Theses and Dissertations

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Analysis of municipal water use in urban regions across the contiguous United States
(Colorado State University. Libraries, 2024) Dezfooli, Donya, author; Arabi, Mazdak, advisor; Sharvelle, Sybil, committee member; Carter, Ellison, committee member; Goemans, Christopher G., committee member
Urban water use in the United States faces increasing social and environmental pressures. Challenges such as population growth, urbanization, extreme weather events, and climate change threaten the balance between water supply and demand, jeopardizing access to safe and reliable drinking water for city dwellers. Additionally, the traditional linear "take-make-waste" approach, once common in addressing water-related issues, has proven unsustainable due to its reliance on finite energy and resources. Therefore, it is imperative to shift from this linear model to a more integrated and sustainable approach, known as "One Water". This shift requires a comprehensive understanding of the mechanisms enabling transitions to sustainable and resilient urban water systems, as well as the development of models and methodologies to guide the transition toward net-zero water communities. To achieve this, the dissertation first aims to deepen the understanding of factors influencing transitions towards sustainable urban water management. This is based on a series of expert interviews conducted with different utilities across North America. The qualitative data analysis provides valuable insights into the complex context of urban water management. The results revealed that achieving social and environmental justice is a prominent driver for utilities to initiate their transition, followed by concerns about climate change, water quality impairments, groundwater depletion, and population growth. Further investigations identified several barriers to the One Water transition. These barriers are not merely financial and technical but also stem from a lack of regulatory frameworks, insufficient community support, and institutional obstacles. Therefore, institutional and regulatory solutions are needed more than technological innovations to support this paradigm shift. Our findings also emphasized the importance of cultural change and the necessity of fostering a One Water mindset among stakeholders at all levels. Additionally, feedback from the participants contributed to a more comprehensive and inclusive definition of One Water. Second, a municipal water demand model was developed using the Integrated Urban Water Model (IUWM) to understand urban water use patterns and influencing factors across urban areas within the Contiguous United States (CONUS). Municipal water use data from 99 cities across the U.S. from 2005 to 2017 was used to calibrate and regionalize model parameters for urban regions across the CONUS. The results identified key factors influencing the regionalization of water model parameters, including "July vapor pressure deficit," "number of employees in other services (except public administration)," and "July precipitation." The study reveals that predictive water use and related uncertainty vary across ecohydrological regions within the CONUS. This variation is significantly influenced by climatic and socio-economic factors, with arid and southern cities showing the highest uncertainty. While densely populated areas exhibit more predictable patterns, small cities demonstrate the highest level of uncertainty in water use projections, primarily due to a higher share of single-family homes and increased outdoor water consumption compared to larger cities. Third, the developed IUWM model was used to estimate municipal water demand across urban areas within the CONUS for the period of 2035-2065 under different future climate and land use scenarios. The results indicated that population growth and land use change are primary drivers of urban water demand. While there are minor annual fluctuations reflecting the effects of different climate scenarios, the hot climate model presents the worst-case scenario, with the lowest reduction in water use intensity and the highest increase in water demand. In this scenario, the average water use demand is projected to increase by 52%, while the average water use intensity (ML/sq.km) will fall by 10%. The projected changes in water use are highly variable across the CONUS, with significant increases expected in urban areas located in the West and Northwest (e.g., Washington and California), Southwest (e.g., Arizona, Utah, Colorado, and New Mexico), Midwest (e.g., Michigan and Wisconsin), and Great Lakes region (e.g., New York and Pennsylvania). Our findings suggest that projections of future municipal water demand are surrounded by considerable uncertainties, particularly in cities located in arid and tropical regions. Furthermore, the results show that while increased urban density typically reduces water use intensity in most areas, increases are expected in parts of the Midwest, Northeast, and West. These trends suggest that once cities reach certain development thresholds (around 50% developed area), densification may no longer effectively reduce municipal water demand, leading to increased indoor and CII (commercial, industrial, and institutional) water consumption, thereby undermining the expected benefits. This highlights the need for effective mitigation strategies, such as demand management and the use of alternative water sources, alongside higher-density development policies to ensure sustainable urban water management in the future. Overall, this dissertation provides a comprehensive understanding of urban water demand in the United States, aiming to achieve sustainable urban water management. The insights gained from this study highlight the importance of integrating land use and water management and fostering collaboration among all stakeholders to achieve the One Water paradigm shift. The results will benefit urban planners and water managers, helping them develop effective strategies to mitigate adverse effects and ensure sustainable water resources for the future.
Open Access
Insights and methodologies in wall-bounded turbulent channel flows
(Colorado State University. Libraries, 2024) Mishra, Harshit, author; Venayagamoorthy, Subhas Karan, advisor; Gates, Timothy K., committee member; Julien, Pierre Y., committee member; Barnes, Elizabeth, committee member
Wall-bounded channel flows are of massive interest to civil and environmental engineers due to their immense application for water supply and management. This dissertation addresses five key aspects of turbulent channel flows relevant to practicing engineers, laboratory researchers, fluid scientists, and consultants leveraging computational fluid dynamics for modeling turbulent flows. In the first study, a device was developed and tested to enable Particle Image Velocimetry (PIV) for free surface flows. Measuring flows reliably requires that illumination provided by the laser sheet remains undisturbed. In open channel flows, introducing the laser sheet from the free surface can be necessary as the bed may be optically opaque. An oscillating free surface can further complicate maintaining an undisturbed laser sheet. This research has shown that the disturbance of the laser sheet, when introduced from the free surface, can be mitigated by introducing an improvised device called an optical coupler. The effect of the coupler on the measured velocity field was systematically studied using independent Laser Doppler Anemometer (LDA) measurements. The effect of the coupler on the measured velocity field was confined to its vicinity near the surface of the flow. The mean flow profile remains largely unaffected. Additionally, appropriate material for fabricating the coupler has been recommended by studying the relative performance of a glass and acrylic coupler. While the glass coupler measurements were closer to the undisturbed flow profile, the durability and ease of handling an acrylic coupler make it a viable alternative. The second study is focused on ensuring fully developed flow in short laboratory flumes. Ensuring a fully developed flow is essential for any experimental or modeling study that involves wall-bounded flows. Flow development in pipes has been extensively studied, and empirical relationships have been widely published. Recently, similar studies on open channels have revealed that the entrance length in laboratory flume is ≈ 100h, where h is the depth of the flow. Such a prescription renders most laboratories unfit for experimental work. Further, the inlet configuration in the flume can also hamper flow development, even after the length requirements are met. In this study, we develop a methodology to obtain developed flow in short channels by modifying the inlet and tripping the boundary layer. Further, we also provide a robust, rapid test to confirm if the flow is fully developed using Direct Numerical Simulation (DNS) datasets. The proposed method is validated using flume experiments for flows with friction Reynolds number Reτ ∼ 1500−3000. Against the current prescription, we show that it is possible to obtain fully developed profiles within a distance of ≈ 20h from the inlet. In the next (third) study, we leverage the DNS data for closed channel flow for a range of friction Reynolds Number (Reτ ∼ 180 − 5000) to develop a new One Point Friction Velocity Method (OPFVM) to calculate friction velocity U∗ in terms of free-surface velocity Um, flow depth h and kinematic viscosity ν for smooth wall-bounded flows. In contrast to prevalent methods that require several cumbersome near-boundary measurements to obtain friction velocity, the OPFVM relies on a single easy-to-measure free-surface velocity measurement. The formulation obtains friction velocity for a closed channel flow (CCF) DNS regime with Reτ = 10049 and on four open channel flow (OCF) DNS regimes with Reτ ∼ 180 − 2000. The same formulation was then experimentally verified in our laboratory. To avoid being prescriptive, a sensitivity analysis was performed to determine the permissible variation in Um to restrict the error in estimated U∗ to 2%. The relationship between the depth-averaged velocity Ub and the maximum free-stream velocity Um is also explored using the DNS datasets and an approximate relationship between Ub and Um is proposed. With advances in remote sensing technology that enables free-stream velocity measurements, this method extends the potential to measure even the friction velocity remotely. Computational Fluid Dynamics (CFD) is an essential tool for analyzing fluid flows. The k − ϵ model is a turbulence model used in Raynold-Averaged Navier-Stokes simulations to close the Reynolds stress terms. The empirical constants used in k − ϵ model were obtained using experiments conducted at low Reynolds numbers several decades ago. In this study, we revisit the turbulent viscosity parameter Cµ, based on the stress-intensity ratio c2 = |uw|k. Here, |uw| and k are the absolute values of the Reynolds stress and turbulent kinetic energy, respectively. Through a-priori comparisons, we find that the widely accepted value of Cµ = 0.09, does not agree with the latest DNS and experimental datasets of wall-bounded turbulent planar flows. Therefore, a new value is suggested by averaging c2 in the equilibrium region, where the production (P) of k is within 10% of the dissipation rate(ϵ), and consequently, c4 ≈ Cµ. We evaluate flows up to friction Reynolds number Reτ ≈ 10000 and find that with increasing Reτ, Cµ approaches a value of 0.06, which is 50% lower than the prevalent value of 0.09. Finally, we perform an a-priori test with the new (proposed) value of Cµ = 0.06 to show that the estimated turbulent viscosity νT for wall-bounded flows is in much closer agreement with the exact (DNS) values than when νT is estimated using Cµ = 0.09. The final study develops a new scaling law for wall-bounded turbulent flows. This formulation eliminates all arbitrary constants and depends only on physical parameters, namely, the free-stream velocity Um, the friction velocity U∗, the kinematic viscosity ν, and the distance from the wall z. This is a significant step towards describing the velocity profile using these pertinent parameters.
Open Access
Assessing irrigation canal seepage reduction using polymer sealants
(Colorado State University. Libraries, 2024) Lund, Ahmad Abdur Rehman, author; Scalia, Joseph, IV, advisor; Gates, Timothy K., advisor; Venayagamoorthy, S. Karan, committee member; Andales, Allan A., committee member
Irrigation canals around the world experience varying degrees of seepage losses, with several potential adverse consequences and influenced by numerous factors. A synthesis and interpretation of field seepage data from peer-reviewed literature (impact factor >1.5) on seepage measurement and control reveals several key insights: (i) seepage rates differ significantly due to diverse field conditions; (ii) the inflow-outflow method is the most reliable for measuring canal seepage in the field; and (iii) polymer sealants (PSs) offer a cost-effective alternative for reducing seepage in irrigation canals. Compared to conventional liners (CLs) such as concrete, geomembranes, or masonry, PSs are not only more affordable but also can be applied selectively, allowing for seepage when the surface water supply is sufficient and groundwater recharge is desirable. Studies show PSs can reduce seepage by 64% to 88%, while CLs achieve reductions of 53% to 95%, highlighting the potential of PSs for further research and application. However, best field application techniques for PSs, the uncertainty in evaluating effectiveness, and ambiguity in potential environmental impacts require more comprehensive investigation. The most widely researched PS for reducing canal seepage is linear anionic polyacrylamide (LAPAM), a synthetic polymer sealant (SPS). When applied to canal water, LAPAM forms flocs through cation bridging with divalent cations (Mg2+ and Ca2+) commonly found in canal water, which settle along the canal perimeter and reduce hydraulic conductivity. Observed seepage reduction from field trials of LAPAM that had been conducted prior to this study on three mid-sized canals (two in Colorado, USA and one in Sindh, Pakistan) using the recommended inflow-outflow method for seepage testing were analyzed. The average pre-LAPAM seepage rate was approximately 0.32 m/day, while the post-LAPAM rate dropped to 0.04 m/day, with results demonstrating seepage reductions between 69% and 100%. An uncertainty analysis of the pre- and post-LAPAM tests indicated an 85% probability that the seepage reductions were due to the LAPAM treatment. While LAPAM has proven effective, the long-term environmental impact of LAPAM treatment remains uncertain, underscoring the need to explore natural alternatives to synthetic polymer sealants. Biopolymer sealants (BPSs) were identified and evaluated through both laboratory and field experiments, designed to mirror the approach used with LAPAM. These experiments were conducted in triplicate (lab) and duplicate (field) to enhance confidence. In the lab, constant head saturated hydraulic conductivity (KSAT) tests simulated irrigation canal perimeter conditions. Five BPSs—pectin citrus (PC), cellulose hydroxyethyl ether (CHE), pullulan desalinated (PD), sodium alginate low viscosity (SALV), and xanthan gum (XG)—were initially tested and compared against LAPAM. The pre-and post-polymer KSAT values revealed that PC, PD, and XG achieved average reductions exceeding 40%, which was used as the threshold for further exploration. Subsequent testing under conditions more representative of irrigation canals identified XG as the most effective BPS. Alternative application rates were assessed, with 20 mg/L identified as the preferred concentration, as higher concentrations did not significantly enhance KSAT reduction. Long-term performance tests in the lab showed that XG, at 40 mg/L, can reduce hydraulic conductivity by over 90% for 9–10 months and by 60–70% over 1.5 months at 20 mg/L. These findings were validated using seepage tests in the field, where XG applied to a 3-km earthen canal reach at 20 mg/L reduced seepage by up to 63% over a month (at which time the canal was taken out of service). While the use of SPSs may still be justified for controlling canal seepage, this research shows that BPSs such as XG, have the potential to replace SPSs for canal sealing. However, further work is needed to optimize application methods and dosage rates, to better understand working mechanisms, to demonstrate long-term effectiveness, and to assess scalability across diverse field conditions.
Open Access
Simulation of successive events for multi-hazard community resilience analysis
(Colorado State University. Libraries, 2024) Harati, Mojtaba, author; van de Lindt, John W., advisor; Shields, Martin, committee member; Heyliger, Paul, committee member; Jia, Gaofeng, committee member
This dissertation, entitled "Simulation of Successive Events for Multi-hazard Community Resilience Analysis," aims to present an integrated framework for enhancing community resilience against natural hazards, with a specific focus on earthquakes and their associated impacts, such as aftershocks and tsunamis. These natural hazards pose significant threats to both coastal and non-coastal communities, leading to loss of life, injuries, and substantial socio-economic damage. A key approach to mitigating these risks is through community resilience analysis, which involves modeling the vulnerability of community infrastructure to combined source earthquake and its subsequent risks—aftershocks or tsunamis in coastal zones. In contrast to using separate fragility curves, this study develops combined earthquake-tsunami and mainshock-aftershock fragility models for a basic portfolio of reinforced concrete (RC) and woodframe structures. Governing parameters for 2D and 3D fragility functions tailored to these prototype buildings are presented, providing accessible tools for informed decision-making and mitigation strategies in community-level studies. The primary objectives are to model infrastructure vulnerability to successive seismic events and provide insights for resilience-informed decision-making. By identifying key vulnerabilities and assessing risk-based damage, dislocation, and functional recovery, the research significantly contributes to multi-hazard engineering. The proposed methodology and fragility models aim to enhance resilience-informed decision-making, allowing for strategies to improve community resilience.
Embargo
Investigating the impact of irrigation and water storage practices on hydrologic fluxes under climate change in a highly managed river basin
(Colorado State University. Libraries, 2024) Almahawis, Mohammed K., author; Bailey, Ryan T., advisor; Grigg, Neil S., committee member; Scalia, Joseph, IV, committee member; Sanford, William E., committee member
Irrigation practices and sources can have significant impacts on water resources and the hydrologic fluxes that control these resources. To better manage water resources and future water supply, the influence of irrigation practices and management on these hydrologic fluxes should be quantified in time and space at varying scales, under potential irrigation management practices. To fulfill this objective, a surface-subsurface modeling approach was applied to simulate watershed-scale hydrologic processes in the Cache la Poudre River Basin, Colorado, USA (4,824 km2), in which both surface water irrigation and groundwater irrigation are prevalent. The model chosen for this study is the watershed model SWAT+, using the spatially distributed, physically based groundwater module gwflow, in which unconfined groundwater storage, flows, and interaction with land surface features are simulated using a collection of grid cells that represent control volumes of the aquifer. Major groundwater inflows and outflows include pumping, recharge, groundwater-channel exchange, groundwater-lake exchange, and tile drainage outflow. To investigate the impact of irrigation practices, detailed surface and groundwater irrigation routines and canal-aquifer interactions were added to the SWAT+ source code, requiring information of irrigation sources and irrigation canal locations throughout the river basin. Model calibration and testing was performed using monthly stream discharge and groundwater head. The calibrated model is used to quantify the impact of surface water and groundwater irrigation scenarios on water availability and hydrologic fluxes within the river basin. A total of 22 scenarios were conducted and grouped into five main groups: irrigation source, irrigation amount, irrigation type, canal bed thickness, and partial or full sealing of earthen irrigation canals. Using groundwater as the only irrigation source decreases groundwater discharge to streams (by 14%) due to lowering groundwater levels; converting flood irrigation to sprinkler irrigation throughout the basin decreases surface runoff by 22%; and sealing earthen canals leads to a lowering of groundwater levels, which decreases groundwater discharge to streams by 9%, leading to an overall decrease in streamflow in the Cache la Poudre River and changes to temporal patterns in streamflow. Overall, irrigation amount and type and canal sealing have a small impact on total groundwater storage, compared to changes in the percent of fields irrigated by groundwater pumping. The potential impacts of climate change on water resources and hydrologic fluxes were analyzed in this study. The calibrated SWAT+gwflow model is run under five different CMIP5 climate models downscaled by MACA, each representing two different climate emission scenarios, RCP4.5 and RCP8.5. Except for the CGCM3 (Warm) model, all climate models and emission scenarios predict an increase in the yearly average temperature. The projected variation in precipitation (that is, snow and rain) depends on the climate model used. However, the average annual precipitation across the entire basin is expected to increase by 6.1% under the RCP8.5 scenario for the NorESM1-M (Mild) model. On the other hand, the IPSL-CM5A-MR (Dry) model shows a maximum decrease rate of 6% from the average climate conditions under the RCP8.5 scenario. The analysis reveals that the IPSL-CM5A-MR-8.5 climate model in the CLP is the most severe, as it combines two climatic stressors: less precipitation and increased temperature. Runoff is observed to be reduced by 47.6%, groundwater recharge to drop by 11%, and a 0.5% reduction in groundwater storage under this climate scenario. Although the climate conditions in the past have been inconsistent, the transboundary water source that flows into the watershed has consistently maintained a stable discharge throughout the investigated historical period. This indicates the existence of regulated water management methods and agreements, irrespective of the impact of climate change. The potential effects of constructing a new reservoir were also assessed in this study, specifically focusing on the influence on streamflow and hydrologic fluxes under changing climatic conditions. The calibrated SWAT+gwflow model was run using two different CMIP5 climate models downscaled by MACA, CNRM-CM5 (Wet) and IPSL-CM5A-MR (Dry) under RCP8.5 emission scenario. The analysis revealed that the CNRM-CM5 (Wet) climate scenario had a higher average monthly diversion rate from the CLP river to the Glade Reservoir during operation months (2.1 m3/s) compared to the IPSL-CM5A-MR (Dry) scenario (1.6 m3/s). Both climate models show a consistent reduction in the average annual streamflow of the CLP river when the reservoir is present. The largest reduction in the average monthly streamflow in CLP river was observed under the IPSL-CM5A-MR (Dry) RCP8.5 with reservoir scenario for the month of June, showing a 78% decrease from the historical average streamflow. The reduction in streamflow, under the reservoir scenario, for both future climate models led to a 13% and 24% reduction in surface water irrigation for the wet and dry climate scenarios, respectively, compared to historical values. Results are helpful for informed decision-making in agriculture water management and can lead to sustainable, efficient, and equitable use of water resources, helping to address the challenges posed by water scarcity and environmental conservation.
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
Flood interventions for socially equitable community resilience
(Colorado State University. Libraries, 2024) Hood, Catherine, author; van de Lindt, John W., advisor; Atadero, Rebecca, committee member; Pena, Anita, committee member
Flood hazard intensity and frequency are increasing due to climate change and diminish the resiliency of the built environment. Although funds for hazard interventions are available through programs such as the National Flood Insurance Program, Hazard Mitigation Assistance, and the US Department of Housing and Urban Development, these resources are often limited to specific flood zones and agencies have yet to fully consider social equity in their allocation. This study utilizes a community model and performs an analysis to evaluate community resilience through a social equity lens for flood intervention practices. As a case study, the computational platform IN CORE was utilized to perform a hazard-damage-consequence model for Lumberton, NC, a community damaged by two consecutive flood events (Hurricanes Matthew and Florence). A numerical model for Lumberton was developed using an existing suite of 15 building archetypes to populate the building inventory, which consists of 20,000 structures, and then households are synthetically populated from the census block level to representatively replicate the Lumberton community. An analysis quantifies the social equity of property acquisitions. To assess the distributional equity of property acquisition scenarios, population dislocation projections and resilience metrics are employed.
Embargo
Strength and consolidation behaviour of remolded Redbed claystone from the Mae Moh Lignite Mine
(Colorado State University. Libraries, 2024) Dongol, Abhishek, author; Bareither, Christopher, advisor; Chao, Kuo-Chieh, advisor; Scalia, Joseph, IV, committee member; Gallen, Sean, committee member
The objective of this study was to evaluate the strength and consolidation behavior of remolded Redbed claystone within a critical state framework. In 2018, a slope failure occurred in the northwestern waste rock pile at the Mae Moh Lignite mine in Thailand. A hypothesis of the failure was the slaking of the claystone at the base of the piles resulted in substantial strength loss relative to the intact blocky mass of the as-placed claystone waste rock. Consolidated undrained (CU) triaxial compression tests were conducted on 38-mm-diameter samples of remolded and intact specimens of the claystone. Remolded specimens were prepared from slurry and consolidated to form normally consolidated clay specimens. One dimensional consolidations test were conducted on remolded and intact claystone specimens prepared in a similar manner. The remolded specimens exhibited contractive, strain-softening behavior in undrained shear typical of normally consolidated clays with effective friction angles ranging between 20° and 21° (M = 0.8). The intact claystone exhibited stiff, dilative behavior in undrained compression with higher shear strength parameters (M = 1.11-1.66). One dimensional consolidation tests on remolded specimens yielded only virgin compression, whereas similar tests on in-tact specimens yielded only negligible recompression. The claystone transitioned from a strong, stiff, dilative material to a soft, contractive soil with a drastic reduction in strength and an increase in compressibility. A modified Cam Clay model was parameterized from the triaxial and consolidation results to model the shear behavior of remolded Redbed claystone. The model predictions showed good agreement with observed laboratory test data, which supports the use of the model to in advanced stress-deformation modeling of the waste rock piles at Mae Moh Lignite Mine.
Embargo
Ethical and equity challenges in engineering: a reflexive thematic analysis of early-career engineers' workplace experiences
(Colorado State University. Libraries, 2024) Agha, Chika Winnifred, author; Atadero, Rebecca, advisor; Omur-Ozbek, Pinar, advisor; Scalia, Joseph, IV, committee member; Most, David, committee member
Society and engineering are inseparable, with engineers' work significantly impacting society. Engineering has a large role in building a sustainable society, and prioritizing ethics and equity is essential. The early stages of an engineer's career are important for shaping professionals who uphold ethical values and champion equity. Understanding how early-career engineers perceive ethical and equity issues in their workplaces is key to fostering ethically conscious and equity-minded engineers capable of navigating evolving roles and responsibilities. This research aims to understand early-career engineers' experiences navigating ethical dilemmas and equity challenges in their professional practices and the implications these experiences have for their professional development. The overall research design of this study is basic qualitative research. Through the analysis of interviews with 13 participants from North America using reflexive thematic analysis (RTA), four key themes were developed that describe early-career engineers' experiences with ethics and equity as they transition to professional practice. The first theme is that schools do not fully prepare early-career engineers when it comes to ethical and equity practices. This includes teaching about simplified concepts, lacking comprehensive preparation, and recognizing that some skills can't be learned in school. The second theme is that characteristics of individual workplaces shape the early-career experiences of engineers. This theme emphasizes how leadership, work culture, exclusionary practices, company policies, and the principle that companies' actions speak louder than words, shape engineers' professional experiences. The third theme, ethical decision-making influences, and processes, explores the pressures that can lead to unethical actions, the importance of policies, rules, and oversight to support ethical decisions, the challenges of managing competing priorities, and the dilemmas of acting on equity issues. The fourth theme about the self-confidence and self-worth of early career engineers underscores the importance of self-confidence, speaking up, asking questions, and knowing one's value. The formative experiences of early-career engineers can profoundly impact their ethical reasoning and commitment to equitable practices throughout their careers. Understanding how early-career engineers engage with these issues is important for developing educational programs, such as case studies and professional systems that support ethical and equitable engineering.
Open Access
Clean Water Act environmental compliance program review of ten air force bases and water quality survey
(Colorado State University. Libraries, 2024) Hoeffner, Jacob, author; Carlson, Kenneth, advisor; Carter, Ellison, committee member; Didier, John, committee member
This study includes two main components. First, environmental compliance program reviews (ECPRs) of ten AF bases investigated the permits, programs, and compliance records at an installation level. Due to the depth of the ECPRs, detailed performance metrics from EPA ECHO, EASIER, and OSD databases were integrated into the ECPRs findings. Second, a survey further investigated trends identified in the ECPRs across 25 participating installations. The relevant performance metrics were used to evaluate the effectiveness of water programs that participated in the survey. Systemic compliance risks in permit management, data management, and stormwater and wastewater infrastructure were identified.
Open Access
Investigating the salinity impacts on current and future water use and crop production in a semi-arid agricultural watershed
(Colorado State University. Libraries, 2024) Hosseini Ghasemabadian, Pardis, author; Bailey, Ryan T., advisor; Arabi, Mazdak, committee member; Smith, Ryan, committee member; Andales, Allan, committee member
Soil salinity can have a significant impact on agricultural productivity and crop yield, particularly in arid and semi-arid irrigated watersheds wherein irrigation and inadequate drainage often combine to increase salt ion concentrations in soil water. In conjunction with intense irrigation in semi-arid agricultural regions, increasing population resulting in boosted water demand, adverse impacts of climate change on water availability, in other words, water scarcity, future land use and land cover changes, changes in applied irrigation practices, and introducing new point-sources and non-point sources of salinity in the region all can govern the salinity and crop yield consequently. Taking into account the aforementioned impactful components on crop reduction via salinity increase, the overall objective of this dissertation is to provide insights for policymakers to better address the current and future salinity issues to sustain crop production in semi-arid regions under progressive salinity. This will be accomplished by i) investigating the controlling factors on salinity in the soil, groundwater, and river water using the SWAT-Salt model which simulates the reactive transport of 8 major salt ions in major hydrological pathways applied to a 1118 km2 irrigated stream-aquifer system located within the Lower Arkansas River Valley (LARV) in southeastern Colorado, USA ii) Assessing the salinity impacts on crops production blue and green water footprint as a measurable indicator for water being used per unit of a given crop production using the SWAT-MODFLOW-Salt model applied to a 732 km2 irrigated stream-aquifer system located in the LARV, iii) quantify the impact of environmental factors alteration including changes in climatic and irrigation practices in the LARV on future salinity content and its impact on crop production in the region using the SWAT-MODFLOW-Salt model. To control salinity, more importantly in semi-arid irrigated areas, the principal step is to identify the key environmental and hydrologic factors that govern the fate and transport of salts in these irrigated regions. To accomplish this objective, global sensitivity analysis was applied to the newly developed SWAT-Salt model (Bailey et al., 2019), which simulates the reactive transport of 8 major salt ions (SO4, Ca, Mg, Na, K, Cl, CO3, and HCO3) in major hydrologic pathways in a watershed system. The model was applied to a saline 1118 km2 irrigated stream-aquifer system located within the Lower Arkansas River Valley in southeastern Colorado, USA. Multiple parameters including plant growth factors, stream channel factors, evaporation factors, surface runoff factors, and the initial mass concentrations of salt minerals MgSO4, MgCO3, CaSO4, CaCO3, and NaCl in the soils and in the aquifer were investigated for control on salinity in groundwater, soils, and streams. The Morris screening method was used to identify the most sensitive factors, followed by the Sobol' variance-based method to provide a final ranking and to identify interactions between factors. Results showed that salt ion concentration in soils and groundwater was controlled principally by hydrologic factors (evaporation, groundwater discharge and up flux, and surface runoff factors) as well as the initial amounts of salt minerals in soils. Salt concentration in the Arkansas River was governed by similar factors, likely due to salt ion mass in the streams controlled by surface runoff and groundwater discharge from the aquifer. Sustainable agriculture in intensively irrigated watersheds, especially those in arid and semi-arid regions, requires improved management practices to sustain crop production. This depends on factors such as climate, water resources, soil conditions, irrigation methods, and crop types. Of these factors, soil salinity and climate change are significant challenges to agricultural productivity. To investigate the long-term impact of salinity and climate change on crop production from 1999 to 2100 in irrigated semi-arid regions, we applied the water footprint (WF) concept using the hydro-chemical watershed model SWAT-MODFLOW-Salt, driven by five General Circulation Models (GCMs) and two climate scenarios (RCP4.5 and RCP8.5), to a 732 km2 irrigated stream-aquifer system within the Lower Arkansas River Valley (LARV), Colorado, USA. In this study we estimated the green (WFgreen), blue (WFblue), and total (WFtotal) crop production WFs for 29 crops in the region, both with and without considering the impact of salinity on crop yield. The results indicate that during the baseline period (1999-2009), the total annual average WFgreen, WFblue, and WFtotal increased by 7.6%, 4.4%, and 6.5%, respectively, under salinity stress, with crop yields decreasing by up to 4.6%, 1.6%, and 2.3% for green, blue, and total crop yield. The combined impact of salinity and the worst-case climate model (IPSL_CM5A_MR) under the higher emission scenario (RCP8.5) resulted in increases of 3.3%, 1.9%, and 3% in green, blue, and total crop production WFs. Additionally, the study found that the proportion of green, blue, and total crop production WFs in the LARV exceeded the world average. This discrepancy was attributed to various factors, including different spatial and temporal crop distribution, irrigation practices, soil types, and climate conditions. Notably, salinity stress had a more significant impact on green crop yield and green WF compared to blue crop yield and blue WF across all GCM models. This finding highlights the need to prioritize management practices that address salinity-associated challenges in the region. The adverse effects of salinity on soil health, crop yield, and environmental ecosystem require comprehensive strategies for managing salinity in agricultural watersheds by adopting improved irrigation practices and effective salinity management strategies for mitigating these impacts and sustaining agricultural productivity in salinity-affected regions. The complex dynamics between various irrigation practices and soil salinity play a pivotal role in shaping agricultural productions and managing soil salinity. In semi-arid regions like the LARV, salinity poses a significant threat to agriculture, exacerbated by climate change and historic irrigation practices. To evaluate the interplay between salinity, climate change, and irrigation management in affecting crop yields within the Lower Arkansas River Valley (LARV), focusing on corn and alfalfa, we utilized the SWAT-MODFLOW-Salt model to examine how changes in irrigation management influence crop production under various scenarios projected through the year 2100. This study addresses the differential responses of corn and alfalfa to the impact of incremental increases and reductions in irrigation efficiency and irrigation water loss (5%, 10%, 15%, and 20%) on corn and alfalfa yields dynamics under salinity stress, utilizing projections from five global climate models under two distinct Representative Concentration Pathway (RCP) scenarios, RCP4.5 and RCP8.5 and two irrigation scenarios. The findings from irrigation practice scenario (1), maintaining a constant amount of irrigation water, revealed that corn yields improved by up to 13.8% under salinity stress and 16.5% under non-salinity conditions with a 20% increase in irrigation efficiency and a 20% reduction in water loss under RCP4.5. Alfalfa, demonstrating greater salinity tolerance, showed similar benefits, with yield increases of 9.1% under salinity stress and even higher improvements under non-salinity conditions. These results highlight the effectiveness of tailored irrigation practices in mitigating environmental stresses. In contrast, scenario (2), which involved reducing irrigation water by half, resulted in more pronounced negative outcomes. Corn yields exhibited greater sensitivity to salinity stress, with yield reductions ranging from -9.8% under salinity stress to -9.3% under non-salinity conditions, particularly under the RCP8.5 scenario. Alfalfa yields also declined, though less severely than corn, with reductions ranging from -8.9% under salinity stress to -8.3% under non-salinity conditions. Despite improvements in irrigation efficiency and reduced water loss, the adverse effects of salinity stress were not fully mitigated in scenario (2), emphasizing the need for adequate water availability to sustain crop yields under salinity and climate change pressures. The research highlights the importance of adopting advanced irrigation technologies and practices that not only counteract the adverse effects of salinity but also adapt to evolving climatic conditions. This study offers valuable insights for policymakers and agricultural managers on strategic water resource management to sustain crop yields in salinity-affected and water-limited agricultural systems. The results of this study can be used in decision-making regarding the most impactful land and water management strategies for controlling salinity transport and build-up in soils, both for this watershed and other similar semi-arid salinity-impacted watersheds for present and future purposes.
Embargo
Improving soil property predictions for applications in tailings and terramechanics
(Colorado State University. Libraries, 2024) Bindner, Joseph R., author; Scalia, Joseph, advisor; Atadero, Rebecca, advisor; Bareither, Christopher, committee member; Niemann, Jeffrey, committee member; Ham, Jay, committee member
Soil properties are used by engineers and scientists to better understand the state and behavior of soils. For example, soil properties can be used to estimate surficial soil strength for vehicle mobility models and can be used to better understand the engineering characteristics of mine waste (tailings) stored in tailings storage facilities. Soil and tailings properties often have high spatial variability and often require high resolution data for engineering analyses. Standard laboratory procedures are commonly used to determine soil properties but are often impractical for large spatial extents. While some existing soil data products provide estimates of surficial soil properties, the fidelity of soil data products is often poorly understood and insufficient for many applications. Additionally, some field tests used to estimate soil properties, such as the cone penetration test (CPT), rely on empirical correlations that cannot be used for some soils. There remains a need for procedures which improve the speed and accuracy of soil property estimates across large spatial extents. The objectives of this study are to (i) evaluate how surficial soil moisture and soil strength vary with soil and landscape attributes across a large spatial extent, (ii) explore the use of field-based hyperspectral sensing and machine learning for the prediction of surficial soil properties across a landscape, and (iii) assess the use of laboratory hyperspectral sensing and machine learning for the prediction of tailings properties for potential application in situ via direct push methods. Soil and landscape attributes were determined at sampling locations across a semi-arid foothills region and used to assess how soil moisture and soil strength vary with soil and landscape attributes. Then, hyperspectral data were captured at select sampling locations and used to train and assess the performance of a convolutional neural network (CNN) for the predictions of soil properties. Finally, a diverse tailings-hyperspectral dataset was prepared in the lab and used to train and assess a CNN to provide proof of concepts for prediction of material properties relevant to TSF stability analyses.
Open Access
Optimizing remote sensing data for actual crop evapotranspiration mapping at different resolutions
(Colorado State University. Libraries, 2024) Costa Filho, Edson, author; Chávez, José L., advisor; Venayagamoorthy, Karan, committee member; Niemann, Jeffrey, committee member; Kummerow, Christian, committee member
This study aimed to advance irrigation water management by developing and evaluating a procedure to improve the multispectral data from sub-optimal remote sensing sensors when using the optimal spectral resolution for a given remote sensing (RS) of crop actual evapotranspiration (ETa) algorithm. Data have been collected at three research sites in Colorado under different irrigation systems, soil textures, and vegetation types. The research site in Greeley (CO) has a five-year dataset (2017-2018 and 2020-2022). The fields in Fort Collins and Rocky Ford (CO) have data from 2020 and 2021. Three categories of ETa algorithms were evaluated in the study: The reflectance-based crop coefficient (RBCC) with three different models based on the normalized difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI), and fractional vegetation canopy cover (fc), the one-source simplified surface energy balance (OSEB) based on a surface aerodynamic temperature approach, and the two-source surface energy balance algorithm (TSEB) using two different resistance approaches (parallel and series). All three ETa modeling categories use either just surface reflectance in the visible and invisible light spectrum (e.g., RED, BLUE, GREEN, Near-infrared) or a combination of multispectral and thermal data as inputs to predict crop ETa, alongside local micrometeorological data from nearby agricultural weather stations. A total of six RS of ETa algorithms were evaluated in this study. A total of five RS sensors were evaluated: three spaceborne sensors (e.g., Landsat-8, Sentinel-2, and Planet CubeSat), one proximal device (multispectral radiometer), and an uncrewed aerial vehicle (UAS). The spatial resolution of the RS sensors varied from 30 m to 0.03 m. The accuracy assessment of the crop ETa predictions considered a statistical performance analysis using, among several statistical metrics, the mean bias error (MBE) and root mean square error (RMSE), and compared estimated ETa values from all seven RS ETa algorithms with observed ETa values obtained from the Eddy Covariance Energy Balance System (Greeley and Fort Collins sites) and a weighing lysimeter (Rocky Ford). The study was divided into three stages: a) the evaluation of different remote sensing (RS) pixel spatial resolutions (scales) as inputs on the estimation of different types of data needed for estimating ETa in hourly and daily time frames; b) the development of a calibration protocol and standards for the use of different imagery spatial resolutions (scales) in RS of ETa algorithms. The calibration approach involved a novel two-source pixel decomposition approach for partitioning surface reflectance into soil and vegetation using a non-linear, physically based spectral model, machine-learning regression, and a novel spatial light extinction model (kp); c) the accuracy evaluation of resulting ETa rates from calibrated/standardized data (for each selected RS of ETa algorithms). Results of stage one of the study indicated that depending on the RS of ETa and RS sensor data (spatial and spectral resolutions), the accuracy (MBE ± RMSE) of estimated ETa predictions varied. For the NDVI and fc RBCC ETa algorithms, Sentinel-2 provided the best RS data for predicting daily maize ETa. Errors were 0.21 (5%) ± 0.78 (18%) mm/d and 0.59 (14%) ± 1.07 (25%) mm/d, respectively. For the OSEB algorithm, Planet CubeSat gave the best RS data since it provided the smallest error for hourly maize ETa, -0.02 (-3%) ± 0.07 (13%) mm/h. For the SAVI RBCC model, the MSR data provided the best results since the maize ETa error was -0.13 (-3%) ± 0.67 (16%) mm/d. For the TSEB in series and parallel, the errors when estimating hourly maize ETa were -0.02 (-3%) ± 0.07 (11%) mm/h and -0.02 (-4%) ± 0.09 (14%) mm/h, respectively when using MSR data. For stage two of the study, the best machine learning regression model for a given RS sensor data and RS of the ETa algorithm depended on the surface reflectance composite (plant or bare soil values). The best machine-learning models for adjusting RS data were the regression tree and the Gaussian Process Regression. Regarding the pixel decomposition approach based on the novel spatial light extinction coefficient model, the novel approach provided reliable predictions of kp using the different RS sensor data. The error in predicting kp was -0.01 (-2%) ± 0.05 (10%) when combining all RS sensor data for the two-year data set at LIRF (years 2018 and 2022). For stage three of the study, results showed improvements in the accuracy of crop ETa estimation after adjusting the RS data using the proposed calibration protocol. At the Greeley site, regarding the RBCC RS of ETa algorithm, adjusted data from Planet CubeSat had better performance when estimating daily crop ETa since the error was reduced from 21% to 16% for the fc-input model. For the SAVI-input model, the RS data that performed better was the UAS. Errors were reduced from -0.42 (-11%) ± 0.76 (20%) mm/d to -0.21 (-5%) ± 0.41 (11%) mm/d. For the NDVI-input model, the adjusted UAS data performed better when estimating daily maize ETa. The improved accuracy was 0.32 (8%) ± 0.40 (10%) mm/d. At the Rocky Ford site, for the fc-input model, adjusted RS optical data from the MSR performed better. Daily maize ETa error was reduced from 17% to 15%. For the SAVI-input model, the RS data that performed better was the Landsat-8, with errors being reduced from -1.84 (-28%) ± 2.61 (39%) mm/d to -1.14 (-17%) ± 1.79 (27%) mm/d. The NDVI-based RBCC model had better performance when using adjusted MSR data daily maize ETa. Regarding the OSEB RS of crop ETa approach, at the Greeley site, the OSEB-adjusted data from UAS performed better. Hourly maize ETa error was reduced from 0.11 (19%) mm/h to 0.07 (13%) mm/h for the OSEB algorithm. For the TSEB parallel algorithm, the RS data that had better performance was the Landsat-8/9 since the error was reduced from 0.19 (34%) mm/h to 0.11 (20%) mm/h. For the TSEB series algorithm, the adjusted UAS data performed better. Daily maize ETa errors decreased from 0.10 (18%) mm/h to 0.05 (9%) mm/h. In summary, this study provided an RS calibration approach to support irrigation water management through the development and evaluation of a method for enhancing optical multispectral data sourced from various RS sensors. This study also highlighted the efficacy of machine learning models, like regression tree and Gaussian Process Regression, in adjusting RS data based on surface reflectance composites. Furthermore, a novel pixel decomposition approach utilizing a spatial light extinction model effectively predicted the light extinction coefficient. Overall, this research showcases the potential of RS data adjustments in improving the accuracy of ETa estimates, which is crucial for optimizing irrigation practices in agricultural settings.
Open Access
Modeling nonpoint-source uranium pollution in an irrigated stream-aquifer system: calibration and simulation
(Colorado State University. Libraries, 2024) Qurban, Ibraheem A., author; Gates, Timothy K., advisor; Bailey, Ryan T., committee member; Grigg, Neil S., committee member; Ippolito, James A., committee member
The Lower Arkansas River Valley (LARV) in southeastern Colorado has been a source of significant agricultural productivity for well over a century, primarily due to extensive irrigation practices. Mirroring trends seen in other semi-arid irrigated areas globally, however, irrigated agriculture in the LARV has resulted in several challenges for the region. In addition to the emergence of waterlogging and soil salinization, leading to decreased crop yields, elevated levels of nutrients and trace elements have appeared in the soil and water. Among these constituents, uranium (U), along with co-contaminants selenium (Se) and nitrate (NO3), has shown particularly high concentrations in groundwater, surface water, and soils. These heightened concentrations pose environmental concerns, impacting human health and the well-being of aquatic life such as fish and waterfowl. Careful monitoring and management practices are crucial to prevent potential harm to water resources. The main goal of this research is to develop a comprehensive numerical model for assessing U pollution in a stream-aquifer system within a large irrigated area. To achieve this, a computational model is built and tested that can predict with reasonable accuracy how U, along with Se and NO3, are mobilized and move within a coupled system of streams and groundwater. The approach combines two key modeling components: a MODFLOW package, which handles the simulation of groundwater and stream flow dynamics, and an RT3D package, which addresses the reactive transport of U, Se, and nitrogen (N) species in both groundwater and interconnected streams. RT3D relies on the simulated flows generated by MODFLOW to track the movement of U, Se, and N species between streams and the aquifer in the irrigated landscape, updating daily to adequately capture changes over time. This integrated model provides an understanding of how these contaminants behave and interact within the stream-aquifer system, aiding in effective pollution assessment and providing insights valuable to the planning of management strategies. The coupled MODFLOW-RT3D flow and reactive transport model is applied to a 550 km² area within the LARV, stretching from Lamar, Colorado, to the Colorado-Kansas border and spanning a period of 14 years. The flow package is compared with observations of groundwater hydraulic head and stream flow, along with estimates of return flow along the Arkansas River. The reactive transport package is assessed by comparing predicted U, Se, and NO3 concentrations against data collected from groundwater monitoring wells and stream sampling sites along with estimates of solute mass loads to the river. To calibrate and refine the model, the PESTPP-iES iterative ensemble smoother (iES) software is employed. This calibration process is dedicated to enhancing the model's accuracy in predicting both flow and transport dynamics. PESTPP-iES addresses calibration uncertainty by establishing prior frequency distributions for key model parameters based on data and expertise, then iteratively adjusts these parameters during calibration to align model predictions with observed data. Post-calibration, posterior distributions reflect updated parameter values and reduced uncertainties. Demonstrating a strong alignment with concentrations of CNO3, CSe, and CU values found in groundwater, streams, and the mass loading entering the Arkansas River, outcomes of the model-based simulations reveal a substantial violation of the Colorado chronic standard (85th percentile = 30 μg/L) for CU throughout the study region. On average, simulated CNO3, CSe, and CU values for groundwater in non-riparian areas in the region are 3.6 mg/L, 41 µg/L, and 126 µg/L, compared to respective averages of 4 mg/L, 53 µg/L, and 112 µg/L observed in monitoring wells. When considering the 85th percentile of simulated CNO3, CSe, and CU values, the figures for non-riparian groundwater are 6 mg/L, 50 µg/L, and 218 µg/L, respectively. Groundwater in riparian areas shows lower average simulated CNO3, CSe, and CU values of 3 mg/L, 26 µg/L, and 72 µg/L, respectively, and 85th percentile values of 5 mg/L, 41 µg/L, and 152 µg/L. Additionally, simulated average mass loading rates for NO3, Se, and U along the river are 8.8 kg/day per km, 0.05 kg/day per km, and 0.27 kg/day/km respectively, compared to stochastic mass balance estimates of 9.2 kg/day per km , 0.06 kg/day per km , and 0.23 kg/day per km. The simulated 85th percentile CNO3, CSe, and CU values in the Arkansas River are 1 mg/L, 11 μg/L, and 87 μg/L, respectively. Notably, the simulated U levels in groundwater exceed the chronic standard across 44% of the region. Along the Arkansas River, concentrations consistently surpass the chronic standard, averaging 2.9 times higher. Predicted Se concentrations also show significant exceedances of the chronic standard, while NO3 violations are slight to moderate. The varying pollutant levels across the region highlight specific areas of concern that require targeted attention, indicating potential contributing factors to these hotspots. Findings outline how serious and widespread the problem is in the LARV, providing a starting point for comparing potential pollution reduction from alternative water and land best management strategies (BMPs) to be explored in future applications of the calibrated model.
Open Access
Comparative analysis of remote sensing platforms for assessing maize crop biophysical characteristics and evapotranspiration estimation
(Colorado State University. Libraries, 2024) Al-Majali, Zaid, author; Chávez, José L., advisor; Davenport, Frances, committee member; O'Connel, Jessica, committee member
The rapid growth in population, climate variability, and decreasing water resources necessitate innovative agricultural practices to ensure food security and resource conservation. This study investigates the effectiveness of various multispectral imagery from remote sensing (RS) platforms (such as Unmanned Aircraft Systems (UAS), PlanetDove microsatellites, Sentinel-2, Landsat 8/9, and proximal MSR-5) in the appropriate estimation of crop biophysical characteristics (CBPCs) and actual crop evapotranspiration (ETa) for maize fields in northeastern Colorado. The research aimed at evaluating the accuracy of vegetation indices (VIs) derived from different sources of RS data in estimating key CBPCs, including leaf area index (LAI), crop height (Hc), and fractional cover (Fc), as well as the ETa. Field experiments were conducted at the USDA-ARS Limited Irrigation Research Farm in Greeley, Colorado, in 2022. Different irrigation strategies were used to assess the maize's water use response. Surface reflectance data was collected using the MSR sensor, and observed LAI, Hc, and Fc values served as ground truth for validating remote sensing estimates. The study applied various statistical analyses to compare the performance of different remote sensing platforms and models. Results indicate that higher-resolution platforms, particularly UAS, provided higher accuracy in estimating VIs and CBPCs than other satellite platforms. The study also highlights the influence of environmental conditions on the accuracy of remote sensing models, with locally calibrated models outperforming those developed in dissimilar conditions. The findings underscore the potential of advanced remote sensing technologies in enhancing precision agriculture practices and optimizing water resource management.
Embargo
Shear and consolidation behavior of slurry-deposited, desiccated tailings and compacted filtered tailings
(Colorado State University. Libraries, 2024) Primus, Justin Michael, author; Bareither, Christopher A., advisor; Scalia, Joseph, IV, committee member; Stright, Lisa, committee member
The objective of this study was to (i) evaluate and compare the undrained shear behavior and (ii) the consolidation behavior of slurry-deposited and desiccated tailings versus compacted filtered tailings. In general, the evaluation supports the hypothesis that desiccation and resaturation of a hard rock mine tailings yield higher peak undrained shear strengths relative to compacted filtered tailings when considering similar initial conditions (e.g., stress and density). The increase in undrained shear strength was attributed to the tailings fabric, which generated a stiffer response to loading and transitional behavior from contractive to dilative tendencies when sheared undrained. Consolidated undrained (CU) triaxial compression tests were conducted on 64-mm-diameter specimens that followed two different procedures. Slurry-deposited tailings were desiccated to a target void ratio and water content, resaturated, and tested in isotropic, consolidated, undrained axial compression. Filtered tailings specimens were prepared to similar initial void ratios as those measured on desiccated tailings specimens and tested in triaxial compression in the same manner. One-dimensional consolidation tests were also conducted on desiccated and filtered tailings specimens in a similar sequence. The desiccated and filtered tailings exhibited contractive, strain-hardening behavior in the triaxial tests and yielded effective stress friction angles of 29.1° for the desiccated tailings and 27.7° for the filtered tailings. Desiccated tailings samples showed a stiffer initial peak deviatoric stress and slower decreasing rate of change in stress relative to the filtered tailings. There was no indication of a difference in stiffness or brittleness between tailings preparation methods. The higher shear strength of the desiccated tailings was attributed to (i) more pronounced inter-particle reinforcing effects and (ii) densification from stress-history of desiccation. One-dimensional consolidation tests yielded a trend of increasing preconsolidation pressure with decreasing initial void ratio for both the desiccated and filtered tailings. There were slightly higher average compression and recompression indexes computed for the desiccated tailings relative to the filtered tailings, providing an indication of the different in the fabric behaviors.
Open Access
Exploration of passive desaturation of in place tailings using wicking geosynthetics
(Colorado State University. Libraries, 2024) Monley, Kendall O., author; Scalia, Joseph, IV, advisor; Bareither, Christopher, committee member; Ross, Matthew, committee member
As global demand for metals and critical minerals increases, so too does the production of tailings. Tailings are what is left behind after extraction of valuable metals and minerals from ore, and consist of finely ground rock, water, unrecoverable metals, chemicals, and organic matter. These residuals are managed in engineered facilities that function to both dewater and store tailings, known as tailings storage facilities (TSF). A common assumption is that the water initially contained in TSFs will drain down to an unsaturated condition after deposition of new tailings ceases. However, a review of literature on geotechnical and hydrotechnical conditions of legacy TSFs (TSFs that have stopped receiving tailings) in arid environments illustrates that achievement of unsaturated conditions in internal fine-grained layers may not always occur. As the tailings are deposited, layers of finer and coarser particles are interbedded. This causes the formation of capillary barriers and may ultimately result in finer-grained layers held at near saturation after drain down. These fine-grained layers are more susceptible to liquefaction concerns and can require costly remedial actions to ensure geotechnical stability. Dewatering is the process of removing water from whole tailings and offers benefits including increasing geotechnical stability and recovering stored water. Tailings dewatering may occur prior to or after deposition into a TSF. In this study, I explore in-situ dewatering via use of capillary (wicking) geotextiles, and the effectiveness of the wicking geotextiles. Beaker and column experiments were created to emulate stratigraphy seen in legacy TSFs. Additionally, shrinkage testing was conducted to compare the final densities and void ratios of samples with and without wicking geotextiles. Column testing reveals the wicking geotextiles accelerated dewatering by 2.8 times the rate of natural drying processes. At the conclusion of testing, the wicking geotextile experiments had reached similar densities and void ratios to control experiments. This novel approach to passively dewatering tailings warrants additional testing.
Open Access
Chloride binding and desorption mechanism in blended cement containing supplementary cementitious materials exposed to de-icing brine solutions
(Colorado State University. Libraries, 2024) Teymouri Moogooee, Mohammad, author; Atadero, Rebecca, advisor; Fantz, Todd, advisor; Jia, Gaofeng, committee member; Bailey, Travis, committee member
Concrete, the most widely used construction material globally, faces significant challenges due to its porous nature, particularly from chloride-induced corrosion. This corrosion, primarily caused by chloride ions penetrating concrete, affects over 7.5% of U.S. concrete bridges, incurring annual costs ranging from $5.9 to $9.7 billion. Chlorides enter concrete from various sources, including de-icing salts. Maritime infrastructures also suffer from severe chloride-induced corrosion because seawater contains a high concentration of chloride ions. Irrespective of how chlorides enter the concrete, chlorides can exist in concrete in two forms: free and bound chlorides. While bound chlorides are beneficial, they can be released due to environmental factors like carbonation and chemical attacks, exacerbating corrosion rates. These attacks cause pH reduction in concrete and subsequently can result in the release of bound chlorides (chloride desorption).This dissertation aims to address three main objectives: (1) investigate factors influencing chloride binding measurements due to lack of a standardized method for chloride binding measurements, (2) study chloride desorption mechanisms in different cementitious systems exposed to de-icing brines, and (3) analyze pH and compositional changes in blended pastes under chloride contamination and carbonation. First, factors impacting chloride binding measurements were identified, such as sample form and saturation level, solution composition, and solution volume. Vacuum-saturated samples exhibited higher chloride binding than partially saturated or dried samples, with powdered samples showing the highest binding. Secondly, chloride desorption mechanisms were investigated in both Ordinary Portland Cement (OPC) pastes and pastes containing supplementary cementitious materials (SCMs) like fly ash, slag, and silica fume. Results indicated that the type of cation in the brine solution influenced bound chloride levels, with SCMs improving chloride binding capacity. Slag inclusion was effective in promoting chloride binding, while silica fume showed the least effect. The degree of chloride desorption under acid attack depended on the acid-to-paste mass ratio. The results reveal that inclusion of fly ash and slag is favorable in terms of chloride desorption, and silica fume is not recommended for use when chloride-induced corrosion is a concern. MgCl2 and CaCl2 de-icers demonstrated a lower chloride desorption compared to NaCl. Finally, the synergistic effects of chloride contamination and carbonation were examined in OPC and fly ash-containing pastes. Carbonation led to over 95% chloride desorption after two weeks, with fly ash-containing pastes exhibiting lower pH levels due to reduced portlandite content. Incorporation of fly ash is not recommended when carbonation is a concern. Therefore, caution should be exercised when considering fly ash inclusion in mixtures where both chloride contamination and carbonation are simultaneous concerns. This dissertation contributes to understanding chloride desorption in cementitious systems, essential for enhancing the durability and service life of concrete structures. This dissertation shed lights on primary factors influencing chloride binding measurements, enhancing the accuracy and comparability of chloride binding results. The results reveal that type of cation present in the solution and type of SCMs have significant influences on the pH, chloride binding capacity, and chloride desorption rates.
Embargo
Integrated assessment of water shortage under climate, land use, and adaptation changes in the contiguous United States
(Colorado State University. Libraries, 2024) Gharib, Ahmed AbdelTawab Fahmy AbdelMeged, author; Arabi, Mazdak, advisor; Goemans, Christopher, committee member; Sharvelle, Sybil, committee member; Warziniack, Travis, committee member
Water scarcity is a critical global challenge. Water managers pursue water supply- and demand-side strategies, including construction or enhancement of water supply systems, conservation, and water reuse, to address water security driven by changes in climate, population, and land use. However, the effects of these strategies to mitigate future water shortages under dynamic climate and socioeconomic conditions at various spatial and temporal scales remain unclear. The overarching goal of this dissertation is to (1) improve understanding of the interconnections and interactions between climate, socioeconomic, hydrological, and institutional factors that influence water shortage at the river basin level, and (2) conduct an integrated assessment of water and land use management strategies. The dissertation is organized into three research studies. The first study explores water shortages in the South Platte River Basin (SPRB) and the potential benefits of investing in storage infrastructure and demand management strategies. The second study develops a methodology to understand the interactions between land use planning, water demands, shortage vulnerability, and effects on associated economic value. The third study expands the integrative assessment framework to assess changes in water demand, supply, and withdrawals, and identify effective mitigation strategies across river basins in the Contiguous United States over a range of climatic and socioeconomic pathways that are forecasted for the coming decades. In the first study, we develop data analysis and modeling tools to project water demands, supply, and shortages in the SPRB by the mid and end of the 21st century, examine the efficacy of adaptation strategies to reduce water shortages, and explore conditions under which reservoir storage and demand management would serve benefits for reduction of the vulnerability of economic sectors to water shortages. We implement two demand modeling tools to simulate the current and future urban and agricultural water demand in the river basin. Water yield is simulated using calibrated and tested Variable Infiltration Capacity (VIC) model. The estimated water demands and supplies are integrated using the Water Evaluation and Planning (WEAP) model to simulate water allocation with a half-monthly timestep to 70 aggregate users in the basin. Population growth, climate change, reservoir operations, and institutional agreements were considered during the modeling. The study reveals that the vulnerability to water shortages across sectors would increase without adaptation strategies. Population growth tends to be the primary driver of water shortages in the river basin. Reservoirs in the basin can relieve the sequences of the earlier seasonal shift of the water supply by capturing water during the high flow to be used in the high-demand seasons. However, additional storage is only beneficial up to a threshold of storage capacity to the water supply mean ratio of 0.64. The second study focuses on integrating the effects of land use planning and water rights institutions into the shortage analysis of the SPRB. The goal is to build a framework to understand the complex interactions between climate change, water rights institutions, urban land use planning, and population growth, and how they collectively impact the water shortage and economic analysis. We apply this framework to the SPRB simulate three water institutions, update the urban demand modeling to be a function of the population density, and test different scenarios of population locations throughout the basin. Results show that changing water rights institutions has a small impact on total shortages compared to climate change, but substantially impacts which users experience shortages. Land use policies influencing population locations have larger impacts on shortage and economic value compared to water rights. Finally, distributing the population more evenly between upstream and downstream regions reduces water shortages and increases associated economic value regardless of water rights institutions and climate conditions. The third study employs an integrative modeling assessment framework to assess water shortage and effective mitigation strategies in river basins across the Contiguous United States. The goals are to improve the methodologies for estimation of water withdrawals, consumptive use, and water shortage, and explore the effectiveness of supply- and demand-side adaptation strategies. The simulated demands are integrated with the water supply components (groundwater, interbasin transfers, water yield, and reservoirs) into a water allocation model for simulating shortage under different scenarios. Results reveal that irrigation has the highest historical and future consumptive use, over 75% of the total consumptive use. Although the consumptive use ratio receives little attention in the literature, it appears to be the most significant parameter for shortage calculations. The allocation model provides comprehensive shortage analysis considering shortage volume, ratio, and frequency across multiple scenarios for the 204 sub-regions –Hydrologic Unit Code 4 watersheds– of the Contiguous United States. Water shortages concentrate between the boundaries of the West Region with both the Midwest and the South regions, in addition to Arizona, Florida, and the center valley of California. Relying only on sustainable groundwater pumping rates is essential to stop the ongoing groundwater depletion, but adds more pressure on demand reduction strategies. The ongoing research examining water demand, supply, and shortage is important and requires further integration of the key influencing variables. This dissertation demonstrates the necessity of an integrated approach to fully understand the relative impacts of the main drivers of water allocation and shortage. We highlight that reservoirs play a vital role in balancing seasonal fluctuations in the water supply. However, their effect on the 30-year mean annual shortage is effective until the storage volume ratio to mean water supply exceeds 64%. Additionally, land use policies carry higher direct significance on water shortages compared to water rights. We find that distributing the population more evenly throughout the river basin provides the lowest shortage. Lastly, the approaches targeting shortage calculation and mitigation should analyze both regional and national scenarios under integrated frameworks comparing demand- and supply-side options.
Embargo
Tools for characterizing and monitoring natural source zone depletion
(Colorado State University. Libraries, 2024) Irianni Renno, Maria, author; De Long, Susan K., advisor; Sale, Thomas C., advisor; Key, Trent A., committee member; Scalia, Joseph, committee member; Stromberger, Mary, committee member
Although natural source zone depletion (NSZD) has gained acceptance by practitioners as a remediation technology for mid- to late-stage sites containing light non-aqueous phase liquids (LNAPL), challenges remain for broader regulatory adoption of NSZD as the sole remedy. Adoption of NSZD as a remedy requires verifying that it is occurring. NSZD can be an efficient and cost-effective solution for LNAPL zones, but acceptance of this bioremediation technology relies on a multiple-lines-of-evidence approach that requires a solid understanding of baseline conditions and effective monitoring. Emerging use of in situ oxidation-reduction potential (ORP) sensors shows promise to resolve spatial and temporal redox dynamics during NSZD processes. Further, next generation sequencing (NGS) of present and active microbial communities can provide insights regarding subsurface biogeochemistry, associated elemental cycling utilized in electron transport (e.g., N, Mn, Fe, S), and the potential for biodegradation. Microbially-mediated hydrocarbon degradation is well documented. However, how these microbial processes occur in complex subsurface petroleum impacted systems remains unclear, and this knowledge is needed to guide technologies to enhance biodegradation effectively. Analysis of RNA derived from soils impacted by petroleum liquids allows for analysis of active microbial communities, and a deeper understanding of the dynamic biochemistry occurring during site remediation. However, RNA analysis in soils impacted with petroleum liquids is challenging due to: 1) RNA being inherently unstable, and 2) petroleum impacted soils containing problematic levels of polymerase chain reaction (PCR) inhibitors (e.g., aqueous phase metals and humic acids) that must be removed to yield high-purity RNA for downstream analysis. Herein, a new RNA purification method that allows for extracting RNA from petroleum impacted soils was developed and successfully implemented to discriminate between active (RNA) and present (DNA) microbes in soils containing LNAPL. A key modification involved reformulation of the sample pretreatment solution by replacing water as the diluent with a commercially available RNA preservation solution consisting of LifeGuard™ (Qiagen) Methods were developed and demonstrated using cryogenically preserved soils from three former petroleum refineries. Results showed the new soil washing approach had no adverse effects on RNA recovery but did improve RNA quality by removing PCR inhibitors, which in turn allows for characterization of active microbial communities present in petroleum impacted soils. To optimally employ NSZD and enhanced NSZD (ENSZD) at sites impacted by LNAPL, monitoring strategies are required. Emerging use of subsurface Soil redox sensors shows promise for tracking redox evolution, which reflects ongoing biogeochemical processes. However, further understanding of how soil redox dynamics relate to subsurface microbial activity and LNAPL biodegradation pathways is needed. In this work, soil redox sensors and DNA and RNA sequencing-based microbiome analysis were combined to elucidate NSZD and ENSZD (biostimulation via periodic sulfate addition and air sparging) processes in columns containing LNAPL impacted soils from a former petroleum refinery. Herein, microbial activity was directly correlated to continuous soil-ORP readings. Results show expected relationships between continuous soil redox and active microbial communities. Continuous data revealed spatial and temporal detail that informed interpretation of the hydrocarbon biodegradation data. Redox increases were transient for sulfate addition, and DNA and RNA sequencing revealed how hydrocarbon concentration and composition impacted microbiome structure and naphthalene biodegradation. When alkanes were present, naphthalene degradation was not observed, likely because naphthalene degraders were outcompeted. Further, the results of the sulfate addition experiment indicated a direct correlation of Desulfovibrio spp. with naphthalene biodegradation and showed that Smithella spp. were enriched in sulfate enhanced soils containing alkanes. Periodic air sparging did not result in fully aerobic conditions suggesting observed increased rates of biodegradation could be explained by stimulating alternative anaerobic metabolisms that were more energetically favorable compared to baseline/control conditions (e.g., iron reduction due to air oxidizing reduced iron). Methods developed and emerging continuous monitoring tools that were tested in lab soil columns were also applied to a mid- and late-stage LNAPL site. Herein, a case study is presented that advances integration of multiple nascent technologies for characterizing mid- and late-stage LNAPL sites including: 1) cryogenic coring, 2) multiple level internet of things (IoT) soil redox and temperature sensors in soil, and 3) application of RNA- and DNA-based molecular biological tools (MBTs) for site characterization. The integration of the data sets produced by these tools allowed for progress of NSZD to be evaluated in parallel under LNAPL site-relevant biogeochemical conditions. Collectively, the research presented in this dissertation support combining cryogenic coring sampling, continuous redox and temperature sensing and microbiome analysis to provide insights beyond those possible with each monitoring tool alone. The synergy achieved between microbiome characterization and soil continuous sensing illustrates how the integration of new characterization tools can provide insight into complex biogeochemical systems. Further understanding of these technologies will lead to improved predictions on remediation outcomes. The modern tools tested for middle- and late-stage LNAPL sites offer opportunities to more effectively and efficiently manage legacy LNAPL sites.