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Allen M. Shapiro - One of the best experts on this subject based on the ideXlab platform.
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The complex spatial distribution of trichloroethene and the probability of NAPL occurrence in the Rock Matrix of a mudstone aquifer.
Journal of contaminant hydrology, 2019Co-Authors: Allen M. Shapiro, Thomas E. Imbrigiotta, Daniel J. Goode, Michelle M. Lorah, Claire R. TiedemanAbstract:Abstract Methanol extractions for chloroethene analyses are conducted on Rock samples from seven closely spaced coreholes in a mudstone aquifer that was subject to releases of the nonaqueous phase liquid (NAPL) form of trichloroethene (TCE) between the 1950's and 1990's. Although TCE concentration in the Rock Matrix over the length of coreholes is dictated by proximity to subhorizontal bedding plane fractures, elevated TCE concentrations in the Rock Matrix are not continuous along the most permeable bedding plane fractures. A complex configuration of subvertical and subhorizontal fractures appears to be responsible for the TCE distribution from prior TCE releases at land surface. Phase partitioning calculations of TCE in the Rock Matrix show that most TCE is adsorbed to solid surfaces because of the large fraction of organic carbon (foc) in the mudstone. Large TCE content in some cores indicate the likely presence of the NAPL form of TCE in the Rock Matrix. Using average values of porosity (n) and foc in phase partitioning calculations identifies a number of locations of possible NAPL occurrence in the Rock Matrix. Samples of mudstone analyzed for n and foc show variability in these properties over several orders of magnitude. Accounting for this variability in phase partitioning calculations identifies a probability of NAPL occurrence, PNAPL. The spatial variability of PNAPL along coreholes identifies a configuration that may be attributed to a TCE source zone that has evolved after emplacement due to NAPL dissolution, adsorption, and Matrix diffusion.
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Variability of organic carbon content and the retention and release of trichloroethene in the Rock Matrix of a mudstone aquifer.
Journal of contaminant hydrology, 2018Co-Authors: Allen M. Shapiro, Rebecca J. BrenneisAbstract:Abstract Contaminants diffusing from fractures into the immobile porosity of the Rock Matrix are subject to prolonged residence times. Organic contaminants can adsorb onto organic carbonaceous materials in the Matrix extending contaminant retention. An investigation of spatial variability of the fraction of organic carbon (foc) is conducted on samples of Rock core from seven closely spaced boreholes in a mudstone aquifer contaminated with trichloroethene (TCE). A total of 378 samples were analyzed at depths between 14 and 36 m below land surface. Mudstone units associated with deep water deposition have the largest foc, with a maximum value of 0.0396, and units associated with shallow water deposition have the smallest foc. Even though foc correlates with depositional conditions, foc still varies over more than an order of magnitude in continuous mudstone layers between boreholes, and there is large variability in foc over short distances perpendicular to bedding. Simulations of diffusion and linear equilibrium adsorption of TCE using spatially variable foc in the Rock Matrix show order of magnitude variability in the adsorbed TCE over short distances in the Matrix and residence times extending to hundreds of years following remediation in adjacent fractures. Simulations using average values of foc do not capture the range of TCE mass that can be retained in a Rock Matrix characterized by spatially variable foc. Bounds on TCE mass within the Rock Matrix can be obtained by simulations with spatially uniform values of foc equal to the maximum and minimum values of foc for a given mudstone unit.
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Bioremediation in Fractured Rock: 2. Mobilization of Chloroethene Compounds from the Rock Matrix
Ground water, 2017Co-Authors: Allen M. Shapiro, Claire R. Tiedeman, Thomas E. Imbrigiotta, Daniel J. Goode, Paul A. Hsieh, Pierre J. Lacombe, Mary F. Deflaun, Scott R. Drew, Gary P. CurtisAbstract:A mass balance is formulated to evaluate the mobilization of chlorinated ethene compounds (CE) from the Rock Matrix of a fractured mudstone aquifer under pre- and postbioremediation conditions. The analysis relies on a sparse number of monitoring locations and is constrained by a detailed description of the groundwater flow regime. Groundwater flow modeling developed under the site characterization identified groundwater fluxes to formulate the CE mass balance in the Rock volume exposed to the injected remediation amendments. Differences in the CE fluxes into and out of the Rock volume identify the total CE mobilized from diffusion, desorption, and nonaqueous phase liquid dissolution under pre- and postinjection conditions. The initial CE mass in the Rock Matrix prior to remediation is estimated using analyses of CE in Rock core. The CE mass mobilized per year under preinjection conditions is small relative to the total CE mass in the Rock, indicating that current pump-and-treat and natural attenuation conditions are likely to require hundreds of years to achieve groundwater concentrations that meet regulatory guidelines. The postinjection CE mobilization rate increased by approximately an order of magnitude over the 5 years of monitoring after the amendment injection. This rate is likely to decrease and additional remediation applications over several decades would still be needed to reduce CE mass in the Rock Matrix to levels where groundwater concentrations in fractures achieve regulatory standards.
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In situ estimation of the effective chemical diffusion coefficient of a Rock Matrix in a fractured aquifer
Hydrogeology Journal, 2008Co-Authors: Robel A. Gebrekristos, Allen M. Shapiro, B. H. UsherAbstract:Se ha desarrollado un método in situ para estimar el coeficiente de difusión efectivo para un constituyente químico que sufre difusión en la porosidad primaria de una roca mediante un cambio abrupto en la concentración del constituyente disuelto en un sondeo en contacto con la matriz de la roca y monitorizando la variación de la concentración en el tiempo. El experimento se desarrolló en un sondeo completo en arcillas en el campus de la Universidad de Free State en Bloemfontein, Sudáfrica. Se han llevado a cabo numerosos ensayos de trazadores en este punto, que ha dejado una concentración residual de cloruro sódico en sondeos que han sufrido difusión en la matriz de la roca durante un periodo de años. El agua dulce se introdujo en el sondeo en contacto con las arcillas, y se observó el incremento variable en el tiempo del cloruro mediante la monitorización de la Conductividad Eléctrica (EC) a varias profundidades en el sondeo. La estimación del coeficiente de difusión efectiva se obtuvo interpretando las medidas de EC durante 34 días. El coeficiente de difusión efectiva a una profundidad de 36 m fue aproximadamente de 7.8×10^−6 m^2/d, pero fue sensible a la porosidad de la matriz asumida. El factor de formación y el flujo de masa para las arcillas también se estimaron a partir del experimento. Une méthode in situ d’estimation du coefficient effectif de diffusion pour un composé chimique qui diffuse dans la porosité primaire d’une roche est développée, en modifiant brusquement la concentration du composé dissous dans un forage en contact avec la matrice rocheuse et en suivant l’évolution de sa concentration dans le temps. L’expérimentation a été réalisée dans un forage équipé dans des argilites sur le campus de l’Université de l’Etat Libre de Bloemfontein (Afrique du Sud). Plusieurs essais de traçage ont été réalisés sur ce site, laissant des concentrations résiduelles en hypochlorite de sodium dans les ouvrages, qui ont diffusé dans la matrice rocheuse au fil des années. De l’eau douce a été injectée dans un forage en contact avec les argilites, et l’augmentation temporelle de la concentration en chlorures a été observée par des mesures étagées de conductivité. L’estimation du coefficient effectif de diffusion est issue de l’interprétation des mesures de conductivité sur une période de 34 jours. Le coefficient effectif de diffusion à 36 m de profondeur est estimé autour de 7.8×10^−6 m^2/j, mais il apparaît sensible à la porosité évaluée. Le facteur de formation et le flux de masse issu des argilites ont également été estimés à partir de ce test. An in situ method of estimating the effective diffusion coefficient for a chemical constituent that diffuses into the primary porosity of a Rock is developed by abruptly changing the concentration of the dissolved constituent in a borehole in contact with the Rock Matrix and monitoring the time-varying concentration. The experiment was conducted in a borehole completed in mudstone on the campus of the University of the Free State in Bloemfontein, South Africa. Numerous tracer tests were conducted at this site, which left a residual concentration of sodium chloride in boreholes that diffused into the Rock Matrix over a period of years. Fresh water was introduced into a borehole in contact with the mudstone, and the time-varying increase of chloride was observed by monitoring the electrical conductivity (EC) at various depths in the borehole. Estimates of the effective diffusion coefficient were obtained by interpreting measurements of EC over 34 d. The effective diffusion coefficient at a depth of 36 m was approximately 7.8×10^−6 m^2/d, but was sensitive to the assumed Matrix porosity. The formation factor and mass flux for the mudstone were also estimated from the experiment.
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In situ estimation of the effective chemical diffusion coefficient of a Rock Matrix in a fractured aquifer
Hydrogeology Journal, 2008Co-Authors: Robel A. Gebrekristos, Allen M. Shapiro, B. H. UsherAbstract:An in situ method of estimating the effective diffusion coefficient for a chemical constituent that diffuses into the primary porosity of a Rock is developed by abruptly changing the concentration of the dissolved constituent in a borehole in contact with the Rock Matrix and monitoring the time-varying concentration. The experiment was conducted in a borehole completed in mudstone on the campus of the University of the Free State in Bloemfontein, South Africa. Numerous tracer tests were conducted at this site, which left a residual concentration of sodium chloride in boreholes that diffused into the Rock Matrix over a period of years. Fresh water was introduced into a borehole in contact with the mudstone, and the time-varying increase of chloride was observed by monitoring the electrical conductivity (EC) at various depths in the borehole. Estimates of the effective diffusion coefficient were obtained by interpreting measurements of EC over 34 d. The effective diffusion coefficient at a depth of 36 m was approximately 7.8×10−6 m2/d, but was sensitive to the assumed Matrix porosity. The formation factor and mass flux for the mudstone were also estimated from the experiment.
Hongbin Zhan - One of the best experts on this subject based on the ideXlab platform.
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reactive solute transport in an asymmetrical fracture Rock Matrix system
Advances in Water Resources, 2018Co-Authors: Renjie Zhou, Hongbin ZhanAbstract:Abstract The understanding of reactive solute transport in a single fracture–Rock Matrix system is the foundation of studying transport behavior in the complex fractured porous media. When transport properties are asymmetrically distributed in the adjacent Rock Matrixes, reactive solute transport has to be considered as a coupled three-domain problem, which is more complex than the symmetric case with identical transport properties in the adjacent Rock Matrixes. This study deals with the transport problem in a single fracture–Rock Matrix system with asymmetrical distribution of transport properties in the Rock Matrixes. Mathematical models are developed for such a problem under the first-type and the third-type boundary conditions to analyze the spatio–temporal concentration and mass distribution in the fracture and Rock Matrix with the help of Laplace transform technique and de Hoog numerical inverse Laplace algorithm. The newly acquired solutions are then tested extensively against previous analytical and numerical solutions and are proven to be robust and accurate. Furthermore, a water flushing phase is imposed on the left boundary of system after a certain time. The diffusive mass exchange along the fracture/Rock Matrixes interfaces and the relative masses stored in each of three domains (fracture, upper Rock Matrix, and lower Rock Matrix) after the water flushing provide great insights of transport with asymmetric distribution of transport properties. This study has the following findings: 1) Asymmetric distribution of transport properties imposes greater controls on solute transport in the Rock Matrixes. However, transport in the fracture is mildly influenced. 2) The mass stored in the fracture responses quickly to water flushing, while the mass stored in the Rock Matrix is much less sensitive to the water flushing. 3) The diffusive mass exchange during the water flushing phase has similar patterns under symmetric and asymmetric cases. 4) The characteristic distance which refers to the zero diffusion between the fracture and the Rock Matrix during the water flushing phase is closely associated with dispersive process in the fracture.
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Reactive solute transport in an asymmetrical fracture–Rock Matrix system
Advances in Water Resources, 2018Co-Authors: Renjie Zhou, Hongbin ZhanAbstract:Abstract The understanding of reactive solute transport in a single fracture–Rock Matrix system is the foundation of studying transport behavior in the complex fractured porous media. When transport properties are asymmetrically distributed in the adjacent Rock Matrixes, reactive solute transport has to be considered as a coupled three-domain problem, which is more complex than the symmetric case with identical transport properties in the adjacent Rock Matrixes. This study deals with the transport problem in a single fracture–Rock Matrix system with asymmetrical distribution of transport properties in the Rock Matrixes. Mathematical models are developed for such a problem under the first-type and the third-type boundary conditions to analyze the spatio–temporal concentration and mass distribution in the fracture and Rock Matrix with the help of Laplace transform technique and de Hoog numerical inverse Laplace algorithm. The newly acquired solutions are then tested extensively against previous analytical and numerical solutions and are proven to be robust and accurate. Furthermore, a water flushing phase is imposed on the left boundary of system after a certain time. The diffusive mass exchange along the fracture/Rock Matrixes interfaces and the relative masses stored in each of three domains (fracture, upper Rock Matrix, and lower Rock Matrix) after the water flushing provide great insights of transport with asymmetric distribution of transport properties. This study has the following findings: 1) Asymmetric distribution of transport properties imposes greater controls on solute transport in the Rock Matrixes. However, transport in the fracture is mildly influenced. 2) The mass stored in the fracture responses quickly to water flushing, while the mass stored in the Rock Matrix is much less sensitive to the water flushing. 3) The diffusive mass exchange during the water flushing phase has similar patterns under symmetric and asymmetric cases. 4) The characteristic distance which refers to the zero diffusion between the fracture and the Rock Matrix during the water flushing phase is closely associated with dispersive process in the fracture.
Govindarajan Suresh Kumar - One of the best experts on this subject based on the ideXlab platform.
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Influence of Fracture Heterogeneity Using Linear Congruential Generator (LCG) on the Thermal Front Propagation in a Single Geothermal Fracture-Rock Matrix System
Energies, 2018Co-Authors: Nikhil Bagalkot, Alireza Zare, Govindarajan Suresh KumarAbstract:An implicit finite difference numerical model has been developed to investigate the influence of fracture heterogeneity on the propagation of thermal front in a single horizontal fracture-Matrix system. Instead of depending on a complex and data-demanding geostatistical method for a precise representation of fracture aperture, a statistical linear congruential generator (LCG) method was applied in the present study to replicate the unpredictable nature of fracture aperture morphology. The results have been compared with the parallel plate model and simple sinusoidal model. Finally, sensitivity analysis of fracture aperture size and fluid flow rate has been carried out to identify the conditions at which fracture heterogeneity is critical. The results indicate that LCG-aperture enhances the heat transfer between fracture and hot Rock Matrix compared to the parallel and sinusoidal fractures. Further, the temperature profiles in hot Rock indicate that there was a greater loss of heat for the case of LCG-aperture (25% loss) compared to sinusoidal (16%) and parallel plate (8%) apertures. It was found that heterogeneity does not play a major role at small fracture aperture size (≤50 μm) and at low flow rates. However, as fracture aperture size increases, the heterogeneity plays a vital part even at low flow rates.
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Numerical modeling on the sensitivity of directional dependent interface heat transfer on thermal transport in a coupled fracture-Matrix system
Geosciences Journal, 2016Co-Authors: Rakesh Thekke Veettil, Govindarajan Suresh KumarAbstract:The conventional dual-porosity model has been modified by considering the heat exchange term at the fracture-Matrix interface in the governing equation for thermal transport within the low permeable Rock-Matrix as against its conventional consideration within the high permeable fracture. A finite volume numerical model has been developed in order to analyze the influence of the source/sink term which defines the heat transfer at the fractureMatrix interface. The comparison of the spatial distribution for temperature within the fracture and within the reservoir Matrix for two different models, (1) conventional model in which the source/sink heat transfer term included in the equation for thermal transport within the fracture; (2) proposed model in which the source/sink heat transfer term included in the equation for thermal transport within the Rock-Matrix, have been performed. In addition, the sensitivity of the reservoir Matrix thermal conductivities, both horizontal and vertical, on thermal energy extraction from the reservoir Matrix has also been analyzed using the proposed model. Numerical results suggest that the estimation of temperature distribution in the fracture and Rock-Matrix and thus quantifying the heat extraction from the reservoir Matrix is underestimated in a fracture-Matrix system by using the conventional thermal transport model. It has been also observed that the temperature distribution obtained in the fracture and the Rock-Matrix by considering the heat transfer term in the thermal transport equation within the fracture shows significant variation from the temperature distribution obtained by considering the heat transfer term in the equation for thermal transport within the Rock-Matrix.
Jalal Abedi - One of the best experts on this subject based on the ideXlab platform.
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application of tracer injection tests to characterize Rock Matrix block size distribution and dispersivity in fractured aquifers
Journal of Hydrology, 2014Co-Authors: Amin Sharifi Haddad, Hassan Hassanzadeh, Jalal Abedi, Zhangxin ChenAbstract:The complexity of mass transfer processes between the mobile and immobile zones in geohydrologic settings and the limitations that currently exist in the characterization of contaminated sites demand the development of improved models. In this work, we present a model that describes the mass transfer in structured porous media. This model considers divergent radial advective–dispersive transport in fractures and diffusive mass transfer inside Rock Matrix blocks. The heterogeneous nature of fractured formations is included with the integration of various distributions of Rock Matrix block sizes into the transport model. Breakthrough curves generated based on the developed model are analyzed to investigate the effects of the rate of injection, dispersivity and the immobile to mobile porosity ratio on mass transfer between mobile and immobile zones. It is shown that the developed model, in conjunction with tracer data collected from a monitoring well, can be used to estimate the dispersivity and fracture intensity. Results reveal that the dispersivity is independent of the Rock Matrix block size distribution for dispersion-dominant transport in fractures. These findings are used to develop a methodology to characterize Rock Matrix block size distribution in fractured aquifers and to estimate dispersivity based on a tracer test, which will improve our decisions concerning the remediation of contaminated sites.
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advective diffusive mass transfer in fractured porous media with variable Rock Matrix block size
Journal of Contaminant Hydrology, 2012Co-Authors: Amin Sharifi Haddad, Hassan Hassanzadeh, Jalal AbediAbstract:Abstract Traditional dual porosity models do not take into account the effect of Matrix block size distribution on the mass transfer between Matrix and fracture. In this study, we introduce the Matrix block size distributions into an advective–diffusive solute transport model of a divergent radial system to evaluate the mass transfer shape factor, which is considered as a first-order exchange coefficient between the fracture and Matrix. The results obtained lead to a better understanding of the advective–diffusive mass transport in fractured porous media by identifying two early and late time periods of mass transfer. Results show that fractured Rock Matrix block size distribution has a great impact on mass transfer during early time period. In addition, two dimensionless shape factors are obtained for the late time, which depend on the injection flow rate and the distance of the Rock Matrix from the injection point.
Zhangxin Chen - One of the best experts on this subject based on the ideXlab platform.
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application of tracer injection tests to characterize Rock Matrix block size distribution and dispersivity in fractured aquifers
Journal of Hydrology, 2014Co-Authors: Amin Sharifi Haddad, Hassan Hassanzadeh, Jalal Abedi, Zhangxin ChenAbstract:The complexity of mass transfer processes between the mobile and immobile zones in geohydrologic settings and the limitations that currently exist in the characterization of contaminated sites demand the development of improved models. In this work, we present a model that describes the mass transfer in structured porous media. This model considers divergent radial advective–dispersive transport in fractures and diffusive mass transfer inside Rock Matrix blocks. The heterogeneous nature of fractured formations is included with the integration of various distributions of Rock Matrix block sizes into the transport model. Breakthrough curves generated based on the developed model are analyzed to investigate the effects of the rate of injection, dispersivity and the immobile to mobile porosity ratio on mass transfer between mobile and immobile zones. It is shown that the developed model, in conjunction with tracer data collected from a monitoring well, can be used to estimate the dispersivity and fracture intensity. Results reveal that the dispersivity is independent of the Rock Matrix block size distribution for dispersion-dominant transport in fractures. These findings are used to develop a methodology to characterize Rock Matrix block size distribution in fractured aquifers and to estimate dispersivity based on a tracer test, which will improve our decisions concerning the remediation of contaminated sites.
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Semianalytical solutions for release of fluids from Rock Matrix blocks with different shapes, sizes, and depletion regimes
Water Resources Research, 2013Co-Authors: Ehsan Ranjbar, Hassan Hassanzadeh, Zhangxin ChenAbstract:[1] Dual-porosity (DP) models have been extensively used to simulate the flow of fluids (water or gas) in aggregate soils and fractured porous media. The fluid exchange between the Rock Matrix blocks and the fracture network is very important in DP models. In this study, we present semianalytical solutions for release of a single-phase liquid or gas from cylindrical and spherical Matrix blocks with various block size distributions and different pressure depletion regimes in the fracture. The nonlinear pressure diffusivity equations for flow of gas and air are solved analytically using an approximate integral method. It is shown that this solution can be simplified to model flow of slightly compressible fluids like water in DP media. The effect of variable block size distribution on the release rate for different block geometries is studied. Practically it is not feasible to model a large-scale fractured reservoir based on a fine grid approach due to the requirement of large computational time. The presented semianalytical model can be incorporated into numerical models for accurate modeling of the amount of transferred fluid between Matrix and fractures using a DP approach. It is shown that the results calculated by the developed model match well with those from fine grid numerical simulations. Furthermore, the developed model can recover the available solutions in the literature for slightly compressible fluids such as water or oil. It can be used to calculate two- or three-dimensional flows in Matrix blocks bounded by two or three sets of fractures, respectively.
