Thesis (doctoral)--Swiss Federal Institute of Technology, Zurich, 1997. / Vita. Includes bibliographical references (p. 121-128).

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.

Thesis (M. Phil.)--University of Hong Kong, 1979.

This dissertation considers modeling groundwater flow under imprecisely known parameters and managing a plume of contaminant. A new approach has been developed to study the effects of parameters uncertainty on the dependent variable, here the head. The proposed approach is developed based on fuzzy set theory combined with interval analysis. The kind of uncertainty modeled here is the imprecision associated with model parameters as a result of machine or human imprecision or lack of information. In this technique each parameter is described by a membership function. The fuzzy inputs into the model are in the form of intervals so are the outputs. The resulting head interval represents the change in the output due to interval inputs of model parameters. The proposed technique is illustrated using a two dimensional flow problem solved with a finite element technique. Three different cases are studied: homogeneous, mildly heterogeneous and highly heterogeneous transmissivity field. The groundwater flow problem analysis requires interval input values for the parameters, the output may be presented in terms of mean value, upper and lower bounds of the hydraulic head. The width of the resulting head interval can be used as a measure of uncertainty due to imprecise inputs. The degree of uncertainty associated with the predicted hydraulic head is found to increase as the width of the input parameters interval increases. Compared to Monte Carlo simulation approach, the proposed technique requires less computer storage and CPU time, however at this stage autocorrelation and crosscorolation are not configured in the presented formulation. In the plume containment problem two formulations are presented using the hydraulic gradient technique to control the movement of the contaminants. The first one is based on multiobjective analysis and the second, on fuzzy set theory. Multiobjective analysis yields a set of alternative strategies each of which satisfies the multiple objectives to a certain degree. Three different techniques have been used to choose a compromise strategy. Although they follow different principles, the same preferred strategies are selected. It is also noticed that rapid restoration results in a large pumping volumes and high costs. Using a fuzzy formulation for plume containment yields the optimum pumping rates and locations in addition to the membership function at each pumping location. The resulting membership functions at these pumping locations can be used to study the sensitivity of each location to a change in objective function and constraints bounds. Overall, both the fuzzy and multiobjective methodologies, presented in this dissertation, provide new and encouraging approaches to groundwater quality management.

published_or_final_version / abstract / toc / Earth Sciences / Master / Master of Philosophy

Project Completion Report, OWRT Project No. A-056-ARIZ / Agreement No. 14-31-0001-5003 / Project Dates: July 1974 - June 1975 / Acknowledgement: The work upon which this report is based was supported by funds provided by the State of Arizona and the United States Department of the Interior, Office of Water Research and Technology as authorized under the Water Resources Research Act of 1964. / Specific objectives of the project included (1) examining the effect of pit recharge, using industrial blowdown effluent, on local ground-water levels and quality in the Tucson basin; and (2) evaluating the applicability of two digital models for modelling the hydraulic response of the aquifer to pumping and recharge. Fourteen pit trials ranging from 1 day to 185 days duration were implemented during a two year period. The total volume of effluent recharged was 157 ac-ft. Pit recharge on a limited basis did not appear to offset the general decline in local ground -water levels. However, recharge deteriorated the quality of ground water in shallow (150 ft) wells but not in a deeper (300 ft) well. A finite difference (FD) model and a finite element model (FEM) were used to simulate hydraulic conditions in a 2000. ft by 2000 ft aquifer region near the pit. An attempt was made to calibrate the models using water level data from a two-week aquifer test on a shallow well. Results were depicted using a three-dimensional graphics technique (SYMVU). Better results were obtained with the FD model than with the FEM, primarily because a finer mesh was used to discretize the region with the FD model than with the FEM. Results of the FEM were also biased by the rectangular configuration of the aquifer boundary. The finite element model was used to simulate aquifer response during a pit recharge test. Again, results were limited by the injudicious selection of elements and boundary configurations.

Geologic applications of Landsat images in northeastern Arizona to the location of water supplies for municipal and industrial uses / A Final Report of Work Performed Under OWRT Matching Grant B-066-ARIZ, Agreement number: 14-34-0001-8060 / April 1979

<p>This study focuses on the development of a Direct Aqueous Injection Gas Chromatographic method with Flame Ionization Detection (DAI-GC/FID) for the analysis of MTBE and TBA. The analytical method was then applied in a site specific study where MTBE contamination was evident. The method achieved detection limits of 1 ppm for MTBE and 0.1 ppm for TBA. The method showed good precision, accuracy and selectivity. The method was selected primarily for its ability to simultaneously analyze MTBE and TBA. The result of the site specific study showed the persistence of high concentrations of MTBE and TBA at the source of contamination, whilst concentrations at the adjacent primary school dropped to below detection limits as a result of rapid natural attenuation. It was found that an overall decrease in MTBE concentrations was met with an increase in TBA concentrations / which is a direct indication of MTBE degradation. Despite the fact that problematic MTBE concentrations persist at the source of contamination, limited evidence of the persistence of MTBE contamination was identified at the adjacent primary school. As such, MTBE health risks from existing pathways were found to be irrelevant for receptors at the adjacent school.</p>

The increase in the contamination of ground-water (GW) with nitrates in both developing and developed countries mainly results from agricultural activities and improper sanitation systems, and is a recent phenomenon that has become a source of great health concern, particularly in regions where people rely on the ground-water as their primary water source. Due to the advantages of using Permeable Reactive Barriers (PRB) including its cost-effectiveness as well as its capability to remove or mitigate the spread of large spectrum of contaminants (including nitrates), a significant increase has been observed in the use of this subsurface treatment technology compared to other methods. However, identifying more economic and reliable reactive media to be used instead of the costly conventional PRB materials is now of key importance. Two local soils namely Berea Red Sand (BRS) and Umgeni Sand (US) were the main focus of this research. In addition to these soils, Zero Valent Iron (ZVI) was also used in this study. Through the use of batch experiments the feasibility of the nitrate reduction was investigated by five substrates including 100% ZVI, 100% BRS, 100% US, mix of 75% ZVI + 25% BRS, and mix of 50% ZVI + 50% BRS. Five concentrations of nitrate synthetic solution including 10 mg/l, 25 mg/l, 50 mg/l, 100 mg/l, and 500 mg/l were used to simulate nitrate-contaminated ground-water. All the batch experiments were performed under semi-aerobic and uncontrolled pH conditions, and only one solid/liquid ratio of 1:10 was used. The two mixes (mix of 75% ZVI + 25% BRS, and mix of 50% ZVI + 50% BRS) exhibited a nitrate removal efficiency of 100%, with all the different initial concentrations that were used with it; besides these two mixes, none of the other substrates showed this performance. 100% ZVI; however, managed complete nitrate reduction when the 10 mg/l and 25 mg/l concentrations were used. Finally, it was concluded that the benefits of using BRS in combination with other materials such as ZVI in the PRB field are promising. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

The impact of septic tank effluent disposal on groundwater quality was investigated at Oxford. The Oxford township can be regarded as typical of many small communities on the Canterbury Plains which have a high density of septic systems serviced by soakage pit drainage. The primary concern with grouped septic systems is the potential for both chemical and microbial groundwater contamination. The alluvial gravel aquifers of the Canterbury Plains are especially susceptible to microbial contamination due to the high rates of groundwater flow which may transport both bacteria and viral contaminants over large distances. Geological investigations established the presence of an areally extensive, tuff derived, clay unit which forms an aquitard beneath the unconfined aquifer in the north of the Oxford area. Recharge of the unconfined aquifer above the clay unit is exclusively from rainfall infiltration while to the south, groundwater levels respond to rainfall infiltration and influent seepage from the Eyre River. The presence of two hydrogeologically distinct gravel units within the unconfined aquifer was determined by application of the column dilution technique. Point dilution tests showed the average groundwater velocity of 130 m/day in the upper gravel unit to be significantly higher than the 40 m/day measured in the underlying gravels. The presence of discrete channels of preferred flow within the unconfined aquifer system was also established by point dilution tests, intrachannel velocities ranging from 210 to 400 m/day. A resistivity salt tracing test indicated groundwater flow in an easterly direction with a velocity of 250 m/day through an observed channel feature. Groundwater quality monitoring showed a significant degree of groundwater contamination close to the Oxford township. Concentrations of faecal coliform bacteria in excess of drinking water standards were detected up to 900 m downgradient of the nearest septic tank. Elevated levels of chemical indicators (N03-N, CL-) were also detected in all monitoring wells. The pattern of groundwater contamination was complex, reflecting both the heterogeneity of groundwater flow through the unconfined aquifer system and the influence of monitoring well location. Predictive modelling indicated the potential for the transport of faecal coliform bacteria up to 2.6 km downgradient of Oxford. Modelling also suggested increased urban development within Oxford to have a relatively minor effect on the overall extent of groundwater contamination. Additional hydrogeological and water quality data, aided by the application of numerical solute transport modelling techniques, may provide a more accurate estimate of the impact of septic tank effluent disposal on groundwater quality. Future sewage disposal options for Oxford have to balance the low potential for microbial contamination of drinking water supplies outside the groundwater zone delineated by this study, against the environmental acceptability continuing contamination of this zone. This study has identified the need for further research into the effects of septic tank effluent discharge on groundwater quality in the Canterbury region, to provide a sound base for future resource management decisions.