1 |
Solute transport and hydrodynamic characteristics in the Chalk aquifer at Tilmanstone, KentWatson, Sally Jane January 2006 (has links)
Research on the hydrodynamic characteristics of the Chalk aquifer is described in relation to the timescales and spatial extent of solute transport, focussing on the Tilmanstone - Eastry valley in east Kent. Groundwater contamination occurred there over a 70-year period as a result of coalfield brine infiltrating from surface lagoons. The resulting contamination is used as a large-scale, long-term conservative solute transport experiment, within which a series of geological and hydrogeological observations, and tracer tests, are used to investigate the transport properties of the Chalk. The objective is to consider appropriate methodologies for application to groundwater contamination investigations in the Chalk and characterisation of Chalk groundwater bodies in the context of the requirements of the EU Water Framework Directive. The geology and hydrogeology of the Tilmanstone area are reassessed in the light of recent work on Chalk lithostratigraphy, using available hydrological data and employing a regional groundwater flow model, coupled with a solute transport model utilising a first order mass transfer coefficient dual porosity approach. Field tests are analysed in terms of aquifer properties pertinent to solute transport at a scale of metres to tens of metres. Vertical profiles of hydraulic conductivity, groundwater velocity, fracture aperture and effective porosity are developed. A profile of chloride concentration in porewater is interpreted in the light of this work to develop a hydrostratigraphy for the area. A 1-D dual porosity model employing Fickian diffusive exchange is used to compute chloride concentration of fracture water and matrix porewater over time. This provides predictions for comparison with observations and the results of the mass transfer coefficient approach in the 3-D regional model. The combined results from the 1-D and 3-D models are used to direct development of a conceptual model of contaminant transport in the Chalk. Emphasis is placed on the effects of diffusive exchange between porewater and fracture water and the effects of the solute exchange approach adopted at different times in the plume history. Results are used to judge the applicability of methods for investigating contaminated groundwater and characterising groundwater bodies in the dual porosity Chalk aquifer.
|
2 |
Physical characterisation of groundwater flow systems of selected poorly productive bedrock aquifers in IrelandNitsche, Janka January 2015 (has links)
Low productivity and typical heterogeneous conditions within poorly productive aquifers have resulted in very few detailed hydrogeological assessments of these bedrock aquifers being carried out in Ireland to date. This study carries out detailed characterisation of aquifer properties and geological structures on three catchment sites in order to refine the current generic conceptual model of poorly productive bedrock, adopted by the Irish Environmental Protection Agency. Hydrogeological properties were determined using hydraulic head data, pumping tests and tracer tests from borehole studies. Structural bedrock properties were investigated using borehole geologging, outcrop fracture analysis, and areal lineament mapping. Hydrological catchment characteristics were investigated by means of simple water balance approaches. Data results were synthesised into one coherent conceptual model of groundwater flow in poorly productive bedrock aquifers, for each of the three study catchments and for one generic-type Irish model. Very low flows encountered in many of the study boreholes proved challenging for conventional borehole flow methods. A new simple, effective pumpback dilution test for single boreholes was developed during this research, which successfully identified hydraulically active fractures which intersect the borehole at depth. This relatively cheap test can be completed in a small number of hours, and is also applicable to other aquifer types. The study concludes that detailed structural and/or tectonic models alone may not always be representative of the open discrete fracture systems which facilitate flow in the aquifer. Instead, emphasis should be placed on identifying representative numbers of hydraulically active fractures at depth in an aquifer, for which distinct fracture sets can be identified and used to generate open fracture network models. Only then may reliable estimates of aquifer permeability and contributions to surface waters be made, for site-specific catchments.
|
3 |
The integration of multi-scale hydrogeophysical data into numerical groundwater flow modelsDickson, Neil Edwin Matthew January 2015 (has links)
Throughout this research, geophysical data is utilised to constrain numerical groundwater flow models at two applied study areas: a sandstone aquifer in Northern Ireland and a basement rock aquifer in Benin, west Africa. In Northern Ireland, airborne passive magnetics data are used to determine regional heterogeneity occurrence combined with methods of upscaling / equivalence and a density function. Furthermore, a stochastic component is undertaken in the form of multiple point statistics. This analysis performs a probability simulation and pattern matching to determine a statistical occurrence of heterogeneity distribution. In Benin, point magnetic resonance sounding data and electrical resistivity tomography surveys are utilised to determine relationships to hydrogeological properties to aid many conceptualisations of the. region. All studies employed finite element groundwater flow modelling, alongside comparative statistics and model ranking to determine the success and applicability of such analysis. In Northern Ireland, the deterministic analysis indicates that an intermediate level of upscaling (between field scale and one regional anisotropy value) provides statistically significant results at regional scale. The stochastic analysis effectively 'cleans' the magnetics data to provide a new distribution of regional heterogeneity. Modelling results are relatively comparable to the deterministic analysis and demonstrate the successful application of continuous geophysical data into model parameterisation. In Benin, all models provide significant results despite variations in model geometry and parameter conceptualisation. Point geophysical data permits effective model creation and parameter distribution through positive correlation to hydro-structural controls. For all models, minimal boundary conditions are applied and no post-processing is performed. As a result, the benefit of adapting geophysics for model parameterisation is clearly evident and suggests new hydrogeological paradigms for the study areas. Further work is required with regard to predicted anthropogenic and climate change scenarios.
|
4 |
Intrusive igneous control on groundwater in the Triassic sandstones of Northern IrelandBurns, Claire Elizabeth Graham January 2014 (has links)
This thesis describes the processes adopted to form the major conclusion that igneous dykes that traverse the Belfast Groundwater Body impede the movement of groundwater in the aquifer to a significant extent. Chapter one introduces the project and its purpose. Chapters two and three are to a large extent literature based, with Chapter two focusing on generic techniques and examples of relevant research on an international scale, where Chapter three focuses on literature specific to the study are" and facilitates a discussion of aquifer behaviour and the formation of an initial conceptual model for groundwater flow. Chapter four describes the re-appraisal of the geological model for the study area using a recently published airborne magnetic geophysical dataset (Tellus). The progression of this Chapter sees the geological model described in the context of the hydrogeological behaviour of the study area, and a discussion at the end facilitates the description of a geological conceptual model of an igneous dyke and an improved understanding of the processes controlling groundwater movement in the Sherwood Sandstone aquifer. Chapter five uses the conceptual understanding developed from previous chapters to construct a numerical model in FeFlow as a tool to assess aquifer sensitivities. The model described progresses from the most basic homogeneous and isotropic representation of the groundwater flow system, and progresses through nine scenarios to be inclusive of homogeneity (transsmissivity and recharge), homogeneous vertical anisotropy, and with the inclusion of three-tier transmissive igneous dyke zones. Chapter six discusses the findings of the research, drawing comparisons from literature, Tellus, and numerical modelling. The discussion includes the schematic understanding of groundwater movement through the aquifer Inclusive of igneous dykes under various pressures. The discussion ends with some recommendations for the implementation of the conceptual model within an industrial and regulatory context. Chapter seven states the major conclusions formed from the research, and makes recommendations for future work.
|
5 |
A study on new approaches for delineating groundwater protection zones in fractured-rock aquifersCarneiro, Julio Ferreira January 2005 (has links)
Delineation of groundwater protection zones in fractured-rock aquifers usually involves the equivalent porous media (EPM) assumption, although research studies have proved that, often, such an assumption is inadequate. This thesis is concerned with the study of flow and transport models that, while preserving the main hydrodynamic features of fractured rocks, are still practical enough to be applied to low-budget studies such as the delineation of groundwater protection zones. Methodologies are developed for three different types of fractured-rock aquifers. The first group comprises composite aquifer systems, a single linear structure in an otherwise homogeneous aquifer. The transport model adopted is based on advection and the procedure for delineation of protection zones involves the derivation of advective velocity and stream function equations. The stream function facilitates visualisation of the capture zones, while isochrones are delineated through particle tracking. Dual and multiple-porosity aquifers, the second group, are dealt with analytically. The well- known flow and transport features of dual-porosity media are used to develop a method that takes into account the influence of matrix diffusion on the shape and size of protection zones. The methodology returns probability related protection zones that, when compared with single- porosity models, show that matrix diffusion has a dramatic effect on protection zones size. Additionally, a new multiple-porosity model is developed, that simulates the hydraulic behaviour of hierarchical fracture systems. Analytical solutions are presented for 2-D flow and 1-D transport. The third group comprises fracture network aquifers. The work conducted involves the implementation of practical tools for simulating solute transport in fracture networks, which are then used to delineate probabilistic protection zones. A first approach applies the Statistical Continuum Method, a hybrid tool that combines the use of Discrete Fracture Networks and Continuum Models. A second method relies on a Continuous Time Random Walk (CTRW). Analytical solutions for modelling solute transport in fracture networks according to a CTRW are found and combined with MODFLOW to simulate solute transport in catchment-scale domains. Additionally, the following are discussed: methodologies for assessing protection zones in fractured-rocks delineated using EPM approaches ways for implementing a 3-D CTRW and the two issues of probability versus concentration and of forward versus reverse particle tracking, when simulating solute transport in fractured-rock aquifers.
|
6 |
Solid organic carbon in UK aquifers : its role in sorption of organic contaminantsSteventon-Barnes, Hannah January 2001 (has links)
A major control on the attenuation of organic contaminants dissolved in groundwater is their sorption onto solid organic matter (OM) in the rock. Sorption modelling is currently based on the amount of solid organic carbon in the rock. However, there are very few available data on the total organic carbon (TOe) content in common UK geological materials. A significant new set of Toe measurements on a range of important formations is presented. Methods to measure TOe in geological, especially carbonate-rich, samples are reviewed and evaluated. The impact of the type of OM on its sorption capacity is not understood. Non-linear isotherms measured on seven samples (of Lincolnshire Limestone, Glacial Till from Norfolk and unconsolidated deposits) had a wide range of organic carbon normalised distribution coefficients (Koc from 7.85 l/g to 767 l/g at 0.01 gil trichloroethene). This indicates the impact of characteristics of the OM. Bulk geochemistry and micro-morphology characteristics of the OM that could be important predictors for sorption capacity are investigated and identified. Organic matter has been isolated, and the isolation technique evaluated. The major element composition of the isolated OM has been determined; elemental results were found to correlate with results of a pyrolysis analysis applied to whole rock samples. Morphological analysis of microscope slides of isolated organic matter provided information on the physical types (visually) and size (by image analysis) of the organic particles. Measured Koc values correlated with the elemental HlO content of the sample's OM and with the pyrolysis measurements, but not with morphological results. The effect of selected empirical isotherms on solute transport was simulated: use of an accurate distribution coefficient is essential, but non-linearity was found not to make a major impact on arrival results. Recommendations are made for the improvement of sorption modelling, and for appropriate analysis methods to supply relevant data on the type of OM in this context.
|
7 |
Dual porosity reactive transport modelingCheng, L. January 2005 (has links)
No description available.
|
8 |
Hydrogeochemistry of seepage entering deep tunnels in crystalline rock : Cruachan Power Station, ScotlandDudgeon, Bruce A. January 2005 (has links)
No description available.
|
9 |
The development of an efficient and stable solution to the advection dispersion equation for saline groundwater flowSeif, Wael January 2004 (has links)
No description available.
|
10 |
Isotopic studies of groundwater diagenesisBarker, Andrew Paul January 1996 (has links)
No description available.
|
Page generated in 0.0295 seconds