Browsing by Author "Blotevogel, Jens, committee member"
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Item Open Access Continuous NAPL loss rates using subsurface temperatures(Colorado State University. Libraries, 2015) Stockwell, Emily Beth, author; Sale, Tom, advisor; Blotevogel, Jens, committee member; Ham, Jay, committee memberTo view the abstract, please see the full text of the document.Item Open Access Effects of capping material on longevity of degradable contaminants in sediments(Colorado State University. Libraries, 2017) Campbell, Calista Emily, author; Sale, Tom, advisor; Blotevogel, Jens, committee member; Butters, Greg, committee memberTo view the abstract, please see the full text of the document.Item Open Access Field-based approaches to characterizing long-term indoor environmental quality in homes(Colorado State University. Libraries, 2022) Purgiel, Andrew, author; Carter, Ellison, advisor; Blotevogel, Jens, committee member; Bond, Tami, committee memberTo view the abstract, please see the full text of the document.Item Open Access Method comparison for analysis of LNAPL natural source zone depletion using CO₂ fluxes(Colorado State University. Libraries, 2015) Tracy, Melissa Kay, author; Sale, Tom, advisor; Blotevogel, Jens, committee member; Butters, Greg, committee memberAccidental releases of subsurface petroleum hydrocarbons, widely referred to as Light Non-Aqueous Phase Liquids (LNAPLs), are a common occurrence in the industrial world. Given potential risks to human health and the environment, effective remediation approaches are needed to address impacts. Natural source zone depletion (NSZD) is a remedial approach gaining wide acceptance, wherein natural mechanisms in the subsurface act to deplete LNAPL in the source zone. Recent research indicates biodegradation of contaminant-related carbon results in a predominantly upward flux of carbon through the vadose zone. Building on this concept, three methods have recently emerged to quantify rates of NSZD using soil gas fluxes; these include the gradient, chamber, and trap methods. Unfortunately, side-by-side field applications of the methods have shown differing estimates of NSZD, leaving concerns about method comparability. The primary objective of this thesis was to conduct a laboratory comparison of the gradient, chamber, and trap methods using uniform porous media, constant environmental conditions, and a known CO₂ flux (i.e., ideal conditions). Given these experimental conditions, challenges associated with field comparisons could be minimized and the fundamental accuracy of the methods could be resolved. Preliminary efforts were also made to understand the effect of surface wind on the accuracy of the methods. A large-scale column (1.52 m high x 0.67 m ID) was filled with dry, homogenous, well-sorted fine sand. Known CO₂ fluxes were imposed through the bottom of the column spanning a range typical of contaminant-related CO₂ fluxes observed at field sites (3.3-15.2 μmol/m²/s). Results under ideal experimental conditions indicated that on average, the chamber and trap methods accurately captured the imposed flux to within ± 7% of the true value, and the gradient method underestimated the imposed flux to within 38% of the true value. Accuracy of the gradient method was largely dependent on estimates of effective diffusion coefficients. Consistent underestimation of the true flux using the gradient method was attributed to the method only quantifying diffusive gas transport. Considering the accuracy of measurements for other subsurface processes (e.g., hydraulic conductivity), the range of accuracy observed among all methods is not surprising. Surface winds were simulated by placing a fan on top of the column; achieved wind speeds ranged from 2.2-5.4 m/s. Laboratory studies identified that all methods were adversely affected by wind; however, the magnitude of laboratory results may have been exaggerated relative to what would be expected at field sites due to the laboratory sand being dry. Wind speeds within the tested range caused the gradient method to further underestimate the true flux to within 44% of the true value. The chamber method underestimated the true flux by 45-47% and 78% for wind speeds ranging from 2.2-3.6 m/s and 4.5-5.4 m/s, respectively. Wind had the opposite effect on the trap method, causing overestimations of the true flux by 60% and 122% for wind speeds ranging from 2.2-3.6 m/s and 4.5-5.4 m/s, respectively. Given similar results under ideal experimental conditions, wind and other environmental factors common to field conditions are suspected to be the primary cause of disagreement observed in side-by-side comparisons of the methods at field sites. Each method has advantages and limitations for field application. Method selection should be predominately driven by site-specific attributes, including environmental factors that may make one method more applicable over another for a given field site. Further consideration of all methods under environmental conditions may provide greater insight into potential biases and support additional recommendations for method selection. Secondary objectives included efforts to test design features specific to the trap method to support continued method development and to advance a model to describe steady-state advective and diffusive transport of a compressible gas through porous media. Results from trap modification studies suggested certain design features of the trap method may have affected the accuracy of measurements. Additional research and method development for the trap method could be undertaken to resolve issues raised in this thesis. Results from modeling efforts suggested gas transport was primarily diffusion driven, accounting for approximately 58-79% of transport, depending on estimates of the effective diffusion coefficient. Analytical modeling did not indicate an appreciable difference in advective and diffusive contributions to gas transport as the imposed flux was varied; however, measured concentration gradients counterintuitively indicated the advective contribution to transport increased as the imposed flux decreased.Item Open Access Method development for long-term laboratory studies evaluating contaminant assimilation processes(Colorado State University. Libraries, 2016) McSpadden, Rachael Lynne, author; Sale, Tom, advisor; Blotevogel, Jens, committee member; Butters, Greg, committee memberRemediation technologies for soil and groundwater that are impacted by chlorinated solvents are limited when reducing contaminant concentrations below maximum contaminant levels (MCLs) established by the US Environmental Protection Agency (EPA). The limited effectiveness of current technologies is partly due to well-documented contaminant back diffusion from low-permeability (k) zones causing long-term impacts on water quality. Back diffusion out of low-k zones for extended periods of time, give strong evidence that assimilation processes are driving the fate and transport of chlorinated solvents within low-k zones. The direct impacts assimilation processes, such as sorption and degradation, have on contaminant concentrations may be slow and negligible on shorter time scales. But for longer time scales assimilation processes could have consequential effects on sites where groundwater concentrations are predicted to exceed MCLs for decades to centuries. Research studies located in the field have been carried out to study assimilation processes in low-k zones. The challenge of such field studies is capturing complete data sets from complex field environments. The challenges include inability to close the mass balance, confidently identifying assimilation mechanisms at work, and are limited to short term studies. Thus, the overall objective of this research is to advance the current knowledge of assimilative processes within low-k zones through the application of long-term (~5-10years) laboratory studies. The goal of the research presented herein, is to create a starting point for long-term laboratory studies in the hopes to quantify assimilation processes within low-k zones. Prior to conducting long-term laboratory experiments, a necessary step of establishing and testing methods need to be conducted. The research described within this thesis applies the use of short-term laboratory studies conducted over a 2 to 3 month time span to test preliminary methods, establish baseline data, and test applicability of mathematical models. The model contaminant used for the short-term laboratory experiments was tetrachloroethene (PCE). For the beginning stages of method development, the assimilation process that was isolated and focused on was sorption. Sorption was evaluated in porous media of differing properties, which included four field soils (Soil A, B, C, and D) and one lab grade soil (LGS). Two short-term column studies were tested to evaluate for viability in collecting data to be used in capturing transport and assimilation processes for use in long-term laboratory studies. The two short-term column study methods are identified throughout this document as headspace vials and ampules. The design setup for both column studies were constructed to utilize diffusive transport of contaminant with a saturated lower boundary layer of PCE, an initially clean water saturated soil column, and headspace at the upper boundary layer. For each column study design, the contaminant is transported via passive diffusion, starting from a volume of high concentration (at the lower boundary layer) to a place of low concentration (throughout the clean soil and the top of the headspace to the clean upper boundary layer). The difference between the two short-term column studies is the method of data collection. The headspace vial method allows for non-destructive sampling of the headspace over time to quantify the diffusive transport of PCE through the soil column. The ampule method utilizes a completely closed system with a destructive sampling technique where the entire ampule is extracted within methanol to help eliminate the potential for mass lost from the system due to volatilization. In addition to the two short-term column studies, batch sorption studies were conducted to gain independent measurements of sorption parameters for the four field soils used throughout the column experiments. Lastly, a numerical solution to the diffusive transport partial differential equation was developed using Mathcad™. Three sorption models are employed: linear, Freundlich and Langmuir models. The parameter values from the batch sorption study were used as inputs for the mathematical model and results were compared to the short-term column study headspace vial experiment. Results from the short-term column studies show that losses from headspace vials may limit the values of the method over time periods greater than one week, but ampules are more stable than headspace vials and show the most potential for application in long-term laboratory studies. Batch sorption studies can complement the diffusive-transport studies by allowing for resolution of sorption parameter values that are independent of transport rates. The validity of the model appears to be challenged by unaccounted losses from the headspace vials, and was therefore unable to estimate experimental data results. The results of the ampules and batch sorption studies are suggested to be used to aid in the design of the long-term studies. The laboratory experiments and modeling described herein will, in hopes, be a step closer to advance the knowledge of assimilative processes and assist in determining the assimilative capacity of low-k zones. Ultimately, this work will hopefully contribute to improved decision-making at contaminated sites, possibly allowing money spent on ineffective remedies to be directed toward more productive solutions.Item Open Access Particle tracking using dynamic water level data(Colorado State University. Libraries, 2017) Gao, Yuan, author; Sale, Thomas, advisor; Ronayne, Michael, committee member; Blotevogel, Jens, committee memberMovement of fluid particles about historic subsurface releases and through well fields is often governed by dynamic subsurface water levels. Factors influencing temporal changes in water levels include changes in river stage, tidal fluctuation, seasonal transpiration from trees and pumping of wells. Motivations for tracking the movement of fluid particles include tracking the fate of subsurface contaminants and resolving the fate of water stored in subsurface aquifers. This research provides novel methods for predicting the movement of subsurface particles relying on dynamic water level data derived from continuously recording pressure transducers or an analytic solution based on a Theis superposition model that predicts water levels about dynamically operated wells in well fields. For particle tracking at field sites without pumping conditions, firstly, the dynamic water level data obtained from sites in Kansas City, Missouri; Pueblo, Colorado; and Honolulu, Hawaii are employed. The basic idea is to use water-level data from at least three wells to solve for the plane of the water table and obtain the hydraulic gradient in the x and y directions. Secondly, based on the Darcy's equation, the position of a particle is moved in the x and y directions at each time step. Finally, by connecting all the positions of particle together, the path line of particle flowed in the subsurface can be obtained. Homogeneous, isotropic and homogeneous, anisotropic conditions with retardation were considered for particle tracking at the three sites in this research. Also, consideration is given to natural degradation of contaminants in the subsurface. By assuming the degradation of contaminants at each site follows first order kinetics, the distance the contaminants can flow within the minimum concentration requirement and the time when the concentration of contaminants arrived at the minimum concentration requirement can be obtained. Based on the results from this research, river stage, seasonal transpiration and precipitation, and tidal fluctuation at three sites all have great influences on local groundwater flow. The great changes of water-level in short periods caused by seasonal recharge and discharge and seasonal transpiration and precipitation make the hydraulic gradient changed greatly, subsequently make the direction of groundwater flow altered. For the site near a harbor, tidal fluctuations make the groundwater level changed, which correspondingly have the hydraulic gradient and direction of groundwater flow changed. Initial review of water-level in rose chart indicates a range of groundwater flow direction and gradient with time. This indicates a wide range of temporally changing flow directions and gradients. Surprisingly, despite temporal variation in flow directions, the net groundwater flow at all field sites is largely constant in one direction. From the results of particle tracking and rose charts, groundwater flow mainly follows the direction of the hydraulic gradients with large magnitudes in rose charts, but does not follow every direction of hydraulic gradient in the rose chart. The explanation for this phenomena is the main direction of groundwater flow is driven by hydraulic gradient with large magnitude, because the time interval for each groundwater flow driven by each hydraulic gradient is the same, according to the Darcy's equation, hydraulic gradient in the direction with small magnitude cannot drive particles flow long enough to make particles flow away from the main direction. Moreover, this research uses dynamic pumping well data to test how particles move under dynamic pumping conditions in well fields. Based on superposition of the Theis solution in both space and time, this research uses an analytical solution to resolve how fluid particles move about wells under dynamic pumping conditions. The results from particle tracking under dynamic pumping conditions in this research provide: firstly, a relatively uniform capture zone in the well field. Secondly, even under continuous pumping and injection conditions, groundwater will not flow far away from the well. Thirdly, particle tracking provides groundwater positions and delineates the position of storage water under dynamic pumping and injection condition.Item Open Access Reuse of oil and gas produced water for irrigation of spring wheat (Triticum aestivum L.): plant physiological and immune system response(Colorado State University. Libraries, 2019) Qiu, Yuheng, author; Borch, Thomas, advisor; Blotevogel, Jens, committee member; Young, Robert, committee memberWater resources for agricultural irrigation in the semiarid western United States are challenged due to increased oil and gas (O&G) activity and increasing water scarcity. Produced water (PW) generated from the O&G industry has been considered as an alternative source for crop irrigation, but there are few studies on the topic. Thus, here a greenhouse study was conducted to evaluate the impacts of PW irrigation on spring wheat (Triticum aesticum L.) with respect to plant morphology, physiology, and immunity to bacterial and fungal pathogens. Plants were irrigated with the following types of water: 100% tap water (TW), 10% and 50% PW (PW10 & PW50) and a salt (NaCl) solution (SW50 control; NaCl concentration is equal to PW50). Furthermore, pathogen treatments containing bacteria (Xanthomonas campestris) and fungi (Septoria tritici) were applied to the wheat plants to test plant immune response. In comparison with the TW control, plants irrigated with PW50 exhibited developmental delay and premature senescence, significant loss of yield, and significant decline in photosynthetic efficiency and immune function. The PW10 and SW50 control both resulted in reduced plant yield and photosynthesis, but PW10 was more damaging than SW50 to plant immune system, despite the high salt contents in SW50. These findings indicate that constituents (e.g., organic contaminants) other than NaCl in PW are contributing to plant stress, and they may play a far greater role in affecting plant immune function than salt stress.Item Open Access The downhole behavior of the chemicals of hydraulic fracturing - an insight to the nature of biocides and surfactants underground(Colorado State University. Libraries, 2016) Kahrilas, Genevieve A., author; Borch, Thomas, advisor; Farmer, Delphine K., committee member; Henry, Charles S., committee member; Blotevogel, Jens, committee memberIn a time period and society surrounded by a surplus of information, there is currently mystery and confusion surrounding the organic chemicals added to hydraulic fracturing ("fracking") fluids. Not only is it unclear what chemicals specifically are being used in some instances, but there is little to no information existing about the transformations these chemicals may undergo once underground ("downhole") and subjected to elevated heat and pressure for the duration of a fracturing operation. Several kilometers downhole, these organic chemicals are exposed to temperatures up to 200 °C, pressures above 10 MPa, high salinities, and a pH range from 5 - 8. Despite this, very little is known about the fate of HFF additives under these extreme conditions. Chemical transformations may directly affect the toxicity of the chemicals as they emerge from the downhole environment with the rest of the "flowback" wastewater. Therefore the following chapters of this dissertation serve to classify existing information and to probe the basic effects of the downhole fracturing environment on chemical stability and transformation. Chapter 1 provides a brief introduction to and rationale for the research presented in the following pages. Some of the general purposes for chemicals within hydraulic fracturing fluids (HFFs) are discussed, as well as some of the reason for the controversy which exists today. Additionally, chapter 1 outlines the research objectives which inspired the original research presented afterwards. Chapter 2 of the dissertation servers as the first existing literature review on the biocides utilized in hydraulic fracturing. Biocides are critical components of hydraulic fracturing ("fracking") fluids used for unconventional shale gas development. Bacteria may cause bioclogging and inhibit gas extraction, produce toxic hydrogen sulfide, and induce corrosion leading to downhole equipment failure. The use of biocides has spurred a public concern and debate among regulators regarding the impact of inadvertent releases into the environment on ecosystem and human health. Chapter 2 provides a review of the potential fate and toxicity of biocides used in hydraulic fracturing operations. Physicochemical and toxicological aspects will be discussed as well as knowledge gaps that should be considered when selecting biocides: (1) uncharged species will dominate in the aqueous phase and be subject to degradation and transport whereas charged species will sorb to soils and be less bioavailable; (2) many biocides are short-lived or degradable through abiotic and biotic processes but some may transform into more toxic or persistent compounds; (3) understanding of biocides' fate under downhole conditions (high pressure, temperature, salt and organic matter concentrations) is limited; (4) several biocidal alternatives exist, but high cost, high energy demands, and/or formation of disinfection byproducts limit their use. Chapter 3 serves as the first research experiment outlining a model for testing the behavior of HFF additives downhole. Here, stainless steel reactors are used to simulate the downhole chemistry of the commonly used HFF biocide glutaraldehyde (GA). The results show that GA rapidly (t1/2 < 1 hr) autopolymerizes, forming water-soluble dimers and trimers, and eventually precipitates out at high temperatures (~140 °C) and/or alkaline pH. Interestingly, salinity was found to significantly inhibit GA transformation. Pressure and shale did not affect GA transformation and/or removal from the bulk fluid. Based on experimental second-order rate constants, this chapter provides a working kinetic model for GA downhole half-life predictions for any combination of these conditions (within the limits researched) was developed. The findings outlined in chapter 3 illustrate that the biocidal GA monomer has limited time to control microbial activity in hot and/or alkaline shales, and may return along with its aqueous transformation products to the surface via flowback water in cooler, more acidic, and saline shales. Chapter 4 builds upon the framework set by chapter 3 to analyze another chemical commonly used in HFFs: nonylphenol ethoxylates (NPEs). NPEs are commonly used as surfactants and corrosion inhibitors in hydraulic fracturing fluids. While known to biodegrade to nonylphenol (NP), a known endocrine disrupting compound, little is known about the fate and mobility of NPEs under the extremes (temperatures, pressures, and salinities) in unconventional reservoirs. Chapter 4 presents evidence of abiotic NPE degradation directly into NP by means of hydrolysis under simulated downhole conditions (100 °C, 20 bar), revealing a previously unrecognized transformation pathway. The effects of both salinity and shale interactions were also studied, indicating that salt (NaCl) drastically accelerated hydrolysis kinetics resulting in a faster and increased production of NP, while shale induced significant sorption. Sorption to colloidal shale may result in transport of the downhole-generated NP to the surface along with the flowback and produced water. The findings presented in chapter 4 suggest that hydraulic fracturing fluids may return via flowback-produced water in a form that is more toxic than what was originally injected. Chapter 5 of the dissertation presents the conclusions of the work presented here as well as future directions for research about downhole behavior of organic chemical additives to HFFs, using this body of work as a platform.