Papers by Kenneth C Carroll
Science of The Total Environment, 2021
PFOS transport in aquifer media is examined. • Transport is observed to be nonideal with asymptot... more PFOS transport in aquifer media is examined. • Transport is observed to be nonideal with asymptotic tailing. • Multiple soil constituents appear to contribute to PFOS sorption.
The shallow (<15 m depth) subsurface environment of a short reach along a bedrock stream was inve... more The shallow (<15 m depth) subsurface environment of a short reach along a bedrock stream was investigated with electrical resistivity and induced polarization (IP) to map details of bedrock and soil sediments. The bedrock is mostly comprised of limestone, and is generally resistive compared to the overlying soil. The soil-bedrock interface was determined through a trial and error approach using a sharp boundary feature in the inversion model. The inferred bedrock surface determined from the inversions exhibited undulating patterns with troughs and ridges. A near continuous trough ran alongside the stream within the floodplain, and is suggestive of a paleochannel among other interpretations of this feature. The structure of the electrical resistivity above the bedrock showed small-scale elongated features. The chargeability from the IP method showed larger scale features. High values of chargeability were associated with the sediments in the floodplain, and low values were associated with bedrock, stream, and soil on the elevated banks above the stream. If the chargeability is associated with membrane polarization characteristic of clayey soils, then IP seems to highlight the mere existence of clay, while the resistivity may be more discernable of the relative proportion of clay. Vegetation differences may also explain the chargeability distribution, where parts of the survey with high chargeability had dense pine with no understory making the soils more organically rich.
Journal of Environmental Chemical Engineering, 2021
Fluoride (F) contamination is widely distributed due to natural or anthropogenic causes. A series... more Fluoride (F) contamination is widely distributed due to natural or anthropogenic causes. A series of mesoporous goethite (α-FeOOH) were synthesized by hydrothermal treatment for rapid F removal from water. The morphology of adsorbents was found to be controlled by varying the hydrothermal and calcination conditions. A highly crystallized FeOOH can be prepared at hydrothermal temperature of 80 • C without further calcination. The sorption isotherm data could be adequately described by Freundlich model and kinetic data followed pseudo-second-order kinetic model. The highest adsorption capacity is as high as 80.1 mg/g. Mesoporous FeOOH exhibited high adsorption capacity in a wide pH range of 3-10 with final pH falling into a stable range (pH 5-6). The presence of Cl -and NO 3 -seldom impacted the adsorption performance, while addition of high concentrations of CO 3 2-and PO 4 3-(30 mg/L) weakened the adsorption capacity up to 18.2%. For the recycle tests with real Fcontaminated groundwater, the removal efficiency dropped slightly from 93.1% (at cycle 1) to 91.8% (at cycle 5), suggesting the adsorbents is powerful for practical use. The FTIR, SEM, and XPS characterization results all confirmed the adsorption of F and revealed that the major adsorption mechanism is the ion-exchange between F ions and hydroxyl groups on the surface of FeOOH.
Water Resources Research, 2020
Mountain-front recharge (MFR), defined as all inflow to a basin-fill aquifer with its source in t... more Mountain-front recharge (MFR), defined as all inflow to a basin-fill aquifer with its source in the mountain block , is an important water budget component globally, particularly in arid and semiarid regions . Shifts in water supply in mountainous systems induced by climate change are likely to alter the timing and magnitude of MFR , and demand-side stresses on basin-fill aquifers will likely increase as surface water supplies become less reliable . As these stresses intensify, we are challenged to predict future MFR. To do this effectively, we must better quantify the processes controlling MFR and the components of MFR with improved characterization of flow and transport time scales. Mountain-front recharge components can be divided into three types: (1) surface MFR, or recharge that occurs as infiltration from ephemeral and perennial streams along the mountain front; (2) diffuse mountain-block recharge (MBR), or spatially distributed subsurface inflow from the mountain block to the adjacent basin fill; and (3) focused MBR, or subsurface inflow that occurs along discrete, permeable geologic features such as a fault or beneath streams in the unconsolidated sediment . Distinguishing between these components is necessary as they operate on different spatial and temporal scales, and thus could respond to climate change in profoundly different ways. However, characterizing MFR components is challenging because, first, they often exhibit similar chemical and stable
Environmental Pollution, 2020
The objective of this study is to compare the consistency between column and batch experiment met... more The objective of this study is to compare the consistency between column and batch experiment methods for measuring solid-phase sorption coefficients and isotherms for per and polyfluoroalkyl substances (PFAS). Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are used as representative PFAS, and experiments are conducted with three natural porous media with differing geochemical properties. Column-derived sorption isotherms are generated by conducting multiple experiments with different input concentrations (multi-C 0 method) or employing elution-front integration wherein the entire isotherm is determined from a single breakthrough curve (BTC) elution front. The isotherms generated with the multi-C 0 column method compared remarkably well to the batch isotherms over an aqueous concentration range of 3e4 orders of magnitude. Specifically, the 95% confidence intervals for the individual isotherm variables overlapped, producing statistically identical regressions. The elution-front integration isotherms generally agreed with the batch isotherms, but exhibited noise and systematic deviation at lower concentrations in some cases. All data sets were well described by the Freundlich isotherm model. Freundlich N values ranged from 0.75 to 0.81 for PFOS and was 0.87 for PFOA and are consistent with values reported in the literature for different geomedia. The results of this study indicate that column and batch experiments can measure consistent sorption isotherms and sorption coefficients for PFOS and PFOA when robust experimental setup and data analysis are implemented.
Water, 2020
Persulfate (PS) is widely used to degrade emerging organic contaminants in groundwater and soil s... more Persulfate (PS) is widely used to degrade emerging organic contaminants in groundwater and soil systems, and various PS activation methods (e.g., energy or chemical inputs) have been considered to increase oxidation strength. This study investigates PS activation through manganese amendment in the form of potassium permanganate (KMnO 4 ) and manganese dioxide (MnO 2 ) to subsequently degrade the emerging and recalcitrant groundwater contaminant 1,4-dioxane (1,4-D). The activation of PS by MnO 2 was confirmed by radical trap and by product formation. The degradation kinetics of 1,4-D by PS was also compared with varying amendments of KMnO 4 and MnO 2 . The results showed that MnO 2 activated PS, which increased the degradation rate constant of 1,4-D. KMnO 4 activation of PS was not observed even though the binary oxidant mixture did enhance the degradation of 1,4-D. These results have implications for applying in situ chemical oxidation in subsurface systems, especially for conditions wherein manganese exists naturally in groundwater or aquifer minerals to support possible PS activation.
Natural Sciences Education, 2020
Agricultural and environmental scientists collaborated with educational technology researchers to... more Agricultural and environmental scientists collaborated with educational technology researchers to create multimedia learning tools to fill gaps in student understanding of key concepts that undergraduates often struggle with, including sorption, cation exchange capacity, inner and outer sphere bonding, and soil system complexity. These resources are freely available online at ScienceOf-Agriculture.org. The modules were evaluated in several soil, environmental science, and agriculture classes using pre-and post-tests via survey tool Qualtrics. After watching the videos, nearly all students (95%) stated the videos would be "extremely valuable" or "valuable" to their studies, and 90% said, "other students in an introductory class on agricultural topics" would benefit from the tools. Key chemistry concepts also gained traction, especially concepts related to soils and charged particles. Before watching "Cation Exchange," 49% of the students identified divalent cations (vs. monovalent) as the ions that would be held tightest in soils typical of temperate regions. After watching, 83% answered correctly. Before watching Cation Exchange, only 56% of students correctly identified clay and organic matter in soil as usually being negatively charged, but after watching, 97% of students correctly identified the particle charge. The study was hampered by the fact that as many as 53% of the survey attempts were not successful, either because the student did not complete both pre-and post-tests or they did not sign the permission page.
Environmental Science & Technology, 2019
The objective of this research was to examine the influence of nonideal sorption/desorption on th... more The objective of this research was to examine the influence of nonideal sorption/desorption on the transport of polyfluorinated alkyl substances (PFASs) in soil, with a specific focus on characterizing and quantifying potential extended, mass-transferlimited elution behavior. Perfluorooctane sulfonic acid (PFOS) was used as a representative PFAS, and miscible-displacement experiments were conducted with two soils comprising contrasting geochemical properties. The influence of nonlinear, rate-limited, hysteretic, and irreversible sorption/desorption on transport was investigated through experiments and model simulations. The breakthrough curves measured for PFOS transport in the two soils were asymmetrical and exhibited extensive elution tailing, indicating that sorption/desorption was significantly nonideal. The widely used two-domain sorption kinetics model could not fully simulate the observed transport behavior, whereas a multirate model employing a continuous distribution of sorption domains was successful. The overall results indicated that sorption/desorption was significantly rate-limited and that nonlinear, hysteretic, and irreversible sorption/desorption had minimal impact on PFOS transport. Comparison of PFOS transport data to data reported for two hydrophobic organic contaminants (HOCs) showed that the HOCs exhibited much more extensive elution tailing, likely reflecting differences in sorption/desorption mechanisms. The projected influence of rate-limited sorption/ desorption on PFOS transport at the field scale was investigated through simulation. The results of the study suggest that ratelimited sorption/desorption may affect the field-scale transport of PFOS and other PFAS for systems influenced by transient or short-residence-time conditions and in some cases could possibly increase the amount of flushing required to reduce PFOS concentrations to levels below those associated with human-health concerns.
Journal of Hydrogeology, 2019
Interest in both environmental impact and potential beneficial uses of produced water (PW) has in... more Interest in both environmental impact and potential beneficial uses of produced water (PW) has increased with growth in unconventional oil and gas production, especially in semi-arid regions, e.g. the Permian Basin, the most productive tight-oil region in the USA. Characterization of PW compositional variability is needed to evaluate environmental impact, treatment, and reuse potential. Geochemical variability of PW from Guadalupian (Middle Permian) to Ordovician formations was statistically and geostatistically evaluated in the western half of the Permian Basin (Delaware Basin, Central Basin Platform, and Northwest Shelf) using the US Geological Survey's Produced Waters Geochemical Database and the New Mexico Water and Infrastructure Data System. Mean total dissolved solids (TDS) of PW increased with depth in the Delaware Basin and Central Basin Platform to the Delaware and Wolfcamp formations (Guadalupian age). Mean TDS decreased with further increases in depth. In contrast, the mean salinity of PW was significantly higher within the shallow, younger formations (largest mean TDS in the Artesia Formation); TDS decreased with depth below Guadalupian age formations in the Northwest Shelf. Kriged contour maps of TDS and major ions illustrated spatial variability across the three geo-structural regions as a function of depth. The occurrence of meteoric waters in upper and deeper formations across the three regions was significant, and was attributed to Laramide Orogeny and Basin and Range extension uplifting and tilting effects and recent water flooding. These results quantify PW composition variability, and suggest that upon treatment, PW would support some uses such as onsite reuse and mining.
Chemosphere, 2019
h i g h l i g h t s g r a p h i c a l a b s t r a c t O 3 and 1,4-dioxane complex within hydroxyp... more h i g h l i g h t s g r a p h i c a l a b s t r a c t O 3 and 1,4-dioxane complex within hydroxypropyl-b-cyclodextrin (HPbCD). O 3 reactivity and 1,4-dioxane removal were enhanced within HPbCD cavity. 1,4-Dioxane removal rate constants increased with HPbCD addition. 1,4-Dioxane removal rate constants increased with co-contaminants. 1,4-Dioxane removal rate constants increased with salt addition.
Chemosphere, 2020
MNA assessment methods for contaminant treatment reagent delivery assessment. Aqueous ozone solut... more MNA assessment methods for contaminant treatment reagent delivery assessment. Aqueous ozone solute transport through porous media with both decay and sorption. Mixed reactors, transport experiments, and modeling had comparable rate constants. Comparable methods for quantification of reagent delivery attenuation kinetics.
Water Research, 2019
A comprehensive compartment model is presented for PFAS retention that incorporates all potential... more A comprehensive compartment model is presented for PFAS retention that incorporates all potential processes relevant for transport in source zones. Miscible-displacement experiments were conducted to investigate separately the impact of adsorption at the air-water and decane-water interfaces on PFAS retention and transport. Two porous media were used, a quartz sand and a soil, and perfluorooctanesulfonic acid (PFOS) was used as the model PFAS. The breakthrough curves for transport under water-unsaturated conditions were shifted noticeably rightward (delayed arrival) compared to the breakthrough curves for saturated conditions, indicating greater retardation due to adsorption at the air-water or decane-water interface. The retardation factor was 7 for PFOS transport in the sand for the air-water system, compared to 1.8 for saturated conditions. PFOS retardation factors for transport in the soil were 7.3 and 3.6 for unsaturated (air-water) vs saturated conditions. Air-water interfacial adsorption is a significant source of retention for PFOS in these two systems, contributing more than 80% of total retention for the sand and 32% for the soil. For the experiments conducted with decane residual emplaced within the sand, adsorption at the decane-water interface contributed more than 70% to total retention for PFOS transport. Methods to determine or estimate key distribution variables are presented for parameterization of the model. Predicted retardation factors were similar to the measured values, indicating that the conceptual model provided adequate representation of the relevant retention processes and that the parameter estimation methods produced reasonable values. The results of this work indicate that adsorption by fluid-fluid interfaces in variably saturated porous media can be a significant retention process for PFAS that should be considered when characterizing their transport and fate behavior in source zones.
Environmental Earth Sciences, 2018
The concept of the Borehole Diffusive Flux Apparatus (BDFA) is presented herein. The BDFA is an i... more The concept of the Borehole Diffusive Flux Apparatus (BDFA) is presented herein. The BDFA is an innovative apparatus designed to provide continuous direct access to an undisturbed column of sediment that can be monitored at multiple discrete vertical intervals to provide high-resolution characterization of local-scale mass transfer and attenuation. The conceptual basis and technical design of the device are presented, along with an example of borehole design and installation at a field site. Mathematical simulations are used to illustrate its application for two scenarios. The results of these simulations indicate that test periods of several weeks to a few months should be sufficient to obtain robust results. The device has the potential to improve our ability to characterize critical mass-transfer and attenuation processes and to quantify the associated rates. This information is key to the evaluation of remediation alternatives, for enhancing the accuracy of mathematical models, and to support more effective long-term management of large groundwater contaminant plumes present at many sites.
Journal of Analytical and Applied Pyrolysis, 2018
Manned spaceflight outside of low-Earth orbit requires significant advances in closed-loop life s... more Manned spaceflight outside of low-Earth orbit requires significant advances in closed-loop life support systems, especially the recycling of solid and liquid wastes to produce oxygen, food, and fresh water. Here, moderate temperature (400-600 °C) slow pyrolysis was tested to transform a high-fidelity spacecraft solid waste simulant into nutrient-rich crop growth medium for food production in space, while recovering water and carbon dioxide. Qualitative results indicated that water recovered from a simple drying process was of poor quality. Produced biochars approximated the characteristics of saline-sodic soils with P, K and micronutrients, low nitrogen, and no meaningful heavy metals, which suggests applicability as growth media. Before being used as growth media, biochar would likely need to be rinsed to remove sodium and supplemented with a source of nitrogen. If uncatalyzed slow pyrolysis is to be used, observations suggest that the produced volatiles should be directly combusted and water recovered from the flue gas, rather than trying to condense and separate the watery bio-oil product. This proof of concept study determined that low-temperature pyrolysis can be used to generate biocharbased soil, which may support agriculture during spaceflight while recycling nutrients and water from waste materials.
Journal of Hydrology, 2018
The Rincon Valley in arid, south-central New Mexico, is especially impacted by reduced surface wa... more The Rincon Valley in arid, south-central New Mexico, is especially impacted by reduced surface water supply because the contribution of groundwater is limited by aquifer constraints. Consecutive surface water allotment shortages in the Elephant Butte Irrigation District (EBID) have reduced recharge. The effects are compounded by farmers continuing to extract groundwater to meet crop requirements. Conjunctive use assumes aquifer resilience (i.e., ability to absorb pumping stress), but not necessarily in drought. This study further develops the water table fluctuation method by analyzing data from the EBID's groundwater monitoring program to reveal conjunctive use controls over the spatial and interannual variability of net storage changes from 2009 to 2016 in the Valley and introduces the term groundwater-surface water ratio of application (GSRA), that has potential for characterizing system resilience in conjunctive use settings. Regression modeling shows that variation in the annual EBID surface water allotment correlates strongly with year-end water table elevations, even more strongly than total annual groundwater extractions for irrigation, suggesting that variable surface water allotments are a primary driver of this system. Dewatering of the aquifer as of 2011 significantly altered the system hydrology such that from 2011 to 2016, net change in storage correlates strongly with the annual surface water allotment, corresponding to large river losses for the same period, but resulting in net gains in storage from 2014 to 2016. Rapid storage loss and rebound in this constrained aquifer system allowed quantification of aquifer resilience, enabling the development of a GSRA as a potential planning metric.
Journal of Contaminant Hydrology, 2018
Recalcitrant organic contaminants, such as 1,4-dioxane, typically require advanced oxidation proc... more Recalcitrant organic contaminants, such as 1,4-dioxane, typically require advanced oxidation process (AOP) oxidants, such as ozone (O 3 ), for their complete mineralization during water treatment. Unfortunately, the use of AOPs can be limited by these oxidants' relatively high reactivities and short half-lives. These drawbacks can be minimized by partial encapsulation of the oxidants within a cyclodextrin cavity to form inclusion complexes. We determined the inclusion complexes of O 3 and three common co-contaminants (trichloroethene, 1,1,1-trichloroethane, and 1,4-dioxane) as guest compounds within hydroxypropyl-β-cyclodextrin. Both direct (ultraviolet or UV) and competitive (fluorescence changes with 6-p-toluidine-2-naphthalenesulfonic acid as the probe) methods were used, which gave comparable results for the inclusion constants of these species. Impacts of changing pH and NaCl concentrations were also assessed. Binding constants increased with pH and with ionic strength, which was attributed to variations in guest compound solubility. The results illustrate the versatility of cyclodextrins for inclusion complexation with various types of compounds, binding measurement methods are applicable to a wide range of applications, and have implications for both extraction of contaminants and delivery of reagents for treatment of contaminants in wastewater or contaminated groundwater.
Journal of Contaminant Hydrology, 2017
Recalcitrant organic groundwater contaminants, such as 1,4-dioxane, may require strong oxidants f... more Recalcitrant organic groundwater contaminants, such as 1,4-dioxane, may require strong oxidants for complete mineralization. However, their efficacy for in-situ chemical oxidation (ISCO) is limited by oxidant decay and reactivity. Hydroxypropyl-β-cyclodextrin (HPβCD) was examined for its ability to stabilize aqueous-phase ozone (O 3 ) and prolong oxidation potential through inclusion complex formation. Partial transformation of HPβCD by O 3 was observed. However, HPβCD proved to be sufficiently recalcitrant, because it was only partially degraded in the presence of O 3 . The formation of a HPβCD:O 3 clathrate complex was observed, which stabilized decay of O 3 . The presence of HPβCD increased the O 3 half-life linearly with increasing HPβCD:O 3 molar ratio. The O 3 halflife in solutions increased by as much as 40-fold relative to HPβCD-free O 3 solutions. Observed O 3 release from HPβCD and indigo oxidation confirmed that the formation of the inclusion complex is reversible. This proof-ofconcept study demonstrates that HPβCD can complex O 3 while preserving its reactivity. These results suggest that the use of clathrate stabilizers, such as HPβCD, can support the development of a facilitated-transport enabled ISCO for the O 3 treatment of groundwater contaminated with recalcitrant compounds.
Water Resources Research, 2016
Two different methods are currently used for measuring interfacial areas between immiscible fluid... more Two different methods are currently used for measuring interfacial areas between immiscible fluids within 3-D porous media, high-resolution microtomographic imaging and interfacial partitioning tracer tests (IPTT). Both methods were used in this study to measure nonwetting/wetting interfacial areas for a natural sand. The microtomographic imaging was conducted on the same packed columns that were used for the IPTTs. This is in contrast to prior studies comparing the two methods, for which in all cases different samples were used for the two methods. In addition, the columns were imaged before and after the IPTTs to evaluate the potential impacts of the tracer solution on fluid configuration and attendant interfacial area. The interfacial areas measured using IPTT are 5 times larger than the microtomographic-measured values, which is consistent with previous work. Analysis of the image data revealed no significant impact of the tracer solution on NAPL configuration or interfacial area. Other potential sources of error were evaluated, and all were demonstrated to be insignificant. The disparity in measured interfacial areas between the two methods is attributed to the limitation of the microtomography method to characterize interfacial area associated with microscopic surface roughness due to resolution constraints.
Environmental Pollution, 2016
We evaluated three types of functionalized, graphene-based materials for activating persulfate (P... more We evaluated three types of functionalized, graphene-based materials for activating persulfate (PS) and removing (i.e., sorption and oxidation) sulfamethoxazole (SMX) as a model emerging contaminant. Although advanced oxidative water treatment requires PS activation, activation requires energy or chemical inputs, and toxic substances are contained in many catalysts. Graphene-based materials were examined herein as an alternative to metal-based catalysts. Results show that nitrogen-doped graphene (N-GP) and aminated graphene (NH 2 -GP) can effectively activate PS. Overall, PS activation by graphene oxide was not observed in this study. N-GP (50 mg L À1 ) can rapidly activate PS (1 mM) to remove >99.9% SMX within 3 h, and NH 2 -GP (50 mg L À1 ) activated PS (1 mM) can also remove 50% SMX within 10 h. SMX sorption and total removal was greater for N-GP, which suggests oxidation was enhanced by increasing proximity to PS activation sites. Increasing pH enhanced the N-GP catalytic ability, and >99.9% SMX removal time decreased from 3 h to 1 h when pH increased from 3 to 9. However, the PS catalytic ability was inhibited at pH 9 for NH 2 -GP. Increases in ionic strength (100 mM NaCl or Na 2 SO 4 ) and addition of radical scavengers (500 mM ethanol) both had negligible impacts on SMX removal. With bicarbonate addition (100 mM), while the catalytic ability of N-GP remained unaltered, NH 2 -GP catalytic ability was inhibited completely. Humic acid (250 mg L À1 ) was partially effective in inhibiting SMX removal in both N-GP and NH 2 -GP systems. These results have implications for elucidating oxidant catalysis mechanisms, and they quantify the ability of functionalization of graphene with hetero-atom doping to effectively catalyze PS for water treatment of organic pollutants including emerging contaminants.
Geothermics, 2015
Cost-effective creation of high-permeability reservoirs inside deep crystalline bedrock is the pr... more Cost-effective creation of high-permeability reservoirs inside deep crystalline bedrock is the primary challenge for the feasibility of enhanced geothermal systems (EGS). Current reservoir stimulation entails adverse environmental impacts and substantial economic costs due to the utilization of large volumes of water "doped" with chemicals including rheology modifiers, scale and corrosion inhibitors, biocides, friction reducers among others where, typically, little or no information of composition and toxicity is disclosed. An environmentally benign, CO 2 -activated, rheoreversible fracturing fluid has recently been developed that significantly enhances rock permeability at effective stress considerably lower than current technology based on laboratory-scale tests. In the present work we evaluate the potential of this novel fracturing fluid for application at geothermal sites under different chemical and geomechanical conditions, by performing laboratory-scale fracturing experiments with different rock sources under different confining pressures, temperatures, and pH environments. The results demonstrate that CO 2 -reactive aqueous solutions of environmentally amenable polyallylamine (PAA) represent a highly versatile fracturing fluid technology. This fracturing fluid consistently and reproducibly creates/propagates fracture networks through highly impermeable crystalline rock from Coso EGS and Newberry EGS sites at significantly lower effective stress as compared to conventional fracturing fluids. In addition, permeability was significantly enhanced (several orders of magnitude). This was evident in all laboratory-scale experiments, including variable rock source/type, operation pressure and temperature (over the entire range for EGS applications), as well as over a wide range of formation-water pH values. This effective, versatile, and environmentally-friendly fracturing fluid technology represents a significant advancement compared to industrially available fracturing fluids for cost-effective and competitive geothermal energy production.
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Papers by Kenneth C Carroll