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  • 1
    Monograph available for loan
    Monograph available for loan
    Introduction to geostatistics : applications to hydrogeology (1997)
    Cambridge [u.a.] : Cambridge Univ. Press
    Details Availability
    Call number: AWI S2-98-0211
    Description / Table of Contents: Engineers and applied geophsicists routinely encounter interpolation and estimation problems when analyzing data from field observations. Introduction to Geostatistics presents practical techniques for the estimation of spatial functions from sparse data. The author's unique approach is a synthesis of classic and geostatistical methods, with a focus on the most practical linear minimum-variance estimation methods, and includes suggestions on how to test and extend the applicability of such methods. The author includes many useful methods often not covered in other geostatistics books, such as estimating variogram parameters, evaluating the need for a variable mean, parameter estimation and model testing in complex cases (e.g., anisotropy, variable mean, and multiple variables), and using information from deterministic mathematical models. Well illustrated with exercises and worked examples taken from hydrogeology, Introduction to Geostatistics assumes no background in statistics and is suitable for graduate-level courses in earth sciences, hydrology, and environmental engineering and also for self-study.
    Type of Medium: Monograph available for loan
    Pages: XX, 249 S.
    ISBN: 0521587476
    Branch Library: AWI Library
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  • 2
    Electronic Resource
    Electronic Resource
    A Method to Infer In Situ Reaction Rates from Push-Pull Experiments (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 36 (1998), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A method to evaluate first-order and zero-order in situ reaction rates from a push-pull test is presented. A single-well push-pull test starts with the rapid injection of a well-mixed slug containing a known quantity of a conservative tracer and a reactive solute into the saturated zone. The slug is then periodically extracted and sampled from the same well. For zero- or first-order reactions, in the absence of sorption and assuming negligible background concentrations, these measurements can be used to evaluate reaction rate coefficients directly. The method does not involve computer-based solute transport models and requires no knowledge of regional ground water flow or hydraulic parameters. The method performs well when the dominate processes are advection, dispersion, and zero- or first-order irreversible reactions. Regional flow velocities must be sufficiently low such that the slug stays within the area of the well during the sampling phase. In the case of zero-order reactions, results using the method proposed here are compared with those obtained through the traditional method of calibrating a computer-based transport model. The two methods give similar estimates of the reaction rate coefficient. The method is general enough to work with a broad range of push-pull experiment designs and sampling techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1998.tb02839.x
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  • 3
    Electronic Resource
    Electronic Resource
    Modeling the Free Surface of an Unconfined Aquifer Near a Recirculation Well (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 31 (1993), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: We examine flow in an unconfined aquifer near a recirculation well, which consists of a source and a sink of equal discharge, with emphasis on understanding the behavior of the free surface. The well is vertical with a pump located between an inlet above and an outlet below to induce recirculation of ground water and thus enhance mixing. The boundary element method is used to model the flow with the free-surface boundary condition. Numerical simulations show that for this arrangement there is a critical pumping rate beyond which the free surface becomes unstable and is drawn down to the well. The value of this critical rate as well as the maximum drawdown of the phreatic surface were determined for a range of well-screen (inlet and outlet) separations. In addition to the numerical model, we developed an analytical approximation that yielded an estimate of the critical pumping rate. The analytical estimate is shown to be in reasonably good agreement with the numerical results. We also examined the effect of approximating the free-surface boundary by a horizontal confining layer. The radius of influence of a single well source-sink pair was only slightly affected by making this approximation, as long as the pumping rate remained below the critical value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1993.tb00850.x
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  • 4
    Electronic Resource
    Electronic Resource
    How Observations and Structure Affect the Geostatistical Solution to the Steady-State Inverse Problem (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 36 (1998), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The solution to the steady-state inverse problem can be expanded into a series of spline functions with weights adjusted to reproduce the observations within the observation error. The splines depend on the model spatial structure, the ground water flow model, and the location of the observations. This representation of the solution, which is a rigorous and exact expansion, provides insight into the form of the best estimate and explicitly shows how observations and the conceptual model may affect the solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1998.tb02192.x
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  • 5
    Electronic Resource
    Electronic Resource
    Mass-Transfer Limitations for Macroscale Bioremediation Modeling and Implications on Aquifer Clogging (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 37 (1999), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: In engineered in situ bioremediation, substrates are injected into the subsurface to stimulate microbial metabolism and growth. Models are useful in the design and optimization of such systems, such as in devising strategies to prevent clogging of soil by large bacterial populations around wells. Such models are macroscale, i.e., they do not resolve pore-scale variability; rather, substrate and biomass concentrations are bulk averages that vary from block to block. These models give unrealistic predictions, in that they predict monotonically increasing biomass growth everywhere except where the limiting substrate concentration is very small. This work examines the possibility of biofilm mass-transfer limitations at the pore scale using both the traditional biofilm model as well as previously published results from an upscaling model. Results from the biofilm model suggest that limitations on biofilm growth due to mass-transfer resistance could be significant in coarse-grained soils with adequate substrate availability. The upscaling approach confirms this result. While these two approaches do not yield identical results, both do agree that coarser grain sizes tend to cause greater mass transfer resistance. These are the conditions most likely to occur near injection well screens of an enhanced bioremediation system, where clogging is most commonly observed. The upscaling approach also indicates that the degree of mass transfer resistance is reduced at higher ground water velocities, which are also most commonly observed near well screens. These results could be useful for improving macroscale bioremediation models to more accurately predict rates of biomass growth and aquifer clogging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1999.tb01138.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of Shear Detachment on Biomass Growth and In Situ Bioremediation (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 37 (1999), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The dispersed growth model incorporating Monod kinetics has often been applied to simulate enhanced in situ bioremediation of contaminants. The dispersed growth model might not adequately address the impacts of the growth of large bacterial populations that can often have the unwanted effect of clogging the porous media. Two mechanisms that could affect model predictions of biomass are biofouling and biomass detachment due to shear stress. A mathematical model was developed to evaluate the potential impact of shear detachment on biomass distribution and the prediction of contaminant biodegradation by comparing the impact of both shear detachment and biofouling together with that of biofouling alone. The results of this examination can aid in designing a system for in situ bioremediation using computer simulations and in evaluating a system's ability to meet remediation goals. The model simulations indicate that shear detachment of biomass can be an important process to include in model simulations used to predict the effectiveness of a bioremediation system and the time before significant clogging occurs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1999.tb01142.x
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  • 7
    Electronic Resource
    Electronic Resource
    Analytical expressions of conditional mean, covariance, and sample functions in geostatistics (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 279-294 
    Details
    ISSN: 1436-3259
    Keywords: Linear estimation ; interpolation ; kriging ; splines ; conditional
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This work presents analytical expressions for the best estimate, conditional covariance function, and conditional realizations of a function from sparse observations. In contrast to the prevalent approach in kriging where the best estimates at every point are determined from the solution of a system of linear equations, the best-estimate function can be represented analytically in terms of basis functions, whose number depends on the observations. This approach is computationally superior when graphing a function estimate and is also valuable in understanding what the solution should look like. For example, one can immediately see that all “singularities” in the best-estimate function are at observation points.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581870
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of macrodispersion through volume averaging: comparison with stochastic theory (1999)
    Springer
    Stochastic environmental research and risk assessment 13 (1999), S. 66-84 
    Details
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Velocity variability at scales smaller than the size of a solute plume enhances the rate of spreading of the plume around its center of mass. Macroscopically, the rate of spreading can be quantified through macrodispersion coefficients, the determination of which has been the subject of stochastic theories. This work compares the results of a volume-averaging approach with those of the advection dominated large-time small-perturbation theory of Dagan [1982] and Gelhar and Axness [1983]. Consider transport of an ideal tracer in a porous medium with deterministic periodic velocity. Using the Taylor-Aris-Brenner method of moments, it has been previously demonstrated [Kitanidis, 1992] that when the plume spreads over an area much larger than the period, the volume-averaged concentration satisfies the advection-dispersion equation with constant coefficients that can be computed. Here, the volume-averaging analysis is extended to the case of stationary random velocities. Additionally, a perturbation method is applied to obtain explicit solutions for small-fluctuation cases, and the results are compared with those of the stochastic macrodispersion theory. It is shown that the method of moments, which uses spatial averaging, for sufficiently large volumes of averaging yields the same result as the stochastic theory, which is based on ensemble averaging. The result is of theoretical but also practical significance because the volume-averaging approach provides a potentially efficient way to compute macrodispersion coefficients. The method is applied to a simplified representation of the Borden aquifer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004770050032
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  • 9
    Electronic Resource
    Electronic Resource
    Advection-diffusion in spatially random flows: Formulation of concentration covariance (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 397-422 
    Details
    ISSN: 1436-3259
    Keywords: Random flow field ; diffusion ; concentration ; fluctuations ; covariance ; variance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The concentration c(x,t) of a nonreactive solute undergoing advection and diffusion in a spatially random divergence-free flow field is analyzed. A leading order formulation for the spatial covariance of the concentration field, $$\overline {c'\left( {x,t} \right)c'\left( {x,t} \right)} $$ , is made. That formulation includes the velocity variability induced macrodispersive flux of the covariance field, and the smoothing effects of diffusion. Previous formulations of the concentration covariance had dropped at least one of these effects. It is shown that both these effects need to be included to obtain a qualitatively correct description of the concentration fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427926
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  • 10
    Electronic Resource
    Electronic Resource
    Generalized Taylor-Aris moment analysis of the transport of sorbing solutes through porous media with spatially-periodic retardation factor (1992)
    Springer
    Transport in porous media 7 (1992), S. 163-185 
    Details
    ISSN: 1573-1634
    Keywords: Moment analysis ; sorbing solute transport ; spatially-periodic retardation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Taylor-Aris dispersion theory, as generalized by Brenner, is employed to investigate the macroscopic behavior of sorbing solute transport in a three-dimensional, hydraulically homogeneous porous medium under steady, unidirectional flow. The porous medium is considered to possess spatially periodic geochemical characteristics in all three directions, where the spatial periods define a rectangular parallelepiped or a unit-element. The spatially-variable geochemical parameters of the solid matrix are incorporated into the transport equation by a spatially-periodic distribution coefficient and consequently a spatially-periodic retardation factor. Expressions for the effective or large-time coefficients governing the macroscopic solute transport are derived for solute sorbing according to a linear equilibrium isotherm as well as for the case of a first-order kinetic sorption relationship. The results indicate that for the case of a chemical equilibrium sorption isotherm the longitudinal macrodispersion incorporates a second term that accounts for the eflect of averaging the distribution coefficient over the volume of a unit element. Furthermore, for the case of a kinetic sorption relation, the longitudinal macrodispersion expression includes a third term that accounts for the effect of the first-order sorption rate. Therefore, increased solute spreading is expected if the local chemical equilibrium assumption is not valid. The derived expressions of the apparent parameters governing the macroscopic solute transport under local equilibrium conditions agreed reasonably with the results of numerical computations using particle tracking techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647395
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