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Browsing by Author "Sale, Thomas C., advisor"

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    A mass balance approach to resolving the stability of LNAPL bodies
    (Colorado State University. Libraries, 2010) Mahler, Nicholas T., author; Sale, Thomas C., advisor; Bau, Domenico A., committee member; McWhorter, David B., committee member
    Light non-aqueous phase liquids (LNAPLs) are commonly present in soils and groundwater beneath petroleum facilities. When sufficient amounts of LNAPL have been released continuous bodies of LNAPL form. These bodies can have detrimental impacts to soil gas and groundwater. Furthermore, with time they can expand or translate laterally. Measurements of LNAPL flux within continuous bodies typically indicate that LNAPL is moving, albeit slowly. Commonly, these fluxes have been used to infer (by continuity) that the bodies as a whole are expanding and/or translating laterally. In conflict with this, dissolved plumes downgradient of LNAPL bodies are widely thought to be stable or shrinking due to natural attenuation. The hypothesis of this research is that natural losses of LNAPL in contiguous bodies can play an important role in limiting expansion and/or lateral translation of LNAPL bodies. Much like dissolved phase plumes, LNAPL bodies can be stable when internal fluxes are balanced by natural losses. As a first step, 50 measurements of LNAPL fluxes through wells from seven field sites are reviewed. All the values were acquired using tracer dilution techniques. The mean and median of the LNAPL flux measurements are 0.15 and 0.064 m/year, respectively. The measured LNAPL fluxes are three to five orders of magnitude less than typical groundwater fluxes. The primary significance of the small magnitude of the LNAPL fluxes relative to groundwater fluxes is that LNAPL discharge to the downgradient body could easily be equal to or less than the natural downgradient LNAPL losses that occur through dissolution into groundwater or evaporation into soil gas. In general no clear correlations are seen between measured LNAPL fluxes and LNAPL thicknesses in wells, lengths to downgradient edges of LNAPL, or the specific gravities (density of LNAPL/ density of water) of the LNAPL. Secondly, a proof-of-concept sand tank experiment is presented. The objective was to resolve if natural LNAPL losses can limit expansion of an LNAPL body given a constant source. An open top glass and stainless steel tank (1 m by 0.5 m by 0.025 m) was filled with uniform coarse sand and water. Water was pumped through the tank producing a water seepage velocity of 0.25 m/day. Methyl tert-butyl ether (MTBE) was added to the tank at constant rates that were step-wise increased five times through a 120 day experiment. In all cases the MTBE body initially expanded followed by subsequent stabilization at a finite length. The key observation was that steady LNAPL pool lengths were achieved with a constant inflow of LNAPL into the system. Lastly, analytical models are developed. The models describe the size of LNAPL bodies and spatial variations in LNAPL fluxes as a function of influent loading, rates of natural losses, and time. Three idealized geometries of LNAPL bodies are considered. These include one dimensional, circular, and oblong. Results indicate LNAPL fluxes decline progressing from the interior to the edges of an LNAPL body. Per the laboratory studies, the solutions show that LNAPL bodies with a constant source reach finite dimensions at large times. Building on this research it seems that a pragmatic goal for management of contiguous LNAPL bodies is attaining a condition where the LNAPL bodies as a whole are stable or shrinking.
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    ItemOpen Access
    Biogeochemical characterization of a LNAPL body in support of STELA
    (Colorado State University. Libraries, 2013) Irianni Renno, Maria, author; De Long, Susan K., advisor; Sale, Thomas C., advisor; Borch, Thomas, committee member; Payne, Fred, committee member
    Microbially-mediated depletion of light non-aqueous phase liquids (LNAPL) has gained regulatory acceptance as a method for managing impacted sites. However, the fundamental microbiology of anaerobic hydrocarbon degradation, in source zones, remains poorly understood. Two site-specific studies (Zeman, 2012 & McCoy, 2012) performed at the Center for Contaminant Hydrology (CCH), Colorado State University (CSU) demonstrated that LNAPL biodegradation increases drastically when temperatures are maintained between 18°C and 30°C as compared to lower or higher temperatures. These results have supported the design of a Sustainable Thermally Enhanced LNAPL Attenuation (STELA) technology that is currently being tested at field scale at a former refinery in Wyoming. The focus of the present study was to perform a depth-resolved characterization of the mixed microbial communities present in LNAPL-impacted soils, as well as to characterize the site's geochemical parameters in order to establish a baseline data set to evaluate the STELA system performance. Seventeen soil cores were collected from the impacted site, frozen on dry ice and subsampled at 6-inch intervals for analysis of biogeochemical parameters. Multi-level sampling systems were installed at the core sites to monitor aqueous and gas phases. Diesel and gasoline range organics and benzene, toluene, ethylbenzene and xylenes (BTEX) present in the cores and in water samples were analyzed. Temperature, inorganic dissolved ions, pH, and oxidation reduction potential (ORP) were also measured. DNA was extracted in triplicate from each subsample corresponding to the study's center core (21 samples). Total Eubacteria and Archaea were quantified via 16S rRNA gene-targeted qPCR. Microorganisms present at selected depth intervals were identified via 454 pyrosequencing of both eubacterial and archaeal 16S rRNA genes. Results indicate that at the study site, the majority of the hydrocarbon contamination is found between 5 and 12 feet below ground surface (bgs). The average of the maximum total petroleum hydrocarbon (TPH) soil concentrations within each core was 17,800 mg/kg with a standard deviation of 8,280 mg/kg. The presence of methane in the vadose zone and depleted sulfate concentrations in water samples suggest that both methanogenesis and sulfate reduction are likely driving LNAPL depletion processes. Four distinct biogeochemical zones where identified within the surveyed aquifer region. Interestingly, the quantity of eubacterial 16S rRNA genes dominate the quantity of archaeal 16S rRNA genes at sampled depths within the aerobic aquifer region. In the strictly anaerobic aquifer regions, these quantities are approximately equal. The latter can be interpreted as evidence of syntrophism, which has been reported in other hydrocarbon biodegradation studies. Pyrosequencing results support these findings as well and contribute to further elucidating the spatial correlation between microbial communities and geochemical parameters. In-situ biodegradation rates are largely controlled by the quantity and activity of key microbes capable of mediating conversion of specific hydrocarbon constituents. Furthermore, it is anticipated that biodegradation rates are governed by complex interactions of diverse microbial communities that vary both in space and time. The overall vision of this initiative is that advancing a better understanding of processes controlling biologically mediated losses of LNAPL will support the development of more efficient treatment technologies for LNAPL releases. In particular, the site specific analysis produced through this study will support the development of STELA.
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    ItemOpen Access
    Feasibility of treating chlorinated solvents stored in low permeability zones in sandy aquifers
    (Colorado State University. Libraries, 2012) Bolhari, Azadeh, author; Sale, Thomas C., advisor; Bau, Domenico A., committee member; Shackelford, Charles D., committee member; Borch, Thomas, committee member
    To view the abstract, please see the full text of the document.
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    Resolving natural losses of LNAPL using CO2 traps
    (Colorado State University. Libraries, 2012) McCoy, Kevin M., author; Sale, Thomas C., advisor; Zimbron, Julio A., advisor; Shackelford, Charles D., committee member; Ronayne, Michael, committee member
    Pools of light non-aqueous phase liquids (LNAPLs) are a legacy of past practices at petroleum facilities. Traditional LNAPL remedies (e.g. hydraulic LNAPL recovery) are often costly and have limited effectiveness. Recent studies have indicated that natural losses of LNAPL can help to stabilize and even shrink subsurface LNAPL bodies once the LNAPL source is removed. Developing an effective understanding of natural losses of LNAPL is an important step in establishing LNAPL management strategies. Estimated rates of natural losses of LNAPL can be used to demonstrate LNAPL stability, form a basis for initiating or discontinuing hydraulic recovery, estimate longevity of LNAPL bodies, and as a benchmark to compare relative effectiveness of different remedial alternatives. Additionally, an understanding of underlying processes gained through field studies can guide development of new, more sustainable LNAPL remediation technologies. A novel integral CO2 Trap was created to measure soil CO2 efflux at grade. This addresses a need for an efficient tool to quantify natural losses of LNAPL. The hypothesis of this thesis is that CO2 Traps can be used to quantify natural losses of LNAPL at field sites. Laboratory and field tests were performed to test the CO2 Traps and demonstrate their utility. First, laboratory experiments were undertaken to demonstrate the ability of the traps to quantitatively capture CO2 and effectively estimate CO2 fluxes. Closed system column testing showed that the selected sorbent media is capable of quantitatively recovering CO2. This testing also verified that the sorption capacity of the media (~30% CO2 by mass) was in the range indicated by the manufacturer. This information is useful when planning maximum field deployment times, and as a means of quality checking field sampling results. Next, an open system column test showed that the CO2 Traps are capable of quantitatively measuring CO2 flux through porous media. The traps were field tested. Results of a single round of CO2 Trap deployment at one field site showed that the traps could distinguish zones of elevated CO2 flux over the LNAPL body, relative to naturally occurring CO2 flux at background locations. Background subtracted LNAPL loss rates ranging from 800 to 12,000 gallons per acre per year (gal/acre/yr) were observed. Carbon isotope analysis was performed on one travel blank sample, two background samples, and one LNAPL area sample. Radiocarbon (14C) results provided an independent means to estimate naturally occurring CO2 flux. Results of the 14C correction agreed well with the background subtraction method for that location. CO2 traps have been deployed at a total of 117 locations at 6 field sties. Seasonal resampling of selected locations has yielded a total of 194 CO2 flux readings. Calculated background corrected LNAPL loss rates for ranged from 400 - 18,000 gal/acre/yr with a mean of 3,500 gal/acre/yr. A detailed analysis of the influence of site and LNAPL characteristics on calculated LNAPL loss rates was performed for one of the six sites. Results indicated that natural losses of LNAPL are largely independent of in-well LNAPL thickness, depth to smear zone, smear zone thickness, or LNAPL type. However, temperature related seasonal trends were observed. Furthermore, natural losses of LNAPL appear to result in self heating of LNAPL zones with a potential benefit of enhancing natural losses. Additional data analysis suggests a link between temperature and natural LNAPL loss rate that may be useful in developing new, more sustainable, LNAPL management technologies.
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    Retardation and reaction in low permeability layers in groundwater plumes
    (Colorado State University. Libraries, 2013) Wahlberg, Jennifer J., author; Sale, Thomas C., advisor; Shackelford, Charles D., committee member; Dandy, David S., committee member
    To view the abstract, please see the full text of the document.
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    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.