Hazardous Waste Containment Research Articles

Evaluation of the Permeability of Clay-Lime Mixtures for Hazardous Waste Insulation Barriers, Case of Southern Algeria (Adrar)

Containment of hazardous waste is one of the methods that can be used today for its disposal worldwide, especially in landfills. In order to preserve groundwater, landfills are constructed on a natural or reconstituted clay layer of low permeability, known as a passive safety barrier. This paper presents an experimental laboratory study that aims to upgrade local materials for use as a passive barrier in the bottoms of hazardous waste storage facilities (HWSCs). The basic materials are clays from the Adrar region in southern Algeria. An experimental study based on physical-chemical characterization and mechanical tests was performed on 2 samples of clayey soils (AA, Adrar clay, and AB, Bouda clay). Physico-chemical and mechanical characterization of Adrar clay (AA) mixtures with lime was conducted to minimize swelling and improve the studied soil. The permeability criterion allowed the adoption of an optimal mixture of Adrar clay + 6 % lime for a permeability lower than 10–12 m/s. HIGHLIGHTS Ideal solution to protect natural groundwater resources using local materials, clay and lime Large area exceeding 30 km2 of clay sources and including sources of oil pollution Noticeable improvement in clay properties thanks to the addition of lime to reduce swelling The treated clay has a very low permeability value, lower than 10−12 m/s and is ideal for hazardous waste storage centers GRAPHICAL ABSTRACT

Mitigation of Chemical Reporting Liabilities through Systematic Modernization of Chemical Hazard and Safety Data Management Systems.

In the United States alone, approximately 2 billion tons of hazardous material products are manufactured each year for both household and industrial applications and contribute to thousands of worker chemical exposures with as many as 50,000 deaths from prolonged exposure each year. The potential hazards and impacts of these chemicals for human health and the environment are primarily communicated to the public through Safety Data Sheets (SDSs) from the chemical vendors or distributors. These documents provide a standardized approach for how and what information is provided to product users to assist them with assessment of precautionary measures, hazard mitigation, emergency response or cleanup procedures, and environmental, health, and safety (EHS) management. Despite the criticality for hazard communication (HAZCOM) precision, legacy SDS management and industry business practices leave the overall ability to effectively manage chemicals vulnerable to significant liability through a lack of full constituent disclosure, injection of data quality errors through various handling of SDS information and manual data entry, and the lack of direct SDS-to-product association. Chemical spills and accidents often require individuals to look for the appropriate SDS on a local computer, online, or in workplace binders; each of which results in information returned that is often found to be outdated or incorrect. Workplace HAZCOM violations remain among the top citations during EHS inspections by regulatory agencies. More important, however, is the lack of precise association of SDS to hazardous products that can occur through chemical management lifecycles. Incorrect SDSs can yield significant liability, as subsequent environmental and occupational health analyses and reporting are based upon incorrect and, in some cases, entirely different chemical formulations. This paper focuses on the need for a paradigm shift in our chemical management systems and how a standardized management system and various recent technological advances can be incorporated into Environmental Management System operations to reduce or eliminate these liabilities. The following advancements can be used to enhance the lifecycle management of workplace chemicals, reduce potential exposure and spill risks, reduce workplace hazards, and increase the efficiency and accuracy of environmental reporting through a more streamlined systems approach. EHS system enhancement applications discussed in this paper include the following: the need for a centralized universal SDS repository with full chemical disclosure of all product constituents and a nationally adopted machine language SDS standard. The use of artificial intelligence/machine learning in environmental systems and how they can be used as a medium to transition toward an automated standard by reverse-engineering and partitioning SDS components into machine-encoded text that can be validated and uploaded to a centralized repository. Algorithmic and meta-algorithmic approaches to SDS requirement and data validation, hazard characteristic code calculations, and determination of potentially less hazardous substitutions. Application of Natural Language Processing methods for real-time updates from scientific journals, regulatory agencies, and other reputable sources to produce "living" SDSs capable of informing users of relevant regulatory updates, news, and research. Embedded SDSs or SDS links in product barcodes with QR code reader technology to retrieve precise SDSs for each product in emergency situations. Use of advanced QR codes embedding authentication layers, authenticity verification, and alerts of potential product or inventory problems or discrepancies. Benefits of radio frequency identification technology in providing accurate SDS associations while also minimizing manual tracking of hazardous material and hazardous waste containers and monitoring for expired shelf life, incompatible storage, temperature sensitivities, and other inventory concerns.

Influence of pore fluid salinity on shrinkage and water retention characteristics of biochar amended kaolin for landfill liner application

Biochar amended clay layer has emerged as a sustainable hydraulic barrier for hazardous municipal waste containment system. The effects of pore fluid salinity on soil shrinkage and water retention characteristics of biochar amended clay are unknown. This study aims to investigate the behavior of soil shrinkage and water retention of biochar amended kaolin under different pore fluid salinity. A series of volumetric shrinkage and water retention tests were conducted on biochar amended kaolin in sodium chloride solution at initial concentrations of 1 %, 5 %, and 10 %. Biochar addition increased the shrinkage limit and minimum void ratio of kaolin by up to 17 % and 11 %, respectively. Air entry value of kaolin increased by 6–88 times with an increase in pore fluid salinity, caused by interparticle aggregation. Micrographs showed that biochar intrapore was filled by kaolin particles, partially hindering the interparticle aggregation of clay in the salt solution. Biochar addition lowered zeta potential on the surface of kaolin particles by 50–75 %, indicating that the immobilisation of excess sodium ions was achieved by biochar. Correspondingly, osmotic suction of pore fluid decreased by 21–64 % due to biochar's ion absorption. The findings highlighted that biochar addition to kaolin specimens minimises NaCl-induced soil shrinkage and reduces the pore fluid salinity. This study indicates that biochar could be potentially helpful for desalinisation and mitigating volumetric change issues for geo-environmental infrastructures.

Soil exploration using ground penetrating radar

Geophysical methods are extensively utilized in the field of geology and in geotechnical engineering such as seismic, gravitational, magnetic and electromagnetic fields. These methods are used to locate or to understand conditions below the ground surface, and the physical properties of subsurface. GPR also known as Radio Detecting and Ranging is based on the electromagnetic waves. It is a specially designed radar unit for transmitting electromagnetic pulses below the ground instead of air. In GPR the medium is soil which is heterogeneous and has higher attenuation rate than air. This method is used to measure the length, depth or to locate the soil layers and its deposits. GPR is one of the most versatile sensors; it provides high resolution profiles for shallow depth. GPR has been used in diverse fields such as archaeology, non-destructive testing, probing underground caves, detecting landmines, mapping pipes and conduits, investigating the reinforcement and conditions of roads, bridges and airport runways, to name a few. Use of this technique/method is being extensively adopted from recent years because of its properties and vast applications. The main applications of GPR in subsurface mapping are: mapping of subsurface utility structures, detection and mapping of unexploded ordnance and mines, extraction of hazardous waste containers or unexploded ammunitions, maintenance or repair of subsurface structures. This paper presents an understanding of the concept or the need of GPR dedicated to civil engineering applications in general and in the field of geotechnical engineering in particular.

Tetracycline Removal from Water by Adsorption on Geomaterial, Activated Carbon and Clay Adsorbents

Abstract The use of antibiotics for breeding and for humans increased considerably in recent years, as a dietary supplement to enhance animal growth. This frequent use leads to the detection of residues in water and wastewater. Thus, the emergence of new strains of bacteria resistant to these antibiotics and, can lead to incurable diseases of livestock, and can lead to a possible transmission of these strains to humans. The purpose of this work is to develop new materials based on treated Maghnia clay, activated carbon, cement, and PVA polymer, named geomaterials. These materials were intended for the containment of hazardous wastes in landfills. The removal of tetracycline from aqueous solution was tested by adsorption onto synthesised geomaterials and their mineral constituents. Adsorption kinetics revealed that tetracycline was rapidly retained by GM and ATMa. This was confirmed by the relatively short equilibrium time of 30 min. The pseudo-second-order and intraparticle models well fitted the adsorption kinetic of the TC-adsorbent studied systems. It was noticed that the adsorption kinetic passes through several mechanisms, was demonstrated by the multi-linearity on the plot of qt against the square root of t. The adsorption capacity (Qa ) of TC onto GM is pH-dependent. Indeed, Qa reaches a maximum value (Qa = 12.58 mg ∙ g–1 at a very acidic pH of 2, then the adsorbed amount decreases to reach a minimum value at pH of 8, and for basic pHsQa increases up to 10 mg ∙ g–1.

Graphene kirigami membrane with superior theoretical permeability and adjustable selection capability

Membrane plays a central role in molecule separation and selection. However, most artificial membranes utilise a fixed passage size and only effective for limited molecule types. Here, via a large series of molecular and first-principles calculations, we reveal the potential of graphene kirigami (GK), a novel structure with nanoscale incisions on one-atom-thick graphene, which can transform into a three-dimensional structure under deformation, as an ultra-membrane for highly adjustable molecule selection and the practical fabrication feasibility of GK-like membranes using a novel selective tearing process on initially defected graphene. Facilitated by the high stretchability of GK-based membranes, we demonstrate a wide range of gas selection capability on a single membrane. The interaction energy of adsorbed gas molecule also shows that the unique geometry of the pores on GK enables a new adsorption channelling mechanism that enhances molecular separation. Compared with nanoporous graphene, the dynamic gas penetration test shows that various GK membranes are capable of 30 times higher pore-size adjustability and up to 1.5–3.4 times higher gas separation rate. The GK ultra-membrane opens new venues for numerous applications in CO2 capture and storage, water desalination, wastewater treatment, hazardous waste containment system, chemical processing, bionics, and pharmaceutical and medical devices.

Adsorption characteristics of Barmer bentonite for hazardous waste containment application

Low hydraulic conductivity and high chemical immobilization are the two characteristics that make bentonite a mandatory construction material for hazardous waste containment applications. We performed a comprehensive batch sorption study on Barmer bentonite (BB), an exclusive construction clay mined in India, using lead (Pb2+) as a model contaminant. The maximum adsorption capacity of BB was obtained as 55 mg g−1 at pH 5 and 27 ± 2℃. Adsorption was extremely rapid, with equilibrium attained <5 min for the BB. Increased adsorbent dosage resulted in higher Pb2+ percentage removal, while adsorption capacity decreased. Ionic strength, salt concentration, valency and ionic radius played a critical role in suppressing the adsorption of Pb2+. Clay fabric change was observed to be dispersed at low ionic strength and gradually attained aggregated face-to-face structures at high ionic strength. The simultaneous presence of other metals/salts strongly influenced Pb2+ removal by BB, while divalent salt exhibited high suppression of adsorptive reaction at low concentrations. Sorption isotherm and kinetic modeling results indicated the possibility of chemisorption of Pb2+ on BB. Based on the thermodynamic analysis, it was noted that Pb2+ adsorption on BB is exothermic, spontaneous and adsorption reaction is less favorable at a higher temperature.

Performance Evaluation of 5TM Sensor for Real-Time Monitoring of Volumetric Water Content in Landfill Cover System

AbstractAccurate measurement of volumetric water content (θ) is essential for studying soil-water interaction efficiently. The accuracy of various types of θ measuring sensors needs to be ascertained before deploying in specific projects. The objective of this study is to evaluate the performance of electromagnetic 5TM sensor for real-time monitoring of θ in a cover system (CS). This CS is provided on top of the hazardous waste containment to isolate it from the surrounding environment and minimize interaction with rain water. The CS consists of different layers of soil and geosynthetics that interact with the atmosphere and undergo changes in θ with changing local weather conditions. Because θ governs the hydraulic and mechanical characteristics of geomaterials, its variation is monitored as a function of space and time for evaluating the performance of CS. Performance assessment of 5TM sensor was carried out under controlled conditions for ten different soil materials that may find application in CS. This study indicates the importance of material specific calibration of a 5TM sensor for improving its measurement accuracy before deploying it for field monitoring. The accuracy of 5TM measurement was marginally better when the polynomial calibration equation was adopted as compared to linear calibration. In the absence of soil-specific calibration, the new set of calibration parameters proposed in this study can be used for the generic soils used in CS. With improved accuracy of 5TM, it was shown that the error in the determination of soil water storage for different layers of a trial CS reduced from 15 to 0.4 %.

Sustainable concrete construction – from recycled demolition aggregate to alkali activated binders

Investigations into the economics, practicalities and technicalities of using recycled demolition aggregate in concrete precast products started in 2001. At that time, there were six demolition contractors around Liverpool and they were using mobile crushers which were suited for road subbase material but not for the smaller sized aggregate required for precast concrete products. It was estimated that if all six worked round the clock, i.e. assuming there was enough feed material, they would still have found it difficult to maintain the required supplies for a single precast factory. Investment in equipment was therefore required to guarantee supply and improve the quality of the recycled demolition aggregate. The market forces and the incentives/drivers for construction companies to adopt sustainable practises have encouraged investment of several million pounds to be made in new recycling plants and this has resulted in “urban quarries”.Work on reducing the carbon footprint of concrete construction needs to consider not only the replacement of the aggregate with recycled ones but also to consider a reduction or complete replacement of Portland cement in concrete mixes. Alkali activated binders and geopolymers have seen applications in ceramics, hazardous waste containment, fire-resistant construction materials and refractories but the most interesting application is their use to replace Portland cement-based concretes. Several factors affecting the reactivity of fly ash as a precursor for geopolymer concrete have been investigated. These include physical and chemical properties of various fly ash sources, inclusion of ground granulated blast furnace slag (ggbs), chemical activator dosages and curing temperature. Alkali-activated fly ash was found to require elevated curing temperatures and high alkali concentrations. A mixture of sodium hydroxide and sodium silicate was used and this was shown to result in high strengths, as high as 70 MPa at 28 days. The partial replacement of fly ash with ground granulated blast furnace slag (ggbs) was found to be beneficial in not only avoiding the need for elevated curing temperatures but also in improving compressive strengths. It became apparent that the main obstacle to commercialisation of these new alternative binders was the cost of the activating solutions, i.e. the sodium hydroxide and the sodium silicate. The latter is the most expensive one and results in geopolymer concretes that cannot compete on price with Portland cement concretes. Attempts therefore concentrated on developing a procedure for the production of sodium hydroxide from waste streams, which in this case was ground glass cullet. Production of eco-friendly concretes thus becomes commercially possible.

Mechanical and durability behaviour of self-compacting concretes for application in the manufacture of hazardous waste containers

In self-compacting concrete (SCC), the amount of coarse aggregates, use of fillers, and type of additives play important roles in its self-compaction, including mechanical and durability properties. The use of SCC is widespread in the precast concrete industry and it can also be employed in the manufacture of containers for the storage of hazardous waste. In addition to the requirements for self-compaction, strict mechanical and durability requirements must be considered. In this work, a study on the effect of variation in the amounts of coarse and fine aggregates, and fillers on the properties of the fresh state (self-compactability) and hardened state (microstructural, mechanical, and durability behaviours) of different dosages is carried out. The factors that have more significant influences on the density of the mixes are the presence of fillers and water-cement ratio. This is because mixes with fillers and low water-cement ratios have higher densities, which agree with the lower porosity and finer porous structure observed in mixes that incorporate fillers. Mixes incorporating siliceous fillers presented better performances in the absorption of water by immersion and capillarity than mixes without them. Measuring the depth of penetration of water under pressure in various mixes makes it possible to identify those that have high compactness and impermeability. Mixes with fillers and higher microstructural densities have lower water penetration depths. After exposure to aggressive environments, none of the mixes, with and without fillers, showed signs of wearing out or deterioration. The presence of fillers in SCCs had a more significant influence on its shrinkage than the amount of coarse aggregates. Thus, it is possible to obtain high performance SCC in relation to its mechanical and durability properties by reducing the coarse aggregate content and incorporating siliceous fillers in the dosage. Moreover, for applications where high mechanical requirements are not necessary, it is possible to produce an SCC with high performance against the attack of aggressive agents such Cl− and SO3 without using siliceous fillers.

Comprehensive review of geosynthetic clay liner and compacted clay liner

Human activity inevitably produces waste materials that must be managed. Some waste can be reused. However many wastes that cannot be used beneficially must be disposed of ensuring environmental safety. One of the common methods of disposal is landfilling. The most common problems of the landfill site are environmental degradation and groundwater contamination caused by leachate produced during the decomposition process of organic material and rainfall. Liner in a landfill is an important component which prevent leachate migration and prevent groundwater contamination. Earthen liners have been widely used to contain waste materials in landfill. Liners and covers for municipal and hazardous waste containment facilities are often constructed with the use of fine–grained, low plasticity soils. Because of low permeability geosynthetic clay liners and compacted clay liners are the main materials used in waste disposal landfills. This paper summaries the important geotechnical characteristics such as hydraulic conductivity, liquid limit and free swell index of geosynthetic clay liner and compacted clay liner based on research findings. This paper also compares geosynthetic clay liner and compacted clay liner based on certain criteria such as thickness, availability of materials, vulnerability to damage etc.

Semipermeability of concrete for hazardous waste containment

Low-level waste is stored in multilayer, overlapping barrier systems for long-term containment, which serve as the primary barrier against leakage. Reinforced concrete is typically used as the container material for radioactive wastes, making the material properties paramount for contaminant control. Strength, density, corrosion resistance and permeability are regulated. This study examined the physico-chemical properties of high-density, lower-permeability concrete for potential to hyperfiltrate chloride solutions (185 and 345 parts per million) under relatively low hydraulic head, similar to encasement. Four hyperfiltration experiments were conducted on intact concrete discs, two experiments for each solution at hydrostatic heads of 0·5 and 1·0 m. Chloride concentrations measured within the experimental cells showed an increase ranging from 126% to 152%. Reflection coefficients ranged from 0·15 to 0·19, suggesting that low-permeability concrete discs exhibit measurable solute rejection capabilities. External chloride penetration may initially be hampered. However, once steady state had been established and salt penetrated at a fixed rate, the concentration polarization layer (CPL) provided a source for continued penetration. With the CPL adjacent to a container, corrosion may accelerate in the reinforcing rebar due to the high chloride concentration and chemical gradient within the pores. The application of electro-osmotic pulses can reverse chloride intrusion.

Chemical and environmental compatibility of red mud liners for hazardous waste containment

Red mud residue from alumina production has been proposed as an alternative liner material. The chemical and environmental compatibility of red mud upon exposure to representative organic (methanol, heptane, TCE, and acetic acid) and inorganic liquids (CaCl2 and seawater) was studied. Chemical compatibility assays comprised Atterberg limits and sedimentation and hydraulic conductivity tests for red mud interacted with the chemical liquids, whereas the environmental compatibility was assessed through the leaching of metals from red mud as permeated with the liquids. Methanol greatly reduced the plasticity at concentrations ≥80 % by volume, but it did not increase the hydraulic conductivity of compacted red mud. High concentrations (≥60 % v/v) of acetic acid reduced the plasticity and enhanced the sedimentation of red mud. Conversely, acetic acid concentrations ≤40 % caused dispersion, but damaged the hydraulic properties and structure of red mud. The percolation of a pH 2 acetic acid solution did not adversely affect the hydraulic performance of the red mud liner. Neither diluted heptane nor TCE affected the red mud. However, pure organics suppressed the plasticity and induced aggregation of red mud, suggesting a great detrimental effect on red mud liners. The red mud exhibited great resistance to attack by inorganic salt solutions. Some concerning leaching of metals (primarily Al and Cr) occurred as water, acetic acid, and CaCl2 solutions percolated through red mud, but effluent metals concentration quickly dropped to permissible levels. In general, red mud exhibited a high resistance against chemical attack; nevertheless, exposure to low-dielectric-constant organic chemicals should be avoided.

Reactive Transport Numerical Model for Durability of Geopolymer Materials

Geopolymers are alternative binders made solely from industrial by-products and/or natural alumino-silicates, comprising no traditional cements. Reactive transport processes in geopolymer materials play a crucial role in both the degradation process of building materials as well as in the containment of hazardous wastes. A numerical model is presented for solving transport coupled to nonlinear ion-exchange equilibria between solid-liquid phases. Bound alkalies provide the geopolymer paste with a large reservoir of exchangeable (soluble) alkalies that allow for a more gradual drop in pH of the pore solution, as compared to a sudden drop when considering only diffusion transport mechanism. The model is robust enough to handle non-linearity of the ion-exchange equations, and presents a more reliable way to obtain long term durability predictions of geopolymer materials.

EXPERIMENTAL STUDY ON CHARACTERIZATION AND POLLUTION POTENTIAL OF CONTAMINATED CHROMIUM HAZARDOUS WASTE

Although many researchers are working on pollution potential and containment of hazardous waste, still there is a need for investigation of its characterization, influence on ground and surface water, its treatment and containment especially on chemical sludges containing heavy metals like chromium which is potential carcinogenic. An industry in Nalgonda District by name M/s. Deccan Chromates Limited situated at Damarcherla (V), Telangana State has left the extremely hazardous hexavalent chromium sludge, a life-threatening compound. This waste is classified under Schedule – II Hazardous Waste substances of the Hazardous Waste (Management, Handling and Transboundary Movement) Rules, 2008. Exposure to about 53,000 tons of chromium sludge can lead to cancer and devastating consequences for the people around it. As of now there is no contingency plan to dispose of the hazardous waste. The accumulation of chromium is contaminating the agricultural fields and water sources. The chemical factory was set up in 1998 to produce Sodium Dichromate, which is used in paints and for leather tanning. During its 10 year existence, the factory dumped the hazardous waste matter in an area of about 3 acres before the plant was shut-down in 2008 leaving the villages in the vicinity facing an alarming crisis. People who inhale the hexavalent chromium over long periods run the risk of contracting lung cancer. Repeated or prolonged exposure can cause sores and ulcers on the feet and in fingers. Hexavalent chromium can cause damage to the respiratory tract, lungs, kidneys, liver and the gastro-intestinal, immune and blood and reproductive systems. Although it has been 6 years that the factory has ceased operating, toxic waste from the plant continues to pollute both Musi and Krishna Rivers. Thousands of sheep and goat have been affected after drinking the contaminated water. The Toxic waste has deeply affected the agricultural lands. Any mishap that occurs can be very damaging. Thus, the toxic waste poses threat to thousands due to cancer-causing chromium left untreated by defunct factory in Nalgonda District. Here an attempt is made to study and highlight the pollution potential of the chrome sludge disposed by the industry, its characterization, treatment for making it non hazardous, implementation of the treatment process on plant scale and techniques of proper engineered landfill with the phases of site selection, design, construction, operation, environmental monitoring, closure and post closure for containment of the hazardous waste.

Utilization of Stone Waste in the Development of Value Added Products: A State of the Art Review

The utilisation of stone waste, in the form of mineral admixture as a pozzolanic and non-pozzolanic material for mortar and concrete has received considerable attention in recent years. This interest is part of the widely spread attention directed towards the utilisation of wastes and industrial by-products in order to minimise Portland cement (PC) and sand consumption, the utilisationof which being environmentally damaging. Another reason is that mortar and concrete, which contain pozzolanic as well as non-pozzolanic materials, exhibit considerable enhancement in durability properties. This paper reviews work carried out on the use of stone waste as a partial non-pozzolanic replacement for sand in mortar and concrete and in the containment of hazardous wastes. The literature demonstrates that different stone wastes is an effective inert filler which causes great improvement in the pore structure and hence the resistance of the concrete to the action of harmful solutions.

Deformation behavior of clay cap barriers of hazardous waste containment systems: Full-scale and centrifuge tests

The objective of this paper is to study the deformation behavior of a clay cap barrier of waste containment system for storing hazardous waste. The risk of bending of a clay barrier in case of differential settlements within underlying waste is focused in the present study. Field bending “bursting tests” were performed in France on clay barriers of 0.7 m thickness at different water contents. An attempt has been made to determine limiting distortion level at which cracks are initiated. The cap clay barrier configuration tested through field bursting tests was simulated at 12.5 g in a geo-centrifuge on model cap clay barriers of 56 mm thickness subjected to bursting mode of failure. Digital image analysis technique was used to ascertain initiation and propagation of cracking at the onset of differential settlements. Further influence of discrete and randomly distributed polypropylene tape fibers in restraining cracking tendency of the clay barrier was evaluated through a centrifuge model test. With an increase in the molding water content and the presence of randomly distributed fibers, an increase in limiting distortion level was observed. Use of 0.5% of fiber dosage and 90 mm long discrete fibers was found to restrain propagation of cracking of a clay barrier subjected to differential movements. Analysis and interpretation of field bursting tests was found to be in good agreement with physically observed centrifuge model test results.

Prediction of the water balance of two soil cover systems

Soil cover systems are widely used for containment of municipal solid waste, hazardous and mine waste, with the objective of limiting the ingress of precipitation and oxygen. The ability to predict their long-term performance is crucial, as their failure would result in the release of contaminants to the environment. However, monitoring covers over the long term to derive the information needed to aid in design is impractical and there are no large-scale covers that have been in use for a long enough period to generate the data needed. Numerical models have been particularly useful as design tools. To improve their reliability these models may be calibrated to field data and then used to make long-term predictions of cover performance. The field performance of two resistive test soil covers on a 20% sloping waste rock platform is predicted using the two-dimensional soil–atmosphere model Vadose/W. Input data for the model included soil, climate and vegetation data obtained either in the field or laboratory. Model results were compared to field data to assess the validity of the program. The model reasonably simulated field response patterns for soil water storage and suction. Divergence between field performance data and model predictions were significantly influenced by snowmelt, interflow and flow through preferential pathways.

Verification of Contaminant Sorption by Soil–Bentonite Barrier Materials Using Scanning Electron Microscopy/Energy Dispersive X-Ray Spectrometry

The performance of a soil.bentonite barrier material as a sorbent for heavy metals was investigated in the laboratory using an influent containing 20 mg/L of Pb\U2\N at a pH of 5. The target parameters were the hydraulic conductivity of the soil.bentonite mix and the difference between Pb\U+2\N concentrations in the influent and effluent. A hydraulic conductivity of 1.010\U-8\N cm/s was achieved, the mixture was found to meet common regulatory specifications for hazardous waste containment. After four pore volumes of flow through specimens placed in a column, no Pb\U+2\N was detected in the effluent. Sorption was verified through acid extraction and identification of Pb\U+2\N on barrier sample cross sections using microanalysis of specimen slices with a scanning electron microscope and the associated energy dispersive x-ray spectrometry. Energy dispersive x-ray spectrometry spectra indicated that the Pb\U+2\N partitioned selectively to the bentonite fraction of the mix. The results confirm the ability of this mixture of soil.bentonite to function as an effective barrier for aqueous Pb\U+2\N solution. This method of microanalysis appears to have promise as an effective tool for assessing relative affinity of contaminants for specific mineralogical constituents of a barrier mixture and may have applications in sorption performance assessments of other multicomponent barrier systems. If each barrier material is tested separately, the effects of the texture of the mix on sorption and hydraulic characteristics of the mix cannot be effectively assessed.

Hydro-mechanical evaluation of soil stabilized with cement-kiln dust in arid lands

This study evaluates the potential use of cement-kiln dust (CKD), a waste product from the cement industry, for enhancing the mechanical as well as the hydraulic properties of soils in arid lands. Stabilized products will play a major role in reducing slope failures, pavement damage and the design of containment barriers for hazardous waste in arid lands. Various tests to determine the different physical properties of the stabilized matrix were conducted and the optimum mixture that produces maximum internal energy and minimum hydraulic conductivity was selected. The effect of soaking and unsoaking of the treated specimens on the mechanical properties was also evaluated. The effect of metal ion concentration and conjugate anions on the resultant hydraulic conductivity was evaluated. The optimum percentage of CKD was calculated by using stress–strain data, Newton's divided difference and Simpson's integration technique. The analyses have shown that 6% by weight of CKD is the optimum mix design, which increases the shear strength and decreases the hydraulic conductivity to less than 10–9 m/s. Therefore, the treated soil could be used as a soil-based barrier layer for containment of hazardous waste.