No description available.

A number of geophysical methods have been used in groundwater exploration in Cyprus. Of these, electrical resistivity has found the widest application in the investigation of the mostly unconsolidated extensive aquifers of the Mesaoria Plain and the alluvial aquifers of the rivers draining the Troodos massif. Special emphasis has been given in this study on the detailed investigation by means of electrical resistivity of the aquifers of Western Mesaoria, Central Mesaoria and the three main Paphos rivers of Dhiarizos, Xeros and Ezusa where the nature of the deposits and the scarcity of exposures diminish the effectiveness of conventional hydrogeological methods. Existing hydrogeological information and specially conducted resistivity measurements of the magnitude and extent of lateral and orientational resistivity variations indicate that conditions in Western Mesaoria, the Paphos rivers and the larger part of Central Mesaoria are on the main suitable for the application of the electrical sounding technique. Over 120 correlation soundings measured in these areas show close correspondence between hydrogeological and electrical layers and enable the establishment of working geoelectrical models according to which the rest of the 904 soundings have been interpreted. In Western Mesaoria subsurface conditions are fairly simple and laterally persistent and two subaquifers to the Western Mesaoria Upper Aquifer are indicated by the electrical and hydrogeological results. In Central Mesaoria subsurface conditions are more variable while groundwater salinity variations complicate the picture. Interpretation of sounding measurements has been based on several geoelectrical models. In the Paphos rivers subsurface conditions are simple and the basic geoelectrical model assumes the presence of two alluvial layers with different physical properties. Aquifer geometry and configuration are accurately defined by the electrical-hydrogeological results. The electrical properties of the aquifers and associated rocks are derived while aquifer potential and hydraulic transmissivity appear to be related directly to the aquifer transverse resistance.

The question that is addressed in this thesis is: can a simultaneous inverse scheme involving thermal and hydrologic data resolve hydrologic model parameters to a better degree than hydrologic data alone? The first chapter sets the framework for this question by first reviewing linear and non-linear inverse problems and then illustrating the advantages of a simultaneous inverse of two different data sets through the use of a simple example. It is the goal of Chapter 2 to examine current methodologies for stating and solving the inverse problem. A review of the maximum likelihood approach is presented, and a construction formalism is adopted by introducing a series of objective functionals (norms) which are minimized to yield a variety of possible models. The inverse is carried out using a modification of a constrained simplex procedure. The algorithm requires no derivative computations and can be used to minimize an arbitrarily complicated non-linear functional, subject to non-linear inequality constraints. The algorithm produces a wide variety of acceptable models clustered about a global minimum, each of which generates data that match observed values. The inverse technique is demonstrated on a series of one and two-dimensional synthetic data sets, and on a hydraulic head data set from Downie Slide, British Columbia, Canada. At this site, four parameters are determined; the free-surface position of the water table and three boundary conditions for the domain. Further simulations using a theoretical data set with assumed properties similar to that of Downie Slide show that with noise free data, and an adequate spacing between points it is possible to interpolate an unbiased estimate of hydraulic head data at all nodes in the equivalent discretized domain. When the inverse technique is applied, the domain's conductivity structure is correctly identified when enough prior log-conductivity information is available. The implications for Downie Slide are that in order to construct anything but a simple hydrogeologic model, accurate field measurements of hydraulic head are required, as well as well-defined estimates of hydraulic conductivity, a better spacing between measurements, and adequate knowledge of the boundary conditions. Chapter 3 is devoted to developing the idea of a joint inversion scheme involving both thermal and hydrologic data. One way of overcoming data limitations (sparse hydraulic head or few hydraulic conductivity estimates) in an inverse problem is to introduce an independently collected data set and apply simultaneous or joint inversion. The joint inversion method uses data from a number of different measurements to improve the resolution of parameters which are in common to one or more functional relationships. One such data set is subsurface temperature, which is sensitive to variations in hydraulic conductivity. In Chapter 3, the basic concepts of heat and fluid transfer in porous media with emphasis on forced convective effects are reviewed, followed by inversion of theoretical data and a re-investigation of the hydrogeology of Downie Slide, augmented with thermal data and a simultaneous inverse. Additional runs on a heterogenous medium presented in Chapter 2 are carried out. With a good temperature data base, thermal properties can be properly resolved. However, in this stochastic problem the addition of thermal data did not condition .the inverse to a greater degree than accomplished with the addition of prior information on log-conductivity. The benefits of including thermal data and applying a joint inversion can be substantial when considering the more realistic problem of uncertain boundary conditions. The simultaneous inverse is also applied to the Downie Slide data set examined in Chapter 2. Unfortunately, with a homogeneous hydraulic conductivity, all that can be determined from a hydraulic head inverse are ratios of flux to hydraulic conductivity. By including thermal data, the value of hydraulic conductivity can be determined at this site. Some of the model parameters (basal heat flux, thermal conductivity, specified head boundaries) are not resolved well by the joint scheme. None theless the constructed models do offer valuable insight into the hydrogeology of the field site. The constructed models persistently show a hydraulic conductivity value of about 1 x 10⁻⁷ m/sec, which is consistent with previous estimates of hydraulic conductivity at the site. A further comparison with the inverse results in Chapter 2 show good agreement between the two inverses for the hydraulic properties. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Peterborough Drumlin Field in southern Ontario, Canada (PDF; Crozier 1975, Karrow 1981, Boyce and Eyles 1991) is a well-documented and extensive drumlin field that hosts many communities dependent upon groundwater resources. Population growth in the area and concerns for the long-term sustainability of these resources has prompted considerable interest in determining the location, extent and potential productivity of subsurface aquifers in the region. The origin of the drumlins within the PDF is still widely debated, despite many years of study, and there is little understanding of the nature, geometry, and connectivity of aquifers within the Quaternary-age sediments beneath the drumlins. This study involves detailed analysis of sedimentological data available from water well logs from selected drumlins and adjacent low areas (swales) in the PDF. These data are used to investigate the subsurface stratigraphy of the drumlins, contribute to the understanding of drumlin formation, and establish hydrogeological characteristics of drumlins within the PDF. A relatively consistent subsurface stratigraphy can be identified in the studied drumlins consisting of patchy units of sand and gravel overlying a southward sloping bedrock surface, a thick diamict (till) package containing discontinuous coarse-grained sand and gravel units, and surface veneers of sand, silt or clay in low areas (swales) between drumlins. This subsurface stratigraphy can be traced between drumlins and adjacent swales and suggests that the drumlins within the PDF formed largely as a result of subglacial erosion of pre-existing sediment. Two major aquifers can be identified beneath the PDF from the water well records; one is a basal aquifer within fractured bedrock and overlying coarse-grained sands and gravels, and the second (upper aquifer) is formed by the discontinuous zone of sands and gravels within till. These coarse-grained interbeds within the till allow it to function as a ‘leaky aquitard’ and produce groundwater flow pathways that are not easy to predict, may not be high-yielding, and may be susceptible to anthropogenic sources of contamination; these characteristics will likely prevent further development of this aquifer for multi-user (communal) water supply. The Hiawatha First Nations (HFN) community is located within the Peterborough Drumlin Field and has been attempting to find a more sustainable, and possibly communal, groundwater supply in the drumlizined terrain. Examination of lithological and hydrogeological data from water well records together with information obtained from four recently drilled on-site wells allowed for a detailed analysis of the till stratigraphy within this portion of the drumlin field. The stratigraphy identified at this site is consistent with that identified elsewhere in the PDF and a basal bedrock aquifer and an upper discontinuous Quaternary aquifer can be discriminated. It is recommended that the HFN community continue to upgrade/maintain individual private wells in the discontinuous upper aquifer and utilize the basal bedrock aquifer for developments that require greater water yields. This study provides insight into the subsurface stratigraphy that may be found beneath drumlins in an extensive drumlin field and may help in determining the origin of these enigmatic landforms. Enhanced understanding of the hydrogeological characteristics of Quaternary-age sediments underlying drumlin fields will assist in the development of appropriate exploration, protection, and remediation strategies for valuable groundwater resources. / Thesis / Master of Science (MSc)

No description available.

Alternative strategies involving in situ remediation technologies have been developed to assist with property clean up, however, cost-effectiveness and discrepancies in success rates and timeliness continue. The objective of my research was to critically demonstrate the application and usefulness of an in situ remediation technology at a petroleum hydrocarbon impacted site. This project was proposed as part of the research programs: Groundwater Plume Formation and Remediation of Modern Gasoline Fuels in the Subsurface and Enhancing In Situ Bioremediation at Brownfield Sites funded by the Ontario Centres of Excellence for Earth and Environmental Technologies as part of the multiphase project entitled “Enhancing in situ Bioremediation at Brownfield Sites”. This research focused on the demonstration of nitrate-enhanced in situ bioremediation at a decommissioned service station. Petroleum hydrocarbon impacted soil and groundwater is a common occurrence at gasoline distribution facilities, where toxicological effects are known for gasoline constituents of interest such as benzene, toluene, ethylbenzene and total xylenes (BTEX). These chemicals are volatile, readily soluble, and persistent in groundwater. In particular, residual contaminants present in the saturated zone were targeted for remediation as they serve as a long term source of contamination and contribute to mobile vapour phase and dissolved phase plumes. Site investigations characterized the complex hydrogeological conditions and contaminant distribution present in order to effectively design an in situ bioremediation treatment system. The addition of nitrate as a terminal electron acceptor (TEA) to an aquifer enhances in situ biodegradation of petroleum hydrocarbons, by providing the microbes with a sustainable energy source to promote cell maintenance and growth of the microbial population. The remediation strategy involved pulsed injections of remedial solution amended with a conservative bromide (200 mg/L Br-) and reactive nitrate (90 to 265 mg/L NO3-) tracers with the purpose of providing a continuous supply of TEA available to the indigenous microbial populations. Nitrate was selected as an alternative electron acceptor over the thermodynamically favoured O2 because of typical challenges encountered using O2 in bioremediation applications in addition to the existing anaerobic environment. In situ anaerobic degradation of BTEX compound using TEA amendments has been well documented; however benzene is often recalcitrant under denitrification conditions. The results of the Br- tracer breakthrough curves indicate that different preferential flow pathways were established under the transient saturated conditions present at the Site, although the behaviour of the injected remedial slug was generally consistent between the different units and the test solution was ultimately delivered to the target zone. The delivery of the remedial test solution was greatly influenced by the hydrogeological conditions present at the time of injection. The injectate was preferentially transported in the high permeability zone of sandy gravel aquifer Unit 3 under high saturated condition and background hydraulic gradients. However the seasonal decline in groundwater levels and hydraulic gradients resulted in the lower portion of Unit 4 comprised of higher permeable materials being able to transmit the test solution more effectively. Given the variable hydrogeological conditions present at the Site influenced by seasonal effects, the delivery of the remedial solution to target zones containing petroleum hydrocarbons at residual saturation is more effective under reduced saturated conditions. The delivery of TEA amended water to enhance the in situ biodegradation of petroleum contaminants is more effective when the treatment water has an increased residence time in the target remedial zone, attributed to low gradients and groundwater transport velocities at the Site. Longer residence periods enable the indigenous microbes to have increased contact time with the TEA which will be preferentially utilized to degrade the contaminants.   A reducing zone enriched with TEA in the anaerobic aquifer was established following consecutive injections of remedial test solution. A cumulative mass of 4 kg of NO3- was added to the target aquifer during the course of the remedial injections. Evidence demonstrating NO3- utilized as a terminal electron acceptor in the bioremediation of the petroleum-contaminated aquifer include: laboratory microcosm study confirming local indigenous microbial population’s ability to degrade hydrocarbons using NO3- as the TEA in addition to observed decrease in NO3- relative to a conservative Br- tracer and generation of nitrite, an intermediate product in denitrification in the pilot-scale operation. Contaminant mass removal likely occurred as Br- tracer evidence indicates that NO3- was utilized in the study area based on the inference of denitrification rates. Post-injection groundwater sampling indicate declining concentrations of toluene, however long term monitoring is recommended in order to evaluate the success of the remediation activity and assess the potential for rebound. Post-injection soil core results are unable to demonstrate the reduction in individual toluene, let alone BTEXTMB hydrocarbon levels, as a result of insufficient quantities of nitrate delivered to the target zone relative to the significant but heterogeneously distributed residual mass in the subsurface.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 123-132). Available also in a digital version from Dissertation Abstracts.

Alternative strategies involving in situ remediation technologies have been developed to assist with property clean up, however, cost-effectiveness and discrepancies in success rates and timeliness continue. The objective of my research was to critically demonstrate the application and usefulness of an in situ remediation technology at a petroleum hydrocarbon impacted site. This project was proposed as part of the research programs: Groundwater Plume Formation and Remediation of Modern Gasoline Fuels in the Subsurface and Enhancing In Situ Bioremediation at Brownfield Sites funded by the Ontario Centres of Excellence for Earth and Environmental Technologies as part of the multiphase project entitled “Enhancing in situ Bioremediation at Brownfield Sites”. This research focused on the demonstration of nitrate-enhanced in situ bioremediation at a decommissioned service station. Petroleum hydrocarbon impacted soil and groundwater is a common occurrence at gasoline distribution facilities, where toxicological effects are known for gasoline constituents of interest such as benzene, toluene, ethylbenzene and total xylenes (BTEX). These chemicals are volatile, readily soluble, and persistent in groundwater. In particular, residual contaminants present in the saturated zone were targeted for remediation as they serve as a long term source of contamination and contribute to mobile vapour phase and dissolved phase plumes. Site investigations characterized the complex hydrogeological conditions and contaminant distribution present in order to effectively design an in situ bioremediation treatment system. The addition of nitrate as a terminal electron acceptor (TEA) to an aquifer enhances in situ biodegradation of petroleum hydrocarbons, by providing the microbes with a sustainable energy source to promote cell maintenance and growth of the microbial population. The remediation strategy involved pulsed injections of remedial solution amended with a conservative bromide (200 mg/L Br-) and reactive nitrate (90 to 265 mg/L NO3-) tracers with the purpose of providing a continuous supply of TEA available to the indigenous microbial populations. Nitrate was selected as an alternative electron acceptor over the thermodynamically favoured O2 because of typical challenges encountered using O2 in bioremediation applications in addition to the existing anaerobic environment. In situ anaerobic degradation of BTEX compound using TEA amendments has been well documented; however benzene is often recalcitrant under denitrification conditions. The results of the Br- tracer breakthrough curves indicate that different preferential flow pathways were established under the transient saturated conditions present at the Site, although the behaviour of the injected remedial slug was generally consistent between the different units and the test solution was ultimately delivered to the target zone. The delivery of the remedial test solution was greatly influenced by the hydrogeological conditions present at the time of injection. The injectate was preferentially transported in the high permeability zone of sandy gravel aquifer Unit 3 under high saturated condition and background hydraulic gradients. However the seasonal decline in groundwater levels and hydraulic gradients resulted in the lower portion of Unit 4 comprised of higher permeable materials being able to transmit the test solution more effectively. Given the variable hydrogeological conditions present at the Site influenced by seasonal effects, the delivery of the remedial solution to target zones containing petroleum hydrocarbons at residual saturation is more effective under reduced saturated conditions. The delivery of TEA amended water to enhance the in situ biodegradation of petroleum contaminants is more effective when the treatment water has an increased residence time in the target remedial zone, attributed to low gradients and groundwater transport velocities at the Site. Longer residence periods enable the indigenous microbes to have increased contact time with the TEA which will be preferentially utilized to degrade the contaminants.   A reducing zone enriched with TEA in the anaerobic aquifer was established following consecutive injections of remedial test solution. A cumulative mass of 4 kg of NO3- was added to the target aquifer during the course of the remedial injections. Evidence demonstrating NO3- utilized as a terminal electron acceptor in the bioremediation of the petroleum-contaminated aquifer include: laboratory microcosm study confirming local indigenous microbial population’s ability to degrade hydrocarbons using NO3- as the TEA in addition to observed decrease in NO3- relative to a conservative Br- tracer and generation of nitrite, an intermediate product in denitrification in the pilot-scale operation. Contaminant mass removal likely occurred as Br- tracer evidence indicates that NO3- was utilized in the study area based on the inference of denitrification rates. Post-injection groundwater sampling indicate declining concentrations of toluene, however long term monitoring is recommended in order to evaluate the success of the remediation activity and assess the potential for rebound. Post-injection soil core results are unable to demonstrate the reduction in individual toluene, let alone BTEXTMB hydrocarbon levels, as a result of insufficient quantities of nitrate delivered to the target zone relative to the significant but heterogeneously distributed residual mass in the subsurface.

Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 248-255).

The Hex River Valley is one of the main centres in South Africa for cultivation of table grapes of export quality. The vines require irrigation water, which must be low in dissolved solids. Approximately two thirds of the annual irrigation requirement is obtained from boreholes and the balance from surface water sources. During the early 1960s a deterioration in the quality of the groundwater was noticed, becoming critical in some areas, and borehole yields also declined. The main objectives of this study were therefore to obtain an understanding of the hydrogeological and hydrogeochemical processes operating in the valley to explain the derogation of the groundwater resource and enable optimum utilisation and management of the resource in the future. To achieve these objectives, field work involving exploration drilling, aquifer tests, hydrocensus, long-term monitoring of groundwater levels and surfacewater flows and extensive sampling of the ground and surface waters was carried out. Analysis of these data gave quantitative information on groundwater occurrence, aquifer hydraulic properties, groundwater recharge and storage, chemical characteristics of the ground and surfacewaters and sources of dissolved species. / KMBT_363 / Adobe Acrobat 9.53 Paper Capture Plug-in