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3.
  • Crawford, J., et al. (author)
  • Determination of the flow-wetted surface in fractured media
  • 2003
  • In: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 61:04-jan, s. 361-369
  • Journal article (peer-reviewed)abstract
    • Diffusion and sorption in the rock matrix are important retardation mechanisms for radionuclide transport in fractured media. For the conditions existing in a deep repository in crystalline rock, interaction with the rock matrix is controlled by the water flowrate in the fractures and the surface area in contact with the flowing water (the so-called flow-wetted surface (FWS)). The flow-wetted surface may be determined from the frequency of open fractures intersecting a borehole. The choice of packer distance used in these hydraulic measurements is crucial, however, since several open fractures may be found in one packer interval. The use of a packer distance that is too large may result in a considerable underestimation of the flow-wetted surface. This is especially important in zones with a high frequency of open fractures (fracture zones) where a small packer distance is a fundamental requirement. A large volume of hydraulic data has been compiled in Sweden from measurements using quite small packer distances. Over the last decade, the most common packer distance used for the hydraulic tests has been 3 m, although some new measurements using a shorter packer distance have also been performed. In several cases, the resolution of these measurements has been less than 0.5 m. All these data have been analysed in detail. From these data, the flow-wetted surface has been calculated and compared with the flow-wetted surface estimated in earlier studies. The results show the importance of using a small packer distance for carrying out borehole transmissivity measurements.
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4.
  • Jansson, Mats, et al. (author)
  • In situ anion diffusion experiments using radiotracers
  • 2004
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 68:3-4, s. 183-192
  • Journal article (peer-reviewed)abstract
    • Diffusion experiments in compacted bentonite have been carried out in situ using the borehole laboratory CHEMLAB. The ordinary anion iodide and the redox-sensitive pertechnetate ion have been investigated. In spite of strongly reducing groundwater conditions, technetium was found to diffuse mostly unreduced as TcO4-, although in some spots in the compacted clay, the activity was significantly higher, which may be explained by reduction of some TcO4- by iron-containing minerals in the bentonite. The measured concentration profiles in the clay cannot be accommodated by assuming one single diffusion process. The experimental data are modeled assuming two diffusion paths, intralamellar diffusion and diffusion in external water. The apparent diffusivity for the intralamellar diffusion was found to be 8.6 x 10(-11) m(2) s(-1) for iodide with a capacity factor of 0.1, while the apparent diffusivity for the diffusion in external water was found to be 5 x 10(-14) m(2) s(-1) with alpha = 2.26. The corresponding values for Tc were found to be D-a = 6 x 10(-11) m(2) s(-1), alpha = 0.1 and D-a = 1 x 10(-13) m(2) s(-1), alpha = 0.46, respectively. The diffusion constants and capacity factors obtained in this study are in accordance with data from laboratory experiments.
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5.
  • Kaluarachchi, J. J., et al. (author)
  • Stochastic analysis of oxygen- and nitrate-based biodegradation of hydrocarbons in aquifers
  • 2000
  • In: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 41:04-mar, s. 335-365
  • Journal article (peer-reviewed)abstract
    • A Lagrangian stochastic framework was used to analyze field-scale aerobic biodegradation in a heterogeneous aquifer, using Monod-kinetics based reactions between the contaminant, oxygen and microbes. Subsurface heterogeneity was represented by closed-form travel time distributions, derived from a spatially correlated random hydraulic conductivity field: with a log-normal distribution. The solution to the coupled and nonlinear, one-dimensional Lagrangian transport equations was obtained using the operator-splitting technique. The presence of nitrate, and considering nitrate as a second electron acceptor, produced significantly different results under intrinsic conditions for different scales of heterogeneity and sorption. In general, nitrate as a second electron acceptor can substantially lower the peak contaminant concentration and increase the maximum remediation under various conditions of heterogeneity and sorption. There exists a critical value for retardation coefficients of both contaminant and microbes that produce complete degradation of mass, and this value depends on the availability of the electron acceptor(s) and is independent of the heterogeneity. Maximum remediation and peak contaminant concentration were sensitive to half-saturation constants, Enhanced remediation using oxygen and nitrate showed that maximum remediation can be increased by approximately 15% when oxygen or nitrate concentration was increased by 50%, but a further increase may be obtained if injection occurred at a more effective location. The proposed stochastic methodology is capable of analyzing field-scale biodegradation using multiple electron acceptors in a simple and computationally attractive manner, producing useful results on design parameters. The key contributions arising from the Lagrangian stochastic framework in field-scale analysis, its limitations and potential approaches for overcoming these limitations are also discussed.
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6.
  • Kienzler, B., et al. (author)
  • Swedish-German actinide migration experiment at ASPO hard rock laboratory
  • 2003
  • In: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 61:04-jan, s. 219-233
  • Journal article (peer-reviewed)abstract
    • Within the scope of a bilateral cooperation between Svensk Karnbranslehantering (SKB) and Forschungszentrum Karlsruhe, Institut fur Nukleare Entsorgung (FZK-INE), an actinide migration experiment is currently being performed at the Aspo Hard Rock Laboratory (HRL) in Sweden. This paper covers laboratory and in situ investigations on actinide migration in single-fractured granite core samples. For the in situ experiment, the CHEMLAB 2 probe developed by SKB was used. The experimental setup as well as the breakthrough of inert tracers and of the actinides Am, Np and Pu are presented. The breakthrough curves of inert tracers were analyzed to determine hydraulic properties of the fractured samples. Postmortem analyses of the solid samples were performed to characterize the flow path and the sorbed actinides. After cutting the cores, the abraded material was analyzed with respect to sorbed actinides. The slices were scanned optically to visualize the flow path. Effective volumes and inner surface areas were measured. In the experiments, only breakthrough of Np(V) was observed. In each experiment, the recovery of Np(V) was less than or equal to40%. Breakthrough of Am(III) and Pu(IV) as well as of Np(IV) was not observed.
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7.
  • Neretnieks, Ivars (author)
  • A stochastic multi-channel model for solute transport - analysis of tracer tests in fractured rock
  • 2002
  • In: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 55:04-mar, s. 175-211
  • Journal article (peer-reviewed)abstract
    • Some of the basic assumptions of the advection-dispersion model (AD-model) are revisited. This model assumes a continuous mixing along the flowpath similar to Fickian diffusion. This implies that there is a constant dispersion length irrespective of observation distance. This is contrary to most field observations. The properties of an alternative model based on the assumption that individual water packages can retain their identity over long distances are investigated. The latter model is called the multi-channel model (MCh-model). Inherent in the latter model is that if the waters in the different pathways are collected and mixed, the dispersion length is proportional to distance, The conditions for when non-mixing between adjacent streams can be assumed are explored. The MCh- and AD-models are found to have very similar residence time distributions (RTD) for Peclet numbers larger than 3. A generalized relation between flowrate and residence time is developed, including the so-called cubic law and constant aperture assumptions. The two models extrapolate very differently when there is strong matrix interaction. The AD-model could severely underestimate the effluent concentration of a tracer pulse and overestimate the residence time. The conditions are explored for when in-filling particles in the fracture will not be equilibrated but will act as if there was seemingly a much larger flow wetted surface (FWS). It is found that for strongly sorbing tracers, relatively small particles can act in this way for systems and conditions that are typical of many tracer tests. The assumption that the tracer residence time found by cautiously injecting a small stream of traced water represents the residence time in the whole fracture is explored. It is found that the traced stream can potentially sample a much larger fraction of the fracture than the ratio between the traced flowrate and the total pumped flowrate, The MCh-model was used to simulate some recent tracer tests in what is assumed to be a single fracture at the Aspo Hard rock laboratory in Sweden. Non-sorbing tracers, HTO and Uranin were used to determine the mean residence time and its variance. Laboratory data on diffusion and sorption properties were used to predict the RTD of the sorbing tracers. At least 30 times larger FWS or 1000 times larger diffusion or sorption coefficients would be needed to explain the observed BTCs. Some possible reasons for such behavior are also explored.
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8.
  • Neretnieks, Ivars, et al. (author)
  • Prediction of some in situ tracer tests with sorbing tracers using independent data
  • 2003
  • In: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 61:04-jan, s. 351-360
  • Journal article (peer-reviewed)abstract
    • Some recent converging tracer tests with sorbing tracers at the Aspo Hard Rock Laboratory in Sweden, the TRUE tests, have been predicted using only laboratory data and hydraulic data from borehole measurements. No model parameters were adjusted to obtain a better fit with the experiments. The independent data were fracture frequency and transmissivity data obtained in the field and laboratory data on sorption and matrix diffusion. Transmissivity measurements in five boreholes in the rock volume containing the region surrounding the injection and collection points show that there is a high frequency of water conducting fractures. Of 162 packed off sections with 0.5 m packer distances, 112 were found to have a transmissivity above the detection limit. The specific flow-wetted surface (FWS) of the rock mass could be estimated from these data. The transmissivities were found to be reasonably well described by a lognormal distribution. Laboratory data on diffusion and sorption properties together with the hydraulic data were used to predict the residence time distribution (RTD) of the sorbing tracers. The results were compared with the experimental breakthrough curves. In these experiments, the water residence time is very small compared to the residence time of the sorbing tracers due to their diffusion and sorption within the rock matrix. We thus could neglect the influence of the water residence time in our predictions. Therefore, no information on water residence times or on dispersion was needed. The dispersion of the sorbing tracers is caused by the different sorbing tracer residence times in different pathways. The sorbing tracer residence time is determined by the ratio of flowrate to the flow-wetted surface in the different pathways and not by the water residence time. Assuming a three-dimensional flow pattern and using the observed fracture frequency and flowrate distribution, breakthrough curves for three strongly sorbing tracers were predicted. Only the laboratory data, the transmissivity measurements and the pumping flowrate were used in the predictions. No information on the water residence time as obtained by the nonsorbing tracers was used. The predictions were surprisingly accurate.
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9.
  • Ohlsson, Y., et al. (author)
  • Rock matrix diffusivity determinations by in-situ electrical conductivity measurements
  • 2001
  • In: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 47:04-feb, s. 117-125
  • Journal article (peer-reviewed)abstract
    • A fast method to determine rock matrix diffusion properties directly in the bedrock would be valuable in the investigation of a possible site for disposal of nuclear waste. An effective diffusivity borehole log would provide important information on the variability of this entity over the area studied. As opposed to traditional matrix diffusion laboratory experiments. electrical conductivity measurements are fast, inexpensive and also easy to carry out in-situ. In this study, electrical resistivity data from borehole logging, as well as from measurements on the actual core, is evaluated with the purpose of extracting matrix diffusivity data. The influence of migration of ions in the electrical double layer, which can be of great importance in low ionic strength pore water. is also considered in evaluating the in-situ data to accurately determine the effective pore diffusivity. The in-situ data compare fairly well to those measured in the rock core.
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10.
  • Wörman, Anders, et al. (author)
  • Kinematic analysis of solute mass flows in rock fractures with spatially random parameters
  • 2003
  • In: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 60:04-mar, s. 163-191
  • Journal article (peer-reviewed)abstract
    • Field data of physical properties in heterogeneous crystalline bedrock, like porosity and fracture aperture, is associated with uncertainty that can have a significant impact on the analysis of solute transport in rock fractures. Solutions to the central temporal moments of the residence time probability density function (PDF) are derived in a closed form for a solute Dirac pulse. The solutions are based on a model that takes into account advection along the fracture plane, diffusion into the rock matrix and sorption kinetics in the rock matrix. The most relevant rock properties including fracture aperture and several matrix properties as well as flow velocity are assumed to be spatially random along transport pathways. The mass transport is first solved in a general form along one-dimensional pathways, but the results can be extended to multi-dimensional flows simply by substituting the expected travel time for inert water parcels. Based on data obtained with rock samples taken at Aspo Hard Rock Laboratory in Sweden, the solutions indicate that the heterogeneity of the rock properties contributes to increasing significantly both the variance and the skewness of the residence time probability density function for a pulse travelling in a fracture. The Aspo data suggests that the bias introduced in the variance of the residence time PDF by neglecting the effect of heterogeneity of the rock properties on the radionuclide migration is very large for fractures thinner than a few tenths of a millimetre.
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11.
  • Xu, S. L., et al. (author)
  • Heterogeneous matrix diffusion in crystalline rock - implications for geosphere retardation of migrating radionuclides
  • 2001
  • In: Journal of Contaminant Hydrology. - 0169-7722 .- 1873-6009. ; 47:04-feb, s. 365-378
  • Journal article (peer-reviewed)abstract
    • As a basis for an analysis of the effect of rock heterogeneity on radionuclide migration in a single fracture, the geostatistics of the main properties governing solute transport in crystalline rock have been determined experimentally for two granitic rock types. The rock samples were collected at the Aspo Hard Rock Laboratory, Sweden and used to deduce the auto-covariance functions for the porosity, effective diffusivity and partition coefficient, k(d). and adsorption kinetics. One-dimensional analytical solutions for the mean values of the temporal moments of the residence time probability density function (PDF) show that the heterogeneity of the rock properties can have a substantial impact on the transport, A case study of the effect of heterogeneity in matrix diffusion for a single fracture could be performed by decomposing the transport problem into a one-dimensional mass transfer problem and a two-dimensional flow problem using a Lagrangian method of description. Monte Carlo simulations of the flow field indicate that the correlation length of the aperture is much longer along the trajectory paths than along an arbitrary direction. Increasing the correlation lengths and variances of the aperture and matrix diffusion increases significantly the variance of the travel time PDF.
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12.
  • André, Magnus, et al. (author)
  • Determination of sorption properties of intact rock samples : New methods based on electromigration
  • 2009
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 103:3-4, s. 71-81
  • Journal article (peer-reviewed)abstract
    • Two new methods for determining sorption coefficients in large rock samples have been developed. The methods use electromigration as a means to speed up the transport process, allowing for fast equilibration between rock sample and tracer solution. An electrical potential gradient acts as a driving force for transport in addition to the concentration gradient and forces the cations through the rock sample towards the cathode. The electrical potential gradient induces both electromigration and electroosmotic flow with a resulting solute transport that is large compared to diffusive fluxes. In one of the methods, the solute is driven through the sample and collected at the cutlet side. In the other, simpler method, the rock sample is equilibrated by circulating the solute through the sample. The equilibration of rock samples, up to 5 cm in length, with an aqueous solution has been accomplished within days to months. Experiments using cesium as a sorbing tracer yield results consistent with considerably more time demanding in-diffusion experiments. These methods give lower distribution coefficients than those obtained using traditional batch experiments with crushed rock. (C) 2008 Elsevier B.V. All rights reserved.
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13.
  • André, Magnus, et al. (author)
  • Specific surface area determinations on intact drillcores and evaluation of extrapolation methods for rock matrix surfaces
  • 2009
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 110:1-2, s. 1-8
  • Journal article (peer-reviewed)abstract
    • Permanent storage of spent nuclear fuel in crystalline bedrock is investigated in several countries. For this storage scenario, the host rock is the third and final barrier for radionuclide migration. Sorption reactions in the crystalline rock matrix have strong retardative effects on the transport of radionuclides. To assess the barrier properties of the host rock it is important to have sorption data representative of the undisturbed host rock conditions. Sorption data is in the majority of reported cases determined using crushed rock. Crushing has been shown to increase a rock samples sorption capacity by creating additional surfaces. There are several problems with such an extrapolation. In studies where this problem is addressed, simple models relating the specific surface area to the particle size are used to extrapolate experimental data to a value representative of the host rock conditions. In this article, we report and compare surface area data of five size fractions of crushed granite and of 100 mm long drillcores as determined by the Brunauer Emmet Teller (BET)-method using N-2-gas. Special sample holders that could hold large specimen were developed for the BET measurements. Surface area data on rock samples as large as the drillcore has not previously been published. An analysis of this data show that the extrapolated value for intact rock obtained from measurements on crushed material was larger than the determined specific surface area of the drillcores, in some cases with more than 1000%. Our results show that the use of data from crushed material and current models to extrapolate specific surface areas for host rock conditions can lead to over estimation interpretations of sorption ability. The shortcomings of the extrapolation model are discussed and possible explanations for the deviation from experimental data are proposed.
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14.
  • Bayer-Raich, Martí, et al. (author)
  • Comment on “Analysis of groundwater contamination using concentration-time series recorded during an integral pumping test: Bias introduced by strong concentration gradients within the plume” by Allelign Zeru and Gerhard Schäfer
  • 2007
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722. ; 90:3-4, s. 240-251
  • Journal article (peer-reviewed)abstract
    • We consider the results of a recent paper in this journal [Zeru, A. and Schäfer, G., 2005. Analysis of groundwater contamination using concentration–time series recorded during an integral pumping test: Bias introduced by strong concentration gradients within the plume. Journal of Contaminant Hydrology 81 (2005) 106–124], which addresses the field-scale characterisation of contaminant plumes in groundwater. There, it is concluded that contaminant concentration gradients can bias Integral Pumping Test (IPT) interpretations considerably, in particular if IPTs are conducted in advective fronts of contaminant plumes. We discuss implications of this setting and also argue that the longitudinal and transverse dispersivities used in the examples of Zeru and Schäfer (2005) of up to 30 m and 3 m, respectively, are generally very high for the here relevant capture zone scale (b20 m). However, regardless of both longitudinal and transverse concentration gradients, we further show through a counter-example that IPT results are unbiased as long as the concentration attenuation along the flow direction is linear over the capture zone extent.
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15.
  • Bendz, David, et al. (author)
  • The dissolution kinetics of major elements in municipal solid waste incineration bottom ash particles
  • 2007
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722. ; 94:3-4, s. 178-194
  • Journal article (peer-reviewed)abstract
    • Leaching and tracer experiments in batches at L/S 20 were performed with 3-month-old MSWI bottom ash separated into eight different particle sizes. The time-dependent leaching of major elements (Ca2+, K+ Na+, Cl- and SO4-2) was monitored for up to 747 It. Physical properties of the particles, the specific surface (BET), pore volume and pore volume distribution over pore sizes (BJH) were determined for all particle classes by N-2 adsorption/desorption experiments. Some common features of physical pore structure for all particles were revealed. The specific surface and the particle pore volume were found to be negatively correlated with particle size, ranging from 3.2 m(2)/g to 25.7 m(2)/g for the surface area and from 0.0086 cm(3)/g to 0.091 cm(3)/g for the pore volume. Not surprisingly, the specific surface area was found to be the major material parameter that governed the leaching behavior for all elements (Ca2+, K+, Na+, Cl- and SO4-2) and particle sizes. The diffusion resistance was determined independently by separate tracer (tritium) experiments. Diffusion gave a significant contribution to the apparent leaching kinetics for all elements during the first 10-40 h (depending on the particle size) of leaching and surface reaction was the overall rate controlling mechanism at late times for all particle sizes. For Ca2+ and SO4-2 , the coupled effect of diffusion resistance and the degree of undersaturation in the intra particle pore volume was found to be a major rate limiting dissolution mechanism for both early and late times. The solubility control in the intra particulate porosity may undermine any attempt to treat bottom ash by washing out the sulfate. Even for high liquid/solid ratios, the solubility in the intra-particular porosity will limit the release rate. (c) 2007 Elsevier B.V. All rights reserved.
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16.
  • Dessirier, Benoît, et al. (author)
  • A global sensitivity analysis of two-phase flow between fractured crystalline rock and bentonite with application to spent nuclear fuel disposal
  • 2015
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 182, s. 25-35
  • Journal article (peer-reviewed)abstract
    • Geological disposal of spent nuclear fuel in deep crystalline rock is investigated as a possible long term solution in Sweden and Finland. The fuel rods would be cased in copper canisters and deposited in vertical holes in the floor of deep underground tunnels, embedded within an engineered bentonite buffer. Recent experiments at the Äspö Hard Rock Laboratory (Sweden) showed that the high suction of unsaturated bentonite causes a de-saturation of the adjacent rock at the time of installation, which was also independently predicted in model experiments. Remaining air can affect the flow patterns and alter bio-geochemical conditions, influencing for instance the transport of radionuclides in the case of canister failure. However, thus far, observations and model realizations are limited in number and do not capture the conceivable range and combination of parameter values and boundary conditions that are relevant for the thousands of deposition holes envisioned in an operational final repository.In order to decrease this knowledge gap, we introduce here a formalized, systematic and fully integrated approach to study the combined impact of multiple factors on air saturation and dissolution predictions, investigating the impact of variability in parameter values, geometry and boundary conditions on bentonite buffer saturation times and on occurrences of rock de-saturation. Results showed that four parameters consistently appear in the top six influential factors for all considered output (target) variables: the position of the fracture intersecting the deposition hole, the background rock permeability, the suction representing the relative humidity in the open tunnel and the far field pressure value. The combined influence of these compared to the other parameters increases as one targets a larger fraction of the buffer reaching near-saturation. Strong interaction effects were found, which means that some parameter combinations yielded results (e.g., time to saturation) far outside the range of results obtained by the rest of the scenarios. This study also addresses potential air trapping by dissolution of part of the initial air content of the bentonite, showing that neglecting gas flow effects and trapping could lead to significant underestimation of the remaining air content and the duration of the initial aerobic phase of the repository.
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18.
  • Eveborn, David, et al. (author)
  • Wastewater treatment by soil infiltration : Long-term phosphorus removal
  • 2012
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 140, s. 24-33
  • Journal article (peer-reviewed)abstract
    • Phosphorus (P) leaching from on-site wastewater treatment systems may contribute to eutrophication. In developed countries the most common on-site treatment technique is septic systems with soil infiltration. However, the current knowledge about long term P removal in soil treatment systems is not well developed and the data used for estimation of P losses from such systems are unreliable. In this study we sampled four filter beds from community-scale soil treatment systems with an age of between 14 and 22 years to determine the long-term P removal and to investigate the chemical mechanisms behind the observed removal. For one site the long-term P removal was calculated using a mass balance approach. After analysis of the accumulated P. it was estimated that on average 12% of the long-term P load had been removed by the bed material. This indicates a low overall capacity of soil treatment systems to remove phosphorus. Batch experiments and chemical speciation modelling indicated that calcium phosphate precipitation was not an important long-term P removal mechanism, with the possible exception of one of the sites. More likely, the P removal was induced by AlPO4 precipitation and/or sorption to poorly ordered aluminium compounds, as evidenced by strong relationships between oxalate-extractable Al and P.
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19.
  • Fagerlund, Fritjof, et al. (author)
  • A partially coupled, fraction-by-fraction modelling approach to the subsurface migration of gasoline spills
  • 2007
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 89:3-4, s. 174-198
  • Journal article (peer-reviewed)abstract
    • The subsurface spreading behaviour of gasoline, as well as several other common soil- and groundwater pollutants (e.g. diesel, creosote), is complicated by the fact that it is a mixture of hundreds of different constituents, behaving differently with respect to e.g. dissolution, volatilisation, adsorption and biodegradation. Especially for scenarios where the non-aqueous phase liquid (NAPL) phase is highly mobile, such as for sudden spills in connection with accidents, it is necessary to simultaneously analyse the migration of the NAPL and its individual components in order to assess risks and environmental impacts.Although a few fully coupled, multi-phase, multi-constituent models exist, such models are highly complex and may be time consuming to use. A new, somewhat simplified methodology for modelling the subsurface migration of gasoline while taking its multi-constituent nature into account is therefore introduced here. Constituents with similar properties are grouped together into eight fractions. The migration of each fraction in the aqueous and gaseous phases as well as adsorption is modelled separately using a single-constituent multi-phase flow model, while the movement of the free-phase gasoline is essentially the same for all fractions. The modelling is done stepwise to allow updating of the free-phase gasoline composition at certain time intervals. The output is the concentration of the eight different fractions in the aqueous, gaseous, free gasoline and solid phases with time.The approach is evaluated by comparing it to a fully coupled multi-phase, multi-constituent numerical simulator in the modelling of a typical accident-type spill scenario, based on a tanker accident in northern Sweden. Here the PCFF method produces results similar to those of the more sophisticated, fully coupled model. The benefit of the method is that it is easy to use and can be applied to any single-constituent multi-phase numerical simulator, which in turn may have different strengths in incorporating various processes. The results demonstrate that the different fractions have significantly different migration behaviours and although the methodology involves some simplifications, it is a considerable improvement compared to modelling the gasoline constituents completely individually or as one single mixture.
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20.
  • Fagerlund, Fritjof, et al. (author)
  • PCE dissolution and simultaneous dechlorination by nanoscale zero-valent iron particles in a DNAPL source zone
  • 2012
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 131:1-4, s. 9-28
  • Journal article (peer-reviewed)abstract
    • While the capability of nanoscale zero-valent iron (NZVI) to dechlorinate organic compounds in aqueous solutions has been demonstrated, the ability of NZVI to remove dense non-aqueous phase liquid (DNAPL) from source zones under flow-through conditions similar to a field scale application has not yet been thoroughly investigated. To gain insight on simultaneous DNAPL dissolution and NZVI-mediated dechlorination reactions after direct placement of NZVI into a DNAPL source zone, a combined experimental and modeling study was performed. First, a DNAPL tetrachloroethene (PCE) source zone with emplaced NZVI was built inside a small custom-made flow cell and the effluent PCE and dechlorination byproducts were monitored over time. Second, a model for rate-limited DNAPL dissolution and NZVI-mediated dechlorination of PCE to its three main reaction byproducts with a possibility for partitioning of these byproducts back into the DNAPL was formulated. The coupled processes occurring in I he flow cell were simulated and analyzed using a detailed three-dimensional numerical model. It was found that subsurface emplacement of NZVI did not markedly accelerate DNAPL dissolution or the DNAPL mass-depletion rate, when NZVI at a particle concentration of 10 g/L was directly emplaced in the DNAPL source zone. To react with NZVI the DNAPL PCE must first dissolve into the groundwater and the rate of dissolution controls the longevity of the DNAPL source. The modeling study further indicated that faster reacting particles would decrease aqueous contaminant concentrations but there is a limit to how much the mass removal rate can be increased by increasing the dechlorination reaction rate. To ensure reduction of aqueous contaminant concentrations, remediation of DNAPL contaminants with NZVI should include emplacement in a capture zone down-gradient of the DNAPL source. 
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21.
  • Grieger, Khara Deanne, et al. (author)
  • Environmental benefits and risks of zero-valent iron nanoparticles (nZVI) for in situ remediation : risk mitigation or trade-off?
  • 2010
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 118:3-4, s. 165-183
  • Journal article (peer-reviewed)abstract
    • The use of nanoscaled zero-valent iron particles (nZVI) to remediate contaminated soil and groundwater has received increasing amounts of attention within the last decade, primarily due to its potential for broader application, higher reactivity, and cost-effectiveness compared to conventional zero-valent iron applications and other in situ methods. However, the potential environmental risks of nZVI in in situ field scale applications are largely unknown at the present and traditional environmental risk assessment approaches are not yet able to be completed. Therefore, it may not yet be fully clear how to consider the environmental benefits and risks of nZVI for in situapplications. This analysis therefore addresses the challenges of comprehensively considering and weighing the expected environmental benefits and potential risks of this emerging environmentally-beneficial nanotechnology, particularly relevant for environmental engineers, scientists, and decision makers. We find that most of the benefits of using nZVI are based on near-term considerations, and large data gaps currently exist within almost all aspects of environmental exposure and effect assessments. We also find that while a wide range of decision support tools and frameworks alternative to risk assessment are currently available, a thorough evaluation of these should be undertaken in the near future to assess their full relevancy for nZVI at specific sites. Due to the absence of data in environmental risk evaluations, we apply a ‘best’ and ‘worst’ case scenario evaluation as a first step to qualitatively evaluate the current state-of-knowledge regarding the potential environmental risks of nZVI. The result of this preliminary qualitative evaluation indicates that at present, there are no significant grounds on which to form the basis that nZVI currently poses a significant, apparent risk to the environment, although the majority of the most serious criteria (i.e. potential for persistency, bioaccumulation, toxicity) are generally unknown. We recommend that in cases where nZVI may be chosen as the ‘best’ treatment option, short and long-term environmental monitoring is actively employed at these sites. We furthermore recommend the continued development of responsible nZVI innovation and better facilitated information exchange between nZVI developers, nano-risk researchers, remediation industry, and decision makers.
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22.
  • Herbert, Roger, 1966- (author)
  • Implications of non-equilibrium transport in heterogeneous reactive barrier systems : evidence from laboratory denitrification experiments
  • 2011
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 123:1-2, s. 30-39
  • Journal article (peer-reviewed)abstract
    • Organic substrates in reactive barrier systems are often heterogeneous material mixtures with relatively large contrasts in hydraulic conductivity and porosity over short distances. These short-range variations in material properties imply that preferential flow paths and diffusion between regions of higher and lower hydraulic conductivity may be important for treatment efficiency. This paper presents the results of a laboratory column experiment where denitrification is investigated using a heterogeneous reactive substrate (sawdust mixed with sewage sludge). Displacement experiments with a non-reactive solute at three different flow rates are used to estimate transport parameters using a dual porosity non-equilibrium model. Parameter estimation from breakthrough curves produced relatively consistent values for the fraction of the porosity consisting of mobile water (β) and the mass transfer coefficient (α), with average values of 0.27 and 0.42 d-1, respectively. The column system removes > 95% of the influent nitrate at low and medium flow, but only 50 – 75% of the influent nitrate at high flow, suggesting that denitrification kinetics and diffusive mass transfer rates are limiting the degree of treatment at lower hydraulic residence times. Reactive barrier systems containing dual porosity media must therefore consider mass transfer times in their design; this is often most easily accommodated by adjusting flowpath length.
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23.
  • Herrmann, Inga, et al. (author)
  • Modeling phosphate transport and removal in a compact bed filled with a mineral-based sorbent for domestic wastewater treatment
  • 2013
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 154, s. 70-77
  • Journal article (peer-reviewed)abstract
    • Phosphorus filter units containing mineral-based sorbents with a high phosphate (PO4) binding capacity have been shown to be appropriate for removing PO4 in the treatment of domestic wastewater in on-site facilities. However, a better understanding of their PO4 removal mechanisms, and reactions that could lead to the formation of PO4 compounds, is required to evaluate the potential utility of candidate sorbents. Models based on data obtained from laboratory-scale experiments with columns of selected materials can be valuable for acquiring such understanding. Thus, in this study the transport and removal of PO4 in experiments with a laboratory-scale column filled with a commercial silicate-based sorbent were modeled, using the hydro-geochemical transport code PHREEQC. The resulting models, that incorporated the dissolution of calcite, kinetic constrains for the dissolution of calcium oxide (CaO) and wollastonite (CaSiO3), and the precipitation of amorphous tricalcium phosphate, Ca3(PO 4)2, successfully simulated the removal of PO4 observed in the experiments.
  •  
24.
  • Holmboe, Michael, et al. (author)
  • Porosity investigation of compacted bentonite using XRD profile modeling
  • 2012
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 128:1-4, s. 19-32
  • Journal article (peer-reviewed)abstract
    • Many countries intend to use compacted bentonite as a barrier in their deep geological repositories for nuclear waste. In order to describe and predict hydraulic conductivity or radionuclide transport through the bentonite barrier, fundamental understanding of the microstructure of compacted bentonite is needed. This study examined the interlayer swelling and overall microstructure of Wyoming Bentonite MX-80 and the corresponding homo-ionic Na+ and Ca2+ forms, using XRD with samples saturated under confined swelling conditions and free swelling conditions. For the samples saturated under confined conditions, the interparticle, or so-called free or external porosity was estimated by comparing the experimental interlayer distances obtained from one-dimensional XRD profile fitting against the maximum interlayer distances possible for the corresponding water content. The results showed that interlayer porosity dominated total porosity, irrespective of water content, and that the interparticle porosity was lower than previously reported in the literature. At compactions relevant for the saturated bentonite barrier (1.4-1.8 g/cm(3)), the interparticle porosity was estimated to <= 3%.
  •  
25.
  • Iraola, Aitor, et al. (author)
  • Microtomography-based Inter-Granular Network for the simulation of radionuclide diffusion and sorption in a granitic rock
  • 2017
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 207, s. 8-16
  • Journal article (peer-reviewed)abstract
    • Field investigation studies, conducted in the context of safety analyses of deep geological repositories for nuclear waste, have pointed out that in fractured crystalline rocks sorbing radionuclides can diffuse surprisingly long distances deep into the intact rock matrix; i.e. much longer distances than those predicted by reactive transport models based on a homogeneous description of the properties of the rock matrix. Here, we focus on cesium diffusion and use detailed micro characterisation data, based on micro computed tomography, along with a grain-scale Inter-Granular Network model, to offer a plausible explanation for the anomalously long cesium penetration profiles observed in these in-situ experiments. The sparse distribution of chemically reactive grains (i.e. grains belonging to sorbing mineral phases) is shown to have a strong control on the diffusive patterns of sorbing radionuclides. The computed penetration profiles of cesium agree well with an analytical model based on two parallel diffusive pathways. This agreement, along with visual inspection of the spatial distribution of cesium concentration, indicates that for sorbing radionuclides the medium indeed behaves as a composite system, with most of the mass being retained close to the injection boundary and a non-negligible part diffusing faster along preferential diffusive pathways.
  •  
26.
  •  
27.
  •  
28.
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29.
  • Larsbo, Mats, et al. (author)
  • The effect of freezing and thawing on water flow and MCPA leaching in partially frozen soil
  • 2018
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 219, s. 72-85
  • Journal article (peer-reviewed)abstract
    • Limited knowledge and experimental data exist on pesticide leaching through partially frozen soil. The objective of this study was to better understand the complex processes of freezing and thawing and the effects these processes have on water flow and pesticide transport through soil. To achieve this we conducted a soil column irrigation experiment to quantify the transport of a non-reactive tracer and the herbicide MCPA in partially frozen soil. In total 40 intact topsoil and subsoil columns from two agricultural fields with contrasting soil types (silt and loam) in South-East Norway were used in this experiment. MCPA and bromide were applied on top of all columns. Half the columns were then frozen at -3 degrees C while the other half of the columns were stored at +4 degrees C. Columns were then subjected to repeated irrigation events at a rate of 5 mm artificial rainwater for 5 h at each event. Each irrigation was followed by 14-day periods of freezing or refrigeration. Percolate was collected and analysed for MCPA and bromide. The results show that nearly 100% more MCPA leached from frozen than unfrozen topsoil columns of Hov silt and Kroer loam soils. Leaching patterns of bromide and MCPA were very similar in frozen columns with high concentrations and clear peaks early in the irrigation process, and with lower concentrations leaching at later stages. Hardly any MCPA leached from unfrozen topsoil columns (0.4-0.5% of applied amount) and concentrations were very low. Bromide showed a different flow pattern indicating a more uniform advective-dispersive transport process in the unfrozen columns with higher concentrations leaching but without clear concentration peaks. This study documents that pesticides can be preferentially transported through soil macropores at relatively high concentrations in partially frozen soil. These findings indicate, that monitoring programs should include sampling during snow melt or early spring in areas were soil frost is common as this period could imply exposure peaks in groundwater or surface water.
  •  
30.
  • Lewis, Jeffrey, et al. (author)
  • The effect of subsurface military detonations on vadose zone hydraulic conductivity, contaminant transport and aquifer recharge
  • 2013
  • In: Journal of Contaminant Hydrology. - : Elsevier. - 0169-7722 .- 1873-6009. ; 146, s. 8-15
  • Journal article (peer-reviewed)abstract
    • Live fire military training involves the detonation of explosive warheads on training ranges. The purpose of this experiment is to evaluate the hydrogeological changes to the vadose zone caused by military training with high explosive ammunition. In particular, this study investigates artillery ammunition which penetrates underground prior to exploding, either by design or by defective fuze mechanisms. A 105 mm artillery round was detonated 2.6 m underground, and hydraulic conductivity measurements were taken before and after the explosion. A total of 114 hydraulic conductivity measurements were obtained within a radius of 3m from the detonation point, at four different depths and at three different time periods separated by 18months. This data was used to produce a three dimensional numerical model of the soil affected by the exploding artillery round. This model was then used to investigate potential changes to aquifer recharge and contaminant transport caused by the detonating round. The results indicate that an exploding artillery round can strongly affect the hydraulic conductivity in the vadose zone, increasing it locally by over an order of magnitude. These variations, however, appear to cause relatively small changes to both local groundwater recharge and contaminant transport.
  •  
31.
  • Li, Xiaodong, et al. (author)
  • A modification of the electromigration device and modelling methods for diffusion and sorption studies of radionuclides in intact crystalline rocks.
  • 2020
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 231, s. 103585-
  • Journal article (peer-reviewed)abstract
    • To determine the diffusion and sorption propertiesof radionuclides in intact crystalline rocks, a newelectromigration devicewas built and tested by running with I-and Se(IV) ions. By introducing a potentiostatto impose a constant voltageover the studied rock sample, the electromigration device cangive more stable and accurateexperimental resultsthan those from the traditional electromigration devices.In addition, the variation in the pHofthe background electrolytes wasminimised by adding a small amount of NaHCO3as buffers.To interpret the experimental results with moreconfidence, anadvection-dispersion model was also developed in thisstudy, which accounts for the most important mechanisms governing ionic transport in the electromigration experiments.Data analysis of the breakthrough curves by the advection-dispersion model, instead of the traditional ideal plug-flowmodel,suggest that the effective diffusivitiesof I-and Se(IV)are (1.15±0.06) ×10-13m2/s and (3.50±0.86) ×10-14m2/s, respectively. The results also show thatI-is more mobile than Se(IV) ions when migrating through the sameintact rock sampleand that theirsorption properties are almost identical.
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32.
  • Löfgren, Martin, et al. (author)
  • Through-electromigration : A new method of investigating pore connectivity and obtaining formation factors
  • 2006
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 87:3-4, s. 237-252
  • Journal article (peer-reviewed)abstract
    • The retardation of radionuclides and other contaminants in fractured crystalline rock is strongly associated with the diffusive properties of the rock matrix. At present, the scientific community is divided concerning the question of long-range pore connectivity in intrusive igneous rock. This paper presents a fast new method, called the through-electromigration method, of obtaining formation factors and investigating pore connectivity. The method involves the migration of an ionic tracer through a rock sample with an electrical potential gradient as the main driving force. The method is analogous to the through-diffusion method but the experimental time is reduced by orders of magnitude. This enables investigations of pore connectivity, as measurements can be made on longer samples. In a preliminary investigation, the new method is compared to the traditional through-diffusion method as well as to rock resistivity methods. The diffusive properties of nine granitic rock samples from Laxemar in Sweden, ranging from 15 to 121 turn in length, have been investigated and the results are compared.
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33.
  • Mahmoudzadeh, Batoul, et al. (author)
  • Solute transport in a single fracture involving an arbitrary length decay chain with rock matrix comprising different geological layers
  • 2014
  • In: Journal of Contaminant Hydrology. - : Elsevier. - 0169-7722 .- 1873-6009. ; 164, s. 59-71
  • Journal article (peer-reviewed)abstract
    • A model is developed to describe solute transport and retention in fractured rocks. It accounts for advection along the fracture, molecular diffusion from the fracture to the rock matrix composed of several geological layers, adsorption on the fracture surface, adsorption in the rock matrix layers and radioactive decay-chains. The analytical solution, obtained for the Laplace-transformed concentration at the outlet of the flowing channel, can conveniently be transformed back to the time domain by the use of the de Hoog algorithm. This allows one to readily include it into a fracture network model or a channel network model to predict nuclide transport through channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant properties. More importantly, the simulations made in this study recommend that it is necessary to account for decay-chains and also rock matrix comprising at least two different geological layers, if justified, in safety and performance assessment of the repositories for spent nuclear fuel.
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34.
  • Meng, Shuo, et al. (author)
  • Development and application of an advection-dispersion model for data analysis of electromigration experiments with intact rock cores
  • 2020
  • In: Journal of Contaminant Hydrology. - : ELSEVIER. - 0169-7722 .- 1873-6009. ; 231
  • Journal article (peer-reviewed)abstract
    • An advection-dispersion model was developed for interpreting the experimental results of electromigration in granitic rock cores. The most important mechanisms governing the movement of the tracer ions, i.e. electromigration, electroosmosis and dispersion were taken into account by the advection-dispersion model, but the influence of aqueous chemistry was ignored. An analytical solution in the Laplace domain was derived and then applied to analyze the measured results of a series of experiments, performed in an updated experimental device using different applied voltages. The modelling results suggested that both studied tracers, i.e. iodide and selenite, are effectively non-sorbing in the intact rock investigated. The effective diffusivities and formation factors evaluated from the model were also found to be in good agreement with data reported in literature and the associated uncertainties are much smaller than those obtained from the classical ideal plug-flow model, which accounts only for the dominant effect of electromigration on ionic transport. To explore further how the quality of parameter identifications would be influenced by neglect of aqueous chemistry, a reactive transport model was also implemented, which may be regarded as a multi-component version of the advection-dispersion model. The analysis showed that the advection-dispersion model works equally well as the reactive transport model but requires much less computational demand. It can, therefore, be used with great confidence to interpret the experimental results of electromigration for studies of diffusion and sorption behavior of radionuclides in intact rock cores.
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35.
  • Moreno, Luis, et al. (author)
  • Modelling radionuclide transport for time varying flow in a channel network
  • 2006
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 86:3-4, s. 215-238
  • Journal article (peer-reviewed)abstract
    • Water flowrates and flow directions may change over time in the subsurface for a number of reasons. In fractured rocks flow takes place in channels within fractures. Solutes are carried by the advective flow. In addition, solutes may diffuse in and out of stagnant waters in the rock matrix and other stagnant water regions. Sorbing species may sorb on fracture surfaces and on the micropore surfaces in the rock matrix. We present a method by which solute particles can be traced in flowing water undergoing changes in flowrate and direction in a complex channel network where the solutes can also interact with the rock by diffusion in the rock matrix. The novelty of this paper is handling of diffusion in the rock matrix under transient flow conditions. The diffusive processes are stochastic and it is not possible to follow a particle deterministically. The method therefore utilises the properties of a probability distribution function for a tracer moving in a fracture where matrix diffusion is active. The method is incorporated in a three dimensional channel network model. Particle tracking is used to trace out a multitude of flowpaths, each of which consists of a large number of channels within fractures. Along each channel the aperture and velocity as well as the matrix sorption properties can vary. An efficient method is presented whereby a particle can be followed along the variable property flowpath. For stationary flow conditions and a network of channels with advective flow and matrix diffusion, a simple analytical solution for the residence time distribution along each pathway can be used. Only two parameter groups need to be integrated along each path. For transient flow conditions, a time stepping procedure that incorporates a stochastic Monte-Carlo like method to follow the particles along the paths when flow conditions change is used. The method is fast and an example is used for illustrative purposes. It is exemplified by a case where land rises due to glacial rebound. It is shown that the effects of changing flowrates and directions can be considerable and that the diffusive migration in the matrix can have a dominating effect on the results.
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36.
  • Mukherjee, Abhijit, et al. (author)
  • Distribution of geogenic arsenic in hydrologic systems : Controls and challenges
  • 2008
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 99:1-4, s. 1-7
  • Journal article (peer-reviewed)abstract
    • The presence of elevated concentration of arsenic (As) in natural hydrologic systems is regarded as the most formidable environmental crisis in the contemporary world. With its substantial presence in the drinking water of more than thirty countries worldwide, and with an affected population of more than 100 million, it has been termed as the largest mass poisoning in human history. In this special issue, we have tried to provide the most recent research advances on controls and challenges of this severe groundwater contaminant. The articles in this issue, originally presented in the 2006 Geological Society of America Annual Meeting, address the distribution of As in various geologic and geographic settings, the controls of redox and other geochemical parameters on its spatial and temporal variability, the influence of sedimentology and stratigraphy on its occurrence, and mechanisms controlling its mobility. The knowledge available from these studies should provide a roadmap for future research in arsenic contamination hydrology.
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37.
  • Mukherjee, Abhijit, et al. (author)
  • Hydrogeochemical comparison and effects of overlapping redox zones on groundwater arsenic near the Western (Bhagirathi sub-basin, India) and Eastern (Meghna sub-basin, Bangladesh) margins of the Bengal Basin
  • 2008
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 99:1-4, s. 31-48
  • Journal article (peer-reviewed)abstract
    • Although arsenic (As) contamination of groundwater in the Bengal Basin has received wide attention over the past decade, comparative studies of hydrogeochemistry in geologically different sub-basins within the basin have been lacking. Groundwater samples were collected from sub-basins in the western margin (River Bhagirathi sub-basin, Nadia, India; 90 samples) and eastern margin (River Meghna sub-basin; Brahmanbaria, Bangladesh; 35 samples) of the Bengal Basin. Groundwater in the western site (Nadia) has mostly Ca-HCO3 water while that in the eastern site (Brahmanbaria) is much more variable consisting of at least six different facies. The two sites show differences in major and minor solute trends indicating varying pathways of hydrogeochemical evolution However, both sites have similar reducing, postoxic environments, (p(e): +5 to -2) with high concentrations of dissolved organic carbon, indicating dominantly metal-reducing processes and similarity in As mobilization mechanism. The trends of SO42- various redox-sensitive solutes (e.g. As, CH4, Fe, Mn, NO3-, NH4+, SO42-) indicate overlapping redox zones, leading to partial redox equilibrium conditions where As, once liberated from source minerals, would tend to remain in solution because of the complex interplay among the electron acceptors.
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38.
  • Neretnieks, Ivars (author)
  • Fast method for simulation of radionuclide chain migration in dual porosity fracture rocks
  • 2006
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 88:04-mar, s. 269-288
  • Journal article (peer-reviewed)abstract
    • In fractured rocks with a porous rock matrix such as granites, radionuclides will flow with the water in the fracture network. The nuclides will diffuse in and out the rock matrix where they can sorb and be considerably retarded compared to the water velocity. A water parcel entering the network will mix and split at the fracture intersections and parts of the original parcel will traverse a multitude of different fractures. The flowrates, velocities, sizes and apertures of the fractures can vary widely. Normally one must solve the transport equations for every fracture and use the effluent concentration as inlet condition to the next fracture and so on. It is shown that under some weakly simplified conditions it suffices to determine one single parameter group containing information on the flow wetted surface that a water parcel contacts along the entire path. It is also shown how this can be obtained. Then, solving the transport equations only once for time and location along the path gives the concentration and nuclide flux of every nuclide in the chain everywhere along a path. The same solution actually is valid for every path in the network. This dramatically reduces the computation effort. The same approach can be used for models based on streamtubes.
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39.
  • Neretnieks, Ivars (author)
  • Saline groundwaters counteract up-flow of contaminants- implications for radionuclide repositories?
  • 2024
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 262
  • Journal article (peer-reviewed)abstract
    • The high-level nuclear waste, HLW, from Swedish and Finnish reactors will be deposited in crystalline rock at depths around 500 m. The waste is enclosed in steel canisters protected against corrosion by a 5 cm thick copper shell, which ensures a lifetime far longer than 100 000 years. Should some canister be breached any leaking nuclides will have decayed to so low activity that even if they reached the biosphere, they would cause minimal risk to humans. The cost of the copper is significant. The dismantling of the nuclear reactors, with induced activity must also be disposed of and this waste volume is much larger than that of the HLW, which makes it impossible to protect it in the same way. This paper explores if by locating the waste at larger depth where the ground water is more saline, and where the hydraulic conductivity of the rock is lower up-flow of contaminated water can be ensured to be negligible because the denser water at larger depth counteracts up-flow due to negative buoyancy. Several processes that could cause local up-flow are addressed, such as infiltration of meteoric water, impact of surface topology, heat production of the waste, geothermal gradient, salinity gradient, hydraulic conductivity heterogeneities and salt migration between seeping water and salt in matrix pore water. Flow and transport simulations using data from extensive field investigations over more than ten years with scores of km deep boreholes suggest that a HLW repository at around one km depth may be sufficient to hinder up-flow to the biosphere.
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40.
  • Parker, Beth L., et al. (author)
  • Determining effective diffusion coefficients of chlorohydrocarbons in natural clays: Unique results from highly resolved controlled release field experiments
  • 2022
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 250
  • Journal article (peer-reviewed)abstract
    • This study aims to precisely determine the effective diffusion coefficients of chlorohydrocarbons in low permeable units under in-situ field conditions. To this end, two controlled release field experiments using TCE and PCE as dense non-aqueous phase liquids (DNAPLs) were conducted in two natural clayey deposits. Several months to years after the controlled DNAPL release, highly resolved concentration profiles were determined for the chlorohydrocarbons that had diffused into the clayey deposits. Effective diffusion coefficients for TCE and PCE were then determined by calibrating a 3D numerical and 1D analytical model, respectively, to the measured high-resolution concentration profiles. The simulations revealed that the effective diffusion coefficients vary by as much as a factor of four within the same low permeability unit being consistent with observed small-scale heterogeneities. The determined chlorohydrocarbon effective diffusion coefficients were further used to determine the equivalent thickness of DNAPL that would completely dissolve in an idealized, parallel-plate fracture by diffusion transport into clayey deposits for the time periods of the controlled release field experiments. The equivalent TCE and PCE DNAPL film thicknesses ranged between 36 and 581 μm, respectively, comparable and exceeding fracture apertures measured in naturally fractured clay rich deposits. Hence, films of DNAPL initially contained within fractures in clay-rich deposits can completely dissolve away within a few months to a few years due to diffusion. This stored contaminant mass poses a risk to adjacent aquifers if it is re-released due to diffusion out of the matrix after source depletion or remediation.
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41.
  • Phenrat, Tanapon, et al. (author)
  • Empirical correlations to estimate agglomerate size and deposition during injection of a polyelectrolyte-modified Fe0 nanoparticle at high particle concentration in saturated sand
  • 2010
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 118:3-4, s. 152-164
  • Journal article (peer-reviewed)abstract
    • Controlled emplacement of polyelectrolyte-modified nanoscale zerovalent iron (NZVI) particles at high particle concentration (1-10 g/L) is needed for effective in situ subsurface remediation using NZVI. Deep bed filtration theory cannot be used to estimate the transport and deposition of concentrated polyelectrolyte-modified NZVI dispersions (> 0.03 g/L) because particles agglomerate during transport which violates a fundamental assumption of the theory. Here we develop two empirical correlations for estimating the deposition and transport of concentrated polyelectrolyte-modified NZVI dispersions in saturated porous media when NZVI agglomeration in porous media is assumed to reach steady state quickly. The first correlation determines the apparent stable agglomerate size formed during NZVI transport in porous media for a fixed hydrogeochemical condition. The second correlation estimates the attachment efficiency (sticking coefficient) of the stable agglomerates. Both correlations are described using dimensionless numbers derived from parameters affecting deposition and agglomeration in porous media. The exponents for the dimensionless numbers are determined from statistical analysis of breakthrough data for polyelectrolyte-modified NZVI dispersions collected in laboratory scale column experiments for a range of ionic strength (1, 10, and 50 mM Na + and 0.25, 1, and 1.25 mM Ca2+), approach velocity (0.8 to 55 × 10-4 m/s), average collector sizes (d50 = 99 μm, 300 μm, and 880 μm), and polyelectrolyte surface modifier properties. Attachment efficiency depended on approach velocity and was inversely related to collector size, which is contrary to that predicted from classic filtration models. High ionic strength, the presence of divalent cations, lower extended adsorbed polyelectrolyte layer thickness, decreased approach velocity, and a larger collector size promoted NZVI agglomeration and deposition and thus limited its mobility in porous media. These effects are captured quantitatively in the two correlations developed. The application and limitations of using the correlations for preliminary design of in situ NZVI emplacement strategies is discussed.
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42.
  • Puranen, Anders, 1977-, et al. (author)
  • A study on the immobilization of selenium oxyanions by H2/Pd(s) in aqueous solution : Confirmation of the one-electron reduction barrier of selenate
  • 2010
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 116:1-4, s. 16-23
  • Journal article (peer-reviewed)abstract
    • Selenium is a trace element of concern in several geochemical contexts, due to the potentially high mobility of the selenium oxyanions and the narrow range between deficiency and toxicity of the element. For high level nuclear waste repositories the long-lived fission product 79Se has been identified as a potential key dose contributor for the long-term safety. This paper deals with the catalytic effect of Pd(s) on the H2 reduction of selenium oxyanions which was studied experimentally in aqueous solutions containing bicarbonate and chloride. Pd-catalysts and hydrogen have been proposed for the remediation of various groundwater contaminants and can also serve as a model substance for catalytic noble metal inclusions present in spent nuclear fuel. In this study selenite (SeO32−) was found to adsorb on Pd. In the presence of hydrogen the rate of selenite removal increased yielding elemental Se. However, no adsorption or reduction of selenate (SeO42−) was observed. A simple radiation chemical experiment revealed a notable barrier towards stepwise one-electron reduction of selenate to selenite. This provides an explanation for the lower reactivity of selenate in systems where reductive immobilization of selenite as well as selenate is thermodynamically favorable.
  •  
43.
  • Salifu, Musah, et al. (author)
  • A simple model for evaluating isotopic (18O, 2H and 87Sr/86Sr) mixing calculations of mine : Impacted surface waters
  • 2020
  • In: Journal of Contaminant Hydrology. - : Elsevier. - 0169-7722 .- 1873-6009. ; 232
  • Journal article (peer-reviewed)abstract
    • This study was aimed at identifying and quantifying mixing proportions in surface waters downstream of historical Cu-W-F skarn mine tailings at Yxsjöberg, Sweden, using 18O, 2H, and 87Sr/86Sr isotopes. In addition, a simple mathematical model was developed to evaluate the consistency of the mixing calculations. Hydrochemical and isotopic data from 2 groundwater wells, 6 surface water and 2 rainwater sampling sites, spanning 6 sampling campaigns between May and October were used. Three mixed surface waters downstream of the tailings were identified, namely: C7, C11 and C14. C7 was directly influenced by groundwater from the tailings whereas C11 was also subsequently influenced by C7. C14 on the other hand, had contributions from C11. Sequential mixing calculations indicated that the contribution of the groundwater to C7 ranges from 1 to 17%. The subsequent contribution of C7 to C11 varied from 49 to 91% whereas C14 had contributions of C11 ranging between 16 and 56%. A strong agreement between the model data (MD) and measured raw data (RD) for C11 and C14 indicated the accuracy of the mixing calculations. Variations between the MD and RD at C7, however, was mainly due to sorption and reductive processes underneath the tailings, which tend to attenuate the amount of dissolved ions reaching the surface waters, resulting in a low ionic contribution of the tailings groundwater to the surface water. The low ionic contribution of the groundwater to C7 suggested that although the tailings impoundment is of environmental concern, its impact on the downstream surface waters is small. The results of this study suggest that mixing calculations in surface waters involving a closed system such as groundwater (as an end-member) must be treated with caution. It is recommended that the interpretation of such mixing results must be coupled with detailed knowledge of the potential hydrogeochemical processes along its flow paths.
  •  
44.
  • Salifu, Musah, et al. (author)
  • A simple model for evaluating isotopic (O-18, H-2 and Sr-87/Sr-86) mixing calculations of mine - Impacted surface waters
  • 2020
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 232
  • Journal article (peer-reviewed)abstract
    • This study was aimed at identifying and quantifying mixing proportions in surface waters downstream of historical Cu-W-F skarn mine tailings at Yxsjoberg, Sweden, using O-18, H-2, and Sr-87/Sr-86 isotopes. In addition, a simple mathematical model was developed to evaluate the consistency of the mixing calculations. Hydrochemical and isotopic data from 2 groundwater wells, 6 surface water and 2 rainwater sampling sites, spanning 6 sampling campaigns between May and October were used. Three mixed surface waters downstream of the tailings were identified, namely: C7, C11 and C14. C7 was directly influenced by groundwater from the tailings whereas C11 was also subsequently influenced by C7. C14 on the other hand, had contributions from C11. Sequential mixing calculations indicated that the contribution of the groundwater to C7 ranges from 1 to 17%. The subsequent contribution of C7 to C11 varied from 49 to 91% whereas C14 had contributions of C11 ranging between 16 and 56%. A strong agreement between the model data (MD) and measured raw data (RD) for C11 and C14 indicated the accuracy of the mixing calculations. Variations between the MD and RD at C7, however, was mainly due to sorption and reductive processes underneath the tailings, which tend to attenuate the amount of dissolved ions reaching the surface waters, resulting in a low ionic contribution of the tailings groundwater to the surface water. The low ionic contribution of the groundwater to C7 suggested that although the tailings impoundment is of environmental concern, its impact on the downstream surface waters is small. The results of this study suggest that mixing calculations in surface waters involving a closed system such as groundwater (as an end-member) must be treated with caution. It is recommended that the interpretation of such mixing results must be coupled with detailed knowledge of the potential hydrogeochemical processes along its flow paths.
  •  
45.
  • Sharma, Prabhakar, 1976-, et al. (author)
  • Gas phase dispersion in compost as a function of differentwater contents and air flow rates
  • 2009
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 107:3-4, s. 101-107
  • Journal article (peer-reviewed)abstract
    • Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as afunction of gas flow velocity and compost volumetric water content using oxygen and nitrogenas tracer gases. The compost was chosen because it has a very wide water content range andbecause it represents a wide range of porousmedia, including soils and biofilter media. Columnbreakthrough curves for oxygen and nitrogen were measured at relatively low pore gasvelocities, corresponding to those observed in for instance soil vapor extraction systems orbiofilters for air cleaning at biogas plants or composting facilities. Total gas mechanicaldispersion–molecular diffusion coefficients were fitted from the breakthrough curves using aone-dimensional numerical solution to the advection–dispersion equation and used todetermine gas dispersivities at different volumetric gas contents. The results showed that gasmechanical dispersion dominated over molecular diffusion with mechanical dispersion for allwater contents and pore gas velocities investigated. Importance of mechanical dispersionincreased with increasing pore gas velocity and compost water content. The results furthershowed that gas dispersivity was relatively constant at high values of compost gas-filledporosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity.Results finally showed that measurement uncertainty in gas dispersivity is generally highest atlow values of pore gas velocity.
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46.
  • Sidborn, Magnus, et al. (author)
  • Long-term oxygen depletion from infiltrating groundwaters : model development and application to intra-glaciation and glaciation conditions
  • 2008
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 100:1-2, s. 72-89
  • Journal article (peer-reviewed)abstract
    • Processes that control the redox conditions in deep groundwaters have been studied. The understanding of such processes in a long-term perspective is important for the safety assessment of a deep geological repository for high-level nuclear waste. An oxidising environment at the depth of the repository would increase the solubility and mobility of many radionuclides, and increase the potential risk for radioactive contamination at the ground surface. Proposed repository concepts also include engineered barriers such as copper canisters, the corrosion of which increases considerably in an oxidising environment compared to prevailing reducing conditions. Swedish granitic rocks are typically relatively sparsely fractured and are best treated as a dual-porosity medium with fast flowing channels through fractures in the rock with a surrounding porous matrix, the pores of which are accessible from the fracture by diffusive transport. Highly simplified problems have been explored with the aim to gain understanding of the underlying transport processes, thermodynamics and chemical reaction kinetics. The degree of complexity is increased successively, and mechanisms and processes identified as of key importance are included in a model framework. For highly complex models, analytical expressions are riot fully capable of describing the processes involved, and in such cases the solutions are obtained by numerical calculations. Deep in the rock the main source for reducing capacity is identified as reducing minerals. Such minerals are found inside the porous rock matrix and as infill particles or coatings in fractures in the rock. The model formulation also allows for different flow modes such as flow along discrete fractures in sparsely fractured rocks and along flowpaths in a fracture network. The scavenging of oxygen is exemplified for these cases as well as for more comprehensive applications, including glaciation considerations. Results show that chemical reaction kinetics control the scavenging of oxygen during a relatively short time with respect to the lifetime of the repository. For longer times the scavenging of oxygen is controlled by transport processes in the porous rock matrix. The penetration depth of oxygen along the flowpath depends largely on the hydraulic properties, which may vary significantly between different locations and situations. The results indicate that oxygen, in the absence of easily degradable organic matter, may reach long distances along a flow path during the life-time of the repository (hundreds to thousands of metres in a million years depending on e.g. hydraulic properties of the flow path and the availability of reducing capacity). However, large uncertainties regarding key input parameters exist leading to the conclusion that the results from the model must be treated with caution pending more accurate and validated data. Ongoing and planned experiments are expected to reduce these uncertainties, which are required in order to make more reliable predictions for a safety assessment of a nuclear waste repository.
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47.
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48.
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49.
  • von Brömssen, Mattias, et al. (author)
  • Geochemical characterisation of shallow aquifer sediments of Matlab Upazila, Southeastern Bangladesh - Implications for targeting low-As aquifers
  • 2008
  • In: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 99:1-4, s. 137-149
  • Journal article (peer-reviewed)abstract
    • High arsenic (As) concentrations in groundwater pose a serious threat to the health of millions of people in Bangladesh. Reductive dissolution of Fe(Ill)-oxyhydroxides and release of its adsorbed As is considered to be the principal mechanism responsible for mobilisation ofAs. The distribution ofAs is extremely heterogeneous both laterally and vertically. Groundwater abstracted from oxidised reddish sediments, in contrast to greyish reducing sediments, contains significantly lower amount of dissolved arsenic and can be a source of safe water. In order to study the sustainability of that mitigation option, this study describes the lithofacies and genesis of the sediments within 60 m depth and establishes a relationship between aqueous and solid phase geochemistry. Oxalate extractable Fe and Mn contents are higher in the reduced unit than in the oxidised unit, where Fe and Mn are present in more crystalline mineral phases. Equilibrium modelling of saturation indices suggest that the concentrations of dissolved Fe, Mn and PO43--tot in groundwater is influenced by 4 secondary mineral phases in addition to redox processes. Simulating As-[I] adsorption on hydroferric oxides using the Diffuse Layer Model and analytical data gave realistic concentrations of dissolved and adsorbed As-[I] for the reducing aquifer and we speculate that the presence of high PO43--tot in combination with reductive dissolution results in the high-As groundwater. The study confirms high mobility of As in reducing aquifers with typically dark colour of sediments found in previous studies and thus validates the approach for location of wells used by local drillers based on sediment colour. A more systematic and standardised colour description and similar studies at more locations are necessary for wider application of the approach.
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50.
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