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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
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Impact of Biomass-Decay Terms on the Simulation of Pulsed Bioremediation (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A numerical model is used for simulating the stimulation of biomass growth by injection of alternating pulses of a primary substrate and oxygen. We consider that the substrate sorbs, whereas oxygen does not undergo mass transfer, and mixing of the reacting compounds is dominated by the chromatographic effect. Different mathematical formulations for biomass growth and decay are compared. In models considering biomass decay, a minimal time of joint exposure to both reactants can be determined. This leads to a multimodal distribution of the biomass after multiple injection cycles. In multidimensional heterogeneous domains, the location of the biomass peaks is determined by the advective arrival time. The biomass is much more homogeneously distributed when biomass decay is neglected, because under this condition there is no constraint by a minimal joint exposure time. For the case of oxygen-dependent biomass decay, an injection scheme using shorter pulses of higher oxygen concentrations is shown to be superior to a scheme with equally long pulses of oxygen and the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb00337.x
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    PARAMETRIC ESTIMATION OF COVARIANCES OF REGIONALIZED VARIABLES (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 23 (1987), S. 0 
    Details
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : The usefulness of stochastic models in describing the spatial variability of hydrogeologic quantities, such as permeability, storativity, piezometric head, seepage velocity, and solute concentrations is now widely recognized. In practice, these quantities are represented as the sum of a well-structured component, or drift, and a more erratic fluctuation component which is described statistically through its covariance function. This paper reviews some of the most recent and most promising methods for the estimation of parameters of these covariances from existing data. They are maximum likelihood, restricted maximum likelihood, minimum-variance unbiased quadratic estimation, and minimum-norm (weighted least squares) estimation. The applicability of such methods to conditional and unconditional probability problems is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1752-1688.1987.tb00832.x
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  • 7
    Electronic Resource
    Electronic Resource
    Travel-Time Based Model of Bioremediation Using Circulation Wells (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Vertical circulation wells can efficiently provide microorganisms with substrates needed for enhanced bioremediation. We present a travel-time based approach for modeling bioreactive transport in a flow field caused by a series of circulation wells. Mixing within the aquifer is due to the differences in sorption behavior of the reactants. Neglecting local dispersion, transport simplifies to a single one-dimensional problem with constant coefficients for each well. Recirculation is characterized by the discharge densities over travel time. We apply the model to the stimulation of cometabolic dechlorination of trichloroethene (TCE) by alternate injection of oxygen and toluene into the circulation wells. Mixing within the wells can be minimized by interposing sufficiently long breaks between the oxygen and toluene pulses. In our simulation, the proposed injection scheme stimulates biomass growth without risking biofouling of the aquifer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2001.tb02326.x
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Geostatistical Estimation of Hydraulic Head Gradients (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 27 (1989), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper describes a technique for estimating gradients of hydraulic head from scattered measurements of head. Gradients of hydraulic head control the flow of ground water in aquifers and their determination is an important part of any ground-water investigation. A best linear unbiased estimator of hydraulic head is derived which allows direct estimation of head gradients and mean square estimation error. The hydraulic head is broken into continuous and discontinuous components. The discontinuous component, which represents random measurement error and small-scale variability, is filtered from the measurements. The technique is applied to measurements of head in the Wolfcamp aquifer in northern Texas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1989.tb01049.x
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  • 10
    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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