Solute transport properties of compacted Ca-bentonite used in FEBEX project

The present Spanish concept of a deep geological high level waste repository includes an engineered clay barrier around the canister. The clay presents a very high sorption capability for radionuclides and a very small hydraulic conductivity, so that the migration process of solutes is limited by sorption and diffusion processes. Therefore, diffusion and distribution coefficients in compacted bentonite (i.e. in "realistic" liquid to solid ratio conditions) are the main parameters that have to be obtained in order to characterise solute transport that could be produced after the canister breakdown. Through-Diffusion (TD) and In-Diffusion (ID) experiments with HTO, Sr, Cs and Se were carried out using compacted FEBEX bentonite, which is the reference material for the Spanish concept of radioactive waste disposal. Experiments were interpreted by means of available analytical solutions that allow the estimation of diffusion coefficients and, in some cases, distribution coefficients. Analytical solutions are simple to use, but rely on hypotheses that do not hold in all the experiments. These experiments were interpreted also using an automatic parameter estimation code that overcomes the limitations of analytical solutions. Numerical interpretation allows the simultaneous estimation of porosity, diffusion and distribution coefficients, accounts for the role of porous sinters and time-varying boundary concentrations, and can use different types of raw concentration data.     

Present state and future directions of modeling of geochemistry in hydrogeological systems

A first step towards understanding and controlling the fate and dissemination of radioactive waste is to create a concise and comprehensive theoretical framework for the rather non-linear processes involved--hence, the need for geochemical models. Two classes of geochemical models are commonly used, i.e., static and hydrodynamic models. In contrast to static models, hydrodynamic models combine geochemical reactions with hydrogeological processes such as ground-water flow, diffusion and dispersion. In this review, we examine the present state of geochemical models in terms of included processes, thermodynamic databases, missing phenomena, numerical behavior and performance. It is shown that over the past decade, significant progress has been made with respect to modeling of geochemistry in hydrodynamic systems: this is illustrated by describing several applications. Finally, we focus on the perspectives of geochemical modeling in the assessment of the safety of nuclear waste disposal.     

Comprehensive evaluation of municipal garbage disposal in Changchun City by the strategic environmental assessment

Purpose

The environmental issues caused by the municipal solid waste disposal are becoming a worldwide concern.

Methods

We studied the situations both domestically and abroad by the strategic environmental assessment (SEA) approach and also conducted comprehensive evaluations of garbage disposal in Changchun City.

Results

On the basis of this study, we found that SEA is of great importance in the municipal solid waste disposal. Moreover, with the rapid socioeconomic development of Changchun City, municipal solid waste production increases on an annual basis, and thus, good waste management planning is of great significance.

Conclusions

Considering the situation of the economic development of Changchun City, garbage disposal was handled mainly in the major sanitary landfills with appropriate use of incineration technology. This plan is environmentally friendly at a relatively high degree and has met the requirements of minimum investment. It also takes into account the requirements of the development of incineration technology. Regarding environmental pollution in terms of groundwater pollution and atmospheric pollution, this plan is a feasible one by meeting various requirements with low environmental impact among the three plans discussed in this study.     

Approximate evaluation of contaminant transport through vertical barriers

Containment of groundwater contamination using physical barriers can be an important element of a subsurface remediation program. This work presents simple analytical tools for predicting the performance of barriers in terms of the steady-state contaminant flux across the barrier, the duration of the transient period following barrier installation, and the time-dependent contaminant concentration distribution within the barrier. The analytical expressions are developed from approximate boundary layer (BL) solutions to the advective–dispersive equation subject to conservative fixed concentration boundary conditions. Critical ranges of important dimensionless quantities are identified for use in barrier performance assessment, for both steady-state and transient conditions. Comparative calculations made with the BL equations and more exact semi-analytical solutions are used to characterize the accuracy and applicability of the BL approach.     

Burning Chemical Wastes as Fuels in Cement Kilns

Hazardous wastes in the environment represent one of our most serious problems. Ever increasing quantities of toxic wastes have contaminated our land, air, and water. Lack of adequate hazardous waste disposal facilities is a critical problem. Landfilling toxic wastes is no longer considered safe. The tragedy of the Love Canal has demonstrated the need for proper hazardous waste disposal facilities. The best organic chemical waste disposal method is process incineration. Cement kilns have been used for burning toxic chemical industrial wastes in Canada, Michigan, New York, Sweden, etc. Existing cement kilns, when properly operated, can destroy most organic chemical wastes. Even the most complex chlorinated hydrocarbons, including PCB can be completely destroyed during normal cement kiln operations, with minimal emissions to the environment. Burning toxic chemical wastes in cement kilns, and other mineral industries, is mutually beneficial to both industry, who generates such wastes, and to society and government, who want to dispose properly of such wastes in a safe, environmentally acceptable manner. The added benefit of energy conservation is important, since large quantities of valuable fuel can be saved in the manufacture of cement when such techniques are employed.     

Reactive transport modeling of column experiments on the evolution of saline-alkaline waste solutions

Leakage of saline-alkaline tank waste solutions often creates a serious environmental contamination problem. To better understand the mechanisms controlling the fate of such waste solutions in the Hanford vadose zone, we simulated reactive transport in columns designed to represent local site conditions. The Pitzer ion interaction module was used, with principal geochemical processes considered in the simulation including quartz dissolution, precipitation of brucite, calcite, and portlandite, multi-component cation exchange, and aqueous complexation reactions. Good matches were observed between the simulated and measured column data at ambient temperature ( approximately 21 degrees C). Relatively good agreement was also obtained at high temperature ( approximately 70 degrees C). The decrease of pH at the plume front is examined through formation of secondary mineral phases and/or quartz dissolution. Substantial formation of secondary mineral phases resulting from multi-component cation exchange suggests that these phases are responsible for a decrease in pH within the plume front. In addition, a sensitivity analysis was conducted with respect to cation exchange capacity, selectivity coefficient, mineral assemblage, temperature, and ionic strength. This study could serve as a useful guide to subsequent experimental work, to thermodynamic models developed for the concentrated solutions at high ionic strength and to other types of waste plume studies.     

Evaluating landfill disposal of chromated copper arsenate (CCA) treated wood and potential effects on groundwater: evidence from Florida

Chromated copper arsenate (CCA) treated wood has been used for more than 50 years. Recent attention has been focused on appropriate disposal of CCA-treated wood when its service life ends. Groups in the US and Europe concerned with the possibility of arsenic migration to groundwater from disposed CCA-treated wood have proposed that consumers be required to dispose of the wood as a hazardous waste, in the most protective of landfills. We examined available data for evidence of arsenic migration from unlined construction and demolition (C&D) debris landfills in Florida, where CCA-treated wood is disposed. Florida was chosen because soil, groundwater, landfill design, weather, and levels of CCA-treated wood use make the state a uniquely sensitive indicator for observing arsenic migration from CCA-treated wood disposal sites, should it occur. We developed and quality-checked a CCA-treated wood disposal model to estimate the amount of wood and associated arsenic disposed. By 2000, an estimated 13 million kg of arsenic in CCA-treated wood was disposed in Florida; however, groundwater monitoring data do not indicate that arsenic is migrating from unlined C&D landfills. Our results provide evidence that highly stringent regulation of CCA-treated wood disposal, such as treatment as a hazardous waste, is unnecessary.     

Transport and fate of organic wastes in groundwater at the Stringfellow hazardous waste disposal site, southern California

In January 1999, wastewater influent and effluent from the pretreatment plant at the Stringfellow hazardous waste disposal site were sampled along with groundwater at six locations along the groundwater contaminant plume. The objectives of this sampling and study were to identify at the compound class level the unidentified 40-60% of wastewater organic contaminants, and to determine what organic compound classes were being removed by the wastewater pretreatment plant, and what organic compound classes persisted during subsurface waste migration. The unidentified organic wastes are primarily chlorinated aromatic sulfonic acids derived from wastes from DDT manufacture. Trace amounts of EDTA and NTA organic complexing agents were discovered along with carboxylate metabolites of the common alkylphenolpolyethoxylate plasticizers and nonionic surfactants. The wastewater pretreatment plant removed most of the aromatic chlorinated sulfonic acids that have hydrophobic neutral properties, but the p-chlorobenzene-sulfonic acid which is the primary waste constituent passed through the pretreatment plant and was discharged in the treated wastewaters transported to an industrial sewer. During migration in groundwater, p-chlorobenzenesulfonic acid is removed by natural remediation processes. Wastewater organic contaminants have decreased 3- to 45-fold in the groundwater from 1985 to 1999 as a result of site remediation and natural remediation processes. The chlorinated aromatic sulfonic acids with hydrophobic neutral properties persist and have migrated into groundwater that underlies the adjacent residential community.     

Estimating national landfill methane emissions: an application of the 2006 Intergovernmental Panel on Climate Change Waste Model in Panama

This paper estimates national methane emissions from solid waste disposal sites in Panama over the time period 1990-2020 using both the 2006 Intergovernmental Panel on Climate Change (IPCC) Waste Model spreadsheet and the default emissions estimate approach presented in the 1996 IPCC Good Practice Guidelines. The IPCC Waste Model has the ability to calculate emissions from a variety of solid waste disposal site types, taking into account country- or region-specific waste composition and climate information, and can be used with a limited amount of data. Countries with detailed data can also run the model with country-specific values. The paper discusses methane emissions from solid waste disposal; explains the differences between the two methodologies in terms of data needs, assumptions, and results; describes solid waste disposal circumstances in Panama; and presents the results of this analysis. It also demonstrates the Waste Model's ability to incorporate landfill gas recovery data and to make projections. The former default method methane emissions estimates are 25 Gg in 1994, and range from 23.1 Gg in 1990 to a projected 37.5 Gg in 2020. The Waste Model estimates are 26.7 Gg in 1994, ranging from 24.6 Gg in 1990 to 41.6 Gg in 2020. Emissions estimates for Panama produced by the new model were, on average, 8% higher than estimates produced by the former default methodology. The increased estimate can be attributed to the inclusion of all solid waste disposal in Panama (as opposed to only disposal in managed landfills), but the increase was offset somewhat by the different default factors and regional waste values between the 1996 and 2006 IPCC guidelines, and the use of the first-order decay model with a time delay for waste degradation in the IPCC Waste Model.     

Avoiding Land Disposal of Hazardous Waste

In response to a growing societal mandate, land disposal of hazardous wastes is gradually being replaced by treatment technologies. This shift to "alternative technologies" is the result of the impacts of past land disposal practices on other environmental media (groundwater, surface water, and air). A prime motivation for adopting alternatives to land disposal is to eliminate these cross-media impacts. Alternative technologies, however, can themselves have cross-media environmental impacts which must be recognized and addressed before such technologies are extensively applied. This paper discusses hazardous waste constituents, common disposal practices, alternative technologies currently being applied, possible cross-media environmental impacts of the alternative technologies, and proposed methods of mitigating these environmental impacts. Case studies from uncontrolled hazardous waste sites and industrial operations are used to illustrate the application of alternative technologies. Case studies include the application of waste treatment technologies as well as the adoption of waste minimization techniques.     

Mercury Measurement and Its Control: What We Know,Have Learned,and Need to Further Investigate

Disposal of mercury waste has always provided unique challenges due to its high degree of complexity and volatility. This study evaluated the feasibility of using waste LF slag to form a cementitious matrix capable of providing an effective stabilization/solidification solution for the treatment of mercury wastes. The new matrix was synthesized and simulated through a combination of alkali activation and autoclaving process and doped with mercury nitrate at increasing dosage while monitoring the final form of the mercury and its effects on the mineral stability and structure of the new matrix. Compressive strength of up to 20 N/mm² was achievable for the original matrix. Promising results were obtained in terms of reduced leachability of the mercury when compared to ordinary Portland cement systems at low doping concentration of around 0.5% by weight. A series of precipitation reactions was found to be the main cause responsible for this successful stabilization, especially the metal sulfide precipitation that occurred with the sulfur present in the original waste LF slag.

Implications: Using waste to treat waste as a concept is a new approach that not only solves waste disposal problems but also minimizes the toxicity and the potential hazard of leaching of heavy metals. This study evaluated the feasibility of using waste ladle furnace slag generated from steel-making industries to form a cementitious matrix capable of providing an effective stabilization/solidification solution for the treatment of mercury-containing wastes. Promising results were obtained, and it clearly showed this approach is feasible, which could be a one-stone-kills-two-birds solution for mercury stabilization as well as an industrial waste disposal problem.     

Concept of sustainable waste management in the city of Zagreb: Towards the implementation of circular economy approach

Improvement of the current waste management is one of the main challenges for most municipalities in Croatia, mainly due to legal obligations set in different European Union (EU) directives regarding waste management, such as reduction of waste generation and landfilling, or increase of separately collected waste and recycling rates. This paper highlights the current waste management in the city of Zagreb by analyzing the waste generation, collection, and disposal scenario along with the regulatory and institutional framework. Since the present waste management system mainly depends upon landfilling, with the rate of separate waste collection and recycling far from being adequate, it is necessary to introduce a new system that will take into account the current situation in the city as well as the obligations imposed by the EU. Namely, in the coming years, the Waste Framework and Landfill Directives of the European Union will be a significant driver of change in waste management practices and governance of the city of Zagreb. At present, the yearly separate waste collection makes somewhat less than 5 kg per capita of various waste fractions, i.e., far below the average value for the (28) capital cities of the EU, which is 108 kg per capita. This is possible to achieve only by better and sustainable planning of future activities and facilities, taking into account of environmental, economic, and social aspects of waste management. This means that the city of Zagreb not only will have to invest in new infrastructure to meet the targets, but also will have to enhance public awareness in diverting this waste at the household level. The solution for the new waste management proposed in this paper will certainly be a way of implementing circular economy approach to current waste management practice in the city of Zagreb.

Implications: Municipal waste management in the developing countries in the EU (new eastern EU members) is often characterized by its limited utilization of recycling activities, inadequate management of nonindustrial hazardous waste, and inadequate landfill disposal. Many cities in Eastern Europe and Zagreb as well are facing serious problems in managing municipal wastes due to the existing solid waste management system that is found to be highly inefficient. The proposed scenario for city of Zagreb in the paper is an innovative upgrading of municipal waste management based on the waste management hierarchy and circular economy approach.     

Guide values for contaminated sites in Baden-Württemberg

The treatment of hazardous sites in Baden-Württemberg is based on three legal documents: the state waste disposal art (LAbfG, 1990), the assessment committee directive (KommissionsVO, 1990), and the guide values directive (UM & SM B-W, 1993). The guide values directive was commonly issued by the Ministry of Labor, Health and Social Affairs and the Ministry of the Environment of the state of Baden-Württemberg (UM & SM B-W, 1993) and contains a three-level hierarchy of numerical criteria and rules which serve as both screening levels during the investigation and as remediation objectives. The decision for the appropriate level of remediation is based on feasibility and environmental balance considerations. The levels are ordered as follows:

? Level 1 (Background-Values) On principle, all remediations have to be based first on background levels. In the case of lack of feasibility or negative environmental balance for level-1 objectives use-specific requirements are considered next.

? Level 2 (Assessment-Values for Worst Case Exposure Conditions) The generic requirements underlying level 2 afford appropriate protection for humans regarding the most sensitive uses of the environment. At least four resources are considered on this level: Ground-water as such and its use, the health of humans on contaminated sites, and soil with respect to growth and quality of plants. Barriers against migration of the contaminants, the effect of dilution, and abandonment of certain uses, etc., are not taken into consideration on level 2.

? Level 3 (Site-Specific Requirements) Lack of feasibility or a negative environmental balance of level-2 objectives lead to consideration of site-specific circumstances which may alleviate the requirements. With respect to groundwater, the distinction is again necessary between groundwater as a resource and the use of groundwater. On level 3 the guideline gives rules of how to derive site-specific remediation objectives for groundwater in the form of concentrations and fluxes of contaminants after taking into account barriers, dilution, and the abandonment of uses.

The guideline is the only directive of its kind in the world that regulates both concentrations and fluxes of contaminants into groundwater.     

Modelling reactions between cement pore fluids and rock: implications for porosity change

The migration of groundwater equilibrated with cement from a deep geological disposal facility for radioactive wastes will perturb the chemical, minerological and physical properties of the geosphere in advance of the migration of radionuclides. Preliminary modelling of a simplified scenario has been conducted to assess these changes using appropriate data for mineral dissolution kinetics, the chemical composition of cement pore fluids, and the hydrogeological characteristics of fractured crystalline rock. Chemical exchanges between rock immediately adjacent to the engineered barriers of a waste disposal facility and pore fluids were evaluated using the speciation-reaction path code. which revealed rapid loss of Ca, and gains in Na and Si of the evolved fluids, with little change in pH. Secondary minerals show a sequence of calcium silicate hydrates, and zeolites. Precise definition of the overall mass balance is uncertain due to the absence of both thermodynamic data for many zeolites and kinetic data for the precipitation of feldspars. Modelling has demonstrated that reaction kinetics will be important in governing chemical exchanges for length scales up to 20 m. Radionuclide retardation will be enhanced by the growth of zeolites and calcium silicate hydrates.     

Public policy impacts on the generation and disposal of hazardous waste in New York State

A number of policies adopted by the federal government and the state have been designed to promote waste reduction or influence the choice of waste disposal technologies employed by generators of hazardous waste. Graphic analysis of smoothed time series data for hazardous wastes manifested in New York State for the period between June 1982 and February 1987 suggests that some of these policies have had the intended effects. Significant shifts in manifested waste volumes are evident that coincide with the following policy interventions: (1) increased state waste-end tax rates; (2) state and federal landfill bans; (3) federal restrictions on burning hazardous wastes and waste oils for energy recovery; and (4) changes in the federal regulatory definition of hazardous waste. Other changes in waste generation and management appear to be attributable to such factors as state and regional economic conditions and changes in instate treatment and disposal facility capacity. Analysis of the management of specific waste types supports evidence from the graphic analysis that waste generators changed from land disposal to "higher" waste handling technologies in response to several policy interventions.     

Recycling of nickel smelter slag for arsenic remediation—an experimental study

In this study, recycled Ni smelter slag has been used as a reactive medium for arsenic (As) removal from aqueous solutions. The results of the study showed that 10.16–11.43-cm long columns containing 451–550 g of slag operated for at least 65 days were able to remove 99–100 % As species from continuously flowing contaminated water at an initial As concentration of 10 mg/L. The removal capacities were found to be 1.039 to 1.054 mg As per g of slag. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy data also showed that electrostatic attraction and oxidation–reduction reactions between As species and mixed iron oxides present in the slag were the main mechanisms for the removal of arsenic from aqueous solutions. Theoretical multiplet analysis of XPS data revealed that the amount of goethite in the slag increased from 22 to 60 % during arsenic removal by adsorption and the percentage of magnetite decreased from 50 to 40 %. These changes indicate that redox-mediated reactions occurred as part of the As(V) removal process. Raman spectroscopy studies confirmed that, in addition to surface reactions, internal interactions between the slag and arsenic also occurred. The findings of the study suggest that recycled Ni smelter slag could be an effective low-cost reactive medium for a subsurface remediation system, such as a permeable reactive barrier. Recycling of waste material (slag) for the removal of another waste (arsenic) can significantly reduce the environmental footprint of metallurgical operations and hence contribute to sustainable development. Such recycling also decreases slag disposal costs and eliminates the need to purchase commercial reactive material or obtain expensive natural material for remediation purposes.     

Intercomparison of reactive transport models applied to UO2 oxidative dissolution and uranium migration

Oxidative dissolution of uranium dioxide (UO(2)) and the subsequent migration of uranium in a subsurface environment and an underground waste disposal have been simulated with reactive transport models. In these systems, hydrogeological and chemical processes are closely entangled and their interdependency has been analyzed in detail, notably with respect to redox reactions, kinetics of mineralogical evolution and hydrodynamic migration of species of interest. Different codes, where among CASTEM, CHEMTRAP and HYTEC, have been used as an intercomparison and verification exercise. Although the agreement between codes is satisfactory, it is shown that the discretization method of the transport equation (i.e. finite elements (FE) versus mixed-hybrid FE and finite differences) and the sequential coupling scheme may lead to systematic discrepancies.     

Influence of seaward boundary condition on contaminant transport in unconfined coastal aquifers.

Contaminant transport in coastal aquifers is complicated partly due to the conditions at the seaward boundary including seawater intrusion and tidal variations of sea level. Their inclusion in modelling this system will be computationally expensive. Therefore, it will be instructive to investigate the consequence of simplifying the seaward boundary condition by neglecting the seawater density and tidal variations in numerical predictions of contaminant transport in this zone. This paper presents a comparison of numerical predictions for a simplified seaward boundary condition with experimental results for a corresponding realistic one including a saltwater interface and tidal variations. Different densities for contaminants are considered. The comparison suggests that the neglect of the seawater intrusion and tidal variations does not affect noticeably the overall migration rate of the plume before it reaches the saltwater interface. However, numerical prediction shows that a more dense contaminant travels further seaward and part of the solute mass exits under the sea if the seawater density is not included. This is not consistent with the experimental result, which shows that the contaminant travels upwards to the shoreline along the saltwater interface. Neglect of seawater density, therefore, will result in an underestimation of the exit rate of solute mass around the coastline and fictitious migration paths under the seabed. For a less dense contaminant, neglect of seawater density has little effect on numerical prediction of migration paths.     

Intercomparison of reactive transport models applied to UO2 oxidative dissolution and uranium migration

Oxidative dissolution of uranium dioxide (UO₂) and the subsequent migration of uranium in a subsurface environment and an underground waste disposal have been simulated with reactive transport models. In these systems, hydrogeological and chemical processes are closely entangled and their interdependency has been analyzed in detail, notably with respect to redox reactions, kinetics of mineralogical evolution and hydrodynamic migration of species of interest.Different codes, where among CASTEM, CHEMTRAP and HYTEC, have been used as an intercomparison and verification exercise. Although the agreement between codes is satisfactory, it is shown that the discretization method of the transport equation (i.e. finite elements (FE) versus mixed-hybrid FE and finite differences) and the sequential coupling scheme may lead to systematic discrepancies.