Christopher T Green, Ph.D.
Biography
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
Data Release for Metamodeling and Mapping of Nitrate Flux in the Unsaturated Zone and Groundwater, Wisconsin, USA
Widespread nitrate contamination of groundwater in agricultural areas poses a major challenge to sustainable water resources. Efficient analysis of nitrate fluxes across large regions also remains difficult. This study introduces a method of characterizing nitrate transport processes continuously across regional unsaturated zones and groundwater based on surrogate, machine-learning metamodels...
Time-fractional flow equations (t-FFEs) to upscale transient groundwater flow characterized by temporally non-darcian flow due to medium heterogeneity
Upscaling groundwater flow is a fundamental challenge in hydrogeology. This study proposed time-fractional flow equations (t-FFEs) for upscaling long-term, transient groundwater flow and propagation of pressure heads in heterogeneous media. Monte Carlo simulations showed that, with increasing variance and correlation of the hydraulic conductivity...
Xia, Yuan; Zhang, Yong; Green, Christopher; Fogg, Graham Machine learning predictions of mean ages of shallow well samples in the Great Lakes Basin, USA
The travel time or “age” of groundwater affects catchment responses to hydrologic changes, geochemical reactions, and time lags between management actions and responses at down-gradient streams and wells. Use of atmospheric tracers has facilitated the characterization of groundwater ages, but most wells lack such measurements. This...
Green, Christopher; Ransom, Katherine Marie; Nolan, Bernard T.; Liao, Lixia; Harter, Thomas Co-transport of biogenic nano-hydroxyapatite and Pb(II) in saturated sand columns: Controlling factors and stochastic modeling
Biogenic nano-hydroxyapatite (bio-nHAP) has recently gained great interest in many domains, especially in the remediation of heavy metal-contaminated soil, due to its high reactivity, low cost, and eco-friendly nature. The co-transport and reaction of bio-nHAP with Pb(II) in saturated porous media, however, are not well understood. This work...
Zhou, Dongbao; Han, Xuan; Zhang, Yong; Wei, Wei; Green, Christopher; Sun, HongGuang; Zheng, Chunmiao Complexity of groundwater age mixing near a seawater intrusion zone based on multiple tracers and Bayesian inference
Aquifer flow systems near seawater interfaces can be complicated by density-driven flows and the formation of stagnation zones, which inevitably introduces uncertainty into groundwater age-dating. While age-dating has proved effective to understand the seawater intrusion and aquifer salinization process in coastal aquifers, further efforts are...
Ju, YeoJin; Massoudieh, Arash; Green, Christopher; Lee, Kang-Kun; Kaown, Dugin Spatial fingerprinting of biogenic and anthropogenic volatile organic compounds in an arid unsaturated zone
Subsurface volatile organic compounds (VOCs) can pose risks to human and environmental health and mediate biological processes. VOCs have both anthropogenic and biogenic origins, but the relative importance of these sources has not been explored in subsurface environments. This study synthesizes 17 years of VOC data from the Amargosa Desert...
Green, Christopher; Luo, Wentai; Conaway, Christopher H.; Haase, Karl B.; Baker, Ronald J.; Andraski, Brian J. Comparison of groundwater age models for assessing nitrate loading, transport pathways, and management options in a complex aquifer system
In an aquifer system with complex hydrogeology, mixing of groundwater with different ages could occur associated with various flow pathways. In this study, we applied different groundwater age estimation techniques (lumped parameter model, and numerical model) to characterize groundwater age distributions and the major pathways of nitrate...
Koh, E.H.; Lee, E.; Kaown, D.; Green, Christopher; Koh, D.C.; Lee, K.K; Lee, S.H. Stratification of reactivity determines nitrate removal in groundwater
Biogeochemical reactions occur unevenly in space and time, but this heterogeneity is often simplified as a linear average due to sparse data, especially in subsurface environments where access is limited. For example, little is known about the spatial variability of groundwater denitrification, an important process in removing nitrate originating...
Kolbe, Tamara; de Dreuzy, Jean-Raynald; Abbott, Benjamin W; Aquilina, Luc; Babey, Tristan; Green, Christopher; Fleckenstein, Jan; Labasque, Thierry; Laverman, Anniet M; Marçais, Jean; Peiffer, Stefan; Zahra Thomas; Pinay, Gilles 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...
Conaway, Christopher H.; Walvoord, Michelle Ann; Thomas, Randall B.; Green, Christopher; Baker, R.J.; Thordsen, James J.; Stonestrom, David A.; Andraski, Brian J. 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...
Nolan, Bernard T.; Green, Christopher T.; Juckem, Paul F.; Liao, Lixia; Reddy, James E. 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...
Green, Christopher T.; Liao, Lixia; Nolan, Bernard T.; Juckem, Paul F.; Shope, Christopher L.; Tesoriero, Anthony J.; Jurgens, Bryant C. 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...
Lu, Bingqing; Zhang, Yong; Zheng, Chunmiao; Green, Christopher T.; O'Neill, Charles; Sun, Hong-Guang; Qian, Jiazhong 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....
Zhang, Yong; Green, Christopher T.; LaBolle, Eric M.; Neupauer, Roseanna M.; Sun, Hong-Guang