published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Groundwater is now being considered as an alternative water supply in the Pearl River Delta (PRD) because of the increasing demand for fresh water coupled with deterioration in river water quality as a result of rapid urbanization and industrialization. There are thick aquitards in the PRD as a result of several times transgression and regression in the Holocene. This study considers this aquitards as a research object because it has a significant impact on the underneath confined aquifer. It is necessary to analyze the hydraulic properties of the aquitards. A slug-test is a reasonable method to determine the hydraulic conductivity and specific storage of the low-permeability aquitards of silt and clay in the PRD. In this study, several slug-test methods were used to determine the hydraulic parameters of aquitards in several piezometers at the key site MZ04in the PRD. The results from these methods were compared to obtain the most reasonable group of hydraulic parameters. A reasonable equivalent numerical method is applied at the key site MZ04 site after the calibration with the C-B-P solution and the KGS model. The natural groundwater regime is obtained, which is helpful for the further research. A three-dimensional numerical model using MODFLOW is carried out under some assumptions and the simplification for the sediments structure. The characteristics of regional groundwater flow and the influence of hydraulic properties of the aquifer-aquitard system on groundwater flow were analyzed. The simulated groundwater level both in the unconfined aquifer and confined aquifer agree reasonably well with the observed data. Study on the water budget of the groundwater showed that the quantity of ground water discharged from participation to participate the water exchange is very small. In the groundwater participated water exchange, 97% of them flow into rivers, while only 3% of them flow into the sea. Moreover, the vertical flow is more important than the horizontal flow to the regional ground water balance in aquitards according to the water budget obtained from the model. The research of the PRD needs numerous data due to the complicated deposition and evolution process of the sediments and the intensive river network. The modeling results are preliminary because of the complexity of the geological and hydrogeological conditions in the PRD and the limitation of the observed water level data. The hydraulic parameters calculated for this study and the model results can provide a basis for further research on groundwater in the PRD. / published_or_final_version / Earth Sciences / Master / Master of Philosophy

An aquitard is not only a confining layer in the aquifer-aquitard system, but also a functional complex for nutrient reservation and microorganism inhabitation. Geochemical characteristics and geomicrobial processes in aquitards play an important role in groundwater quality, and should be well studied. The Pearl River Delta is dominated by clay-rich aquitards and was intensively influenced by Holocene transgression. In this thesis, the aquifer-aquitard system in the PRD was studied from various perspectives including geophysics, geochemistry and geomicrobiology. Sediment and groundwater samples were taken from representative locations in the PRD at different lithological units. Particle size distribution, computed axial tomography, optically stimulated luminescence dating and scanning electron microscopy were analyzed to understand the geophysical properties. Concentrations of major ions and abundances of environmental isotopes were measured for geochemical analysis. Bacterial 16S rRNA gene clone libraries were constructed to analyze microbial identifications and community structures in different strata. Gene abundances of anammox 16S and bacteria amoA in both sediment and groundwater samples were quantitatively analyzed with 15N isotope at the same depth. The mixing process of seawater and river water was the dominant factor controlling the isotopic and chemical characterizes of groundwater in the system. Isotopic fractionation in the aquitards was majorly controlled by chemical and biological reactions other than diffusion. Chemical pattern in this system was mainly controlled by topography and sea level in the Holocene. Independent sedimentary centers of strong reducing environment were located in the depressions controlled by fault zones, and generated massive amount of pyrite minerals in the sediment and NH4+ in the groundwater. The sea level and depositional environment in the Holocene determined the physical structures of the sediment and seawater/river-water ratio in the estuary. Isotopic research also demonstrated that South Asia Monsoon was the major source of atmospheric precipitation in the PRD. Bacterial species in the PRD sediment were identified. Canonical correspondence analysis between bacterial linages and environment factors showed that community structures were significantly modified by geological conditions. High bacterial diversity was observed in samples from the Holocene aquitard M1 and aquifer T1, while in the older aquitard M2 and basal aquifer T2, the bacterial diversity was much lower. Chloroflexi, γ-proteobacteria and δ-proteobacteria were the dominant phyla in the aquitard sediment. β-proteobacteria was the dominant phylum in sediment which was strongly influenced by fresh water. Anammox was the controlling biochemical process in microbial-derived ammonium loss, as demonstrated by gene abundance coupling with 15N isotope and ammonium concentration. The 16S gene abundance of anammox bacteria ranged from approximately 105 to 106 copies/g in the aquitard sediment, and ranged from 104 to 105 copies/g in aquifers. amoA gene abundance was 1-2 orders lower than anammox bacteria 16S in aquitard sediment, but in aquifers, the gene abundances of amoA and anammox 16S were similar. Interface between aquifer and aquitard was demonstrated as biochemically enhanced zone. The results of this study significantly benefited the understanding of geochemistry and microbiology in the aquifer-aquitard system, and showed directions for future work on geomicrobiology in aquitards. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

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Emirate of Abu Dhabi is located in an arid region, where the main source of fresh water is desalination plants. The vulnerability of desalination plants renders planning for an alternative source of freshwater essential. In this study the feasibility of aquifer storage and recovery in the Liwa area, in Emirate of Abu Dhabi, United Arab Emirates was investigated. Based on operational data collected from the pilot project, the model was set up and calibrated. The calibrated model was used to study the affect of various operational parameters, namely storage duration, pumping rate, screen location, multiple cycle operation and periodic recharge, as well as some aquifer characteristics factors: dispersion and salinity profile. This study can be utilized to optimize the operation of the Liwa ASR project. / text

Implementing geological carbon sequestration at a scale large enough to mitigate emissions will involve the injection of supercritical CO₂ into deep saline aquifers. The principal technical risks associated with such injection are that (i) buoyant CO₂ will migrate out of the storage formation; (ii) pressure elevation during injection will limit storage rates and/or fracture the storage formation; and (iii) groundwater resources will be contaminated, directly or indirectly, by brine displaced from the storage formation. An alternative to injecting CO₂ as a buoyant phase is to dissolve it into brine extracted from the storage formation, then inject the CO₂-saturated brine into the storage formation. This "surface dissolution" strategy completely eliminates the risk of buoyant migration of stored CO₂. It greatly mitigates the extent of pressure elevation during injection. It nearly eliminates the displacement of brine. To gain these benefits, however, it is essential to determine the costs of this method of risk reduction. This work provides a framework for optimization of the process, and hence for cost minimization. Several investigations have tabulated the storage capacity for CO₂ in regions around the world, and it is widely accepted that sufficient pore volume exists in deep subsurface formations to permit large-scale sequestration of anthropogenic CO₂. Given the urgency of implementing geologic sequestration and other emissions-mitigating technologies (storage rates of order 1 Gt C per year are needed within a few decades), the time required to fill a target formation with CO₂ is just as important as the pore volume of that formation. To account for both these practical constraints we describe in this work a time-weighted storage capacity. This modified capacity integrates over time the maximum injection rate into a formation. The injection rate is a nonlinear function of time, formation properties and boundary conditions. The boundary conditions include the maximum allowable injection pressure and the nature of the storage formation (closed, infinite-acting, constant far-field pressure, etc.) The time-weighted storage capacity approaches the volumetric capacity as time increases. For short time intervals, however, the time-weighted storage capacity may be much less than the volumetric capacity. This work describes a method to compute time-weighted storage capacity for a database of more than 1200 North American oil reservoirs. Because all of these reservoirs have been commercially developed, their formation properties can be regarded as representative of aquifers that would be attractive targets for CO₂ storage. We take the product of permeability and thickness as a measure of injectivity for a reservoir, and the product of average areal extent, net thickness and porosity as a measure of pore volume available for storage. We find that injectivity is not distributed uniformly with volume: the set of reservoirs with better than average injectivity comprises only 10% of the total volumetric storage capacity. Consequently, time weighted capacity on time scale of a few decades is 10% to 20% of the nominal volumetric capacity. The non-uniform distribution of injectivity and pore volume in the database coupled with multiphase flow effects yields a wide distribution of “filling times”, i.e. the time required to place CO₂ up to the boundaries of the formation. We define two limiting strategies based on fill times of the storage structures in the database and use them to calculate resource usage for a target storage rate. Since fill times are directly proportional to injectivity, smallest fill time corresponds to best injectivity and largest fill time corresponds to smallest injectivity. If best injectivity structures are used first, then the rate at which new structures would be needed is greater than if worst injectivity structures are used first. A target overall storage rate could be maintained for longer period of time when worst injectivity structures are used first. Because of the kh vs PV correlation, most of the pore volume remains unused when no extraction wells are used. Extraction wells require disposal of produced brine, which is a significant challenge, or beneficial use of the brine. An example of the latter is the surface dissolution process described in this thesis, which would enable use of a much greater fraction of the untouched pore volume. / text

No description available.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1983. / Bibliography: leaves 190-192. / Microfiche. / x, 192 leaves, bound ill. 29 cm

The islands of Hawaii face increasing ground-water demands due to population growth in the last decades. Analytical and numerical models are essential tools for managing sustainable ground-water resources. The models require estimates of hydraulic properties, such as hydraulic conductivity and storage parameters. Four methods were evaluated to estimate hydraulic properties for basalts on the island of Maui. First, unconventional step-drawdown tests were evaluated. The results compare favorably with those from classical aquifer tests with a correlation of 0.81. Hydraulic conductivity is log-normally distributed and ranges from 1 to 2,500 m/d with a geometric mean of 276 m/d and a median of 370 m/d. The second approach developed a simplified parameter-estimation scheme through an empirical relationship between specific capacity and hydraulic parameters that utilized Hawaii's state well database. For Maui's basalts, the analysis yields a geometric-mean and median hydraulic conductivity of 423 and 493 m/d, respectively. Results from aquifer tests and specific-capacity relationships were used to generate island-wide hydraulic-conductivity maps using kriging. The maps are expected to be of great benefit in absence of site-specific field assessments. In the third approach, ocean-tide responses in the central Maui aquifer were used to estimate an effective hydraulic diffusivity of 2.3 x 10^7 m^2/d. The position of the study area necessitated refining the existing analytical solution that considers asynchronous and asymmetric tidal influence from two sides in an aquifer. Finally, measured ground-water responses to wave setup were used to estimate hydraulic parameters. Setup responses were significant as far as 5 km inland and dominated barometric-pressure effects during times of energetic swell events. The effective diffusivity estimated from setup was 2.3 x 10^7 m^2/d, matching that based on tides. Additionally, simple numerical ground-water flow models were developed to assess the accuracy of results from analytical solutions for step-drawdown tests, dual-tides and wave setup, and to evaluate sediment-damping effects on tidal propagation. The estimated mean hydraulic conductivities of the four methods range between 300 and 500 m/d for basalts in Maui. The results of different methods are consistent among each other and match previous estimates for basalts. / USGS Pacific Island Water Science Center

The study focuses on the adjacent Tenthill and Ma Ma catchments which converge onto the heavily cultivated alluvial plain of Lockyer Creek. Groundwater extracted from the alluvial aquifers is the primary source of water for intensive irrigation. Within the study the hydrogeology is investigated, a conceptual groundwater model produced and a numerical groundwater flow model is developed from this. The hydrochemistry and stable isotope character of groundwater are also investigated to determine processes such as recharge and evaporation. Examination of bore logs confirms the Quaternary alluvium comprises a laterally continuous gravel aquifer with an average thickness of 4.5 m, overlain by mixed sands and clays which form a semi-confining layer with an average thickness of 22 m. Variations in long term groundwater hydrographs indicate the aquifer changes from confined to unconfined in some locations as water levels drop, while bores adjacent to creek banks display a rapid response to a flood event. Pump testing of bores screened in the gravel produces estimates of hydraulic conductivity ranging from 50-80 m/day and storativity of 0.00166 which are both within realistic bounds for this aquifer material. Major ion chemistry of surface water collected during a flood is Mgdominated, similar to alluvial groundwater in the Tenthill catchment and the Lockyer plain, suggesting a strong connection between surface and groundwater in these locations. Alluvial groundwater salinity in Tenthill catchment is typically less than 3500 ìS/cm but may approach 6000ìS/cm on the Lockyer plain. By contrast Ma Ma catchment alluvial groundwater is Na-dominated with conductivity up to 12000 ìS/cm and more associated with groundwater from the underlying sandstone bedrock. Stable isotope analyses of alluvial groundwater from throughout both catchments and the Lockyer plain are compared with basalt and sandstone groundwater. A range of processes have been identified including recharge to alluvium from basalt groundwater and evaporated surface water; and alluvial-bedrock groundwater mixing at some locations. Integration of the components of the study enabled the production of a conceptual hydrogeological model of the Lockyer alluvial plain, proposing two hydrostratigraphic units; the gravel aquifer and the overlying mixed sand and clay which acts as a semi confining unit. Hydrochemical and stable isotopic evidence suggests seepage from creek channels as the dominant recharge process. A single layer groundwater flow model using MODFLOW was developed, based on groundwater extraction data, to represent flow in the gravel aquifer. The model was calibrated to transient conditions with groundwater fluctuations, incorporating both drought and flood conditions. A sensitivity analysis for each of the aquifer properties demonstrates the model is insensitive to variations within realistic bounds for the gravel aquifer material, however, the model is highly sensitive to changes in the chosen boundary conditions. Predictive simulations with several annual extraction scenarios ranging from 1.75 to 0.5 ML/ha indicate the resulting minimum saturated aquifer thickness ranges from 0.03 to 1.4 m.