Thesis (M.S.)--University of Nevada, Reno, 2006. / "December, 2006." Includes bibliographical references. Online version available on the World Wide Web.

Thesis (Ph. D.) -- Lincoln University, 2005. / Also available via the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on November 20, 2009). Thesis advisor: Dr. Mitchell Schulte. Includes bibliographical references.

M.Tech. Biomedical Technology / Previous studies have reported on the potential health risks associated with direct contact with chemicals (such as DNAPLs) via inhalation or drinking of contaminated groundwater. Dense Non-Aqueous Phase Liquids (DNAPLs) enter into groundwater through incorrect storage or disposal and pose risk to human health. Industrialization contributes considerably to contamination of ground water with waste disposal practices leading to the deposition of hazardous waste at geologically/hydro-geologically unsuitable locations. Many hazardous chemicals found their way into groundwater by this mean and might cause problems if ingested in drinking water. Most of these compounds undergo only limited degradation in the subsurface, and persist for long periods of time while slowly releasing soluble organic constituents that present hazardous health effects (both toxic and non-toxic) to humans.

Two digital- computer models of the ground -water reservoir of the Tucson basin, in south - central Arizona, were constructed to study errors in digital models and to evaluate the worth of additional basic data to models. The two models differ primarily in degree of detail -- the large -scale model consists of 1,890 nodes, at a 1/2 -mile spacing; and the small -scale model consists of 509 nodes, at a l -mile spacing. Potential errors in the Tucson basin models were classified as errors associated with computation, errors associated with mathematical assumptions, and errors in basic data: the model parameters of coefficient of storage and transmissivity, initial water levels, and discharge and recharge. The study focused on evaluating the worth of additional basic data to the small -scale model. A basic form of statistical decision theory was used to compute expected error in predicted water levels and expected worth of sample data (expected reduction in error) over the whole model associated with uncertainty in a model variable at one given node. Discrete frequency distributions with largely subjectively- determined parameters were used to characterize tested variables. Ninety -one variables at sixty - one different locations in the model were tested, using six separate error criteria. Of the tested variables, 67 were chosen because their expected errors were likely to be large and, for the purpose of comparison, 24 were chosen because their expected errors were not likely to be particularly large. Of the uncertain variables, discharge /recharge and transmissivity have the largest expected errors (averaging 155 and 115 feet, respectively, per 509 nodes for the criterion of absolute value of error) and expected sample worths (averaging 29 and 14 feet, respectively, per 509 nodes). In contrast, initial water level and storage coefficient have lesser values. Of the more certain variables, transmissivity and initial water level generally have the largest expected errors (a maximum of 73 per feet per 509 nodes) and expected sample worths (a maximum of 12 feet per 509 nodes); whereas storage coefficient and discharge/ recharge have smaller values. These results likely are not typical of those from many ground -water basins, and may apply only to the Tucson basin. The largest expected errors are associated with nodes at which values of discharge /recharge are large or at which prior estimates of transmissivity are very uncertain. Large expected sample worths are associated with variables which have large expected errors or which could be sampled with relatively little uncertainty. Results are similar for all six of the error criteria used. Tests were made of the sensitivity of the method to such simplifications and assumptions as the type of distribution function assumed for a variable, the values of the estimated standard deviations of the distributions, and the number and spacing of the elements of each distribution. The results are sensitive to all of the assumptions and therefore likely are correct only in order of magnitude. However, the ranking of the types of variables in terms of magnitude of expected error and expected sample worth is not sensitive to the assumptions, and thus the general conclusions on relative effects of errors in different variables likely are valid. Limited studies of error propagation indicated that errors in predicted water levels associated with extreme erroneous values of a variable commonly are less than 4 feet per node at a distance of 1 mile from the tested node. This suggests that in many cases, prediction errors associated with errors in basic data are not a major problem in digital modeling.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science in hydrogeology, School of Geosciences. Johannesburg, 23 May 2016. / Groundwater treatment by chemical precipitation is a popular form of remediation at mines that are in operation. The water quality status at the implementation of the PAT in this study was compared to the water quality status after a six-month period of active remediation. Chromium is very important as an industrial metal owing to its numerous uses in a variety of industries. The objective of the remedial action is to intercept the Cr(VI) plume, abstract contaminated groundwater and chemically treat it on the surface. The long-term (15-year) objective is to eventually reduce Cr(VI) concentrations in the aquifer(s) to below 0.05 mg/ℓ. The PAT system was implemented as a mediumterm (5-year) strategy to intercept the Cr(VI) contamination plume during migration to prevent it from negatively impacting on groundwater users downstream of the mine. In the vicinity of the three PAT systems’ abstracting wells, water levels declined by an average of 2 m compared to the same period in 2014. Periodical fluctuations in the fractured aquifer are reflective of the influence of fractures on groundwater flow. In the aquifer, hydrochemical signatures show evidence of mixing between the primary and secondary aquifers. The treatment system has been successful in reducing Cr(VI) to Cr(III) and precipitating Cr(OH)3. The treatment system was designed to treat Cr(VI), other elevated constituents and generally high dissolved ions are not treated in this remedial process. Sulphate concentrations increase after treatment as a result of the addition of Fe(II)SO4 for chromate contamination treatment purposes. The simulated reaction path shows that the transformation of CrO4 2- to Cr2O3 in the treatment system is not immediate. The Cr(VI) to Cr(III) transformation is irreversible, this is beneficial as the water is abstracted from more reducing conditions, and the treatment ponds are open to the atmosphere thus the conditions following dosing with Fe(II)SO4 are oxic and chromate complexes are stable over a wider range of Eh-pH conditions than Cr(III) compounds. This ensures that the efficiency of the dosing system is not reversed in Settling Pond B. The modelled flow paths are similar to the inferred flow vectors in the plume capture zone. Fracture flow is the dominant type of flow, the fault zones and dykes create high permeability conduits to flow. Flow paths are parallel to fault lines or the lateral dimension of dykes; flow occurs along fractures and deformation zones. The reduction of Cr(VI) concentrations in some of the peripheral sampling points indicates that the PAT system has been successful in capturing the chromate contaminated water through pumping. Keywords: Hexavalent chromium, groundwater pollution, remediation, pump-and-treat, fractured aquifers / GR2016

No description available.

The inverse problem of groundwater hydrology is difficult to solve and yet critical for the reliability of model predictions. In this dissertation, the problem is posed within the framework of maximum likelihood estimation by means of an estimation criterion which includes head measurements as well as prior information of the model parameters. Parameters that can be estimated include the principal values and directions of transmissivity (or hydraulic conductivity), storativity (or specific storage), recharge rates, boundary heads or fluxes, leakances, and parameters controlling the error structure of the data. In transient problems, the initial steady-state of the system can also be derived and/or taken advantage of. To minimize the estimation criterion, its gradient is evaluated by a finite element adjoint state method which leads to considerable savings in computer time and storage. The minimization -, performed -by a -combination- of gradient methads, is sbawn, bath theoretically and with examples, to result in stable solutions for a wide range of realistic situations. Synthetic and field examples are included to demonstrate various features of the approach. Applications of the methodology to problems of model selection, network design, and quantification of the worth of data are highlighted.

The groundwater travel time along the fastest path of likely radionuclide transport is a regulatory criterion used to assess the hydrogeologic quality of a high - level radioactive waste repository. Hydrologists and engineers are limited in their ability to define with confidence the fastest path, owing to the heterogeneous nature of geologic materials. Field measurements of hydraulic properties such as in test or observation wells, are inherently averages of properties at scales smaller than the scale of the field measurement. As a result of averaging, subscale information is lost and there is uncertainty in defining the fastest trajectory of groundwater. This scale problem is explained through a review of the continuum and REV concepts in groundwater hydrology. The application of hydrodynamic dispersion concepts is recommended as a means of incorporating the effect of subscale heterogeneity on the fastest groundwater travel time. Sources of uncertainties in predicting groundwater travel time are discussed in the report. The uncertainties are mainly attributed to the heterogeneous nature of geologic formations. The heterogeneity of geologic materials can, however, be characterized quantitatively using geostatistical methods. Important statistical parameters include mean and variance. as well as the spatial correlation structures of the hydrologic properties within the hydrogeologic system. These parameters may he obtained from limited data base. Stochastic methods, reviewed and explained in this report, can take advantage of the geostatistical characterization to predict large -scale groundwater flow and solute transport. Several examples from recent scientific literature are provided to illustrate the application of stochastic methods to the groundwater travel time analysis. Stochastic methods in subsurface hydrology have only recently been evaluated under field conditions for a few locations, and validation of the theories is incomplete, especially in unsaturated fractured rocks. Nevertheless, research efforts should continue to improve the state -of -the art. Geostatistics and stochastic methods will be valuable tools in addressing the groundwater travel time objective