Browsing by Author "Sale, Tom, committee member"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Open Access A method using drawdown derivatives to estimate aquifer properties near active groundwater production well fields(Colorado State University. Libraries, 2014) Lewis, Alan, author; Ronayne, Michael, advisor; Sale, Tom, committee member; Sanford, William, committee memberThis thesis describes the development of a new inverse modeling approach to estimate aquifer properties in the vicinity of continuously-pumped well fields. The specific emphasis is on deep bedrock aquifers where monitoring well installation is often not practicable due to high drilling costs. In these settings, water levels from groundwater production wells offer a transient dataset that can be used to estimate aquifer properties. Well interference effects, if detectable at neighboring production wells, allow for an interrogated aquifer volume that is larger (and therefore more representative at the well field scale) when compared to single well hydraulic tests. The parameter estimation method utilizes drawdown derivatives to estimate the aquifer transmissivity and storativity. The forward model consists of an initial water level (or a recoverable water level drift function), an analytical solution for aquifer drawdown, and a correction term for well loss. The aquifer drawdown component is based on superposition of the Theis solution, although other analytical solutions are also applicable. The observed dataset was judiciously trimmed to reduce computer run-time while retaining enough points to adequately characterize aquifer and well parameters. By limiting observation points to special domains, the calculated drawdown and observed well water level derivatives with respect to time are independent of well loss, and therefore the transmissivity and storativity can be estimated without knowledge of the recoverable water level or loss coefficient for individual pumping wells. Aquifer properties in the forward model were estimated by minimizing the difference between the modeled and observed drawdown derivatives. The parameter estimation method is tested using hourly water level and pumping data from municipal well fields producing groundwater from sandstone aquifers of the Denver Basin. Data collected over a seven-year period from two distinct well fields, one operating in the Denver aquifer and another operating in the Arapahoe aquifer, are considered. The estimated transmissivities are 30.0 m2/d and 46.5 m2/d for the Denver and Arapahoe aquifers, respectively, whereas the storativities are 4.7×10-4 and 2.0×10-4, respectively. These estimates are within the range of previously reported values, indicating that production well data can be used to derive reasonable aquifer properties. A separate synthetic aquifer test case was considered to further test the parameter estimation methodology, as well as to evaluate the appearance of Theis-like response behavior at the wells. Synthetic water levels were generated using a numerical model with geostatistically-simulated heterogeneity that is characteristic of the Denver Basin (sandstone bodies separated by less permeable inter-bedded siltstone and shale). Analysis of the synthetic water levels revealed meaningful hydraulic properties; the effective hydraulic conductivity (best-fit transmissivity divided by the modeled aquifer thickness) was slightly higher than the geometric mean hydraulic conductivity of the heterogeneous field. In addition to aquifer properties, observed water level data were used to estimate the well-loss coefficient and recoverable water level for individual pumping wells. Loss coefficients obtained for wells in the Denver Basin indicate that this mechanism (head losses due to turbulence around the well screen) may contribute between 20 and 150 m of the total drawdown (based on a pumping rate of 1500 m3/d) commonly observed in these wells. The recoverable water level at each well, when fit with a linear drift function, provides a means of investigating the prevailing trend in aquifer heads due to other regional influences outside the modeled well field.Item Open Access Application of semi-analytical multiphase flow models for the simulation and optimization of geological carbon sequestration(Colorado State University. Libraries, 2014) Cody, Brent M., author; Bau, Domenico, advisor; Labadie, John, committee member; Sale, Tom, committee member; Chong, Edwin, committee memberGeological carbon sequestration (GCS) has been identified as having the potential to reduce increasing atmospheric concentrations of carbon dioxide (CO2). However, a global impact will only be achieved if GCS is cost effectively and safely implemented on a massive scale. This work presents a computationally efficient methodology for identifying optimal injection strategies at candidate GCS sites having caprock permeability uncertainty. A multi-objective evolutionary algorithm is used to heuristically determine non-dominated solutions between the following two competing objectives: 1) maximize mass of CO2 sequestered and 2) minimize project cost. A semi-analytical algorithm is used to estimate CO2 leakage mass rather than a numerical model, enabling the study of GCS sites having vastly different domain characteristics. The stochastic optimization framework presented herein is applied to a case study of a brine filled aquifer in the Michigan Basin (MB). Twelve optimization test cases are performed to investigate the impact of decision maker (DM) preferences on heuristically determined Pareto-optimal objective function values and decision variable selection. Risk adversity to CO2 leakage is found to have the largest effect on optimization results, followed by degree of caprock permeability uncertainty. This analysis shows that the feasible of GCS at MB test site is highly dependent upon DM risk adversity. Also, large gains in computational efficiency achieved using parallel processing and archiving are discussed. Because the risk assessment and optimization tools used in this effort require large numbers of simulation calls, it important to choose the appropriate level of complexity when selecting the type of simulation model. An additional premise of this work is that an existing multiphase semi-analytical algorithm used to estimate key system attributes (i.e. pressure distribution, CO2 plume extent, and fluid migration) may be further improved in both accuracy and computational efficiency. Herein, three modifications to this algorithm are presented and explored including 1) solving for temporally averaged flow rates at each passive well at each time step, 2) using separate pressure response functions depending on fluid type, and 3) applying a fixed point type iterative global pressure solution to eliminate the need to solve large sets of linear equations. The first two modifications are aimed at improving accuracy while the third focuses upon computational efficiency. Results show that, while one modification may adversely impact the original algorithm, significant gains in leakage estimation accuracy and computational efficiency are obtained by implementing two of these modifications. Finally, in an effort to further enhance the GCS optimization framework, this work presents a performance comparison between a recently proposed multi-objective gravitational search algorithm (MOGSA) and the well-established fast non-dominated sorting genetic algorithm (NSGA-II). Both techniques are used to heuristically determine Pareto-optimal solutions by minimizing project cost and maximizing the mass of CO2 sequestered for nine test cases in the Michigan Basin (MB). Two performance measures are explored for each algorithm, including 1) objective solution diversity and 2) objective solution convergence rate. Faster convergence rates by the MOGSA are observed early in the majority of test optimization runs, while the NSGA-II is found to consistently provide a better search of objective function space and lower average cost per kg sequestered solutions.Item Open Access Assessment of water quality, toxicity and treatment strategies downstream of NPDES oil and gas produced water discharges intended for beneficial reuse(Colorado State University. Libraries, 2019) McLaughlin, Molly Cook, author; Borch, Thomas, advisor; Blotevogel, Jens, advisor; Argueso, Juan Lucas, committee member; Mouser, Paula, committee member; Sale, Tom, committee memberProduced water is the largest waste stream associated with oil and gas operations. This complex fluid contains petroleum hydrocarbons, heavy metals, salts, naturally occurring radioactive materials (NORMs) and any remaining chemical additives. In the United States, west of the 98th meridian, the federal National Pollutant Discharge Elimination System (NPDES) exemption allows release of produced water for agricultural beneficial reuse if it is of "good enough quality." Due to the complex and variable composition of produced water as well as the variations in permit effluent limits and treatment approaches, the downstream impacts of NPDES produced water releases are not fully understood. The goal of this dissertation was to determine if the current NPDES produced water permit effluent limits are adequate and if not, to identify additional steps that can be taken to improve water quality. As a first step towards this goal, a detailed chemical and toxicological analysis was conducted on a stream composed of produced water released for agricultural beneficial reuse. Over 50 geogenic and anthropogenic organic chemicals not specified in the effluent limits were detected at the discharge including hydrocarbons, halogenated compounds, and surfactants. Most were removed within 15 km of the discharge due to volatilization, biodegradation, and sorption to sediment. Additionally, the attenuation rate increased substantially in a wetland downstream of the discharge point. Tens of inorganic species were also detected in the watershed, including many sourced from produced water. In contrast to organic chemicals, the concentrations of most inorganic species increased downstream due to water evaporation. This included contaminants of concern such as boron, selenium and total dissolved solids (TDS). An assessment of regulatory health thresholds revealed that eight of the organic species detected at the discharge were listed by the U.S. Environmental Protection Agency (EPA) and the International Agency for Research on Cancer (IARC) to be known, probable or possible carcinogens. Mutagenicity of this water was assessed using a yeast mutation assay that analyzed copy number variation (CNV) duplications, CNV deletions, forward point mutations and reversion point mutations. These mutations are established as having a role in human disease, including cancer. Higher rates of mutation were observed at the discharge point and decreased with distance downstream. This correlated with the concentrations of known carcinogens detected in the stream including benzene and radium. Mutation rate increases were most prominent for CNV duplications and were higher than mutation rates observed in mixtures of known composition containing all detected organic carcinogens in the discharge. In addition, samples were evaluated for acute toxicity in Daphnia magna and developmental toxicity in zebrafish (Danio rerio). Acute toxicity was minimal, and no developmental toxicity was observed. Finally, in response to the observation that attenuation of organic chemicals increased in wetlands, constructed wetlands downstream of three different NPDES produced water discharges, including the discharge of focus in the chemical and toxicological analysis, were evaluated for their viability to polish produced water. The results showed that wetlands are effective at attenuating commonly used non-ionic surfactants, as well as a commonly used biocide. Attenuation was not only due to degradation, but also accumulation in sediments. Sediment accumulation has the potential to limit the lifetime of the wetlands or increase the frequency with which sediment must be excavated. The results of this dissertation identified multiple improvements that can be made to NPDES produced water regulations. Current regulations apply to the discharge site only. This dissertation shows that downstream changes in water quality must be considered to adequately evaluate potential impacts of produced water discharges, as exemplified by the increasing concentrations of inorganic species downstream. Secondly, toxicological results showed that chemical analysis alone is insufficient to assess impacts of these releases and that a thorough assessment of chronic toxicity is necessary to fully assess produced water for beneficial reuse. Current regulations require acute toxicity testing, but no assessment of chronic toxicity. Finally, prior to widespread implementation of constructed wetlands for produced water treatment, additional research is needed to assess the impact of oil and gas chemical additives on the maintenance schedules of these systems, as well as the long-term impact to soil health. If these waters can be reused safely and economically, many stakeholders stand to benefit. If this practice is expanded prematurely, the quality and health of water, soil, crops and downstream users could be negatively impacted. The research contained in this dissertation is one step in a life-cycle analysis of the costs, impacts and benefits associated with oil and gas extraction.Item Open Access Effects of long-term pumping on recharge processes in an alluvial-bedrock aquifer system(Colorado State University. Libraries, 2019) Cognac, Kristen, author; Ronayne, Michael, advisor; Sanford, William, committee member; Sale, Tom, committee memberThe response to pumping in multi-aquifer systems involves complex processes which can significantly affect regional water budgets. Particularly where long-term pumping has occurred, drawdown might take decades to propagate regionally. Failure to incorporate changes caused by long-term pumping into regional hydrogeologic conceptual models can lead to mischaracterization of critical water budget components like recharge, inter-aquifer fluxes, and groundwater-surface water exchange. Accurate description of these budget components is necessary for managing water resources and making predictions about future water supplies. This study analyzes long-term changes in an area of the Denver Basin aquifer system with high historical groundwater withdrawals to characterize the effects of long term pumping on recharge, inter-aquifer fluxes, and groundwater-surface water exchange. An evaluation of historical water level data (1960s to 2010s) documents large hydraulic head declines (>50m in some areas) and a deepening bedrock water table relative to the stream and alluvial aquifer. Results indicate a muti-decade transition from upward to downward hydraulic gradients in the vicinity of major streams, a change that affects the water budget of bedrock aquifers. Implications for regional water budgets are evaluated using a 2D variably saturated finite-difference model which quantifies fluxes across stream, alluvium, and bedrock interfaces in a vertical sequence. Modeling results demonstrate that long-term head decline can produce complex saturation conditions beneath the alluvial aquifer including a transition period of partial desaturation and ultimately a perched saturated zone in the alluvium underlain by an unsaturated region in the bedrock aquifer. The results illustrate how inter-aquifer fluxes eventually stabilize, with no further changes caused by additional lowering of the bedrock water table. Saturation levels and fluxes across interfaces are strongly dependent on geologic heterogeneity, particularly with respect to hydraulic conductivity contrasts between and within aquifers and the location and connectivity of channelized sandstones. Modeling results demonstrate the importance of considering heterogeneity and saturation when managing aquifers that have undergone long term pumping. The results of this study provide insight into the mechanics of long-term water budget change, including controls on the transition to induced recharge and recharge rates. This has important implications for assessing the aquifer response to ongoing and future stresses.Item Open Access Geological control on aquifer storage and recovery (ASR) feasibility and efficiency in carbonate aquifers (Edwards aquifer and Floridan aquifer)(Colorado State University. Libraries, 2024) Simbo, Christophe Wakamya, author; Sutton, Sally, advisor; Sale, Tom, committee member; Ronayne, Michael, committee member; Ridley, John, committee memberAquifer storage and recovery (ASR) is increasingly being used to enhance freshwater security and sustainability. Though proven technology, ASR implementation and efficiency are mainly controlled by the aquifer system's geological characteristics. Aquifer or reservoir quality, aquifer geochemistry and heterogeneity, and ASR-induced stress exerted on aquifer systems affect the operation of ASR and, hence, ASR recovery feasibility and efficiency. This dissertation evaluates the feasibility of ASR operations in two major carbonate aquifers in the USA: the brackish portion of the Edwards aquifer and the Floridan aquifer. Aquifer matrix petrology and geochemistry, groundwater geochemistry, surface water geochemistry, and time series water chemistry coupled with numerical modeling with PHAST and Geochemists' Workbench (GWB), and analytical modeling were used to understand the aquifers and evaluate ASR optimization strategies. The Edwards Aquifer petrography provides insights into the aquifer texture, fabric, and aquifer/reservoir quality controlled by depositional and post-depositional processes. Though the development of porosity and permeability are likely controlled by the precursor texture of the aquifer matrix, diagenetic processes, mainly dolomitization together with fracturing and dissolution, may be the main agents affecting aquifer quality for ASR operation. Suitable aquifer zones for water storage are characterized by permeability likely controlled by intercrystalline, fracture, and vuggy porosity in dolomitic zones. Bulk aquifer geochemistry documents major and trace elements, with high MgO/CaO revealing extensive dolomitization preferentially located towards the middle of the Person and Kainer Formations, aquifer units within the Edwards aquifer system. The relatively higher content of SiO2, Al2O3, and, to some extent, K2O and TiO2 in confining layers points to a modest increase in clay minerals compared to aquifer sections. Clay minerals, together with compaction features observed in confining layer thin sections, potentially reduce confining layer permeability and porosity. However, high fracture porosity within the Regional Dense Member (RDM) confining layer separating both Edwards aquifer zones offers potential pathways connecting both zones. That these fractures may, in fact, be pathways is supported by changes in groundwater hydrochemistry in the non-targeted aquifer zone (Kainer) during the initial ASR recharge cycle. Based on injectant and groundwater chemistry and time series water chemistry of recovered water samples during the first ASR operation cycle, initial and evolved hydrochemical facies were evaluated in the Edwards aquifer ASR operation (in New Braunfels). Forward GWB water-water and water-rock interaction modeling revealed the mixing of the injectant and the native groundwater to be the main contributing factor in the hydrochemical facies evolution of groundwater during the first ASR recharge cycle. Estimated hydraulic conductivity values using the numerical PHAST model and corroborated by the Hemker analytical model support the combined effect of lateral flow and vertically-induced flow of high total dissolved solids (TDS) groundwater from the Kainer Formation into the Person Formation via the RDM confining layer during ASR recovery. Estimated hydraulic property values (hydraulic conductivity and porosity) of these three aquifer layers aided in predicting the recovery rate to optimize ASR operations. Implementation of two ASR wells, respectively screened in the Person and Kainer Formations, presents a potential long-term ASR optimization strategy at the Edwards aquifer study site. Induced arsenic releases to concentrations higher than their maximum contaminant level (MCL) of 10 μg/L hinder aquifer storage and recovery (ASR) operations worldwide. Statistical data and time series analyses of the recovered water hydrochemical data were used to assess the operational methodology maintaining the buffer zone for arsenic attenuation during ASR operations in the Floridan aquifer. Additionally, based on Injectant and groundwater hydrochemical data with geochemical data of the aquifer matrix , 1D GWB reactive transport model was used to assess the buffer zone operation methodology that holds promise in managing arsenic releases during ASR operations in the Floridan aquifer. Time series data from the Tampa ASR operations show a positive correlation between percent recovery and arsenic concentration in the recovered water, with high recovery percentages inducing mobilization of arsenic up to 38 μg/L, a value roughly four times the arsenic maximum contaminant level of 10 μg/L. Further, the developed 1D forward reactive transport model suggests underlying processes that control arsenic behavior upon injection of oxygenated source water into a reducing carbonate storage zone. Two model scenarios were used in this study. Model scenario 2 developed such that a larger oxygen front expanded up to 565 m away from the ASR well, three times further than in scenario 1, and promoted the production of Fe(III) oxides/oxyhydroxides with abundances up to 18,700 µg/Kg formed at 555 m away from the ASR well. These Fe(III) oxides/oxyhydroxides may provide sorbing sites that attenuate arsenic concentrations in the groundwater.Item Open Access Hydrothermal fluid and ore paragenesis of the gold-bearing Rattlesnake Hills Alkaline Complex, Wyoming(Colorado State University. Libraries, 2012) Ripple, Ashley, author; Ridley, John, advisor; Hannah, Judy, committee member; Sale, Tom, committee memberTo view the abstract, please see the full text of the document.