Browsing by Author "Sanford, William, committee member"

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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 member
This 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.
Open Access
Catalytic strategies for enhancing electrochemical oxidation of 1,4-dioxane: TiO2 dark activation and microbial stimulation
(Colorado State University. Libraries, 2016) Jasmann, Jeramy R., author; Borch, Thomas, advisor; Blotevogel, Jens, advisor; Farmer, Delphine, committee member; Neilson, James, committee member; Sanford, William, committee member; Elliot, Michael, committee member
1,4-dioxane, a probable human carcinogen, is an emerging contaminant currently being reviewed by the U.S. Environmental Protection Agency for possible health-based maximum contaminant level regulations. As both stabilizer in commonly used chlorinated solvents and as a widely used solvent in the production of many pharmaceuticals, personal care products, (PPCPs), 1,4-dioxane has been detected in surface water, groundwater and wastewater around the U.S. It is resistant to many of the traditional water treatment technologies such as sorption to activated carbon, air stripping, filtering and anaerobic biodegradation making 1,4-dioxane removal difficult and/or expensive. State-of-the art technologies for the removal of 1,4-dioxane usually apply advanced oxidation processes (AOPs) using strong oxidants in combination with UV-light and sometimes titanium dioxide (TiO2) catalyzed photolysis. These approaches require the use of expensive chemical reagents and are limited to ex situ (i.e. pump and treat) applications. Here, at Colorado State University’s Center for Contaminant Hydrology, innovative flow-through electrolytic reactors have been developed for treating groundwater contaminated with organic pollutants. The research presented in this dissertation has investigated catalytic strategies for enhancing electrochemical oxidation of 1,4-dioxane in flow-through reactors. Two types (abiotic and biotic) of catalysis were also explored: (1) dark, electrolytic activation of insulated, inter-electrode TiO2 pellets to catalyze the degradation of organic pollutants in the bulk solution by reactive oxygen species (ROS), and (2) adding permeable electrodes upstream of dioxane-degrading microbes, Pseudonocardia dioxanivorans CB1190, to pre-treat mixed contaminant water and provide O2 stimulation to these aerobic bacteria. For the abiotic form of catalysis, we characterized the properties of novel TiO2 inter-electrode material, and elucidated the properties most important to its catalytic activity, using 1,4-dioxane as the model contaminant. The TiO2 was novel in its use as an “inter-electrode” catalyst (not coated on the electrode and not used as a TiO2 slurry) and in the mechanism of its catalytic activation occurring in dark (not photocatalysis) and insulated (not typical electrocatalysis) conditions. Further studies were performed using electrochemical batch reactors and probe molecules in order to gain mechanistic insights into dark catalysis provided by detached TiO2 pellets in an electrochemical system. The results of our investigations show that electrolytic treatment, when used in combination with this catalytically active inter-electrode material, can successfully and efficiently degrade 1,4-dioxane. Benefits of catalyzed electrolysis as a green remediation technology are that (1) it does not require addition of chemicals during treatment, (2) it has low energy requirements that can be met through the use of solar photovoltaic modules, and (3) it is very versatile in that it could be applied in situ for contaminated groundwater sites or installed in-line on above-ground reactors to remediate contaminated groundwater. Although, 1,4-dioxane appears to be resistant to natural attenuation via anaerobic biodegradation, some aerobic bacteria have been shown to metabolize and co-metabolize 1,4-dioxane. For example, growth-supporting aerobic metabolism/degradation of 1,4-dioxane by Pseudonocardia dioxanivorans CB1190, has been demonstrated in laboratory studies. However, previous studies showed that this biodegradation process is inhibited by the presence of chlorinated solvents such as 1,1,1-trichlorethane (1,1,1-TCA) and trichloroethene (TCE). This could dramatically impact the success for in situ 1,4-dioxane biodegradation with P. dioxanivorans since chlorinated solvents are common co-contaminants of 1,4-dioxane. Our previous investigations into electrolytic treatment of organic pollutants both ex and in situ showed that effective degradation of chlorinated solvents like TCE was achievable. In addition, the electrolysis of water generates molecular O2 required by the CB1190 bacteria as well. This led us to hypothesize that the generation of O2 could enhance aerobic biodegradation processes, and the concurrent degradation of co-solvents could reduce their inhibitory impact on 1,4-dioxane biodegradation. In flow-through sand column studies presented here, we investigate the electrolytic stimulation of Pseudonocardia dioxanivorans CB1190, with the expectation that anodic O2 generation would enhance aerobic biodegradation processes, and concurrent degradation of TCE would reduce the expected inhibitory impact on 1,4-dioxane biodegradation. Results show that when both electrolytic and biotic processes are combined, oxidation rates of 1,4-dioxane substantially increased suggesting that aerobic biodegradation processes had been successfully stimulated. In summary, the results of this dissertation provide evidence of (1) efficient removal of recalcitrant 1,4-dioxane, especially with the addition of inter-electrode TiO2 catalysts, (2) elucidate possible mechanistic pathways for electro-activated dark TiO2 catalysis, and (3) provide evidence for successful synergistic performance for electro-bioremediation treatment during simulated mixed, contaminant plume conditions.
Open Access
Characterization of peat soil hydraulic conductivity and its dependence on vegetation type in mountain wetlands
(Colorado State University. Libraries, 2015) Crockett, Audrey, author; Ronayne, Michael, advisor; Cooper, David, committee member; Sanford, William, committee member
Peat-forming wetlands enhance biodiversity and provide carbon storage in mountain environments. Persistence of these wetlands requires sustained water inflows. Reduced or altered inflows associated with climate change could lower the water table, potentially resulting in peat oxidation and carbon release to the atmosphere, as well as the loss of wetland plant and animal species. An understanding of the hydrology and site hydraulic properties is necessary to manage mountain wetlands and assess their vulnerability to climate change. This study characterized the hydraulic conductivity of wetland peat soils in Rocky Mountain National Park (RMNP). Peat-forming wetlands in RMNP are classified as fens because their main source of water is groundwater. Fens in RMNP contain a broad range of vegetation. Dominant vegetation type is one factor that may influence peat hydraulic conductivity, so the fens in this study were divided based on dominant vegetation type. The three vegetation classifications used were “large sedge,” “small sedge,” and “heterogeneous,” indicating that the fens were dominated by large sedges (mainly Carex); small sedges (Eleocharis quinqueflora); or a mixture of woody plants, sedges, and moss; respectively. In this study, field measurements were combined with a numerical model and parameter estimation scheme to produce estimates of hydraulic conductivity with a high degree of confidence. Single-ring infiltration tests were performed in the field. A numerical model was constructed, and a parameter estimation scheme was used to find the hydraulic conductivity that best reproduced the results of the single-ring infiltration test. The fens dominated by small sedges have significantly lower hydraulic conductivity than the fens dominated by large sedges or heterogeneous vegetation. Fens which have relatively high hydraulic conductivity (those dominated by large sedges or a heterogeneous mixture of plants) may be especially at risk of draining under changing climate regimes. Small-sedge fens may be more likely to maintain a high water table due to their low hydraulic conductivity.
Open Access
Characterizing tailings professional labor demand
(Colorado State University. Libraries, 2021) Spencer, Louise, author; Scalia, Joseph, IV, advisor; Bareither, Christopher, advisor; Sanford, William, committee member
A low-carbon future necessitates increased extraction of critical minerals via mining. The act of mining includes not only extraction of commodities, but also management of tremendous volumes of waste. Despite the need for mining to support green technologies, mining is experiencing a credibility crisis due to historic legacies of environmental damage and recent catastrophic failures of tailings (mine waste) facilities. To regain social trust and environmental credibility, the mining industry must do better at managing tailings. The recently issued Global Industry Standard on Tailings Management (GISTM) places significant demand on tailings professionals worldwide. Given these pressures, this study addresses the question: is the current tailings professional labor pool sufficient to provide the specialized labor needed to meet new guidance designed to make tailings facilities safer, and if not, how can this shortage be rectified? To address this question, a coupled qualitative-quantitative approach was undertaken. Research was conducted to characterize the current (Spring 2021) industry practitioner perspectives on the state of tailings labor resources. Then, future tailings labor demand under the GISTM was calculated quantitatively by estimating professional labor demand based on guidelines presented in the GSITM and applied to the estimated number of tailings facilities worldwide. Finally, opportunities to address current and future tailings labor demand were identified through tailing practitioner perspectives. According to current practitioners, there is shortage of qualified tailings professionals, related to increased labor needs, difficulties of recruitment into and retention within the industry, as well as senior-level professionals retiring. Managing the minimum estimated 16,000 tailings facilities worldwide was estimated to require as many as 17,800 full-time equivalent, qualified and trained personnel. Finally, current actions to train future tailings professionals are provided, as well as recommendations for actions via collaboration between academia, industry, consultants, regulators, and non-governmental organizations (NGOs) to fortify tailings recruitment activities, training programs, and educational opportunities.
Open Access
Combined source infrastructure assessment model
(Colorado State University. Libraries, 2012) Maurer, Anne, author; Sale, Tom, advisor; Bau, Domenico, committee member; Sanford, William, committee member
Integrated utilization of surface and groundwater is a promising strategy that has the potential to reduce the costs associated with water system infrastructure projects and improve the sustainability of yields from finite water resources. Planning and design of conjunctive use systems can be complicated. Key challenges include resolving the timing of withdrawals, timing of storage, sizing of infrastructure components, and efficiently estimating costs. A combined source infrastructure assessment model (CSIAM) has been developed in this study using a decision programming approach. The CSIAM is designed for single-and multi-source water systems including surface water-only, groundwater-only, and combined surface water and groundwater sources. Aquifer Storage and Recovery (ASR) via groundwater injection wells is a primary component of the CSIAM when there is surplus surface water available to store. Primary model inputs include project life-span, per capita demands, initial population, population growth rate, surface water treatment capacity, number of existing wells, inflows, reservoir stage-storage, evaporative and seepage losses, and unit costs for capital expenditures and operations and maintenance. Model outputs include project water demands, surface reservoir storage, volume of monthly surface water treatment, groundwater extraction and/or injection volumes, cumulative groundwater extraction and/or injection volumes, number of wells, capital costs, operation and maintenance costs, life-cycle costs, and present value. The model is demonstrated via analysis of three scenarios involving groundwater-only, combined groundwater and surface water, and surface water-only. The scenarios are predicated on data provided by the town of Castle Rock, Colorado. While the Town of Castle Rock provides a basis for applying the model, the results should not be viewed as having direct bearing on future actions in the Town of Castle Rock. Many of the key issues that will ultimately drive the Town's water supply plans are not included in this analysis. Use of a combined groundwater and surface water system is $91 million and $231 million less than a groundwater-only system and streamflow-only system, respectively. Furthermore, the use of a combined groundwater and surface water system reduces groundwater depletion by 55%, relative to a groundwater-only system. In addition, a total of 107 pumping wells will need to be installed in a groundwater-only system versus 67 pumping wells in a combined groundwater/surface water system. Both deterministic and stochastic inputs are used in the model, wherein the principle stochastic input is urban irrigation demands. The differences between results using deterministic and stochastic inputs vary depending on the output. In general, analyses using stochastic inputs lead to a need for infrastructure with greater capacities and higher costs. The CSIAM also can be used to resolve costs as a function of groundwater depletion by testing different surface water treatment plant sizes.
Open Access
Coupled analytical modeling of water level dynamics and energy use for operational well fields in the Denver Basin aquifers
(Colorado State University. Libraries, 2013) Davis, Jennifer Anne, author; Ronayne, Michael, advisor; Sale, Thomas, advisor; Sanford, William, committee member; Bau, Domenico, committee member
The South Metro Denver area in Colorado has been experiencing rapid growth in recent years and many municipalities in this region rely on the groundwater resources available in the Denver Basin as their chief water supply. As the population continues to increase, municipal water demands must be met with a sustainable approach. The Denver Basin aquifer system consists of four major aquifers that are composed of interbedded layers of sandstones, siltstones, and shales. The aquifers receive limited annual recharge and consequently the groundwater within them has the potential to be depleted. Declining water levels associated with groundwater depletion, interference between pumping wells, and fouling of wells is leading to losses in well productivity. Furthermore, declining water levels translates to higher electrical energy costs associated with water production. Regional-scale numerical models developed for the Denver Basin aquifer system do not capture the local-scale drawdown about pumping wells, which is needed to effectively manage existing groundwater well fields. This research project utilizes production well data from the town of Castle Rock, Colorado to test the merits of using a Theis based approach to model water levels about production wells in the Denver and Arapahoe aquifers in Castle Rock. The model applies superposition of the Theis solution throughout both space and time to resolve the combined effects of pumping from multiple wells. This research demonstrated that the analytical method can be successfully applied as a predictor of continuous water levels at pumping wells. In addition, the analytical model provided a novel method for estimating aquifer properties using data from an operational well field, and it contributed a better understanding of the cross-well interferences that increase well drawdown. The model results were used to evaluate alternative pumping scenarios intended to reduce electrical energy costs associated with water production and increase sustainable yields from these aquifers. The alternative pumping scenarios achieved a net reduction in energy consumption ranging from 1.62% to 13.0% and led to a stronger conceptual understanding of how each aquifer responds to varying pumping conditions. This research demonstrates that the analytical solution modeling approach may be beneficial for application to many other projects involving groundwater supply management and optimization.
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 member
The 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.
Open Access
Hydrogeologic characterization of an alpine glacial till, Snowy Range, Wyoming
(Colorado State University. Libraries, 2011) Houghton, Tyler B., author; Ronayne, Michael, advisor; Stednick, John, committee member; Sanford, William, committee member
Characterization of sediment hydraulic properties is essential to understanding groundwater movement. In many mountain watersheds, surficial geologic material, such as glacial till, plays an important role in water and nutrient chemical cycling. Hydraulic properties of alpine glacial tills are infrequently measured, requiring efforts to characterize this complex geologic material. This research involved the use of multiple measurement techniques to determine the saturated hydraulic conductivity of surficial glacial tills at the Glacier Lakes Ecosystem Experiments Site (GLEES) in south-central Wyoming. During the summer of 2010, three in situ methods (double-ring infiltrometer, mini disk infiltrometer, and Guelph permeameter) were used to measure field-saturated hydraulic conductivity (K sat) at 32 locations around GLEES. Estimated K sat values obtained with the double-ring infiltrometer had a geometric mean of 0.12 cm/min and range of 0.007 to 0.40 cm/min. The Guelph permeameter had a geometric mean of 0.094 cm/min and range of 0.003 cm/min to 0.776 cm/min, and the mini disk infiltrometer obtained estimates with a geometric mean of 0.014 cm/min and ranged from 0.002 cm/min to 0.043 cm/min. The double-ring infiltrometer and Guelph permeameter measure K sat at a physical scale that is large enough to incorporate the large mixture of particle sizes that comprise the till. With a smaller physical measurement scale, the mini disk is predominantly influenced by the fine-grained fraction of the till. Using geometric mean K sat values obtained with the double-ring and mini disk infiltrometers and available snowpack data from the 2005 water year, a physically-based hydrologic and energy-balance model was used to simulate snowpack depletion, soil moisture changes, and groundwater recharge. Simulated sediment moisture changes were used to estimate vertical flow rates toward the water table. Using a higher K sat obtained at a larger physical measurement scale, the calculated flow rate 2 m below the surface is approximately three times that of the low K sat scenarios. Thus, the scale dependency of hydraulic conductivity is important when quantifying groundwater recharge in mountain watersheds.
Open Access
Hydrogeophysical investigation of unconfined aquifer drainage behavior using temporal microgravity and water level data
(Colorado State University. Libraries, 2020) Sturdivant, Matthew, author; Ronayne, Michael, advisor; Sanford, William, committee member; Sale, Thomas, committee member
Unconfined aquifers are commonly characterized by an analysis of water level changes in response to groundwater pumping during an aquifer test. Traditional analytical models predict the rate and extent of water level changes based on transmissive and storage properties of the aquifer. These models commonly assume instantaneous and complete dewatering of the pore space above a falling water table, which neglects time-dependent storage changes in the unsaturated zone. By sensing pumping-induced water mass changes in both the saturated and unsaturated zones, gravity surveys provide an opportunity for improved characterization of unconfined aquifers. In this study, a time-lapse microgravimetric survey was performed during pumping from a shallow unconfined aquifer in northern Colorado. Water level data were collected at four monitoring wells located along a radial transect at 6.34, 15.4, 30.7. and 61.2 meters from the pumping well. Gravity measurements were collected adjacent to the second well at 15.4 meters. Pumping from the aquifer resulted in a water level decline ranging from 0.35 meters at the distant well to 1.5 meters at the closest well. A total of 3.89 ∙ 106 kg of water mass was pumped during the test, resulting in a decline in gravitational acceleration of 27.2 microGals at the fixed measurement location. The gravity data are not adequately explained by traditional analytical models that predict negligible mass changes as the water table beings to stabilize. This highlights potential inaccuracies in drawdown model assumptions that are not readily discernible with water level data alone.
Open Access
Hydrologic characterization of upper Permian-Cenozoic sedimentary strata of Larimer County: prospective aquifer storage and recovery targets
(Colorado State University. Libraries, 2017) Adam, Adam, author; Sutton, Sally, advisor; Sanford, William, committee member; Sale, Thomas, committee member
Providing adequate water storage is an on-going problem along the northern Colorado Front Range. This study compiles existing hydrogeological data from water wells to identify potential ASR sites in eastern Larimer County, Colorado. These water well data are used to evaluate both geographic localities and individual lithologic units. All stratigraphic units younger than the Pennsylvanian-Permian Fountain Formation and reported to host water wells in eastern Larimer County are considered here. A total of 1094 AquaMap water well reports have been mined for data, including depth, pumping level, static water level, lithology, location, date drilled, and yield. Additionally, specific capacity has been calculated for each well. The data points were plotted using ArcGIS and geological maps from US Geological Survey as base maps. The main parameters considered are water well yields and specific capacities. Yield is an indication of the ability of an aquifer to permit movement of water, but the yield data available may not reflect the maximum ability of a well to produce or store water. This is because water is pumped out according to the usage or purpose of the well, with irrigation and livestock wells typically yielding more than household wells. In some locations the aquifers considered can likely produce more than indicated by reported yields. Based on both hydrogeological properties and widespread occurrence in the study area the Pierre Shale Formation, the Lytle Formation, and the Ingleside Formation appear to show the greatest promise as ASR targets. Additional units that could be worth further consideration include the Jelm and Lykins Formations. Based solely on hydrogeological data, the White River, Laramie, and Fox Hills Formations would be the strongest candidates for ASR, but are geographically limited to the far northeast corner of the county. In addition, well data from unconsolidated alluvial deposits suggest strong potential for ASR, especially near the eastern edge of the County, but the combination of very high permeability and surface exposure would make ASR in these deposits challenging because of difficulty maintaining control of stored water. Based on well data, there are some specific localities that may merit further consideration for ASR, including the vicinity of Laporte, where several stratigraphic units host wells with high yields and high specific capacities. Similarly, there are wells in several stratigraphic units, including the Pierre Shale Formation, CarlileGraneros-Mowry Shales, Owl Canyon Formation, Lyons Formation, and Lytle Formation, in an area to the west of Loveland that show promise for ASR. Additionally, the Pierre Shale Formation hosts several clusters of wells indicating strong potential for ASR; the best developed of these clusters are in the northern third of the Larimer County, specifically northwest of Wellington.
Open Access
Hydrologic impacts of lined gravel pits, Colorado Front Range
(Colorado State University. Libraries, 2018) Rach, Gavin, author; Ronayne, Michael, advisor; Sanford, William, committee member; Bailey, Ryan, committee member
Sand and gravel quarries are a major source of natural aggregate. Gravel pits often excavate below the water table and therefore can influence alluvial aquifer groundwater flow directions and groundwater-surface water interaction. By regulation in the state of Colorado, low-permeability liners are installed after extraction to minimize water seepage into the pit. The liner impedes flow and disturbs the local water table, creating mounding on the upgradient side and shadow drawdown on the downgradient side. To better understand the magnitude and extent of these effects, numerical groundwater modeling was conducted for a study area along the Saint Vrain Creek alluvial aquifer in Colorado that contains an active gravel pit. The numerical model was based on a revised conceptual model, including a reinterpretation of the bedrock surface, and was calibrated using measured groundwater levels and estimated groundwater-surface water exchange rates constrained by streamflow gaging data. Two transient modeling scenarios were developed: a base case pre-mining scenario and a post-mining lined-pit scenario. The hydrologic effects of the pit liner were quantified through a detailed comparison of the scenarios. Model results indicate that the liner has a significant effect on water-table elevation in the vicinity of the pit during the non-irrigation season (October-March). In March, upgradient mounding produced by the liner exceeds 0.5 m at an approximate distance of 100 m, whereas the drawdown exceeds 0.3 m at this distance on the downgradient side of the pit. The magnitude of these liner-induced changes is less than other seasonal variability in hydraulic head, particularly the variability associated with irrigated agriculture (seasonally active irrigation ditches). During the irrigation season, simulated hydraulic heads are similar in both model scenarios, demonstrating that irrigation ditches are a major control on groundwater flow. Despite significant water table elevation change in parts of the year, groundwater discharge to the stream increased by 0.11% of the total streamflow at its maximum, demonstrating this particular pit liner has a negligible effect on the Saint Vrain Creek.
Open Access
Influence of subsurface heterogeneity on the performance of aquifer storage and recovery in the Denver Basin
(Colorado State University. Libraries, 2016) Cannan, Catharine, author; Ronayne, Michael, advisor; Sale, Thomas, committee member; Sanford, William, committee member
Aquifer storage and recovery (ASR) is a process through which water is injected into an aquifer for storage and recovered for later use. As water demand worldwide increases there is a growing need to evaluate alternative approaches to water storage, including ASR. Increasing our understanding of the fate of injected water and the subsurface conditions in which ASR is being performed can guide operational choices and decisions on the feasibility of ASR in new regions. Previous evaluations of ASR performance have often assumed homogeneity in the subsurface, overlooking the existence of preferential flow paths created by the combination of transmissive and non-transmissive inter-beds. Because these pathways can influence the lateral transport of water away from injection wells, ASR performance may be impacted. In this study a groundwater flow model within the Denver Basin, Colorado were used to evaluate ASR performance in a heterogeneous subsurface environment. Geologic data in the vicinity of Highlands Ranch, Colorado were synthesized to create heterogeneous, three-dimensional aquifer analogs using multiple-point geostatistical simulation. Flow simulation for these aquifer models was performed to evaluate ASR cycles comprised of injection, storage, and extraction phases, and results were compared to a homogeneous aquifer model. Three metrics were used to assess ASR performance: the extent of hydraulic head changes in the aquifer, fate of injected water particles, and recovery efficiency. Results show that the travel distance of injected water particles was influenced by the presence of heterogeneity and that preferential pathways increase both the variability and maximum distance traveled by injected water particles. Predicted recovery efficiency decreased slightly when heterogeneity was incorporated, while head change extent was far less sensitive to the presence of heterogeneous structures. These results demonstrate not only the influence of aquifer heterogeneity on ASR performance, but also the potential for geostatistical analysis and numerical modeling to be used as tools for planning future ASR operations.
Open Access
Investigation of mineral bentonite barriers optimized for hydraulic compatibility and shear strength
(Colorado State University. Libraries, 2024) Jacob, Samuel Robert, author; Scalia, Joseph, IV, advisor; Bareither, Christopher, committee member; Sanford, William, committee member
Liners are a foundation tool of environmental geotechnics. Modern liners are constructed using natural and polymeric materials with low hydraulic conductivity (k), often at the expense of having low shear strength. These liners are often subject to high stresses on the order of hundreds to thousands of kPa which can lead to decreased performance over time and failure of the liner in shear. This research investigates mineral-bentonite mixtures in the context of high-stress liner applications. Mixtures containing varying amounts of sand, bentonite, and rock flour were created in the laboratory. Hydraulic conductivity of specimens was measured using flexible wall permeameters in accordance with ASTM D7100 using either de-ionized (DI) water, 10 mM, or 500 mM CaCl2 solutions. Specimens were removed from permeameters once k termination criteria were met and subsequently tested in direct shear at either 35 kPa or 825 kPa effective stress to obtain peak (φ´peak) and ultimate (φ´u) friction angles. Mixtures generally achieved a final k of 10- 9 m/s with bentonite contents of 4.5% and 8% when permeated with DI water and 10 mM CaCl2 solutions, respectively. Adding rock flour to mixtures containing bentonite lowered final equilibrium k but rock flour was not suitable as a complete replacement for bentonite. At 35 kPa effective stress, shear strength increased until approximately 15% equivalent fines, whereas shear strength was relatively constant at 825 kPa with increasing equivalent fines from 0-15%. At 825 kPa, shear strength substantially dropped at equivalent fines greater than 15%, which is the approximate percentage of fines that the sand matrix began to lose grain-grain contact due to the displacement by fines. The results from this study highlight that while low k and high φ´ can be achieved, even at high effective stresses, care and precision during design and construction of a mineral-bentonite barrier is required to ensure that all design criteria are met.
Open Access
Modeling artificial groundwater recharge and low-head hydroelectric production: a case study of southern Pakistan
(Colorado State University. Libraries, 2016) Siddiqui, Rafey Ahmed, author; Bailey, Ryan T., advisor; Grigg, Neil S., committee member; Sale, Thomas, committee member; Sanford, William, committee member
DHA City Karachi (DCK), a city designed for approximately one million people, is envisaged to become a satellite city to the second largest city in the world, Karachi, which has a population of 25 million. The upcoming city is located 21 miles north of main metropolitan Karachi in the arid southern part of Pakistan. The region receives little rainfall with an annual average of 217 mm and temperatures ranging from an average of 88°F in the summers to 68°F in the winters. The town has a projected water demand in the fully developed stage of 45 Million Gallons per Day (MGD) and 500 Mega Watts (MW) of electricity. Since water and electricity are prized and expensive commodities in the region, alternate and renewable sources of both need to be explored for DCK to meet its goal of sustainability and conservation. Two options for these sources, artificial recharge and hydroelectric product, are explored in this study. Artificial recharge to replenish groundwater resources is becoming more common in arid areas. In this thesis, the capacity of small lakes to produce significant seepage and recharge to the underlying aquifer within city limits is explored for DCK. The lakes are fed by treated effluent from Sewage Treatment Plants (STP), which then ponds and creates downward seepage to the water table. Artificial recharge and resulting groundwater flow within the aquifer is simulated using a three-dimensional groundwater flow model (MODFLOW). A variety of pumping scenarios are explored to determine the quantity of groundwater that can be pumped for water supply. An optimal placement of 50 pumps throughout the city also is determined, with drawdown used as the variable to be minimized so as to minimize pumping costs. In the fully developed stage of artificial recharge, the lakes feed almost 7.9 MGD of water to the aquifer, out of which 6.6 MGD can be pumped out and consumed sustainably on a daily basis through the 50 planned wells. Since DCK is to be developed and inhabited in 3 phases, analysis revealed that quantities of 1.4 and 3.5 MGD can be pumped out sustainably for the short and mid-term developmental plans. A sustainable hydroelectric system was also designed for using the hydraulic structures of the small lakes. System control was introduced by application of Artificial Neural Networks (ANN) and Model Predictive Control (MPC) to maintain the hydroelectric potential and constant head against variation in flow as delivered from the STPs. The results show an output of 13.92 MW of green and sustainable hydroelectricity which can be produced at a very low cost. A cost-benefit analysis projects a savings of $11,550 and $60,000 per day due to the artificial groundwater recharge and hydroelectric production respectively, with the cost of construction of these projects being paid off within 5 and 2 years at this rate, including the cost of operation and maintenance. Results, however, should be used with caution due to the preliminary nature of the models and calculations.
Open Access
Modeling sediment yield and deposition using the SWAT model: a case study of Cubuk I and Cubuk II reservoirs, Turkey
(Colorado State University. Libraries, 2015) Duru, Umit, author; Wohl, Ellen, advisor; Rathburn, Sara, committee member; Arabi, Mazdak, committee member; Sanford, William, committee member
Better understanding of which factors determine sediment yield rate to reservoirs can facilitate estimation of the probable lifespan of a reservoir and appropriate mitigation measures to limit reservoir sedimentation. Therefore, the research summarized here enhances understanding of correlations between potential control variables on suspended sediment yield and the resulting sediment yields to reservoirs. The Soil and Water Assessment Tool (SWAT) was applied to a portion of the Ankara River catchment, which comprises an area of 4932 km² in the central Anatolia region of Turkey. SWAT was calibrated and validated using monthly data from an upstream (1239 Ova Cayi – Eybek) sediment gaging site draining approximately 322 km². A local sensitivity analysis was performed on 18 and 22 input parameters in terms of model outputs such as water and sediment yields, respectively. The most sensitive model parameters affecting stream flow are GW_DEL (ground water delay time) and Alpha_BF (base-flow regression coefficient). For sediment yield, the most sensitive model parameters are SOL_Z (soil thickness), and CH_N1 (Manning coefficient of the channel). Besides these parameters, all other dominant hydrological parameters were determined and a reduction of the number of model parameters was performed in order to improve the Nash-Sutcliffe coefficient of efficiency and R². The SWAT model was performed to simulate water balance, stream flow, and sediment yield during recent decades. The Nash-Sutcliffe efficiency coefficient (NSE) and Relative Error were used to assess accuracy of the model. SWAT outputs indicate that the model performs well, because monthly stream flow of NSE= 0.79 and monthly suspended sediment load of NSE= 0.81 are within the acceptable range of RE and R², which are 0.58-1.55 (RE) and 0.89-0.93 (R²), respectively. According to multiple regression analysis, sediment yields in the watershed are dominantly influenced by stream flow, drainage area, and channel width. No other variables can be considered as prime control factors on sediment yield in the region. Finally, remote sensing and Geographic Information System software were used to assess sedimentation through time in the Cubuk I and Cubuk II reservoirs. Results indicate that a significant amount of siltation occurred between 1978 and 1983: Cubuk I reservoir accumulated 3 m of sediment within 6 years and Cubuk II accumulated about 10 m. Siltation is the most significant problem in the catchment, so efficient siltation management practices for the reservoirs should be performed to control sediment accumulation in these human made structures. However, there is considerable uncertainty associated with the model predictions in the Ankara Basin, due to lack of finer resolution soil data, as well as sediment stations for model parameterization, calibration, and validation. Future studies in the Cubuk catchment should focus on improving the database by obtaining higher resolution soil data and more accurate climate data, which will likely help to reduce model uncertainty. Testing the applicability of the SWAT model in the watershed and identifying the source of uncertainty has laid the groundwork for further research in the region.
Open Access
Numerical modeling investigation of long-term hydrologic change due to surface water and groundwater withdrawals from a high Andean headwater basin, southern Peru
(Colorado State University. Libraries, 2024) Stansfield, William J., author; Ronayne, Michael J., advisor; Cooper, David, committee member; Sanford, William, committee member
Reliable surface water and groundwater resources are of critical importance in the arid central Andes of Southern Peru. Low elevation cities and towns in coastal regions are dependent on water derived from relatively humid mountains and high elevation basins on the Andean Altiplano. The Huaytire Basin, located on the Altiplano at approximately 4,450 meters above mean sea level, is a headwater basin that has experienced hydrologic change in recent years. Surface water diversions from the perennial Lake Suches began in the 1960s, followed by groundwater pumping starting in the 1980s. These water development activities have been accompanied by observations of declining surface water quantity in the downgradient Rio Callazas and deteriorating phreatophytic vegetation within the basin itself. A review of precipitation and pan evaporation data from weather stations in the region did not reveal any clear climate-related trends that would impact water resource availability. A numerical groundwater flow model was constructed using MODFLOW to estimate the impact of long-term pumping on local hydrology and to investigate the sustainability of the Huaytire Basin pumping regime. The model accounted for groundwater-surface water interaction, including lake-aquifer exchange and stream-aquifer exchange along three major streams that originate within the basin. Surface water levels and flow rates were computed as part of the numerical solution, dependent on the simulated hydraulic head in the aquifer, which controls the amount of groundwater-surface water exchange. Three different recharge scenarios were considered to acknowledge uncertainty associated with groundwater recharge rates on the Altiplano. All three scenarios resulted in the study area converting from an open basin with surface water outflow to a closed basin within 50 years of the start of development. Other simulated impacts of pumping include a reduction in the stage and areal extent of Lake Suches and significant reductions in head-dependent outflows for the aquifer system. Relative to predevelopment conditions, groundwater discharge to Lake Suches, groundwater discharge to gaining stream reaches, phreatophytic evapotranspiration, and underflow out of the basin were all lower at the end of the 63-year transient simulation (by ~ 9.5, 50, 18, and 51%, respectively, using base-case recharge rates). It was concluded that groundwater development in the Huaytire Basin is a key factor that explains the observed hydrologic changes and that current pumping rates may be unsustainable.
Open Access
Origins and movements of invasive piscivores determined from otolith isotopic markers
(Colorado State University. Libraries, 2011) Wolff, Brian, author; Johnson, Brett, advisor; Clements, William, committee member; Sanford, William, committee member
I examined the utility of the strontium isotope (87Sr/86Sr) ratio in fish otoliths to determine the origins and movements of invasive piscivores in the Upper Colorado River Basin (UCRB). My goal was to determine if invasive piscivores entered riverine habitat of endangered fishes in the UCRB by escaping from reservoirs, and if so, determine their likely origins. Fishes were collected from 14 reservoirs and rivers directly downstream. My objectives were to examine the distinctiveness of 87Sr/86Sr ratios from fishes in different reservoirs, and temporal stability and interspecies variability of 87Sr/86Sr ratios of fishes within reservoirs. Variance components analysis and model selection using an information theoretic approach were used to rank relative importance of reservoir location, species and year on 87Sr/86Sr ratios. My results showed that in most cases 87Sr/86Sr ratios were unique across reservoirs, overlapped among species in a given reservoir, and were temporally stable across years. I was able to identify the likely reservoir of origin of river-caught fish, and I was able to determine, in some cases, the year of escapement. Overall, my results demonstrate the utility of 87Sr/86Sr ratios for tracking fish movement and origin in river-reservoir systems and provide important insights into processes that affect escapement risk such as dam operations, weather conditions, fish behavior and fish physiology. Analysis of stable isotopes hydrogen (δ2H), carbon (δ13C), and oxygen (δ18O) were performed on a sub-set of otoliths from the 87Sr/86Sr ratio analysis to determine if additional markers aid in discriminating between groups, particularly when 87Sr/86Sr ratios are similar among different locations. A canonical discriminant function analysis was used to visually differentiate different locations using natural isotopes. These results showed that δ13C and δ18O provide very useful separation among different groups, particularly when in conjunction with 87Sr/86Sr ratios.
Open Access
Proposed laboratory investigation into electroosmotic dewatering of mine tailings
(Colorado State University. Libraries, 2020) Vander Vis, Kimberly Ann, author; Bareither, Christopher, advisor; Scalia, Joseph, advisor; Sanford, William, committee member
Geotechnical concerns of tailings storage facilities (TSFs) often depend on the water content of the tailings. Tailings with low hydraulic conductivity often have high-water contents with low undrained shear strength at the time of mine closure which limits the ability to close the TSF. The purpose of this study is to explore undrained shear strength gain in surficial mine tailings using electroosmotic dewatering (EOD) to help promote closure and reclamation of TSFs. Electroosmotic dewatering uses electrodes to apply an electrical direct current to induce flow through a porous medium. An experiment was developed to assess the effectiveness of dewatering methods at bench-scale to increase undrained shear strength of tailings via three different methods: EOD, surcharge consolidation, and evaporation only. The proposed research will evaluate if EOD (1) increases undrained shear strength of saturated surficial mine tailings more rapidly and (2) increases undrained shear strength as a function of depth more effectively, compared to the other techniques. Factors that influence EOD were preliminarily evaluated and include electrodes used, pore fluid chemistry, degree of saturation, voltage gradient and electrode configuration. Additionally, electroosmotic dewatering of mine tailings has not been implemented on a large-scale possibly due to lack of developed procedure, difficult water removal, and lack of a commercially available EOD unit. A goal of the proposed research plan is to develop field-scale implementation methods and water removal techniques via a moisture wicking synthetic capillary drain unit to be coupled with electroosmotic dewatering (i.e., EO-Plant) for field-scale applications.
Open Access
Stream nutrient response to contemporary timber harvest practices in western Oregon
(Colorado State University. Libraries, 2017) Harbin, Andrea, author; Stednick, John D., advisor; Fassnacht, Steven, committee member; Sanford, William, committee member
Timber harvesting has historically been shown to increase nutrient concentrations in stream waters by decreasing vegetative cover and nutrient uptake, allowing more nutrients to be leached into stream waters. Contemporary timber harvest practices, in which a streamside buffer is left in place, have not been studied. This study quantified the effects of contemporary timber harvesting practices, with a streamside buffer, in a Douglas-fir dominated watershed in the Oregon Coast Range, using a paired-watershed design. In the treatment (Needle Branch) and the control (Flynn Creek) watersheds, water quality samples collected from October 2006 through March 2016 were analyzed for nutrients. A clearcut harvest took place in the upper basin in 2009 (Phase 1), and in the lower basin in 2014 (Phase 2), and water samples were tested for nitrate (NO3-N), total nitrogen (TN), ammonia (NH3), orthophosphate (OP), and total phosphorus (TP). Intra-watershed comparisons of nutrient concentrations were made using a Wilcoxon Rank Sum Test to determine statistical significance between sites and treatments. A Before-After Control-Impact (BACI) design was used to compare the treatment watershed to the control watershed across treatments. Results at Needle Branch showed statistically significant increases (α < 0.05) in NO3-N between pre-treatment (0.59 mg/L) and Phase 1 (0.97 mg/L), and between pre-treatment and Phase 2 (0.90 mg/L) at the outlet. TN also showed statistically significant increases between pre-treatment (0.87 mg/L), and Phase 1 (1.06 mg/L), and between pre-treatment and Phase 2 (0.92 mg/L). NH3 was also shown to be statistically significant between pre-treatment (0.011 mg/L) and Phase 1 (0.013 mg/L). OP showed statistically significant increases between pre-treatment (0.018 mg/L) and Phase 1 (0.024 mg/L), and between pre-treatment and Phase 2 (0.022 mg/L), as did TP (0.018, 0.026, 0.020 mg/L during pre-treatment, Phase 1, and Phase 2, respectively). Results in Flynn Creek showed statistically significant increases in NH3 between pre-treatment (0.010 mg/L) and Phase 1 (0.013 mg/L). OP also showed statistically significant increases between pre-treatment (0.029 mg/L) and Phase 1 (0.034), and between pre-treatment and Phase 2 (0.032). TP also showed significantly significant increases between pre-treatment (0.028 mg/L) and Phase 1 (0.036 mg/L). Because similar results were observed in both the treatment and control watersheds, changes in these three constituents within the treatment watershed cannot be attributed to timber harvest. Neither NO3-N nor TN showed any change between phases within Flynn Creek, therefore, changes in these constituents within Needle Branch can be attributed to timber harvest. Contemporary timber harvest practices appear to have similar results as past harvesting practices, regarding nutrient concentrations in stream waters. With a streamside buffer, NO3-N and TN concentrations were significantly increased following harvest. Contemporary timber harvest practices, however, did not affect NH3, OP, and TP concentrations.
Open Access
The fresh groundwater lenses in the Arabian Peninsula: formative, stability and management assessments
(Colorado State University. Libraries, 2019) Alrashidi, Mosaed, author; Bailey, Ryan, advisor; Grigg, Neil, committee member; Sale, Thomas, committee member; Sanford, William, committee member
The formation of fresh groundwater lenses (FGLs) overlying denser, saline or brackish groundwater is a fascinating hydrologic phenomenon that creates groundwater supplies of great potential value for humans and ecosystems in several formation settings, such as coastal areas, atoll islands, riverine floodplains, and subterranean oases in arid regions. In particular, FGLs in subterranean oases are a critical source of freshwater supply in arid regions, due to a general lack of perennial rivers and lakes. These FGLs are in danger of salinization due to natural events and anthropogenic stresses. Although extensive research has been conducted on FGLs in general, the FGLs in subterranean oases in arid regions have received less attention. Key knowledge gaps include the quantity and frequency of natural recharge to these FGLs; reliable estimates of environmental aquifer dispersivity at the scale of subterranean FGLs; the timing of lens development; and the impact of anthropogenic activities on lens dynamics. This dissertation focuses on the FGLs of subterranean oases in the Arabian Peninsula (AP), using the Rawdatain FGL in Kuwait as a case study. Among the FGLs in the AP, the Rawdatain FGL in Kuwait is perhaps a unique candidate because of its size and the availability of extensive subsurface data for the pre-development period. The main objectives of this study are as follows: (1) estimate long-term average annual recharge for the Rawdatain FGL and investigate the timing of lens depletion due to climate change; (2) provide a realistic range of longitudinal (αL), horizontal transverse (αh), and vertical transverse (αv) dispersivity values for the aquifer; and (3) assess the impacts of historical and future anthropogenic activities and evaluate artificial recharge alternatives for lens recovery storage (LSR). In this study, a 3D density-dependent groundwater flow and solute transport model using the SEAWAT modeling code is developed using the following pre-development period calibration targets: (1) groundwater head, (2) spatially-variable total dissolved solids (TDS) groundwater concentration, (3-5) three groundwater volume targets, (6-8) three vertical thickness targets of stored groundwater of three different water quality TDS ranges (0−700, 700−1000, and 1000−2000 mg/L), and (9) geometrical shape features of the lens along cross-sections. In addition, groundwater age data of the Rawdatain FGL was used as an independent factor to constrain the dispersivity and recharge rate during the simulated period of lens development. Moreover, a sensitivity analysis was performed to explore the effects of the hydraulic conductivity, boundary conditions, and vertical transverse dispersivity on lens geometry. Based on a comparison of twelve annual recharge amount scenarios using a constant recharge mechanism (CRM) (R1 to R12: 0.2 to 5.0 million m³/year) with data targets, the R5 (0.5 million m³/year) recharge scenario is selected to represent the long-term average annual recharge. These results demonstrated that the annual natural replenishment of the Rawdatain FGL is minimal compared with its size. A macro-scale stability assessment shows that a 50% reduction in annual recharge within a 100-year time frame would reduce the lens volumes by 21%, 17% and 9% for the three water quality categories. A multi-criteria score-based method was performed to rank the best performance of 28 dispersivity sets (D1 to D28: 1 to 500 m) among all of the targets with an equal weight, on a scale of 0 to 300 x 106 m3. The results illustrated that the D16 dispersivity set (αL = 50 m: αh = 5 m: αv = 0.1 m) represents the best large-scale environmental dispersivity values for the Rawdatain FGL and can be used for analyzing the natural mixing between the ambient brackish water and fresh water. A new baseline model for the predevelopment period using a pulse recharge mechanism (PRM) was established to assess the recharge frequency along with the longitudinal dispersivity. The results revealed that the 50 m longitudinal dispersivity set and one pulse recharge every two years had the best performance, and they were selected to simulate the effects of the infrequent rainfall events and anthropogenic impacts simultaneously. During the groundwater abstraction from 1963 to 2018, the reduction in the stored volumes was 28%, 17% and 12% for the three quality categories. The future pumping scenarios (2019-2100) suggested that the 0.16×106 m3/year is a suitable alternative for long-term use, 0.5×106 m³/year)is an appropriate option for short-term use, and extraction scenarios greater than 1.0×106 m³/year will cause a remarkable degeneration of the Rawdatain FGL. Artificial recharge scenarios (2019-2028) imply that a successful LSR for the Rawdatain FGL depends on selecting appropriate well locations and amounts of injected water. For instance, the I2 alternative could achieve a 100% storage recovery within 7.5, 8 and 9 years for the three water quality categories. This study provides a first attempt to model the formation of a FGL, assess the historical anthropogenic stresses, and evaluate future management scenarios in subterranean oases in arid regions. Implementing multiple data targets and water age is a unique process of calibration that was helpful in eliminating several non-unique calibration parameters and in decreasing the uncertainty of the calibrated parameters. The methodology presented herein provides a general approach that can be extrapolated to other FGLs with similar climatic and environmental circumstances. The outputs of this dissertation enhance the understanding of the formation, stability, and management of these lenses and will be very valuable to water managers for establishing appropriate water supply plans for these valuable water reserves, leading to preferable future water security in the AP.