Browsing by Author "Ronayne, Michael J., committee member"
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Item Open Access A nonlinear synthetic unit hydrograph method that accounts for channel network type(Colorado State University. Libraries, 2018) Czyzyk, Kelsey A., author; Niemann, Jeffrey D., advisor; Gironás, Jorge, committee member; Ronayne, Michael J., committee memberStormflow hydrographs are commonly estimated using synthetic unit hydrograph (UH) methods, particularly for ungauged basins. Current synthetic UHs either consider very limited aspects of basin geometry or require explicit representation of the basin flow paths. None explicitly considers the channel network type (i.e., dendritic, parallel, pinnate, rectangular, and trellis). The goal of this study is to develop and test a nonlinear synthetic UH that explicitly accounts for the network type. The synthetic UH is developed using kinematic wave travel time expressions for hillslope and channel points in the basin. The effects of the network structure are then isolated into two random variables whose distributions are estimated based on the network type. The proposed method is applied to ten basins from each classification and compared to other related methods. The results suggest that considering network type improves the estimated UHs with the largest improvements seen for dendritic, parallel, and pinnate networks.Item Open Access Aquifer test methods to estimate transmissivity and well loss via a single pumping well(Colorado State University. Libraries, 2019) Roman, James Anthony, author; Sale, Tom C., advisor; Sterrett, Robert J., committee member; Ronayne, Michael J., committee memberReducing the energy, environmental impacts, and costs required to produce groundwater from wells is emerging as a critical concern in the modern world. Establishing and maintaining pumping wells with minimal excess drawdown is thus important. Numerous methods have been devised to quantify the aquifer and well contributions of the total drawdown in a pumping well. The most common single-well methods involve step-drawdown test analyses that are inherently subjective and cumbersome. The limitations are overcome here using simple, analytical methods following the equations of Theis, Jacob, and Rorabaugh to estimate an aquifer's transmissivity and a well's well-loss parameters and excess drawdown due to well-loss effects. The major steps involve derivative analysis, solving systems of equations, and making elementary assumptions. The proposed methods analyze data from independent constant-rate tests at single pumping wells. In fact, Jacob's well-loss coefficient of 4.6x10-7 day2/m5 and 0.39x10-7 day2/m5 were estimated at a pumping well via Jacob's (1947) traditional step test analysis and the proposed method, respectively. The reduced subjectivity of the proposed method suggests it produced the more accurate estimate. The required energy and associated economic and environmental equivalences of pumping the well loss are then calculated to suggest when further development of a new well or the rehabilitation of a preexisting well is needed. The overall goal of this thesis is to advance the proposed methods for more straightforward and objective analyses of aquifer test data in academia and industry to promote the energy efficiency of groundwater production.Item Open Access Climatic and hydrologic processes leading to recent wetland losses in Yellowstone National Park, USA(Colorado State University. Libraries, 2012) Schook, Derek M., author; Cooper, David J., advisor; Ronayne, Michael J., committee member; Kampf, Stephanie K., committee memberWetlands provide vital habitat within functioning environments and act as landscape indicators by integrating catchment-scale hydrologic processes. Wetland drying during the past few decades in Yellowstone National Park's Northern Range has caused concern among National Park managers and the public at large. My research was initiated to develop an understanding of the processes controlling wetland water levels and contributing to wetland decline in the Northern Range. To do this I integrated analyses of hydrology, climate, soils, and vegetation. In 2009 I selected 24 study wetlands and instrumented each with an average of five shallow groundwater monitoring well-and-piezometer nests. To quantify historic wetland area I mapped hydric soils, analyzed aerial photographs, and identified geomorphic indicators of higher water. Vegetation was sampled to characterize wetlands and plant-water relationships, and I also conducted a soil seed bank study. The Trumpeter Lake focal site revealed groundwater changes through time and was used to identify the timescale on which an important wetland varies. Climate data indicated that warming and drying occurred during the 20th century, but that this pattern was within the natural range of variation for the study region during the past 800 years. Hydrologic data revealed that study sites included locations of groundwater discharge, recharge, and flow-through as well as water perched above the regional water table. Hydrologic regimes were classified using a shape-magnitude framework and seven wetland classes were characterized. Wetland classes exhibited variable hydrologic permanence within and between the two study summers. Aerial photographs and hydric soil delineation both confirmed formerly greater wetland abundance. These changes were linked to the wetland classes and the presence or absence of surface water outlets. Wetland plant species inhabited areas of distinct water table depth and variation, and can be used to infer subsurface hydrologic regime in the absence of extensive monitoring well networks. Continued monitoring of these wetland basins and their watersheds is critical to expanding our understanding of the processes supporting Northern Range wetlands and allowing us to better manage these valuable habitats.Item Open Access Enhancement of coupled surface / subsurface flow models in watersheds: analysis, model development, optimization, and user accessibility(Colorado State University. Libraries, 2018) Park, Seonggyu, author; Bailey, Ryan T., advisor; Grigg, Neil S., committee member; Ronayne, Michael J., committee member; Sale, Thomas, committee memberTo view the abstract, please see the full text of the document.Item Open Access Fluorescent nanosphere transport: groundwater tracing and implications for nanoparticle migration through groundwater systems(Colorado State University. Libraries, 2015) King, Charlene N., author; Sanford, William E., advisor; Li, Yan Vivian, advisor; Ronayne, Michael J., committee member; Sale, Thomas, committee memberEngineered nanoparticles (NPs) are being introduced to water supplies and many NPs have been shown to have deleterious effects on plants and animals; however, their behavior in natural substrates is not well characterized. In an effort to characterize nanoparticle migration through porous media a dual-tracer of fluorescent carbon nanospheres (CNP) and bromide (Br) were deployed through columns of porous media designed to be homogeneous, have dual-porosity, or be reactive. The CNP are hydrophilic, non-toxic, inert, and only 5 to 10 nm in diameter. Unlike other colloid tracers CNP are designed to be inexpensive, easy to identify, and not susceptible to pore throat filtering or settling making them an ideal particle tracer. The results of the homogeneous tests show that CNP and Br had identical breakthrough curves with retardation factors close to 1, confirming that CNP transport conservatively through silica sand. The results of the dual-porosity tests suggested that CNP may undergo slightly less transverse diffusion (mass transfer) into the immobile zone than the solute tracer Br. However the differences were less than expected because molecular diffusion was overwhelmed by the high pore velocities in the experiments. The results of the reactive media tests showed that in columns with surface-modified zeolite (SMZ) the CNP transported conservatively, while Br had a retardation factor 11 to 18 times higher, due to sorption. This means that the CNP can function as the conservative species used in a multiple tracer test to quantify the surface area exposure of other minerals or contaminants with a surface charge along preferential flow paths. During each of these experiments the average mass recovery for CNP was 95% indicating that there was minimal mass loss from pore throat filtering, settling, or sorption. Not only are CNP an extremely useful new tracer for groundwater systems, but they also provide insight as to how other NPs might be transported once introduced into the subsurface. NPs with surfaces that have been functionalized to be hydrophobic or preferentially sorb to a target constituent behave differently. If NPs which sorb to a particular contaminant are introduced to the subsurface it could facilitate transport of that contaminant or facilitate sorption. Similarly the rapid transport properties of hydrophilic NPs should be considered where any toxic NP is being introduced to natural systems.Item Embargo Improvements in GRACE-based terrestrial water storage anomalies for groundwater depletion and ecohydrological analyses(Colorado State University. Libraries, 2022) Ukasha, Muhammad, author; Niemann, Jeffrey D., advisor; Grigg, Neil S., committee member; Bailey, Ryan T., committee member; Ronayne, Michael J., committee memberTo view the abstract, please see the full text of the document.Item Open Access Limiting membrane and diffusion behavior of a compacted sand-bentonite mixture for hydraulic and chemical containment(Colorado State University. Libraries, 2017) Fritz, Cameron John, author; Scalia, Joseph, IV, advisor; Shackelford, Charles D., advisor; Ronayne, Michael J., committee memberSodium-bentonite (Na-bentonite) commonly is used either as an additive component or as the sole component of engineered barriers used for waste containment applications, because the tendency of Na-bentonite to exhibit high swell can result in the restriction of advective and diffusive contaminant transport. Additionally, compacted mixtures of Na-bentonite and sand can be an effective and economical alternative to barrier materials consisting only of natural clay (e.g., compacted clay liners) if the use of natural clay is not logistically or economically feasible. The existence of membrane behavior, i.e., the ability of a porous material to exhibit selective restriction of migrating chemical species from the clay pores, previously has been shown for typical engineered bentonite-based barriers commonly used in hydraulic and chemical containment applications, including compacted sand-bentonite (SB) mixtures. However, the extent to which clay membrane behavior may persist in the presence of highly concentrated chemical solutions, which have been shown to have an adverse effect on the magnitude of membrane behavior in clays, remains largely unknown, with few studies having quantified the limiting membrane and diffusion behavior of bentonite-based barrier materials. Moreover, the limiting membrane and diffusion behavior of compacted SB mixtures has not yet been evaluated. Based on these considerations, the purpose of this study was to quantify the limiting membrane and diffusion behavior of two specimens of a compacted SB mixture comprising 15 % Na-bentonite (by dry weight) by determining the threshold salt concentration at which measurable membrane behavior was eliminated. The specimens were exposed to a series of boundary monovalent salt solutions with increasingly higher source concentrations, Cot, until measured values of the membrane efficiency coefficient, ω (0 ≤ ω ≤ 1), were effectively nil (i.e., 0.000), representing the limiting condition at which measurable membrane behavior was eliminated. Overall, ω decreased from an average of 0.032 to 0.000 as Cot increased from 160 mM KCl to 3.27 M NaCl, resulting in a threshold concentration between 1.63 M and 3.27 M NaCl for both specimens that was much higher than the range of salt concentrations for which measurable membrane behavior previously was thought to exist. Effective diffusion coefficients, D*, for nonreactive chloride (Cl-) also were measured during membrane testing to evaluate possible changes in diffusion behavior corresponding to the progressive destruction of membrane behavior. However, D* was relatively constant throughout all testing stages (2.1 x 10-10 m2/s ≤ D* ≤ 3.0 x 10-10 m2/s), indicating that the corresponding decrease in ω from 0.032 to 0.000 had little to no effect on the diffusion of Cl-.Item Open Access Modeling the distribution of major salt ions in regional agricultural groundwater and surface water systems: model calibration and application(Colorado State University. Libraries, 2020) Javed, Abdullah B., author; Gates, Timothy K., advisor; Bailey, Ryan T., advisor; Ronayne, Michael J., committee memberIrrigated lands in Colorado's Lower Arkansas River Valley (LARV), like many irrigated agricultural areas worldwide, suffer from salinization of soil, groundwater, and adjacent river systems. Waterlogging and salinization are prevalent throughout the LARV, which have diminished the crop yields and threatened the long-term sustainability of irrigated agriculture. Increased salinity concentrations are primarily due to the presence of salt minerals and high rates of evapotranspiration in the LARV, coupled with inefficient irrigation practices. Shallow groundwater in the LARV drives saline groundwater back to the stream network, thereby degrading the surface water quality, which affects the downstream areas where it evapo-concentrates when saline water is diverted for additional use. The goal of the current study is to develop, calibrate and test a physically-based, spatially distributed numerical model to assess soil, groundwater and surface water salinity at a regional scale to better understand the baseline nature of the problem. Several salinity models have been developed in recent decades; however, no attempts thus far have been made at simulating the fate, storage, and transport of salt ions at a regional scale in both groundwater and streams within an irrigated stream-aquifer system. The model used in this thesis links MODFLOW-SFR2, which simulates the groundwater heads and stream flows, with RT3D/SEC-OTIS which addresses reactive solute transport in variably- saturated soil and stream-aquifer systems. Sources and sinks within an agricultural system such as canal seepage, infiltrated water from flood and sprinkler irrigation, groundwater pumping, evapotranspiration from both the unsaturated and shallow saturated zones; root zone processes such as cycling of salt ions, crop uptake, and leaching to the water table; addition of salt mass via fertilizer and irrigation water; chemical kinetics affecting salt ions such as influence of dissolved oxygen and nitrate; equilibrium chemistry processes such as precipitation-dissolution, complexation and cation exchange; and 1D transport of salt ions in the streams due to advection, dispersion and sorption are addressed. The coupled flow and reactive transport model is applied to an approximately 552 km2 salinity-affected irrigated stream-aquifer system of the LARV between Lamar, Colorado and the Colorado-Kansas border. The model is tested against an extensive set of field data (soil salinity data from field salinity surveys, groundwater salinity collected from a network of groundwater monitoring wells, salt loading from the aquifer to the Arkansas River, and salt concentrations measured from in-stream sampling). Model calibration and parameter estimation include manual and automated calibration using PEST. Runs were conducted to describe the current levels of root zone salinity which markedly exceeds threshold levels for crop yield reduction. Spatiotemporal distribution of groundwater levels and concentrations, mass and return flow rates to streams, and stream concentrations are also simulated for current baseline conditions. The calibrated and tested regional scale salinity model is in need of further refinement but shows promise for future implementation to explore potential solution strategies for the irrigated valley of the LARV, and similar salt-afflicted areas of the world, by applying different best management practices.Item Open Access Numerical modeling and hydrochemical analysis of the current and future state of seawater intrusion in the Todos Santos aquifer, Mexico(Colorado State University. Libraries, 2019) Fichera, Marissa M., author; Sanford, William E., advisor; Ronayne, Michael J., committee member; Bailey, Ryan T., committee memberThe Todos Santos aquifer, Baja California Sur, Mexico, provides the sole source of freshwater to the town of Todos Santos, and is utilized for domestic and agricultural needs crucial to the town's economy. The region is characterized by an arid climate. Major recharge to the aquifer is supplied from intermittent cyclones. Irregular and unpredictable recharge rates combined with population growth resulting from resort development put the Todos Santos aquifer at risk of overexploitation, causing potentially permanent water quality degradation by salinization as a result of seawater intrusion. Understanding the complex response of seawater intrusion to variable pumping rates and sea-level rise is critical to water resource management in Todos Santos. This study utilized numerical simulation of variable-density groundwater flow, using SEAWAT, in conjunction with temporal and spatial hydrochemical analysis, to evaluate the current and future extent of seawater intrusion in the area. Forecasting simulations were run for five, ten, and twenty years following 2017, for five different hydrologic scenarios, which implemented various pumping rates, sea-level rise, and overexploitation of significant surface water resources. Hydrochemical analysis shows an increase in groundwater specific conductance and chloride concentration within two kilometers of the coastline from 2007 to 2017. This combined with the distribution of groundwater samples exhibiting chloride concentration above the permissible limit for potable water (250 mg/L) suggest that the Todos Santos aquifer is experiencing effects of seawater intrusion up to 1.6 kilometers inland as of 2017. Analysis of groundwater cation exchange reactions indicates widening of the freshwater-seawater mixing zone from 2007 to 2017, further suggesting the exacerbation of seawater intrusion over this time span. Forecasting simulation results indicate that the extent of seawater intrusion is exacerbated by increased water withdrawal, overexploitation of surface water resources, the current rate of sea-level rise (~ 4 mm/yr), and an increased rate of sea-level rise of 25 mm/yr.Item Open Access Numerical modeling of streamflow accretion by conjunctive use at Tamarack Ranch State Wildlife Area, Colorado(Colorado State University. Libraries, 2013) Roudebush, Jason A., author; Stednick, John D., advisor; Ronayne, Michael J., committee member; Fassnacht, Steven R., committee memberConjunctive use of groundwater at Tamarack Ranch State Wildlife Area is used to augment streamflow in the Platte River during low flow periods, critical for aquatic species. As part of a cooperative Tri-State Agreement (TSA) with Nebraska and Wyoming, Colorado's portion of the TSA is to pump alluvial groundwater (up to 1,233 ha-m) during periods of unappropriated flow in the river, to recharge ponds located in upland eolian sand deposits, where the water infiltrates into the ground and returns to the river at a later time. Understanding the location of these recharge ponds and the timing of streamflow accretion is critical for evaluating the effectiveness of recharge operations at Tamarack but has proven difficult to physically measure. To better understand the streamflow-aquifer system changes, a detailed numerical model was created using the MODFLOW Streamflow-Routing technique to simulate physically based groundwater-surface water interaction from managed groundwater recharge. The simulation modeled groundwater pumping from December 2012 through March 2013 and showed that managed groundwater recharge at Tamarack is producing a quantifiable contribution to streamflow in the desired period of April to September and on the Tamarack property. Streamflow accretion began ten days after the pumps were turned off and the center of mass arrived at the river 16 days later. The total volume of streamflow accretion simulated in this study at the Red Lion Bridge was 878,000 m3, 13% of the 6,887,000 m3 of groundwater pumped into the recharge ponds in water year 2013. Streamflow accretion had not fully diminished by the end of model simulation in August 2013, warranting further study to better account for all streamflow accretions.Item Open Access Regional selenium cycling in an irrigated agricultural groundwater system: conceptualization, modeling, and mitigation(Colorado State University. Libraries, 2012) Bailey, Ryan T., author; Gates, Timothy K., advisor; Baù, Domenico A., advisor; Arabi, Mazdak, committee member; Ronayne, Michael J., committee member; Ma, Liwang, committee memberSelenium (Se) is an element that occurs naturally as a trace constituent in geologic formations and associated soils and, although an essential nutrient for animals and humans, can prove detrimental to health at high concentrations. Over the previous decades, the presence of either deficient or elevated concentrations of Se in groundwater, surface water, and associated plants and cultivated crops has emerged as a serious issue in many regions of the world, including the United States, northern and western Europe, the Middle East, and East Asia. Regardless of the nature of concern regarding Se, whether concentrations are deficient or elevated in water supplies and cultivated crops, there is a basic need for a thorough description of the movement and chemical processes of Se within a dynamic soil-aquifer system influenced by agricultural practices, and for the development of numerical simulation tools that allow these processes to be simulated in assessing baseline conditions and exploring remediation best-management practices (BMPs). While the individual processes controlling Se speciation, transformation, and movement within soil systems have been well documented, their synthesis into a comprehensive numerical model of Se fate and transport within an alluvial aquifer system influenced by agricultural practices has not yet been realized. This dissertation presents the development of a numerical model that can simulate the fate and transport of Se species in irrigation-influenced agricultural soil and groundwater systems at a regional scale. The model was developed by first, linking RT3D, modified to handle multi-species reactive transport in variably-saturated porous media, to MODFLOW, which uses the UZF1 (Unsaturated Zone Flow) package to simulate groundwater flow in the unsaturated zone; and second, developing an Se reaction module for RT3D that accounts for the cycling, chemical activity, and transport of Se species in regional-scale agricultural soil and groundwater systems. The module also accounts for the influence of other chemical species such as dissolved oxygen and nitrate (NO3). The resulting model, referred to as UZF-RT3DAG, is applied to a 50,600 ha regional site in the Lower Arkansas River Valley (LARV) in southeastern Colorado for the years 2006 through 2009. Using the calibrated model, multiple BMPs for remediation of Se contamination in the LARV are investigated. These strategies include decreasing annual loading of nitrogen fertilizer, decreasing species concentration in canal water, decreasing applied volume of irrigation water, and increasing chemical activity within riparian areas. Research results are presented through a series of published and submitted articles and modeling results that outline the progression of model development and model application. Results of the BMP scenario testing indicate that alternative land-management practices can have a significant impact in decreasing the concentration of dissolved Se in groundwater by up to 5-8% as well as mass loadings of Se to the Arkansas River by as much as 20-30%. Practices also have a significant impact on decreasing NO3 concentrations and loadings by up to 50% and 45%, respectively. As the alluvial aquifer in the LARV is similar to other Se-contaminated aquifer systems, the results of this research are pertinent to the assessment and remediation of Se contamination world-wide.Item Open Access Regional-scale groundwater flow and salt transport models for exploring agro-environmental remediation strategies in an irrigated river valley(Colorado State University. Libraries, 2014) Morway, Eric D., author; Gates, Timothy K., advisor; Labadie, John W., committee member; Baù, Domenico A., committee member; Ronayne, Michael J., committee memberTo view the abstract, please see the full text of the document.Item Open Access Salt transport in the South Platte river system: modeling, controlling factors, and management strategies(Colorado State University. Libraries, 2021) Hocking, Craig, author; Bailey, Ryan T., advisor; Ronayne, Michael J., committee member; Niemann, Jeffrey D., committee memberIncreasing salinity poses a severe threat to urban and agricultural areas. Excess salt can accumulate in soils and groundwater, thereby impacting crop growth and productivity. This thesis aims to quantify the influence of the driving forces behind salt transport in Colorado's agro-urban South Platte River network, which has an approximate drainage area of 24,300 mi2 (62,937 km2), and investigates possible mitigation strategies to reduce salinity levels in both urban and agricultural river reaches. For this study, a one-dimensional in-river salt transport model was developed for the South Platte River system utilizing StateMod (Colorado's Division of Water Resources water allocation model) to simulate streamflow. The model accounts for multiple inputs and outputs of salt within the river network, including tributaries, wastewater treatment plants, road salt, runoff return flows from irrigation, and groundwater discharge, the latter from interpolated groundwater concentration maps generated from sampling data provided by the Agricultural Water Quality database. These concentration data are combined with the StateMod-simulated streamflow to simulate salt flow through the river network. The flow and salt models were run on a monthly basis over five years between 2002 and 2006. Based on Nash-Sutcliffe Coefficient of Efficiency (NSCE) statistics for the flow and salt models, 85% of the flow model's monthly NSCE values and approximately 68% of the salt model's monthly NSCE values fell within the acceptable range of zero to one. A global sensitivity analysis was implemented to determine the controlling factors behind salt transport in the river system. Two different scenarios were run: a reach-to-reach sensitivity study where the South Platte River was divided into five different reaches, and a seasonal sensitivity study performed over the entire South Platte River for spring (March to May), summer (June to August), fall (September to November), and winter (December to February). For urban areas located in the upstream region of the basin, controlling factors include wastewater treatment plant (WWTP) effluent concentration, salt in urban return flows, the initial concentration of salinity in upstream river water, and road salt loading. For agriculture areas located in the downstream region of the basin, controlling factors include the WWTP effluent concentration, salt in urban return flows, salt in agricultural return flows, and road salt loading, indicating the influence of upstream salinity loadings on downstream river water. Based on the sensitivity studies results, an assessment of potential management practices (MPs) was carried out for both urban and agricultural reaches. A total of 256 different MP trials were run each month. The final MP results were then calculated as the averages of the individual monthly results. A point system was assigned to help rank the trials by how efficient they were at reducing salinity levels. For the urban region, the most efficient MP during the spring and summer months is to reduce WWTP effluent concentration by 35%, resulting in a salinity concentration of 340 mg/L, a decrease of 17% from the baseline value. During the fall and winter months, the most efficient MP is to reduce road salt by 35%, resulting in a salinity concentration of 730 mg/L, a decrease of 19% from the baseline value. For agricultural areas, very few MP combinations achieve an in-river salinity concentration less than 1000 mg/L, which is approximately the level in irrigation water at which crop yield decreases. The most effective MP to accomplish this consists of a 35% reduction in WWTP effluent concentration, salt in urban return flows, salt in agricultural return flows, and road salt loading. These results point to the extreme challenge of managing salinity in the South Platte River Basin and the aggressive approaches that must be implemented to sustain irrigation practices in the basin's downstream regions. In general, this thesis provides a framework for assessing salinity movement and mitigation in a large-scale urban-agricultural river basin.Item Open Access Selected factors affecting measurement of the hydraulic conductivity of geosynthethic clay liners(Colorado State University. Libraries, 2018) Popang, Monika Aprianti, author; Scalia, Joseph, IV, advisor; Shackelford, Charles D., advisor; Ronayne, Michael J., committee memberGeosynthetic clay liners (GCLs) are thin (~7 to 10 mm), factory manufactured hydraulic barriers typically comprising a layer of sodium bentonite sandwiched between two geotextiles. Upon hydration and permeation with water at low effective stress (σ´) (e.g., typically ≤ ~30 kPa [4 psi]), the bentonite in GCLs, which typically is initially in an air-dried condition, swells to form a low hydraulic conductivity (k) layer (i.e., k of ~2-3×10-11 m/s) that is suitable for use as a barrier in hydraulic and chemical containment applications. However, adverse physico-chemical interactions between the bentonite in GCLs and both the hydrating and permeating liquids may yield substantially higher k than what is typically acceptable for design (i.e., k ≤ 1×10-9 m/s). Accordingly, this study pertained to evaluating the effects of the type of permeant liquid and the magnitude of σ´ on the measurement of k of two GCLs, a higher grade needle-punched (HGN) GCL and a lower grade needle-punched (LGN) GCL. The permeant liquids included tap water (TW), conservative water (CW), and several calcium chloride (CaCl2) solutions, and the σ´ included 27.3 kPa (4 psi) and 61.7 kPa (9 psi). The resulting measured ratios of final k for the HGN GCL relative to the LGN GCL (kf HGN/kf LGN) at ~24-27 kPa (4 psi) were ~28 (1.5 orders of magnitude), ~194 (2.3 orders of magnitude), and ~1975 (3.3 orders of magnitude) based on permeation with 5, 10, and 20 mM CaCl2, respectively. Thus, an increase in the fiber bundles density of the needle-punched fibers of the GCL adversely impacted the k of this GCL. Tests using dyed permeant liquids revealed that the high k was attributable to preferential flow along the fiber bundles of the GCL. Also, an increase in σ´ from 27.3 kPa (4 psi) to 61.7 kPa (9 psi) did not appreciably impact the measured k. Finally, permeation of the HGN GCL with the more dilute liquids (TW, CW, 1 and 2.5 mM CaCl2) resulted in consistently low k of ~2×10-11 m/s. The results of this study also illustrate the importance of achieving not only hydraulic equilibrium but also chemical equilibrium before terminating the k tests, as the measured k at hydraulic equilibrium based on the higher ionic strength solutions (i.e., 5, 10, and 20 mM CaCl2) typically were lower and, therefore, more unconservative than the measured k at chemical equilibrium. This study also evaluated the use of different methods to measure the k of the HGN GCL, including the falling headwater, constant tailwater method and the constant rate-of-flow method using a flow pump with pressure transducers. The results indicated that neither method proved substantially effective at achieving chemical equilibrium faster, although employing higher hydraulic gradient (i) was shown to expedite the attainment of chemical equilibrium. This result is associated with flushing action in the intergranular pore spaces that effectively maintaining higher concentration gradient between within and outside the bentonite granules. Also, prehydrating the specimens with the permeant liquid tended to enhance the osmotic swell of the bentonite resulting in a lower k at lower pore volumes of flow. Finally, diffusion of solutes from interlayer to intergranular pore spaces within the GCL specimens permeated with CW was shown to be the rate-limiting mechanism for attaining chemical equilibrium.Item Open Access Semi-analytical tool for optimal management of alluvial aquifers hydraulically connected to streams(Colorado State University. Libraries, 2013) Hassan, Azzah Salah El-Din, author; Baù, Domenico, advisor; Grigg, Neil S., committee member; Ronayne, Michael J., committee memberConjunctive water resources use is becoming an important tool in water management, especially with the increase in demands in all life sectors, and the decrease in available water resources with all the evolving obstacles of climate change, growing populations in addition to the conflicts over water resources in some areas of the world. A groundwater/surface water conjunctive management problem of a hydraulically connected aquifer/stream system is addressed in this research under the prior appropriation doctrine of water allocation practiced in the western states of the USA including Colorado. One approach for applying the concept of conjunctive groundwater/surface water management is achieved by techniques of artificial recharge of aquifers, where water is injected and stored in aquifers when surface water surplus is available for that purpose and pumped in the future when there is a need. Within the prior allocation doctrine, groundwater users in Colorado historically started extracting water from the aquifers underlying their agricultural lands after surface water rights were fully allocated. Consequently, in a system of hydraulically connected aquifers and streams as in the South Platte River Basin, ground water users are junior water right holders, who are allowed to divert surface water only when all senior water right holders have had their full allocation. From this perspective, the objective of the groundwater management problem is to minimize the impact of artificial recharge injection and extraction operations on the stream connected to the targeted aquifer, meaning, when extracting water from the aquifer, the pumped amount should be equal to the injected volumes, else wise the aquifer will compensate for the difference by depleting the stream. An important effect characterizing artificial recharge and groundwater pumping is the change in aquifer head levels during operations, as excessive injection might cause water mounds and over pumping might result in a stressed aquifer. In this study, groundwater pumping and artificial recharge effects on aquifers are simulated using the semi-analytical models describing the effect of an operating well in the aquifer and the interconnected stream. These models are derived from the formulated analytical solutions for aquifer drawdown and stream depletion obtained by Theis (1935) and Glover and Balmer (1945) In the first part of this research, a number of semi-analytical models are derived and implemented in MATLAB codes to simulate the response of both the aquifer and the stream to cyclically operating wells. These models can handle the cases of laterally infinite aquifers, semi-infinite aquifers limited by a stream or an impermeable boundary, and finite aquifer comprised between an impermeable boundary and a stream or between two streams. In the second part of the research, these models are used to solve a groundwater management problem that seeks to minimize the absolute value of the volume of stream depletion/accretion over a given time period while meeting prescribed constraints on aquifer water levels, irrigation demands and injection water availability. This problem is tackled using linear programming algorithms, which is proven to be effective in providing first-hand estimations of optimal injection-extraction schemes for the management of systems characterized by large numbers of operating wells, within a reasonably small computation time.Item Open Access Simulating the fate and transport of salinity species in a semi-arid agricultural groundwater system: model development and application(Colorado State University. Libraries, 2018) Tavakoli Kivi, Saman, author; Bailey, Ryan T., advisor; Gates, Timothy K., advisor; Ronayne, Michael J., committee member; Bhaskar, Aditi, committee memberMany irrigated agricultural areas worldwide suffer from salinization of soil, groundwater, and nearby river systems. Increased salinity concentrations, which can lead to decreased crop yield, are due principally to the presence of salt minerals and high rates of evapotranspiration. High groundwater salt loading to nearby river systems also affects downstream areas when saline river water is diverted for additional uses. Irrigation-induced salinity is the principal water quality problem in the semi-arid region of the western United States due to the extensive background quantities of salt in rocks and soils. Due to the importance of the problem and the complex hydro-chemical processes involved in salinity fate and transport, a physically-based spatially-distributed numerical model is needed to assess soil and groundwater salinity at the regional scale. Although several salinity transport models have been developed in recent decades, these models focus on salt species at the small scale (i.e. soil profile or field), and no attempts thus far have been made at simulating the fate, storage, and transport of individual interacting salt ions at the regional scale within a river basin. The required model must be able to handle variably-saturated groundwater systems; sources and sinks of groundwater within an agricultural system such as canal seepage, infiltrated water from flood and sprinkler irrigation, groundwater pumping, and evapotranspiration from both the unsaturated and shallow saturated zones; root zone processes such as salt ions cycling, crop uptake, and leaching to the water table; addition of salt mass via fertilizer and irrigation water; chemical kinetics affecting salt ions such as the influence of dissolved oxygen and nitrate on the chemical processes of anions such as sulfate (SO4); and equilibrium chemistry processes such as precipitation-dissolution, complexation, and cation exchange. This dissertation develops a physically-based, spatially-distributed groundwater reactive transport model that simulates the fate and transport of major salt ions in an agricultural groundwater system and can be applied to regional scale areas to address salinity problems. The model is developed by 1) constructing an equilibrium chemistry model that includes all the fate and transport processes that affect salt ions in an agricultural soil-groundwater system, including precipitation-dissolution of salt minerals, ions complexation, and cation exchange; and 2) coupling the module with UZF-RT3D (Bailey et al., 2013) a MODFLOW-based numerical modeling code that simulates the transport of multiple interacting reactive solutes in a variably-saturated soil-groundwater system. The model accounts for dissolved oxygen, nitrogen cycling in the soil-plant system (crop uptake, organic matter decomposition, mineralization/immobilization), oxidation-reduction reactions, including chemical reduction of dissolved oxygen and nitrate in the presence of marine shale, and sorption. UZF-RT3D has been amended to also include processes that directly affect SO4, one of the major salt ions, such as sulfur cycling in the plant-soil system and the release of SO4 from pyrite (FeS2)-laden marine shale in the presence of dissolved oxygen and nitrate. The developed model is applied to a salinity-affected irrigated alluvial stream-aquifer region to demonstrate its applicability and to assess remediation strategies on soil and groundwater salinity, salt mass loading to streams, and crop yield. The study area is a 500 km2 region of the Lower Arkansas River Valley (LARV) in southeastern Colorado, with the model tested against an extensive set of field data (soil salinity, groundwater salinity, salt loading from the aquifer to the Arkansas River) for the years 2006-2009. Parameter estimation is accomplished via a mixed manual-automated method, with estimation of both equilibrium and kinetic chemical parameters. Research results are presented through published and submitted articles. Results of preliminary best management practice (BMP) scenario testing indicates that reducing the volume of applied irrigation water and sealing earthen irrigation canals can have a significant effect on the root zone salinity, groundwater salinity, groundwater salt loading from the aquifer to the river network, and crop yield.