No description available.

Groundwater is one of the least studied environments, yet many people rely on groundwater for their sole drinking water supply. Little is known about the indigenous microflora, but it is believed to be similar to oceanic planktobacteria due to the low nutrient concentrations occurring in both ecosystems. That is, groundwater microorganisms are atypically small, mostly Gram-negative cells. Also like the oceanic planktobacteria, they may have no affinity for surface attachment and may rely on dissolved low molecular weight organic substrates in dilute solution for their nutrition. Periods of metabolic dormancy may occur when natural substrate concentrations drop below the level required to sustain vegetative cell function. In these studies total cells present were determined by 4'6-diamidino-2-phenylindole (DAPI) epifluorescent counts. The percentage of those bacteria which were metabolically active was determined by a modification of the 2-(p-iodophenyl)-3-(p- nitrophenyl)- 5-phenyl tetrazolium chloride (INT) reduction method. Advantages of this method over others include more specific fluorochrome staining, ease of transfer of the cells to the slide, time saved, and ease of microscopic viewing. Heterotrophic uptake of aspartate, succinate, glucose and fructose by indigenous bacteria was measured and calculations of maximum uptake velocity (V_max) and a constant (K_t + S_n) equalling the natural substrate concentration (S_n) plus the half-saturation concentration (K_t) were made based on net assimilation (cellular retention) of radiolabeled substrate. Total counts by DAPI staining were 4-12.1 x 10⁴ cells/ml of which 17.4 to 20.85% were metabolically active (INT+). Mean maximum uptake velocities ranged from 1.73 to 2000 nmol/l/hr with aspartate being taken up at the highest rate followed by fructose, succinate and glucose. / Master of Science

Approximately 80% of Virginians with private drinking water (PDW) sources are unaware of the quality of their drinking water. Strontium is a water quality contaminant gaining recognition at the federal level. At concentrations >1.5 mg/L, strontium substitutes calcium in the bones leading to bone density disorders (e.g. rickets). This is particularly problematic for children and individuals with low calcium and low protein diets. Because most Virginians do not know the quality of their PDW and since strontium poses a public health risk, this study investigates the sources of strontium in PDW in Virginia and identifies the areas and populations most vulnerable. Physical factors such as rock type, rock age, and fertilizer use have been linked to elevated strontium concentrations in drinking water. Meanwhile, social factors such as poverty, poor diet, and adolescence also increase social vulnerability to health impacts of strontium. Thus, this study identifies both physically and socially vulnerable regions in Virginia using water quality data from the Virginia Household Water Quality Program and statistical and spatial analyses conducted in RStudio 1.0.153 and ArcMap 10.5.1. Physical vulnerabilities were highest in the Ridge and Valley province where geologic formations with high strontium concentrations (e.g., limestone, dolomite, sandstone, and shale) are the dominant the aquifer rocks. The complex relationship between agricultural land use and strontium concentrations made it difficult to determine the impact of fertilizer use on strontium concentrations in PDW in Virginia. In general, the spatial distribution of social vulnerability factors was distinct from physical factors with the exception of food deserts. This study provides information and analysis to help residents of Virginia understand their risk of strontium exposure in PDW. / Master of Science / There are 1.7 million residents in Virginia that rely on private drinking water supplies in their homes. Those individuals are responsible for knowing how often to test their water, what to test their water for, and how to treat their water, if needed, to achieve safe drinking standards. Unfortunately, approximately 80% of Virginians with private drinking water sources (e.g., wells, cisterns, and springs) do not know if their water is safe to drink. Strontium, an element closely related to calcium, is a contaminant that the federal government recognizes as dangerous because in high quantities (>1.5 mg/L of water) it can replace calcium in bones making them brittle (e.g. rickets). These health impacts are more extreme in children and individuals with low calcium and low protein diets. Since strontium poses a public health risk, this study identified areas and populations in Virginia that have higher chances of being exposed to strontium and higher chances of their health being impacted by high levels of strontium. Physical factors such as rock type, rock age, and fertilizer use have been linked to elevated strontium concentrations in drinking water, indicating various physical vulnerabilities. Meanwhile, social factors such as poverty, poor diet, and adolescence also increase social vulnerability to the health impacts of strontium. This paper investigates regions in Virginia that are likely to contain high strontium levels and thus potential health impacts from strontium. Statistical and spatial analyses of water quality data from Virginia Cooperative Extension’s Virginia Household Water Quality Program combined with risk factor data identified vulnerable areas in Virginia. The highest chance of exposure was in counties near the western border of the state (e.g., Augusta, Fredrick, Highland, Montgomery, Shenandoah, and Wythe) due to the presence of limestone, dolomite, sandstone, and shale, all of which naturally contain high amounts of strontium. The land use data indicated that there were no strong patterns of strontium occurrence relative to fertilizer use. In general, the spatial distribution of social vulnerability factors was distinct from physical factors with the exception of food deserts occurring at high rates in the same areas as the samples with high strontium levels (e.g., Augusta, Fredrick, Highland, Montgomery, Shenandoah, and Wythe). The presence of food deserts prevents individuals from obtaining a high calcium and high protein diet, which makes them more vulnerable to the impacts of strontium. Overall, this study can help people in Virginia who are not on public water systems understand their risk of from being exposed to strontium.

The 1972 amendments to the Federal Water Pollution Control Act provide for major changes to reduce and eventually eliminate water pollution by 1985. In contrast, projections indicate that the volume of wastes generated by population and economic growth in the near future will be very large and the cost of treating it by standard methods will be extremely high. Hence, all possible systems and methods of waste disposal must be considered and ways of reducing the amount of waste discharges sought. In attempting to reach the goal of zero waste discharges, one alternative which must be considered in certain situations is the employment of deep well waste disposal (DWWD). This method accomplishes long term isolation of highly toxic liquid industrial wastes in confined subsurface geologic strata. This study undertakes a preliminary investigation of the potential of DWWD as a waste management tool. The analysis is conducted from an economic standpoint with the relevant economic concepts and issues being identified and examined as they apply to both users and regulators of the method as well as the general public. The direct cost for the system and its operation was discussed with particular attention paid to its derivation. Numerous site specific variables prevent generalizations concerning the cost of DWWD relative to surface treatment methods. On occasions, however, the method appears to have a greater initial capital outlay requirement but a much less operating and maintenance cost than alternative forms of wastewater management achieving the same effect. The social costs and benefits of deep well waste disposal were viewed in detail. Suggestions were made as how society might compensate the firm for the creation of social benefits in excess of social costs, and how they may be internalized into the firm's decision making process. Finally, the industrial potential for employing DWWD in the study area, designated as the Mid and South Atlantic states, is derived and discussed. / Master of Science

The problem of this thesis consists of a bacterial analysis of twenty-five representative wells within a radius of thirty miles of Canyon, Texas. An attempt has been made to determine the possible presence of the typhoid organism in these wells.

Agriculture and, more recently, oil and gas development have contributed to extensive degradation and loss of temperate grasslands. I investigated the landscape-scale effects of oil and gas development, and roads, on grassland birds in southern Alberta using abundance, clutch size and nesting success data collected from 2010-2014. I estimated: (i) the distance at which there are effects of edge, and effects of shallow gas well density, using piecewise regressions; (ii) the locations and extent of habitat affected by infrastructure for obligate grassland species– Baird’s Sparrow (Ammodramus bairdii), Chestnut-collared Longspur (Calcarius ornatus) and Sprague’s Pipit (Anthus spragueii); and generalist species – Clay-colored Sparrows (Spizella pallida), Horned Lark (Eremophila alpestris), Savannah Sparrow (Passerculus sandwichensis), Vesper Sparrow (Pooecetes gramineus) and Western Meadowlark (Sturnella neglecta), and (iii) the total area affected by wells and roads. My findings suggest that the effects of roads, overall, extended to further distances than edge effects associated with natural gas wells, obligate species had more habitat affected by infrastructure than generalist species and shallow gas wells affected more habitat than did oil wells, due to their greater density on the landscape. Additionally, obligates, on average, were negatively affected by proximity to edge where as generalists were more productivity closer to edge. Reducing fragmentation caused by roads, minimizing the spread of non-native vegetation and management of cattle around gas wells could improve habitat quality for these focal species. / February 2016

Electron spin relaxation and carrier recombination were investigated in gallium indium nitride arsenide (GaInNAs) multiple quantum wells, using picosecond optical pulses. Pump-probe experiments were carried out at room temperature, using pulses produced by a Ti:sapphire pumped optical parametric oscillator. The peak wavelengths of the excitonic resonances for the quantum well samples were identified using linear absorption measurements, and were found to be in the range 1.25µm-1.29µm. Carrier recombination times were measured for three samples of varying nitrogen content, and were observed to decrease from 548 to 180ps as nitrogen molar fractions were increased in the range 0.45-1.24%. Carrier recombination times were also measured for samples which had undergone a post-growth annealing process, and were found to be signicantly shorter compared to times measured for as-grown samples. Electron spin relaxation time was investigated for samples with quantum well widths in the range 5.8-8nm, and was found to increase with increasing well width, (i.e. decreasing quantum confinement energy), a trend predicted by both D'Yakonov-Kachorovskii and Elliott-Yafet models of spin relaxation in quantum wells. In a further study, longer spin relaxation times were exhibited by samples containing higher molar fractions of nitrogen, but having nominally constant quantum well width. Spin relaxation times increased from 47ps to 115ps for samples containing nitrogen concentrations in the range 0.45-1.24%. Decreases in spin relaxation time were observed in the case of those samples which had been annealed post-growth, compared to as-grown samples. Finally, all-optical polarisation switching based on spin relaxation of optically generated carriers in GaInNAs multiple quantum wells was demonstrated.

Hydrocarbon reserves are generally produced through wells drilled into reservoir pay zones. During production, gas liberation from the oil phase occurs due to pressure decline in the wellbore. Thus, we expect multiphase flow in some sections of the wellbore. As a multi-phase/multi-component gas-oil mixture flows from the reservoir to the surface, pressure, temperature, composition, and liquid holdup distributions are interrelated. Modeling these multiphase flow parameters is important to design production strategies such as artificial lift procedures. A wellbore fluid flow model can also be used for pressure transient test analysis and interpretation. Considering heat exchange in the wellbore is important to compute fluid flow parameters accurately. Modeling multiphase fluid flow in the wellbore becomes more complicated due to heat transfer between the wellbore fluids and the surrounding formations. Due to mass, momentum, and energy exchange between the wellbore and the reservoir, the wellbore model should be coupled with a numerical reservoir model to simulate fluid flow accurately. This model should be non-isothermal to consider the effect of temperature. Our research shows that, in some cases, ignoring compositional effects may lead to errors in pressure profile prediction for the wellbore. Nearly all multiphase wellbore simulations are currently performed using the "black oil" approach. The primary objective of this study was to develop a non-isothermal wellbore simulator to model transient fluid flow and temperature and couple the model to a reservoir simulator called General Purpose Adaptive Simulator (GPAS). The coupled wellbore/reservoir simulator can be applied to steady state problems, such as production from, or injection to a reservoir as well as during transient phenomena such as well tests to accurately model wellbore effects. Fluid flow in the wellbore may be modeled either using the blackoil approach or the compositional approach, as required by the complexity of the fluids. The simulation results of the new model were compared with field data for pressure gradients and temperature distribution obtained from wireline conveyed pressure recorder and acoustic fluid level measurements for a gas/oil producer well during a buildup test. The model results are in good agreement with the field data. Our simulator gave us further insights into the wellbore dynamics that occur during transient problems such as phase segregation and counter-current multiphase flow. We show that neglecting these multiphase flow dynamics would lead to unreliable results in well testing analysis.

Zugleich: Diss. Kiel, 2007. / Register. Literaturverz.

Hydraulic fracturing is essential for producing gas and oil at an economic rate from low permeability sands. Most fracturing treatments use water and polymers with a gelling agent as a fracturing fluid. The water is held in the small pore spaces by capillary pressure and is not recovered when drawdown pressures are low. The un-recovered water leaves a water saturated zone around the fracture face that stops the flow of gas into the fracture. This is a particularly acute problem in low permeability formations where capillary pressures are high. Depletion (lower reservoir pressures) causes a limitation on the drawdown pressure that can be applied. A hydraulic fracturing process can be energized by the addition of a compressible, sometimes soluble, gas phase into the treatment fluid. When the well is produced, the energized fluid expands and gas comes out of solution. Energizing the fluid creates high gas saturation in the invaded zone, thereby facilitating gas flowback. A new compositional hydraulic fracturing model has been created (EFRAC). This is the first model to include changes in composition, temperature, and phase behavior of the fluid inside the fracture. An equation of state is used to evaluate the phase behavior of the fluid. These compositional effects are coupled with the fluid rheology, proppant transport, and mechanics of fracture growth to create a general model for fracture creation when energized fluids are used. In addition to the fracture propagation model, we have also introduced another new model for hydraulically fractured well productivity. This is the first and only model that takes into account both finite fracture conductivity and damage in the invaded zone in a simple analytical way. EFRAC was successfully used to simulate several fracture treatments in a gas field in South Texas. Based on production estimates, energized fluids may be required when drawdown pressures are smaller than the capillary forces in the formation. For this field, the minimum CO2 gas quality (volume % of gas) recommended is 30% for moderate differences between fracture and reservoir pressures (2900 psi reservoir, 5300 psi fracture). The minimum quality is reduced to 20% when the difference between pressures is larger, resulting in additional gas expansion in the invaded zone. Inlet fluid temperature, flowrate, and base viscosity did not have a large impact on fracture production. Finally, every stage of the fracturing treatment should be energized with a gas component to ensure high gas saturation in the invaded zone. A second, more general, sensitivity study was conducted. Simulations show that CO2 outperforms N2 as a fluid component because it has higher solubility in water at fracturing temperatures and pressures. In fact, all gas components with higher solubility in water will increase the fluid’s ability to reduce damage in the invaded zone. Adding methanol to the fracturing solution can increase the solubility of CO2. N2 should only be used if the gas leaks-off either during the creation of the fracture or during closure, resulting in gas going into the invaded zone. Experimental data is needed to determine if the gas phase leaks-off during the creation of the fracture. Simulations show that the bubbles in a fluid traveling across the face of a porous medium are not likely to attach to the surface of the rock, the filter cake, or penetrate far into the porous medium. In summary, this research has created the first compositional fracturing simulator, a useful tool to aid in energized fracture design. We have made several important and original conclusions about the best practices when using energized fluids in tight gas sands. The models and tools presented here may be used in the future to predict behavior of any multi-phase or multi-component fracturing fluid system. / text