Christopher T Green, Ph.D.
Christopher Green is a Research Hydrologist with the USGS Water Resources Mission Area.
Research Interests
- Flow and reactive transport in complex geological media
- Nitrogen cycling and fluxes in groundwater in agricultural areas
- Flow and solute transport in the unsaturated zone
- Gas transport in the unsaturated zone
- Effects of biofuels crops on groundwater quality
Science and Products
Filter Total Items: 45
Unsaturated zone CO2, CH4, and δ13C-CO2 at an arid region low-level radioactive waste disposal site
Elevated tritium, radiocarbon, Hg, and volatile organic compounds associated with low-level radioactive waste (LLRW) at the USGS Amargosa Desert Research Site (ADRS) have stimulated research on factors and processes that affect contaminant gas distribution and transport. Consequently, we examined the sources, mixing, and biogeochemistry of CO2 and CH4, two additional important species in the unsat
Authors
Christopher H. Conaway, Michelle Ann Walvoord, Randall B. Thomas, Christopher Green, R.J. Baker, James J. Thordsen, David A. Stonestrom, Brian J. Andraski
Metamodeling and mapping of nitrate flux in the unsaturated zone and groundwater, Wisconsin, USA
Nitrate contamination of groundwater in agricultural areas poses a major challenge to the sustainability of water resources. Aquifer vulnerability models are useful tools that can help resource managers identify areas of concern, but quantifying nitrogen (N) inputs in such models is challenging, especially at large spatial scales. We sought to improve regional nitrate (NO3−) input functions by cha
Authors
Bernard T. Nolan, Christopher T. Green, Paul F. Juckem, Lixia Liao, James E. Reddy
Regional variability of nitrate fluxes in the unsaturated zone and groundwater, Wisconsin, USA
Process-based modeling of regional NO3− fluxes to groundwater is critical for understanding and managing water quality, but the complexity of NO3− reactive transport processes make implementation a challenge. This study introduces a regional vertical flux method (VFM) for efficient estimation of reactive transport of NO3− in the vadose zone and groundwater. The regional VFM was applied to 443 well
Authors
Christopher T. Green, Lixia Liao, Bernard T. Nolan, Paul F. Juckem, Christopher L. Shope, Anthony J. Tesoriero, Bryant C. Jurgens
Comparison of time nonlocal transport models for characterizing non-Fickian transport: From mathematical interpretation to laboratory application
Non-Fickian diffusion has been increasingly documented in hydrology and modeled by promising time nonlocal transport models. While previous studies showed that most of the time nonlocal models are identical with correlated parameters, fundamental challenges remain in real-world applications regarding model selection and parameter definition. This study compared three popular time nonlocal transpor
Authors
Bingqing Lu, Yong Zhang, Chunmiao Zheng, Christopher T. Green, Charles O'Neill, Hong-Guang Sun, Jiazhong Qian
Bounded fractional diffusion in geological media: Definition and Lagrangian approximation
Spatiotemporal Fractional-Derivative Models (FDMs) have been increasingly used to simulate non-Fickian diffusion, but methods have not been available to define boundary conditions for FDMs in bounded domains. This study defines boundary conditions and then develops a Lagrangian solver to approximate bounded, one-dimensional fractional diffusion. Both the zero-value and non-zero-value Dirichlet, Ne
Authors
Yong Zhang, Christopher T. Green, Eric M. LaBolle, Roseanna M. Neupauer, Hong-Guang Sun
Regional oxygen reduction and denitrification rates in groundwater from multi-model residence time distributions, San Joaquin Valley, USA
Rates of oxygen and nitrate reduction are key factors in determining the chemical evolution of groundwater. Little is known about how these rates vary and covary in regional groundwater settings, as few studies have focused on regional datasets with multiple tracers and methods of analysis that account for effects of mixed residence times on apparent reaction rates. This study provides insight int
Authors
Christopher T. Green, Bryant C. Jurgens, Yong Zhang, Jeffrey Starn, Michael J. Singleton, Bradley K. Esser
Peclet number as affected by molecular diffusion controls transient anomalous transport in alluvial aquifer-aquitard complexes
This study evaluates the role of the Peclet number as affected by molecular diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numer
Authors
Yong Zhang, Christopher T. Green, Geoffrey R. Tick
Multimodel analysis of anisotropic diffusive tracer-gas transport in a deep arid unsaturated zone
Gas transport in the unsaturated zone affects contaminant flux and remediation, interpretation of groundwater travel times from atmospheric tracers, and mass budgets of environmentally important gases. Although unsaturated zone transport of gases is commonly treated as dominated by diffusion, the characteristics of transport in deep layered sediments remain uncertain. In this study, we use a multi
Authors
Christopher T. Green, Michelle Ann Walvoord, Brian J. Andraski, Robert G. Striegl, David A. Stonestrom
The effects of numerical-model complexity and observation type on estimated porosity values
The relative merits of model complexity and types of observations employed in model calibration are compared. An existing groundwater flow model coupled with an advective transport simulation of the Salt Lake Valley, Utah (USA), is adapted for advective transport, and effective porosity is adjusted until simulated tritium concentrations match concentrations in samples from wells. Two calibration a
Authors
Jeffrey Starn, Amvrossios C. Bagtzoglou, Christopher T. Green
Simulating water-quality trends in public-supply wells in transient flow systems
Models need not be complex to be useful. An existing groundwater-flow model of Salt Lake Valley, Utah, was adapted for use with convolution-based advective particle tracking to explain broad spatial trends in dissolved solids. This model supports the hypothesis that water produced from wells is increasingly younger with higher proportions of surface sources as pumping changes in the basin over tim
Authors
J. Jeffrey Starn, Christopher T. Green, Stephen R. Hinkle, Amvrossios C. Bagtzoglou, Bernard J. Stolp
Accuracy of travel time distribution (TTD) models as affected by TTD complexity, observation errors, and model and tracer selection
Analytical models of the travel time distribution (TTD) from a source area to a sample location are often used to estimate groundwater ages and solute concentration trends. The accuracies of these models are not well known for geologically complex aquifers. In this study, synthetic datasets were used to quantify the accuracy of four analytical TTD models as affected by TTD complexity, observation
Authors
Christopher T. Green, Yong Zhang, Bryant C. Jurgens, J. Jeffrey Starn, Matthew K. Landon
Rapid removal of nitrobenzene in a three-phase ozone loaded system with gas-liquid-liquid
This study explores the removal rate of nitrobenzene (NB) using a new gas-liquid-liquid (G-L-L) three-phase ozone loaded system consisting of a gaseous ozone, an aqueous solvent phase, and a fluorinated solvent phase (perfluorodecalin, or FDC). The removal rate of NB was quantified in relation to six factors including 1) initial pH, 2) initial NB dosage, 3) gaseous ozone dosage, 4) free radical sc
Authors
Shiyin Li, Jiangpeng Zhu, Guoxiang Wang, Lixiao Ni, Yong Zhang, Christopher T. Green
Science and Products
Filter Total Items: 45
Unsaturated zone CO2, CH4, and δ13C-CO2 at an arid region low-level radioactive waste disposal site
Elevated tritium, radiocarbon, Hg, and volatile organic compounds associated with low-level radioactive waste (LLRW) at the USGS Amargosa Desert Research Site (ADRS) have stimulated research on factors and processes that affect contaminant gas distribution and transport. Consequently, we examined the sources, mixing, and biogeochemistry of CO2 and CH4, two additional important species in the unsat
Authors
Christopher H. Conaway, Michelle Ann Walvoord, Randall B. Thomas, Christopher Green, R.J. Baker, James J. Thordsen, David A. Stonestrom, Brian J. Andraski
Metamodeling and mapping of nitrate flux in the unsaturated zone and groundwater, Wisconsin, USA
Nitrate contamination of groundwater in agricultural areas poses a major challenge to the sustainability of water resources. Aquifer vulnerability models are useful tools that can help resource managers identify areas of concern, but quantifying nitrogen (N) inputs in such models is challenging, especially at large spatial scales. We sought to improve regional nitrate (NO3−) input functions by cha
Authors
Bernard T. Nolan, Christopher T. Green, Paul F. Juckem, Lixia Liao, James E. Reddy
Regional variability of nitrate fluxes in the unsaturated zone and groundwater, Wisconsin, USA
Process-based modeling of regional NO3− fluxes to groundwater is critical for understanding and managing water quality, but the complexity of NO3− reactive transport processes make implementation a challenge. This study introduces a regional vertical flux method (VFM) for efficient estimation of reactive transport of NO3− in the vadose zone and groundwater. The regional VFM was applied to 443 well
Authors
Christopher T. Green, Lixia Liao, Bernard T. Nolan, Paul F. Juckem, Christopher L. Shope, Anthony J. Tesoriero, Bryant C. Jurgens
Comparison of time nonlocal transport models for characterizing non-Fickian transport: From mathematical interpretation to laboratory application
Non-Fickian diffusion has been increasingly documented in hydrology and modeled by promising time nonlocal transport models. While previous studies showed that most of the time nonlocal models are identical with correlated parameters, fundamental challenges remain in real-world applications regarding model selection and parameter definition. This study compared three popular time nonlocal transpor
Authors
Bingqing Lu, Yong Zhang, Chunmiao Zheng, Christopher T. Green, Charles O'Neill, Hong-Guang Sun, Jiazhong Qian
Bounded fractional diffusion in geological media: Definition and Lagrangian approximation
Spatiotemporal Fractional-Derivative Models (FDMs) have been increasingly used to simulate non-Fickian diffusion, but methods have not been available to define boundary conditions for FDMs in bounded domains. This study defines boundary conditions and then develops a Lagrangian solver to approximate bounded, one-dimensional fractional diffusion. Both the zero-value and non-zero-value Dirichlet, Ne
Authors
Yong Zhang, Christopher T. Green, Eric M. LaBolle, Roseanna M. Neupauer, Hong-Guang Sun
Regional oxygen reduction and denitrification rates in groundwater from multi-model residence time distributions, San Joaquin Valley, USA
Rates of oxygen and nitrate reduction are key factors in determining the chemical evolution of groundwater. Little is known about how these rates vary and covary in regional groundwater settings, as few studies have focused on regional datasets with multiple tracers and methods of analysis that account for effects of mixed residence times on apparent reaction rates. This study provides insight int
Authors
Christopher T. Green, Bryant C. Jurgens, Yong Zhang, Jeffrey Starn, Michael J. Singleton, Bradley K. Esser
Peclet number as affected by molecular diffusion controls transient anomalous transport in alluvial aquifer-aquitard complexes
This study evaluates the role of the Peclet number as affected by molecular diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numer
Authors
Yong Zhang, Christopher T. Green, Geoffrey R. Tick
Multimodel analysis of anisotropic diffusive tracer-gas transport in a deep arid unsaturated zone
Gas transport in the unsaturated zone affects contaminant flux and remediation, interpretation of groundwater travel times from atmospheric tracers, and mass budgets of environmentally important gases. Although unsaturated zone transport of gases is commonly treated as dominated by diffusion, the characteristics of transport in deep layered sediments remain uncertain. In this study, we use a multi
Authors
Christopher T. Green, Michelle Ann Walvoord, Brian J. Andraski, Robert G. Striegl, David A. Stonestrom
The effects of numerical-model complexity and observation type on estimated porosity values
The relative merits of model complexity and types of observations employed in model calibration are compared. An existing groundwater flow model coupled with an advective transport simulation of the Salt Lake Valley, Utah (USA), is adapted for advective transport, and effective porosity is adjusted until simulated tritium concentrations match concentrations in samples from wells. Two calibration a
Authors
Jeffrey Starn, Amvrossios C. Bagtzoglou, Christopher T. Green
Simulating water-quality trends in public-supply wells in transient flow systems
Models need not be complex to be useful. An existing groundwater-flow model of Salt Lake Valley, Utah, was adapted for use with convolution-based advective particle tracking to explain broad spatial trends in dissolved solids. This model supports the hypothesis that water produced from wells is increasingly younger with higher proportions of surface sources as pumping changes in the basin over tim
Authors
J. Jeffrey Starn, Christopher T. Green, Stephen R. Hinkle, Amvrossios C. Bagtzoglou, Bernard J. Stolp
Accuracy of travel time distribution (TTD) models as affected by TTD complexity, observation errors, and model and tracer selection
Analytical models of the travel time distribution (TTD) from a source area to a sample location are often used to estimate groundwater ages and solute concentration trends. The accuracies of these models are not well known for geologically complex aquifers. In this study, synthetic datasets were used to quantify the accuracy of four analytical TTD models as affected by TTD complexity, observation
Authors
Christopher T. Green, Yong Zhang, Bryant C. Jurgens, J. Jeffrey Starn, Matthew K. Landon
Rapid removal of nitrobenzene in a three-phase ozone loaded system with gas-liquid-liquid
This study explores the removal rate of nitrobenzene (NB) using a new gas-liquid-liquid (G-L-L) three-phase ozone loaded system consisting of a gaseous ozone, an aqueous solvent phase, and a fluorinated solvent phase (perfluorodecalin, or FDC). The removal rate of NB was quantified in relation to six factors including 1) initial pH, 2) initial NB dosage, 3) gaseous ozone dosage, 4) free radical sc
Authors
Shiyin Li, Jiangpeng Zhu, Guoxiang Wang, Lixiao Ni, Yong Zhang, Christopher T. Green