The main aim of this study is to develop a suitable method for the calibration and validation of mathematical models of large and complex aquifer systems. Since the calibration procedure depends on the nature of the model to be calibrated and since many kinds of models are used for groundwater, the question of model choice is broached first. Various aquifer models are critically reviewed and a table to compare them as to their capabilities and limitations is set up. The need for a general calibration method for models in which the flow is represented by partial differential equations is identified from this table. The calibration problem is formulated in the general mathematical framework as the inverse problem. Five types of inverse problems that exist in modeling aquifers by partial differential equations are identified. These are, to determine (1) parameters, (2) initial conditions, (3) boundary conditions, (4) inputs, and (5) a mixture of the above. Various methods to solve these inverse problems are reviewed, including those from fields other than hydrology. A new direct method to solve the inverse problem (DIMSIP) is then developed. Basically, this method consists of transforming the partial differential equations of flow to algebraic equations by substituting in them the values of the various derivatives of the dependent variable (which may be hydraulic pressure, chemical concentration or temperature). The parameters are then obtained by formulating the problem in a nonlinear optimization framework. The method of sequential unconstrained minimization is used. Spline functions are used to evaluate the derivatives of the dependent variable. Splines are functions defined by piecewise polynomial arcs in such a way that derivatives up to and including the order one less than the degree of polynomials used are continuous everywhere. The natural cubic splines used in this study have the additional property of minimum curvature which is analogous to minimum energy surface. These and the derivative preserving properties of splines make them an excellent tool for approximating the dependent variable surfaces in groundwater flow problems. Applications of the method to both a test situation as well as to real-world data are given. It is shown that the method evaluates the parameters, boundary conditions and inputs; that is, solves inverse problem type V. General conditions of heterogeneity and anisotropy can be evaluated. However, the method is not applicable to steady flows and has the limitation that flow models in which the parameters are functions of the dependent variable cannot be calibrated. In addition, at least one of the parameters has to be preassigned a value. A discussion of uncertainties in calibration procedures is given. The related problems of model validation and sampling of aquifers are also discussed.

The Geropotamos aquifer on the north‐central coast of Crete, Greece, is invaded in some places by salt water from the Aegean Sea, with impact on freshwater supplies for domestic and business uses, including agriculture. The geological setting of the study area is considered complex, as Miocene biogenic limestones, marls, clays and conglomerates crop out in the central and the western part and clastic limestones and dolomites of the Tripolis and Plattenkalk nappe (the bedrock) in the eastern part of the study area. The phyllitequartzite nappe (which forms the oldest rock of the study area) lays on the northern part of Geropotamos basin. The local tectonic regime of the study area is characterized by faults of NW‐SE and NE‐SW directions. Investigation of the aquifer using Transient ElectroMagnetic method (TEM) and Vertical Electrical Resistivity (VES) measurement technique has resulted in 1D models and 2D/3D imaging of geoelectric structures, depicting the zones of salination of groundwater in the aquifer. 1179 TEM soundings in 372 sites have been carried out in a detailed survey grid (about 200m in X and Y dimension) and 3 VES soundings were acquired in three different sites (different geological conditions). For the 2 of them, multidirectional measurements were also acquired since the structure is more complex than a 1D model that VES technique is able to model. Moreover, 3 water samplings carried out. At each sampling, samples from 22 boreholes and 2 springs were analysed and 16 chemical parameters were determined. Detailed geochemical analysis, including Piper, Durov, Ternary, Stiff, Wilcox, Dispersion diagrams and Factors controlling the groundwater quality, was accomplished showing very good results and the relationship with the geophysical methods. All data were inserted in GIS environment and Groundwater Quality Maps were produced. Furthermore, Remote Sensing application, geological mapping and hydro‐lithological data showed that the physical characteristics of geomorphology and geology are in great relationship with the chemical and geophysical properties as well. Suggestions that Miocene evaporites led to groundwater salination are unconfirmed, and seawater intrusion is the most probable cause, supported by the results of this research. It is indicated that saline intrusion is likely to occur along fractures in a fault zone through otherwise low‐permeability phyllite‐quartzite bedrock, and it is emphasized the critical role of fracture pathways in salination problems of coastal aquifers.

A research report submitted to the Faculty of Science school of Geosciences in partial fulfillment of the requirements for the degree of Masters of Science in Hydrogeology. Johannesburg, June 2017. / The Masama Sandstone Aquifer is located in a semi-arid region of south-eastern Botswana where there are no perennial rivers. Groundwater is the main source of water supply for the communities. Historically many water drilling programs have been carried out in this area and the hydrogeological system has been conceptualized. An integrated approach coupling environmental isotopes, radioisotopes and multivariate statistical analysis of the hydrochemical variables was employed to study the origin, age, recharge conditions, rock-water interaction and the hydrological link between the aquifer and geological structures. The major ions in this area are Na+, Ca2+, Mg2+ and HCO-3. Groundwater in the Masama area fall in the transition from a Na-HCO-3 –type through Ca-Na-HCO-3 to Ca-Mg-HCO-3 -type waters from the western to the eastern part of the area. The water types are as a result of cation exchange, carbonate dissolution and rock-weathering processes. The δ18O and δ2H values vary spatially depending on the source of moisture, rainfall season, geology, topography and groundwater circulation depth. Deep circulating groundwaters are isotopically depleted whilst shallow circulating groundwaters are isotopically enriched with respect to winter rain. Low tritium values < 0.8TU and 14C values < 80pmc testifies for recharge. Recent rainfall amount in the area is not sufficient enough to make a profound replenishment in the aquifer. Tritium, 14C and Chloride Mass Balance helped in identifying recharge location and hydrologic connections between structures and the sandstone aquifer elucidating that recharge zones are in the NE and NW of the study area. High recharge rates occur in the north-eastern part and the Makhujwane fault act as a conduit for groundwater recharge. This study provides a better understanding of the aquifer and the information contained herein can be incorporated into future works for sustainable use of the groundwater resource. / XL2017

Diversos métodos geofísicos têm sido empregados para a identificação de zonas fraturadas em rochas cristalinas a fim de locar pontos de perfuração de poços tubulares. Os métodos geoelétricos têm tido um papel importante na identificação destas zonas fraturadas, no entanto, em áreas urbanas sofrem com a falta de espaço e interferências diversas, o que limita suas aplicações. O presente trabalho visou correlacionar as anomalias geoelétricas típicas de zonas fraturadas em rochas cristalinas, com medidas de emanação natural de radônio a fim de estabelecer parâmetros que possam ser aplicados em áreas onde os fatores externos impeçam a execução dos métodos geoelétricos, uma vez que os fatores que interferem na aplicação desses métodos não interferem na emanação do radônio. Os resultados encontrados nas áreas investigadas mostraram uma boa correlação entre as anomalias geoelétricas e as anomalias de emanação de radônio, bem como foram boas as correlações com os resultados de vazão dos poços existentes nas áreas investigadas. A metodologia aqui proposta alcançou os objetivos podendo ser uma excelente ferramenta para prospecção de água subterrânea, tanto como método auxiliar, quanto como ferramenta principal de prospecção de aqüíferos em áreas onde outros métodos não possam ser aplicados devido a interferências diversas tais como: tubulações metálicas, fiações elétricas, entre outras. Estes tipos de interferências são bastante comuns em áreas urbanas, justamente onde a perfuração de poços é mais requerida. / A several geophysical methods have been used for the identification of shear zones in crystalline rocks in order to mark points to water well drilling. The geoelectrical methods have had an important role on the identification of these shear zones. However, in urban areas they suffer with the lack from space and diverse interferences, what it limits the application of these ones. The present research aimed to correlate the typical electrical anomalies of shear zones in crystalline rocks, with measures of natural emanation of radon, in order to establish parameters that can be applied in areas where the external factors hinder the execution of the geoelectrical methods, because the factors that intervene with the application of these methods do not intervene with the emanation of the radon. The results found in the investigated areas had shown a good correlation with the electrical anomalies and the radon emanation anomalies, as well as had been good the correlations with the results of yield of water wells on the investigated areas. The methodology proposal reached the objectives being able to be an excellent tool for groundwater prospection, as a auxiliary method auxiliary, as a main tool of prospection of fractured aquifers in areas where other methods cannot be applied due several interferences, as metallic pipes, electric wirings, and others. These types of interferences are sufficiently common in urban areas, exactly where the water well drilling its more necessary.

Photocopy of typescript. / Digitized by Kansas Correctional Industries

Electrical imaging of groundwater that interacts with surface watercourses provides detail on the extent of intervention needed to accurately manage both resources. It is particularly important where one resource is saline or otherwise polluted, where spatial quantification of the interacting resources is critical to water use planning and where losses from surface waterways need to be minimized in order to transport water long distances. Geo-electric arrays or transient electromagnetic devices can be towed along watercourses to image electrical conductivity (EC) at multiple depths within and beneath those watercourses. It has been found that in such environments, EC is typically related primarily to groundwater salinity and secondarily to clay content. Submerged geo-electric arrays can detect detailed canal-bottom variations if correctly designed. Floating arrays pass obstacles easily and are good for surveying constricted rivers and canals. Transient electromagnetic devices detect saline features clearly but have inferior ability to detect fine changes just below beds of watercourses. All require that water depth be measured by sonar or pressure sensors for successful elimination of effects of the water layer on the data. The meandering paths of rivers and canals, combined with the sheer volume of data typically acquired in waterborne surveys, results in a geo-referencing dilemma that cannot be accommodated using either 2D imaging or 3D voxel imaging. Because of this, software was developed by the author which allows users to view vertical section images wrapped along meandering paths in 3D space so that they resemble ribbons. Geo-electric arrays suitable for simultaneous imaging of both shallow and deep strata need exponentially spread receiver electrodes and elongated transmitter electrodes. In order to design and facilitate such arrays, signed monopole notation for arrays with iv segmented elongated electrodes was developed. The new notation greatly simplified generalized geo-electric array equations and led to processing efficiency. It was used in the development of new array design software and automated inversion software including a new technique for stable inversion of datasets including data with values below noise level. The Allen Exponential Bipole (AXB) array configuration was defined as a collinear arrangement of 2 elongated transmitter electrodes followed by receiver electrodes spaced exponentially from the end of the second transmitter electrode. A method for constructing such geo-electric arrays for use in rivers and canals was developed and the resulting equipment was refined during the creation of an extensive set of EC imaging case studies distributed across canals and rivers of the Australian Murray- Darling Basin. Man made and natural variations in aquifers connected to those canals and rivers have been clearly and precisely identified in more than 1000 kilometres of EC imagery.

Arsenic (As) in groundwater systems is a problem in many parts of the world owing to ever-increasing extraction of groundwater resources to meet the needs of growing populations. Surprisingly, the occurrence of elevated As concentrations in coastal sandy aquifers has only recently been published as a result of this research. Sandy aquifers are commonly used as a clean and reliable source of water for domestic, agricultural and industrial needs due to their high recharge rates and the filtering capacity of sands. Water quality monitoring in Australian sandy aquifers is usually limited to a small suite of major elements and salinity measurements to determine the quality of groundwater and to identify any potential problems from seawater intrusion as a result of over extraction. Minor and trace elements, particularly toxic elements, have largely been ignored in regular monitoring programs. Prompted by an emerging pattern of human health problems in a community reliant on groundwater, hydrogeochemical investigations of the Stuarts Point coastal sand aquifer, on the North Coast of New South Wales, Australia, identified elevated As concentrations of up to 337 ????g/L in the catchment's Pleistocene barrier sands. These concentrations are well in excess of the World Health Organisation and the Australian National Health and Medical Research Council water quality criteria of 10 and 7 ????g/L respectively. From research into the Stuarts Point geology, geochemistry, geomorphology, hydrogeology and hydrogeochemistry, and with the assistance of environmental isotopes, the spatial distribution, occurrence and mobilisation processes of As were determined. The presence and distribution of elevated As concentrations in the regional coastal aquifer system are sporadic and involve a series of complex hydrogeochemical processes. No single hydrogeochemical process can describe the release of As from solid phase to groundwater system on the regional scale. Processes of competitive exchange with PO43- and HCO3-, reductive dissolution of Fe oxyhydroxides and arsenical pyrite oxidation, though not forming dominant correlations, are still evident and influence As chemistry at this scale. Detailed investigations of the hydrogeochemistry on the vertical scale have identified two main processes as causing As to be released and mobilised. The first process is associated with the oxidation of arsenical pyrite in Acid Sulphate Soils and metal hydrolysis reactions which mobilise As in the acidic environment. In the absence of dissolved oxygen (DO), NO3- acts as the oxyanion facilitating arsenical pyrite oxidation and releasing As into solution. The second process that mobilises As from the sediments is the liberation of As from metal-oxyhydroxides in the carbon-rich environment, where HCO3- originates from the dissolution of shell material in the Pleistocene barrier sands. The marine influenced depositional history and geomorphology of the aquifer provide opportunities for As to become incorporated into the aquifers matrix in a variety of mineral forms, which is an occurrence not considered to be unique to the Stuarts Point catchment. The findings presented here are amongst the first detailed studies of naturally occurring As in an Australian groundwater system as well as in the Pleistocene coastal sand aquifer environment. The understanding of As accumulation and mobilisation identified as a result of this research emphasises the need for potential As occurrences in similar groundwater systems in other coastal environments in Australia, and globally, to be considered.

Water recycling schemes are increasingly being implemented across Australia as an effective means of converting wastewater into a valuable resource. There is currently a lack of specific guidelines for the monitoring of groundwater resources associated with these schemes. This is despite it being widely acknowledged that a monitoring system is a fundamental component of a scheme, due to the risk of altering the hydrogeological processes and resource devaluation. The aim of this research was to address this information gap, by developing guidelines that provide a platform for the continuous improvement in groundwater monitoring systems for recycling schemes. To achieve the stated aim, an action research strategy formed the methodological approach for the implementation of the objectives. Existing guidelines for monitoring systems were reviewed, consolidated and refined, in consultation with industry expertise. The developed guidelines were then verified through the implementation of a case study at the Hawkesbury Water Recycling Scheme (HWRS), with the resulting information providing for a preliminary characterisation of the resources. Designed on current best practice, and to meet statutory requirements, the guidelines addressed the identified information gap. The research recommends the integration of groundwater monitoring systems into the environmental management system for recycling schemes, to provide for continuous refinement through the interpretation of the knowledge base developed in previous cycles. Adoption of this practice will initiate improved decision making and management processes, and provide for future resource protection and enhancement. / Master of Science (Hons)

Water recycling schemes are increasingly being implemented across Australia as an effective means of converting wastewater into a valuable resource. There is currently a lack of specific guidelines for the monitoring of groundwater resources associated with these schemes. This is despite it being widely acknowledged that a monitoring system is a fundamental component of a scheme, due to the risk of altering the hydrogeological processes and resource devaluation. The aim of this research was to address this information gap, by developing guidelines that provide a platform for the continuous improvement in groundwater monitoring systems for recycling schemes. To achieve the stated aim, an action research strategy formed the methodological approach for the implementation of the objectives. Existing guidelines for monitoring systems were reviewed, consolidated and refined, in consultation with industry expertise. The developed guidelines were then verified through the implementation of a case study at the Hawkesbury Water Recycling Scheme (HWRS), with the resulting information providing for a preliminary characterisation of the resources. Designed on current best practice, and to meet statutory requirements, the guidelines addressed the identified information gap. The research recommends the integration of groundwater monitoring systems into the environmental management system for recycling schemes, to provide for continuous refinement through the interpretation of the knowledge base developed in previous cycles. Adoption of this practice will initiate improved decision making and management processes, and provide for future resource protection and enhancement. / Master of Science (Hons)

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 91-95). Available also in a digital version from Dissertation Abstracts.