Flow and Containment of Injected Wastes

Proper design, construction, testing and maintenance of Class 1 (hazardous waste) injection wells can guarantee that all waste is delivered to the injection zone. To assess the effects of waste injection, analytical models were developed which predict waste movement and pressure increases within the injection zone, and describe upward permeation through confining layers.
A basic plume model was used to track waste from several injection wells with varied injection history at DuPont's Victoria Texas site. To determine the maxi-mum distance that any portion of the waste might travel, special purpose models were employed to account for (1) density differences between the waste and the native formation brine, and (2) layered permeability variation within the injection zone. The results were generalized to a "multiplying factor concept," which facilitates development of a worst-case scenario.
A pressure distribution model based on the Theis (1935) equation for radial flow was applied to the Victoria site, with modifications to account for multiple wells, injection history and geological complexities.
Permeation into an intact confining layer was investigated by a new technique based on the Hantush and Jacob (1955) "leaky aquifer" theory. The model defines the maximum permeation distance, taking into account post-injection pressure decay.
Defects within confining layers, such as faults, fractures and abandoned wells, have been considered. Studies to evaluate their detailed characteristics are continuing. Initial results indicate that faults and fractures are not likely to provide conductive pathways in Gulf Coast settings, and site-specific evaluations are required to assess the impact of abandoned wells.     

Quantifying the transferability of hydraulic parameters using geostatistics: The Boom Clay Case

The Boom Clay is currently investigated as potential host formation for the deep disposal of high-level and/or long-lived radioactive waste in Belgium. As such, the formation is expected to play a role of natural barrier, to slow the migration of radionuclides towards the biosphere for a sufficiently long time when the man-made barriers are no longer effective. In this context, the Boom Clay aquitard requires to be precisely characterized in terms of hydrogeological parameters, to confirm its role of geological barrier between its surrounding aquifers. Therefore, hydraulic conductivity and migration parameters have been intensively measured over the years in a few boreholes in Belgium; the latter are mainly located in the Mol-Dessel area, assuming historically a good lateral continuity of the geology. Combining these measurements with more densely acquired geophysical information allows quantifying their spatial variability and consolidating the continuity assumption. From a methodological point of view, the modeling of hydrogeological parameters requires to solve several issues. First, it is required to find a consistent geo-reference coordinate system allowing to laterally correlate thin observations derived from boreholes separated by several tens of kilometers. Then, in order to provide a reliable 3D model, it is compulsory to integrate the correlation between the scarcely sampled target parameters (core measurements) and numerous geophysical logs (gamma ray, resistivity). Geostatistics provides a suitable framework to analyze and solve these issues. Finally, a 3D model of the target parameters is proposed, together with an uncertainty envelope. This uncertainty quantification is of significant added value to assess the efficiency of the geological barrier. Besides the actual modeling of target parameters, the paper also presents sampling recommendations for forthcoming boreholes.     

Radionuclide Transport Behavior in a Generic Geological Radioactive Waste Repository

We performed numerical simulations of groundwater flow and radionuclide transport to study the influence of several factors, including the ambient hydraulic gradient, groundwater pressure anomalies, and the properties of the excavation damaged zone (EDZ), on the prevailing transport mechanism (i.e., advection or molecular diffusion) in a generic nuclear waste repository within a clay‐rich geological formation. By comparing simulation results, we show that the EDZ plays a major role as a preferential flowpath for radionuclide transport. When the EDZ is not taken into account, transport is dominated by molecular diffusion in almost the totality of the simulated domain, and transport velocity is about 40% slower. Modeling results also show that a reduction in hydraulic gradient leads to a greater predominance of diffusive transport, slowing down radionuclide transport by about 30% with respect to a scenario assuming a unit gradient. In addition, inward flow caused by negative pressure anomalies in the clay‐rich formation further reduces transport velocity, enhancing the ability of the geological barrier to contain the radioactive waste. On the other hand, local high gradients associated with positive pressure anomalies can speed up radionuclide transport with respect to steady‐state flow systems having the same regional hydraulic gradients. Transport behavior was also found to be sensitive to both geometrical and hydrogeological parameters of the EDZ. Results from this work can provide useful knowledge toward correctly assessing the post‐closure safety of a geological disposal system.     

Modeling and Remediation of Ground Water Contamination at the Engelse Werk Wellfield

Contaminants have been threatening the Engelse Werk wellfield located between the town of Zwolle and the IJssel River in the Netherlands. Chemical analysis of water samples taken in production wells, both at the IJssel River and near the Zwolle railway station, indicated elevated concentrations of mainly organic contaminants including benzene, bentazon, acenaftene, trichloroethane, and bromacil. Immediate contaminant prevention and remediation measures are needed to safeguard the production wells. Ground water flow and transport models were developed to assist in the design of remediation strategies. Ground water flow models indicated that the IJssel River and a waste disposal ditch at the railway station are within the capture zone of the wellfield. A chloride transport model simulated minimum travel times in the order of four to 13 years for contaminants in the IJssel River to reach the production wells of the wellfield. A transport model for benzene was set up to advise on the remediation measures to be taken at the waste disposal ditch to clean up the contamination in the upper aquifer between this site and the Engelse Werk wellfield. The designed remediation system consists of 12 pumping wells with a combined capacity of 1650 m³/day. The system is capable of reducing the benzene levels at the threatened production wells at the Engelse Werk wellfield to a permissible level below 0.1 μg/L within a period of 5 years.     

ISMISIP: an inexact stochastic mixed integer linear semi-infinite programming approach for solid waste management and planning under uncertainty

An inexact stochastic mixed integer linear semi-infinite programming (ISMISIP) model is developed for municipal solid waste (MSW) management under uncertainty. By incorporating stochastic programming (SP), integer programming and interval semi-infinite programming (ISIP) within a general waste management problem, the model can simultaneously handle programming problems with coefficients expressed as probability distribution functions, intervals and functional intervals. Compared with those inexact programming models without introducing functional interval coefficients, the ISMISIP model has the following advantages that: (1) since parameters are represented as functional intervals, the parameter’s dynamic feature (i.e., the constraint should be satisfied under all possible levels within its range) can be reflected, and (2) it is applicable to practical problems as the solution method does not generate more complicated intermediate models (He and Huang, Technical Report, 2004; He et al. J Air Waste Manage Assoc, 2007). Moreover, the ISMISIP model is proposed upon the previous inexact mixed integer linear semi-infinite programming (IMISIP) model by assuming capacities of the landfill, WTE and composting facilities to be stochastic. Thus it has the improved capabilities in (1) identifying schemes regarding to the waste allocation and facility expansions with a minimized system cost and (2) addressing tradeoffs among environmental, economic and system reliability level.     

Βedrock instability of underground storage systems in the Czech Republic,Central Europe

Underground storage systems are currently being used worldwide for the geological storage of natural gas (CH₄), the geological disposal of CO₂, in geothermal energy, or radioactive waste disposal. We introduce a complex approach to the risks posed by induced bedrock instabilities in deep geological underground storage sites. Bedrock instability owing to underground openings has been studied and discussed for many years. The Bohemian Massif in the Czech Republic (Central Europe) is geologically and tectonically complex. However, this setting is ideal for learning about the instability state of rock masses. Longterm geological and mining studies, natural and induced seismicity, radon emanations, and granite properties as potential storage sites for disposal of radioactive waste in the Czech Republic have provided useful information. In addition, the Czech Republic, with an average concentration radon of 140 Bq m^?3, has the highest average radon concentrations in the world. Bedrock instabilities might emerge from microscale features, such as grain size and mineral orientation, and microfracturing. Any underground storage facility construction has to consider the stored substance and the geological settings. In the Czech Republic, granites and granitoids are the best underground storage sites. Microcrack networks and migration properties are rock specific and vary considerably. Moreover, the matrix porosity also affects the mechanical properties of the rocks. Any underground storage site has to be selected carefully. The authors suggest to study the complex set of parameters from micro to macroscale for a particular place and type of rock to ensure that the storage remains safe and stable during construction, operation, and after closure.     

From models to performance assessment: the conceptualization problem

Today, models are ubiquitous tools for ground water analyses. The intent of this paper is to explore philosophically the role of the conceptual model in analysis. Selection of the appropriate conceptual model is an a priori decision by the analyst. Calibration is an integral part of the modeling process. Unfortunately a wrong or incomplete conceptual model can often be adequately calibrated; good calibration of a model does not ensure a correct conceptual model. Petroleum engineers have another term for calibration; they refer to it as history matching. A caveat to the idea of history matching is that we can make a prediction with some confidence equal to the period of the history match. In other words, if we have matched a 10-year history, we can predict for 10 years with reasonable confidence; beyond 10 years the confidence in the prediction diminishes rapidly. The same rule of thumb applies to ground water model analyses. Nuclear waste disposal poses a difficult problem because the time horizon, 1000 years or longer, is well beyond the possibility of the history match (or period of calibration) in the traditional analysis. Nonetheless, numerical models appear to be the tool of choice for analyzing the safety of waste facilities. Models have a well-recognized inherent uncertainty. Performance assessment, the technique for assessing the safety of nuclear waste facilities, involves an ensemble of cascading models. Performance assessment with its ensemble of models multiplies the inherent uncertainty of the single model. The closer we can approach the idea of a long history with which to match the models, even models of nuclear waste facilities, the more confidence we will have in the analysis (and the models, including performance assessment). This thesis argues for prolonged periods of observation (perhaps as long as 300 to 1000 years) before a nuclear waste facility is finally closed.     

利用电磁方法探测内蒙古塔木素高放废物预选场址岩体的内部构造

高放废物地质处置库选址要求围岩完整稳定,它与岩体深部地质结构密切相关,因此是场址评价中必须考虑的因素.在高放废物储库选址新区内蒙阿拉善塔木素岩体,采用可控源音频大地电磁法进行了剖面探测.分析了典型测深曲线,区分了地质构造和完整围岩的响应特征;针对高放废物预选场址的特点,对原始数据进行了处理;结合已有地质、钻井及测井资料完成了解释;结果表明,利用可控源音频大地电磁法有效地查明了该地岩体内部结构,该岩体存在裂隙和破碎,完整性欠佳.     

INVERSION OF FIRST-BREAK TRAVELTIME DATA OF DEEP SEISMIC REFLECTION PROFILES1

First breaks of 2D deep reflection data were used to construct velocity-depth models for improved static corrections to a deeper datum level and for geological interpretations. The highly redundant traveltime data were automatically picked and transformed directly into a velocity-depth model by maximum depth methods such as the Giese- and the Slichter-method. Comparisons with the results of synthetic calculations and a tomographic approach using iterative inversion methods (ART, SIRT) showed that maximum depth methods provide reliable velocity models as a basis for the computation of static corrections. These methods can economically be applied during data acquisition in the field. They provide particularly long-period static anomalies, which are of the order of 20–40 ms (0.5-1 wavelength) within CMP gathers of an example of a deep reflection profile in SW-Germany sited on crystalline basement. Reprocessing of this profile, which was aimed at the comparison between the effects of the originally used and the new statics, did not result in dramatically improved stacking quality but showed a subtle influence on the detailed appearance of deep crustal events.     

Assessing hydrological model predictive uncertainty using stochastically generated geological models

In distributed and coupled surface water–groundwater modelling, the uncertainty from the geological structure is unaccounted for if only one deterministic geological model is used. In the present study, the geological structural uncertainty is represented by multiple, stochastically generated geological models, which are used to develop hydrological model ensembles for the Norsminde catchment in Denmark. The geological models have been constructed using two types of field data, airborne geophysical data and borehole well log data. The use of airborne geophysical data in constructing stochastic geological models and followed by the application of such models to assess hydrological simulation uncertainty for both surface water and groundwater have not been previously studied. The results show that the hydrological ensemble based on geophysical data has a lower level of simulation uncertainty, but the ensemble based on borehole data is able to encapsulate more observation points for stream discharge simulation. The groundwater simulations are in general more sensitive to the changes in the geological structure than the stream discharge simulations, and in the deeper groundwater layers, there are larger variations between simulations within an ensemble than in the upper layers. The relationship between hydrological prediction uncertainties measured as the spread within the hydrological ensembles and the spatial aggregation scale of simulation results has been analysed using a representative elementary scale concept. The results show a clear increase of prediction uncertainty as the spatial scale decreases. Copyright © 2015 John Wiley & Sons, Ltd.     

地磁倒转与生物灭绝因果关系研究五十年

地磁场源于地球内部的地核发电机,经由近3000 km厚的地幔和地壳到达地面,穿过生物圈、大气层和电离层后延展至太空形成磁层.地磁场对生物圈有双重保护作用:阻挡了高能粒子向内入侵,也避免了氧和水等挥发性物质向外逃逸.尽管地磁场在几十亿年的时间里帮助维持了地球的宜居性,人们仍认为地磁倒转所导致的保护作用削弱会给生物圈带来深刻的负面影响,甚至是生物灭绝.本文梳理地磁倒转与生物灭绝因果关系研究的五十年发展历程,结合历史背景评介早期"一对一"假说的得与失,并着重阐述空间环境变化在最新提出的"多对一"假说中的重要作用.这些研究成果已经清晰地说明,从地核到磁层的地球各圈层是一个耦合的复杂系统,地球演化中的重大事件应当从地球系统科学的角度来看待,并借助比较行星学来研究和理解.     

Application of 3D hydrodynamic and particle tracking models for better environmental management of finfish culture

Hydrographic conditions, and particularly current speeds, have a strong influence on the management of fish cage culture. These hydrodynamic conditions can be used to predict particle movement within the water column and the results used to optimise environmental conditions for effective site selection, setting of environmental quality standards, waste dispersion, and potential disease transfer. To this end, a 3D hydrodynamic model, MOHID, has been coupled to a particle tracking model to study the effects of mean current speed, quiescent water periods and bulk water circulation in Mulroy Bay, Co. Donegal Ireland, an Irish fjard (shallow fjordic system) important to the aquaculture industry. A Lagangrian method simulated the instantaneous release of “particles” emulating discharge from finfish cages to show the behaviour of waste in terms of water circulation and water exchange. The 3D spatial models were used to identify areas of mixed and stratified water using a version of the Simpson-Hunter criteria, and to use this in conjunction with models of current flow for appropriate site selection for salmon aquaculture.The modelled outcomes for stratification were in good agreement with the direct measurements of water column stratification based on observed density profiles. Calculations of the Simpson-Hunter tidal parameter indicated that most of Mulroy Bay was potentially stratified with a well mixed region over the shallow channels where the water is faster flowing. The fjard was characterised by areas of both very low and high mean current speeds, with some areas having long periods of quiescent water. The residual current and the particle tracking animations created through the models revealed an anticlockwise eddy that may influence waste dispersion and potential for disease transfer, among salmon cages and which ensures that the retention time of waste substances from cages is extended.The hydrodynamic model results were incorporated into the ArcView^TM GIS system for visualisation and interrogation of results and to allow effective holistic environmental management and site selection for fish cage aquaculture.     

Dispersion dependence on retardation in a real fracture geometry using lattice-gas cellular automaton

Fractures have been recently identified in potential host rock for high level nuclear waste disposal, like indurated argilite formations. These fractures appear as potential rapid pathways for radionuclides transport and hydrodynamic properties of the transport inside these systems must thus be characterized. Miscible non-sorbing and sorbing tracers displacements were performed on a 2-D model derived from a real fracture geometry observed in the Tournemire argilite formation with a lattice-gas cellular automaton (LGA). LGA was shown to easily handle the complex geometry of such a fracture. The numerical breakthrough curves obtained were inverted with the 1-D CDE and MIM transport models. Two main conclusions were drawn: (i) at the length scale of the study, the non-sorbing tracer transport in our fracture geometry was more accurately interpreted in terms of the MIM model rather than in terms of the classical CDE model; (ii) in order to correctly model the sorbing tracers migration, the hydrodynamic dispersion coefficient value was found to increase with the increase of the retardation factor. A semi-empirical relation based on the Taylor–Aris theory was then used to describe this dependency.     

GEOPHYSICAL METHODS USED IN SOLVING SOME GEOLOGICAL PROBLEMS ENCOUNTERED IN THE CONSTRUCTION OF THE TREBIšNJIGA WATER POWER PLANT (in YUGOSLAVIA) *

The design and construction of hydroelectric works, and more particularly of storage reservoirs and dams, in karst areas pose extremely varied and complex engineering, geological and hydrogeological problems, for the solution of which no widely applied techniques have yet been developed. In addition to conventional geological and hydrogeological methods for the study of karst phenomena, the application of more efficient methods of a primarily geophysical nature is called for. These methods, which provide the best means for solving the complex problems encountered in karst, are steadily gaining acceptance. The Miru?e storage reservoir and the Gran?arevo dam are the key structures in the Trebi?njica hydroelectric complex and are located in an area of typical Dinaric karst. Many of the engineering, geological and hydrogeological problems connected with their design and construction were solved with the aid of electrical geophysical prospecting methods (especially the resistivity method). The investigations provided data on the depth of karstification (the relief of the base level of karst erosion), the position of intensively karstified and tectonically broken zones, as well as on the general orientation of the process of karstification. All these data were helpful in providing a more accurate insight into the impermeability of the rocks that formed the storage reservoir (in relation to the proposed impounding level); they also enabled the consolidation structures (impervious curtains), aimed at preventing excessive losses due to seepage, to be designed more economically.     

Practical Application of Theoretical Models to Magnetometer Surveys on Hazardous Waste Disposal Sites — A Case History

Wastes were to be exhumed and removed from a hazardous and chemical waste disposal site. The major disposal practice was shallow burial of wastes in metal drums in parallel trenches. The actual boundaries of the trenches beneath the landscaped cover were not accurately known.
Theoretical two-dimensional models were used to evaluate the application of magnetic methods to define trench boundaries on the disposal site. The models predicted that both the total field and the vertical component anomalies were diagnostic; however, the vertical component anomaly was more focused on the trench boundaries.
A survey with a vertical component fluxgate magnetometer was successful in defining trench boundaries. Observations made along traverses that trended perpendicular to the long axis of the parallel trenches indicated vertical magnetic intensity values with a cyclical pattern of large positive values over trenches and large negative values over intertrench corridors. Vertical magnetic intensity values determined with theoretical two-dimensional models compared favorably to the observed vertical magnetic values. The models were used to constrain the interpretation of the field observations to define trench boundaries; the magnetic survey defined trench boundaries with an accuracy within ± 2 feet.     

Effects of shield brine on the safe disposal of waste in deep geologic environments

The salinity of groundwater increases with depth in the Canadian Shield (up to 1.3 kg/L of density). The existence of brine can be critically important for the safe geologic disposal of radioactive wastes, as dense brine can significantly retard the upward migration of radionuclides released from repositories. Static and flushing conditions of the deep brine are analyzed using a U-tube analogy model. Velocity reduction due to the presence of dense brine is derived under flushing conditions. A set of illustrative numerical simulations in a two-dimensional cross section is presented to demonstrate that dense brine can significantly influence regional groundwater flow patterns in a shield environment. It is implied from the results that (1) the existence of Shield brine can be an indicator of a hydrogeologically stable environment, (2) activities near ground surface may not perturb the stable groundwater environment in the deep brine region, and thus, (3) the deep brine region can be considered as a candidate geologic site for the safe disposal of waste. In addition to brine, other issues associated with long-term waste disposal, such as geological, glacial and seismic events, may need to be considered for the safe storage of spent nuclear fuel in a shield environment.     

Vadose Zone Characterization of Low-Permeability Sediments Using Field Permeameters

Measurement of the saturated hydraulic conductivity of material in the unsaturated zone beneath proposed surface impoundments is important for predicting seepage rates of water and contaminants. Hazardous waste disposal facilities are commonly sited on the basis of the low permeability of the geologic materials beneath the site. Field measurement of the saturated hydraulic conductivity of low-permeability materials may be accomplished using air-entry permeameters and borehole permeameters. The results of a coordinated field and laboratory investigation of low-permeability materials at a hazardous waste facility are presented. The different methods of testing and analysis are compared and discussed. In general, air-entry permeameters and borehole permeameters are useful for measuring the saturated hydraulic conductivity of low-permeability materials.     

Chemical Fate of Injected Wastes

The chemical fate of wastes put into disposal wells can be determined using standard chemical engineering techniques. The concentration of hazardous constituents is typically reduced by reactions within the waste itself or by reactions with the injection zone material, thus reducing any potential impact on the environment. Such reactions include neutralization, hydrolysis, ion exchange, adsorption, precipitation, co-precipitation and microbial degradation.
Extensive research was done to quantify these phenomena, so they could be used in a predictive model.
Neutralization, hydrolysis and precipitation were modeled using data from the open literature: reaction rates and equilibrium constants for the dominant reactions were incorporated into a sophisticated computer simulation that calculates solid-liquid equilibria of aqueous electrolyte solutions.
The model predicted the fate of two waste streams: (1) high-pH, cyanide-containing waste injected into sandstone is made less hazardous by hydrolysis and sand dissolution, and (2) FeCl₃-FeCl₂ HCl-H₂ O waste is made non-hazardous by reaction with dolomite. Experiments are planned to confirm certain model predictions. Further development and public access of the model are planned.     

Design of Lysimeter Leak Detector Networks for Surface Impoundments and Landfills

Sampling of soil pore moisture in the vadose zone underneath land disposal facilities (landfills and surface impoundments) for hazardous waste has been suggested as an "early warning system" to detect leakage from these facilities. Some states require vadose zone moisture sampling at such sites. Given a leak of a particular size, mathematical models can estimate the necessary moisture sample volume collection times and lysimeter spacings to guarantee detection of the leak in a homogeneous medium. Examination of 47 hazardous waste sites existing in 1984 indicated the most were located in areas with water tables too shallow to permit vadose zone detection monitoring. Several of the 47 sites had soils that could be described as loamy sand, silt loam or silty clay. Using these three soils as examples, the process of lysimeter leak-detector network design has been illustrated. For a particular loamy sand with a saturates hydraulic conductivity of 10^-6 cm/ sec, the maximum ceramic lysimeter spacing is 15.5 feet at a depth of 30 feet to collec a moisture sample of 10 mL in one week from a 1 ft2 leak. For a silt loam, maximum lysimeter spacing would be 17 feet at depth of 15 feet. For silty clays, the maximum lysimeter spacing is 7 feet at a depth of 2 feet; maximum emplacement depth is about 9 feet. Calculations show that in some soils, suction lysimeters will not be able to collect usable moisture samples. Since soil properties vary widely and lysimeter spacing is strongly dependent on soil-moisture characteristics appropriate soil measurements and modeling must be performed at each disposal facility to estimate lysimete performance and to select locations for emplacement.     

Using geophysical methods to characterize an abandoned uranium mining site,Portugal

A major plan for Portugal Mainland is being envisaged to use old open pits from abandoned uranium mining sites as “Waste Containment Deposits”. These areas will store mining waste from other adjacent mines. The old mining sites classification to this kind of usage is carried out accordingly to its location, accessibility, geological and hydrogeological conditions. Mining waste deposition in the open pits may however cause environmental problems related with geological and hydrogeological features that must be predicted and prevented before a particular site is chosen. Therefore, the identification of faults and conductive zones that may promote groundwater circulation and the spread of contaminated waters is of great importance, since the surrounding area is highly populated. The possible negative environmental impacts of the presence of such potential waste disposal sites are therefore being assessed using geophysical methods and geological outcrop studies in several geological and hydrogeological critical areas. The abandoned Quinta do Bispo uranium mine is one of such places. This old open pit, chosen as one of the sites to be used in the near future as a “Waste Containment Deposit” (accordingly to the above mentioned criteria), needs to be characterized at depth to prevent any possible negative environmental impacts. Thus, the acquisition, processing and interpretation of electromagnetic, electrical and both seismic refraction and reflection have been carried out. 2D schematic models have been constructed, showing alteration and faults zones at depth. These fault zones control groundwater circulation and therefore, future water circulation problems with negative environmental impact may be predicted and prevented.