0 /HDPE system, reaction between carbon tetrachloride and Fe0 did not occur due to a lack of water in the polymer matrix. A glycerol-modified Fe0 /HDPE membrane successfully increased the lag time before breakthrough by 13–16 fold compared to HDPE alone. Calculations estimate that only 2.5–3.0% of the Fe0 initially present in the membrane reacted before breakthrough of carbon tetrachloride. Extrapolations of these results to practical situations with larger membrane thicknesses and lower contaminant concentrations predict lag times on the order of years.

Effect of Dispersivity of Filling Material on Performance of Contaminant Barrier

Abstract The performance of pollution barriers is discussed using solute soil dispersion parameters. Masa sandy loam and Toyoura sand, with dispersivities of 0.21 and 0.17 cm at saturation, respectively, were used as barrier material. 2.5 wt.% of the synthetic P-type zeolite was mixed with the soil to control the adsorption capacity of the barrier without changing soil structure. Soils were packed into an acrylic plastic column to form model barriers with different thicknesses. Adsorption capacity of the columns was between 6.1 and 7.5 mmolc per column. 42 mg·dm−3 Cd as nitrate solution was applied to the column under water saturated conditions, and effluent was collected at the bottom of the column. A relatively thin barrier, i.e., five times greater than the dispersivity, resulted in the detection of Cd with only 0.075 mmolc load of Cd, while a thicker barrier, 30 times greater than dispersivity, showed no leak of Cd with a 0.9 mmolc load of Cd added to the column.

Long-term performance of contaminant barrier systems

This lecture describes the latest findings with respect to the long-term performance of modern municipal solid waste (MSW) landfill barrier systems. Field data relating to the clogging of leachate collection systems and the latest techniques for predicting their performance are examined. It is indicated that the primary leachate collection systems may have service lives that range from less than a decade to more than a century, depending on the design details, waste characteristics and mode of operation. Recent data indicate that landfill liner temperatures can be expected to reach at least 30–40°C for normal landfill operations. With recirculation of leachate the liner temperature increases faster than under normal operating conditions, and may be expected to exceed 40°C. Temperatures (up to 40–60°C) may occur at the base of landfills where there is a significant leachate mound. Temperature is shown to have a significant impact on both contaminant migration and the service life of the liner system. Field measurements and theoretical calculations show that composite liners are substantially better than single liners in terms of controlling leakage from landfills. Also, the leakage rates with a composite liner are very small, and diffusion will dominate as a transport mechanism for contaminants that can readily diffuse through a geomembrane (GM). Composite liners involving a GM over a geosynthetic clay liner (GCL) gave rise to substantially less leakage than those involving a compacted clay liner (CCL). The observed leakage through composite liners can be explained by the holes in, or adjacent to, wrinkles/waves in the GM, and this leakage can be calculated using simple equations. High-density polyethylene (HDPE) GMs provide an excellent diffusive barrier to ions. However, some organic compounds readily diffuse through HDPE GMs, and a combination of GM and an adequate thickness of liner and attenuation layer are required to control impact to negligible levels. The long-term performance of HDPE GMs is discussed. Based on the currently available data, the service life for HDPE GM in MSW landfill is estimated to be about 160 years for a primary liner at 35°C and greater than 600 years for a secondary GM provided it is at a temperature of less than 20°C. Clay liners are susceptible to both shrinkage and cracking during construction (due to heating by solar radiation or freezing) and after placement of the waste (due to temperature gradients generated by the waste). The former can be controlled by quickly covering the liner with a suitable protection layer. The latter can be controlled by appropriate design. The use of numerical models for predicting the service lives of engineered systems and long-term contaminant transport is demonstrated.

Design Principles and Concepts for Enhancing Long-Term Cap Performance and Confidence

The siting of new waste containment systems is becoming increasing difficult as the public and stakeholders want more confidence that contaminant barrier systems will perform effectively for very long durations and owners want to store more wastes in the least area while knowing and limiting their long-term liabilities. These developments motivate reexamination of long-term performance issues and their implications for barrier designs. Accordingly, design principles are herein considered from the standpoint of long-term performance and management, including the ability to monitor and repair barriers. Then, some design concepts that may be implemented on the basis of these principles, especially evapotranspiration (ET) caps are discussed. Five design principles are recommended on the basis of considerations of infrastructure implementation experience and facility management experiences in other fields. The principles are: establishment of a clear and defendable design basis; design for ease of monitoring and repair; analysis of barriers as dynamic systems; working with nature and not against it; and recognition that increased complexity can reduce, not enhance, net performance. The ET caps are an excellent embodiment of these design principles. The principles are applied to ET caps, as well as design variants such as erosion armor, capillary breaks, biointrusion layers, and low permeability material layers.

MICROBIAL CONTAMINATION OF HAEMODIALYSIS CATHETER CONNECTIONS

Bacterial contamination and colonisation of the haemodialysis catheter is a reason for infection in dialysis patients. One reason for contamination may be frequent routine connections at the beginning, during and end of dialysis. Higher infection rates observed with double lumen catheters may be due to the absence of the sterile, disposable device that is fitted between the blood tubing and the catheter hubs with single lumen catheters. A sterile, disposable extension was implemented at the author's unit for use in dialysis with double lumen catheters. The proximal and distal ends of the extension were assessed for microbial contamination after standard dialysis. Results show microbial contamination in almost 30% of the samples retrieved from the extensions. Experiences in PD and the behaviour of skin bacteria on polymers, suggest that disposable extensions might have the potential to serve as a barrier or absorber for bacterial contamination.

Polyacrylamide sorption opportunity on interlayer and external pore surfaces of contaminant barrier clays

Physico-chemical interactions among polymer molecules in aqueous solution and clay mineralogical/textural characteristics influence the sorption of polymer molecules on clay barrier minerals. Amendment of potentially unstable barrier clays with aqueous polymers can improve barrier material resistance to environmental stresses during service. In this research, the ability of molecular coils of polyacrylamide (PAM) to overlap in solution and to enter interlayer space in Na-montmorillonite (specific surface = 31.82 ± 0.22 m 2 g −1) and kaolinite (specific surface = 18 ± 2 m 2 g −1) were analyzed theoretically and experimentally, using solution viscosity measurements, and X-ray diffractometry. Experimental data on two theoretical indices: relative size ratio (RSR); and molecular availability ( M a) that are formulated to scale polymer molecular sorption on clay interlayer, indicate that the sorption of PAM A ( M w = 4 000 000) and PAM B ( M w = 7 000 000) does not produce any significant change in the d-spacing of both clay minerals. Although the negative M a values of −3.51 g l −1 for PAM A and −3.88 g l −1 for PAM B indicate high levels of entanglement of polymer molecular coils in solution, sorption data confirm that the entangled coils are still able to sorb onto Na-montmorillonite highly and kaolinite to a lesser extent.

Response to Comment on “A Polymer Membrane Containing Fe0 as a Contaminant Barrier”

ADVERTISEMENT RETURN TO ISSUEPREVCorrespondence/Rebut...Correspondence/RebuttalResponse to Comment on “A Polymer Membrane Containing Fe0 as a Contaminant Barrier”T. Shimotori, W. A. Arnold, E. E. Nuxoll, and E. L. CusslerView Author Information Department of Civil Engineering University of Minnesota 500 Pillsbury Drive SE Minneapolis, Minnesota 55455 Department of Chemical Engineering and Materials Science University of Minnesota 421 Washington Avenue SE Minneapolis, Minnesota 55455Cite this: Environ. Sci. Technol. 2004, 38, 19, 5264Publication Date (Web):August 28, 2004Publication History Published online28 August 2004Published inissue 1 October 2004https://doi.org/10.1021/es040490lCopyright © 2004 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views155Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (16 KB) Get e-AlertsSUBJECTS:Anions,Contamination,Impurities,Membranes,Polymers Get e-Alerts

Comment on “A Polymer Membrane Containing Fe0 as a Contaminant Barrier”

Comment on “A Polymer Membrane Containing Fe⁰ as a Contaminant Barrier”

Characterization of Clay Particle Surfaces for Contaminant Sorption in Soil Barriers Using Flow Microcalorimetry

Clays such as kaolinite and bentonite are widely used in various industries as sorbents. The sorptive characteristics of clays are exploited when they are used in contaminant barrier systems. To use clays effectively, their surface characteristics need to be known; especially, when they are used for contaminant sorption. Available surface area of clay minerals and the characteristics that depend on it are very sensitive to environmental changes such as those that can be induced by changes in the composition of pore fluid. Flow microcalorimetry with a down-stream concentration was used to determine the heats and amounts of adsorption of acids and bases on the clays. Test results presented herein revealed that both kaolinite and bentonite exhibit significantly different adsorption isotherms and heat of wetting under high pH and low pH conditions. Kaolinite has the capacity to adsorb both acidic and basic molecules almost equally. However, it has a tendency to adsorb more base than acid because of its stronger complexation capacity with acids than with bases. On the other hand, bentonite has a tendency to adsorb more acidic than basic molecules per gram. These results also indicate that both kaolinite and bentonite have different heats of wetting characteristics. As the concentrations of the acids and bases increase, the heat of wetting of kaolinite decreases while that of bentonite increases.

Contaminant Barrier Material Textural Response to Interaction with Aqueous Polymers

An experimental investigation of the use of polymers dissolved in aqueous solutions to enhance the resistance of clay-based barrier materials to freeze-thaw action and desiccation was performed. The polymers considered included a nonionic polysaccharide (guar gum) and a cationic polyacrylamide (PAM). Concentrations ranging from 0.25 to 8.00 g/L were used and mixed with three barrier materials, namely, 100% Na-montmorillonite clay, a mixture of 70% sand, 30% clay, and a mixture of 90% sand, 10% clay (by weight). Freeze-thaw and desiccation tests were used to investigate material durability. The effects of freeze-thaw action on the materials were assessed in terms of crack measurements, while the drying rates as well as crack measurements were used to assess the influence of desiccation. The extent to which crack formation was mitigated by polymer amendment varied according to polymer type, mode of crack initiation, and clay fraction. In particular, unmodified mixtures of 70% sand and 30% clay exposed to desiccation stress resulted in crack area density values as high as 11.9% while modification with guar or PAM reduced this to 2.7 and 3.4%, respectively, as revealed by analysis of the computed tomography-generated images. Increases or reductions in performance are attributed to polymer–clay interactions and relative hydration between clay and polymer phases.

A polymer membrane containing Fe(0) as a contaminant barrier.

A poly(vinyl alcohol) (PVA) membrane containing iron (Fe(0)) particles was developed and tested as a model barrier for contaminant containment. Carbon tetrachloride, copper (Cu2+), nitrobenzene, 4-nitroacetophenone, and chromate (Cr04(2-)) were selected as model contaminants. Compared with a pure PVA membrane, the Fe(0)/PVA membrane can increase the breakthrough lag time for Cu2+ and carbon tetrachloride by more than 100-fold. The increase in the lag time was smaller for nitrobenzene and 4-nitroacetophenone, which stoichiometrically require more iron and for which the PVA membrane has a higher permeability. The effect of Fe(0) was even smaller for CrO4(2-) because of its slow reaction. Forty-five percent of the iron, based on the content in the dry membrane prior to hydration, was consumed by reaction with Cu2+ and 15% by reaction with carbon tetrachloride. Similarly, 25%, 17%, and 6% of the iron was consumed by nitrobenzene, 4-nitroacetophenone, and CrO4(2-), respectively. These percentages approximately double when the loss of iron during membrane hydration is considered. The permeability of the Fe(0)/PVA membrane after breakthrough was within a factor of 3 for that of pure PVA, consistent with theory. These results suggest that polymer membranes with embedded Fe(0) have potential as practical contaminant barriers.

Evaluation of an HDPE geomembrane after 14 years as a leachate lagoon liner

A geomembrane – compacted clay composite liner system used to contain municipal solid waste (MSW) landfill leachate for 14 years is evaluated. Field observations of the geomembrane revealed many defects, including holes, patches, and cracks. Physical, chemical, and mechanical tests conducted on samples collected from five different locations of the liner suggest that samples continuously exposed to sunlight and high temperatures experienced more degradation compared to samples that were covered by leachate or soil. Sorption and diffusion tests revealed that the permeation coefficients of volatile organic compounds were in the range of 4 × 10–12 to 6 × 10–11 m2/s and that, with respect to these parameters, there was no significant difference between samples with different exposure levels. However, the permeation coefficients were between four and five times lower than values obtained for unaged HDPE geomembranes typical of present day production. Contaminant modelling of the entire lagoon liner suggests that the geomembrane liner most likely stopped being effective as a contaminant barrier to ionic species sometime between 0 and 4 years after the installation.Key words: liquid containment, composite liner, diffusion, HDPE geomembrane, performance.

Geophysical response of filled sinkholes, soil pipes and associated bedrock fractures in thinly mantled karst, east-central Illinois

Karst aquifers are often protected by a thin mantle of unconsolidated sediment. Soil pipes and sinkholes may breach this natural protective barrier and open pathways for contaminants to quickly reach bedrock aquifers. Geophysical surveys offer a quick and noninvasive way to identify these features; such surveys may also be sequenced to reveal increasing detail in critical areas. At a study site in east-central Illinois, electromagnetic (EM) surveys mapped high conductivity anomalies over filled sinkholes and soil pipes that penetrated the unconsolidated cover. Two-dimensional inverted resistivity sections, made over these anomalies, depict filled sinkholes and soil pipes as conductive zones above deeply weathered bedrock fractures. Borings verified the geophysical models and suggest high conductivities associated with the filled sinkholes are the result of enhanced moisture near active soil pipes. EM surveys also identified conductive zones in the overburden above a probable bedrock fracture linking sinkhole areas 0.5 km apart. Resistivity and EM methods, used in a phased and sequential manner, thus proved useful in mapping filled sinkholes and in delineating the vertical and lateral connections between soil pipes and hydraulically active bedrock fractures.

The Times, They Are Changing Again

The Times, They Are Changing Again

Diffusion and sorption experiments using a DKS permeameter

The analysis of contaminant transport through clay liner is a relevant aspect in the design of industrial, urban and mining waste disposal systems, since these areas must be designed and operated to prevent contaminating substances from reaching underground water systems in unacceptable concentrations. The design requires an estimate of the potential contaminant transport rate. However, before any attempt at quantification can be made, values for transport mechanism control parameters must be established. Clayey materials are frequently used as contaminant barriers. In these materials, which have low hydraulic conductivity, the main contaminant transport mechanism is molecular diffusion. Parameters controlling transport for these conditions are the diffusion coefficient and sorption parameters. These parameters depend on soil constituents and characteristics as well as on the chemical constitution of the contaminant. The great complexity of the factors involved makes it necessary to determine the parameters of each type of soil. This paper discusses an equipment called DKS permeameter (diffusion, convection, sorption), for the study of soil-contaminant transport mechanisms, designed at the Institute for Soil Mechanics of the Ruhr-University Bochum, and some results obtained from its use at COPPE/Federal University of Rio de Janeiro (UFRJ), Brazil. This equipment determines the effective diffusion coefficient and sorption parameter with a better reflection of field conditions. The soil under study is a mix of sodium–bentonite that has low hydraulic conductivity (k=10 −9 cm/ s) with adequate liner characteristics. The result indicated the relevance of determining sorption parameters for structured soils, since the sorption perceived from batch test results using pulverised soil represents maximum soil capacity. Designs based on this parameter would overestimate the attenuation capacity of the liner.

Recrystallization of polycrystalline silicon films on ceramics by electron beam

The formation of large-grain poly-silicon films on high-reflective alumina ceramics has been investigated by means of electron beam recrystallization technique. Sample structure is Polysilicon layer/buffer layers (SiN x /SiO x ) on Alumina ceramics substrate. These layers are deposited by high-rate Electron Cyclotron Resonance Plasma Chemical Vapor Deposition method. We have found that the SiO x layers act as a thermal buffer and an impurity contamination barrier against the ceramics, and SiN x layer has an important role in obtaining good wettability of molten silicon. We have also found that there are optimal thickness of buffer layers, scanning speed, and electron beam power to obtain good quality grains without agglomeration and cracks.