Download or read book A Parameter Estimation Model for Contaminant Transport in Porous Media Given Sparse Data written by Alexander Chukwuemeka Okeke and published by . This book was released on 1983 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Parameter Estimation and Uncertainty Analysis of Contaminant First Arrival Times at Household Drinking Water Wells written by Mary Kang and published by . This book was released on 2007 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: Exposure assessment, which is an investigation of the extent of human exposure to a specific contaminant, must include estimates of the duration and frequency of exposure. For a groundwater system, the duration of exposure is controlled largely by the arrival time of the contaminant of concern at a drinking water well. This arrival time, which is normally estimated by using groundwater flow and transport models, can have a range of possible values due to the uncertainties that are typically present in real problems. Earlier arrival times generally represent low likelihood events, but play a crucial role in the decision-making process that must be conservative and precautionary, especially when evaluating the potential for adverse health impacts. Therefore, an emphasis must be placed on the accuracy of the leading tail region in the likelihood distribution of possible arrival times. To demonstrate an approach to quantify the uncertainty of arrival times, a real contaminant transport problem which involves TCE contamination due to releases from the Lockformer Company Facility in Lisle, Illinois is used. The approach used in this research consists of two major components: inverse modelling or parameter estimation, and uncertainty analysis. The parameter estimation process for this case study was selected based on insufficiencies in the model and observational data due to errors, biases, and limitations. A consideration of its purpose, which is to aid in characterising uncertainty, was also made in the process by including many possible variations in attempts to minimize assumptions. A preliminary investigation was conducted using a well-accepted parameter estimation method, PEST, and the corresponding findings were used to define characteristics of the parameter estimation process applied to this case study. Numerous objective functions, which include the well-known L2-estimator, robust estimators (L1-estimators and M-estimators), penalty functions, and deadzones, were incorporated in the parameter estimation process to treat specific insufficiencies. The concept of equifinality was adopted and multiple maximum likelihood parameter sets were accepted if pre-defined physical criteria were met. For each objective function, three procedures were implemented as a part of the parameter estimation approach for the given case study: a multistart procedure, a stochastic search using the Dynamically-Dimensioned Search (DDS), and a test for acceptance based on predefined physical criteria. The best performance in terms of the ability of parameter sets to satisfy the physical criteria was achieved using a Cauchy's M-estimator that was modified for this study and designated as the LRS1 M-estimator. Due to uncertainties, multiple parameter sets obtained with the LRS1 M-estimator, the L1-estimator, and the L2-estimator are recommended for use in uncertainty analysis. Penalty functions had to be incorporated into the objective function definitions to generate a sufficient number of acceptable parameter sets; in contrast, deadzones proved to produce negligible benefits. The characteristics for parameter sets were examined in terms of frequency histograms and plots of parameter value versus objective function value to infer the nature of the likelihood distributions of parameters. The correlation structure was estimated using Pearson's product-moment correlation coefficient. The parameters are generally distributed uniformly or appear to follow a random nature with few correlations in the parameter space that results after the implementation of the multistart procedure. The execution of the search procedure results in the introduction of many correlations and in parameter distributions that appear to follow lognormal, normal, or uniform distributions. The application of the physical criteria refines the parameter characteristics in the parameter space resulting from the search procedure by reducing anomalies. The combined effect of optimization and the application of the physical criteria performs the function of behavioural thresholds by removing parameter sets with high objective function values. Uncertainty analysis is performed with parameter sets obtained through two different sampling methodologies: the Monte Carlo sampling methodology, which randomly and independently samples from user-defined distributions, and the physically-based DDS-AU (P-DDS-AU) sampling methodology, which is developed based on the multiple parameter sets acquired during the parameter estimation process. Monte Carlo samples are found to be inadequate for uncertainty analysis of this case study due to its inability to find parameter sets that meet the predefined physical criteria. Successful results are achieved using the P-DDS-AU sampling methodology that inherently accounts for parameter correlations and does not require assumptions regarding parameter distributions. For the P-DDS-AU samples, uncertainty representation is performed using four definitions based on pseudo-likelihoods: two based on the Nash and Sutcliffe efficiency criterion, and two based on inverse error or residual variance. The definitions consist of shaping factors that strongly affect the resulting likelihood distribution. In addition, some definitions are affected by the objective function definition. Therefore, all variations are considered in the development of likelihood distribution envelopes, which are designed to maximize the amount of information available to decision-makers. The considerations that are important to the creation of an uncertainty envelope are outlined in this thesis. In general, greater uncertainty appears to be present at the tails of the distribution. For a refinement of the uncertainty envelopes, the application of additional physical criteria is recommended. The selection of likelihood and objective function definitions and their properties are made based on the needs of the problem; therefore, preliminary investigations should always be conducted to provide a basis for selecting appropriate methods and definitions. It is imperative to remember that the communication of assumptions and definitions used in both parameter estimation and uncertainty analysis is crucial in decision-making scenarios.

Download or read book Comprehensive Dissertation Index written by and published by . This book was released on 1989 with total page 984 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2007 with total page 902 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Approaches to Modeling Contaminant Transport in Porous Media written by Pascual Horacio Benito and published by . This book was released on 2008 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Random Process Model for Dispersion in Contaminant Transport Through Porous Media written by Jeffrey Victor Butera and published by . This book was released on 1997 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book American Doctoral Dissertations written by and published by . This book was released on 1995 with total page 896 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scale Effect of Contaminant Transport in Saturated Porous Media Identified by the Time Fractional Advection dispersion Equation written by Rhiannon Maire Garrard and published by . This book was released on 2017 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: Time nonlocal transport models such as the time fractional advection-dispersion equation (t-fADE) were proposed to capture well-documented non-Fickian dynamics for conservative solutes transport in heterogeneous media, with the underlying assumption that the time nonlocality (which means that the current concentration change is affected by previous concentration load) embedded in the physical models can release the effective dispersion coefficient from scale dependency. This assumption however has never been systematically examined using real data. This study fills this historical knowledge gap by capturing non-Fickian transport (likely due to solute retention) documented in literature (Huang et al. 1995) and observed in our laboratory from small to intermediate spatial scale using the promising, tempered t-fADE model. Fitting exercises show that the effective dispersion coefficient in the t-fADE, although differing subtly from the dispersion coefficient in the standard advection-dispersion equation, increases nonlinearly with the travel distance (varying from 0.5 to 12 m) for both heterogeneous and macroscopically homogeneous sand columns. Further analysis reveals that, while solute retention in relatively immobile zones can be efficiently captured by the time nonlocal parameters in the t-fADE, the retention-independent solute movement in the mobile zone is affected by the spatial evolution of local velocities in the host medium, resulting in a scale-dependent dispersion coefficient. The same result may be found for the other standard time nonlocal transport models, such as the well-known multi-rate mass transfer (MRMT) model and the hydrologic version of continuous time random walk (CTRW), that separate solute retention and jumps (i.e., displacement). Therefore, the t-fADE with a constant dispersion coefficient cannot capture scale-dependent dispersion in saturated porous media, challenging the application for stochastic hydrogeology methods in quantifying real-world, pre-asymptotic transport. Hence, improvements on time nonlocal models using, for example the novel subordination approach, are necessary to incorporate the spatial evolution of local velocities without adding cumbersome parameters. Future improvements are also explored, given knowledge obtained in this study.

Download or read book Stochastic Analysis of Contaminant Transport written by and published by . This book was released on 1992 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: A reliability algorithm is used to develop probabilistic (stochastic) models or contaminant transport in porous media. The models are based on advective-dispersive transport equations, and utilize the reliability algorithm with existing one- and two-dimensional analytical and numerical solutions. Uncertain variables in the models include: groundwater flow velocity (or permeability in the numerical model), dispersivity, diffusion coefficient, bulk density, porosity, and solute distribution coefficient. Each uncertain variable is assigned a mean, covariance, and marginal distribution. The models yield an estimate of the probability that the contaminant concentration will equal or exceed a target concentration at a selected location and time. The models also yield probabilistic sensitivity measures which identify those uncertain variables with most influence on the probabilistic outcome. The objective of this study is to examine the basic behavior and develop general conclusions regarding transport under certain conditions as modeled using a reliability approach.

Download or read book Review of Contaminant Transport Modeling in Porous Media Using Multi processor Computing Environment written by P. Oduro and published by . This book was released on 1998 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Current Awareness in Particle Technology written by and published by . This book was released on 1984 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Advection diffusion Theory of Contaminant Transport for Stratified Porous Media microform written by Edward Allan Sudicky and published by National Library of Canada. This book was released on 1983 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book NUMERICAL MODELING OF CONTAMINANT TRANSPORT IN FRACTURED POROUS MEDIA USING MIXED FINITE ELEMENT AND FINITE VOLUME METHODS written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A mathematical model for contaminant species passing through fractured porous media is presented. In the numerical model, we combine two locally conservative methods, i.e. mixed finite element (MFE) and the finite volume methods. Adaptive triangle mesh is used for effective treatment of the fractures. A hybrid MFE method is employed to provide an accurate approximation of velocities field for both the fractures and matrix which are crucial to the convection part of the transport equation. The finite volume method and the standard MFE method are used to approximate the convection and dispersion terms respectively. The model is used to investigate the interaction of adsorption with transport and to extract information on effective adsorption distribution coefficients. Numerical examples in different fractured media illustrate the robustness and efficiency of the proposed numerical model.

Download or read book Mathematical Modeling of Fluid Flow Contaminant Transport and Biofilm Growth in Porous Media written by Hristo V. Kojouharov and published by . This book was released on 1998 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Contaminant Transport Models in Layered Porous Media written by Jong Seong Im and published by . This book was released on 1988 with total page 530 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Study of Contaminant Transport in Porous Media written by Jian Chyun Wang and published by . This book was released on 1997 with total page 624 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Stochastic Analysis of Contaminant Transport Final Report July 1 1989 November 1 1991 written by and published by . This book was released on 1992 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: A reliability algorithm is used to develop probabilistic (stochastic) models or contaminant transport in porous media. The models are based on advective-dispersive transport equations, and utilize the reliability algorithm with existing one- and two-dimensional analytical and numerical solutions. Uncertain variables in the models include: groundwater flow velocity (or permeability in the numerical model), dispersivity, diffusion coefficient, bulk density, porosity, and solute distribution coefficient. Each uncertain variable is assigned a mean, covariance, and marginal distribution. The models yield an estimate of the probability that the contaminant concentration will equal or exceed a target concentration at a selected location and time. The models also yield probabilistic sensitivity measures which identify those uncertain variables with most influence on the probabilistic outcome. The objective of this study is to examine the basic behavior and develop general conclusions regarding transport under certain conditions as modeled using a reliability approach.