High Capacity Wells and Baseflow Decline in The Wolf River Basin, Northeaster Wisconsin (USA)

The baseflow of the Wolf River (drainage area of 1,200 km2) in northeastern Wisconsin (USA) has declined by over 30% during the last thirty years, whereas climatic, land cover, and soil characteristics of the basin have remained unchanged. Because groundwater basins do not always coincide with surface water basins, estimating groundwater discharge to streams using variables only pertinent to the surface water basin can be ineffective. The purpose of this study is to explain the decline in the baseflow of the Wolf River by developing a multiple regression model. To take into account variables pertaining to the groundwater basin, withdrawal rates from high capacity wells both inside the Wolf River basin and in two adjacent basins were included in the regression model. The other explanatory variables include annual precipitation and growing degree days. Groundwater discharge to the river was calculated using streamflow records with the computer program Groundwater Toolbox from the United States Geological Survey. Without the high capacity wells data, the model only explained 29.6% of the variability in the groundwater discharge. When the high capacity wells data within the Wolf River basin were included, r2 improved to be 0.512. With the high capacity wells data in adjacent basins, r2 improved to be 0.700. The study suggests that human activity taking place outside of the basin has had an effect on the baseflow, and should be taken into account when examining baseflow changes

Dynamic Behavior of CO2 in a Wellbore and Storage Formation: Wellbore-Coupled and Salt-Precipitation Processes during Geologic CO2 Sequestration

For investigating the wellbore flow process in CO2 injection scenarios, coupled wellbore-reservoir (WR) and conventional equivalent porous media (EPM) models were compared with each other. In WR model, during the injection, conditions for the wellbore including pressure and temperature were dynamically changed from the initial pressure (7.45–8.33 MPa) and temperature (52.0–55.9°C) of the storage formation. After 3.35 days, the wellbore flow reached the steady state with adiabatic condition; temperature linearly increased from the well-head (35°C) to the well-bottom (52°C). In contrast, the EPM model neglecting the wellbore process revealed that CO2 temperature was consistently 35°C at the screen interval. Differences in temperature from WR and EPM models resulted in density contrast of CO2 that entered the storage formation (~200 and ~600 kg/m3, resp.). Subsequently, the WR model causing greater density difference between CO2 and brine revealed more vertical CO2 migration and counterflow of brine and also developed the localized salt-precipitation. Finally, a series of sensitivity analyses for the WR model was conducted to assess how the injection conditions influenced interplay between flow system and the localized salt-precipitation in the storage formation

Anomalous Transport in Three‐Dimensional Discrete Fracture Networks: Interplay Between Aperture Heterogeneity and Injection Modes

We study how the interplay between fracture aperture heterogeneity and tracer injection mode controls fluid flow and tracer transport in three‐dimensional (3D) discrete fracture networks (DFNs). The direct 3‐D DFN simulations show that tracer injection mode has substantial effects on tracer spreading across all levels of aperture heterogeneity. The key controlling factor for effective transport is the initial Lagrangian velocity distribution, which is determined by the interplay between injection mode and aperture heterogeneity. The fundamental difference between initial Lagrangian velocity distribution and domain‐scale Eulerian velocity distribution plays a vital role in determining anomalous transport. We effectively capture the observed anomalous transport using an upscaled transport model that incorporates initial velocity distribution, stationary velocity distribution, velocity correlation length, and average advective tortuosity. With the upscaled transport model, we accurately capture the evolution of Lagrangian velocity distribution and predict longitudinal spreading in 3‐D DFN.PKK acknowledges the College of Science & Engineering at the University of Minnesota and the George and Orpha Gibson Endowment for its generous support of Hydrogeology. PKK and WSH acknowledge a grant from Korea Environment Industry and Technology Institute (KEITI) through Subsurface Environmental Management (SEM) Project, funded by the Korea Ministry of Environment (MOE) (2018002440003). MD acknowledges the support of the European Research Council (ERC) through the project MHetScale (617511), and the support of the Spanish Ministry of Science and Innovation through a Severo Ochoa project (No. CEX2018324 000794‐S), and the project HydroPore (PID2019‐106887GB‐C31). JDH acknowledges support from the LANL LDRD program office Grant 20180621ECR and thanks to the Department of Energy (DOE) Basic Energy Sciences program (LANLE3W1) for support as well.Peer reviewe

A Batch Experiment of Cesium Uptake Using Illitic Clays with Different Degrees of Crystallinity

Radiocesium released by the severe nuclear accident and nuclear weapon test is a hazardous material. Illitic clays play a key role in the spatial distribution of radiocesium in groundwater environments due to selective uptake sites at the illite mineral, such as frayed edge sites. However, the cesium uptake capabilities of illitic clays are diverse, which could be associated with the illite crystallinity. This study was performed to determine the cesium uptake of illitic clays and evaluate the crystallinity effects on cesium uptake using statistical approaches. A total of 10 illitic clays showed various crystallinity, which was parameterized by the full width at half maximum (FWHM) at 10 Å XRD peak ranging from 0.15 to 0.64. The uptake behavior of illitic clays was well fitted with the Freundlich model (i.e., r2 > 0.946). The uptake efficiency of illitic clays increased with the decrease in dissolved cesium concentrations. The cesium uptake was significantly correlated with the FWHM and cation exchange capacity, suggesting that the uptake becomes higher with decreasing crystallinity through expansion of the edge site and/or formation of ion-exchangeable sites

A Batch Experiment of Cesium Uptake Using Illitic Clays with Different Degrees of Crystallinity

Radiocesium released by the severe nuclear accident and nuclear weapon test is a hazardous material. Illitic clays play a key role in the spatial distribution of radiocesium in groundwater environments due to selective uptake sites at the illite mineral, such as frayed edge sites. However, the cesium uptake capabilities of illitic clays are diverse, which could be associated with the illite crystallinity. This study was performed to determine the cesium uptake of illitic clays and evaluate the crystallinity effects on cesium uptake using statistical approaches. A total of 10 illitic clays showed various crystallinity, which was parameterized by the full width at half maximum (FWHM) at 10 Å XRD peak ranging from 0.15 to 0.64. The uptake behavior of illitic clays was well fitted with the Freundlich model (i.e., r2 > 0.946). The uptake efficiency of illitic clays increased with the decrease in dissolved cesium concentrations. The cesium uptake was significantly correlated with the FWHM and cation exchange capacity, suggesting that the uptake becomes higher with decreasing crystallinity through expansion of the edge site and/or formation of ion-exchangeable sites

CO2 Leakage-Induced Contamination in Shallow Potable Aquifer and Associated Health Risk Assessment

Leakage of stored CO2 from a designated deep reservoir could contaminate overlying shallow potable aquifers by dissolution of arsenic-bearing minerals. To elucidate CO2 leakage-induced arsenic contamination, 2D multispecies reactive transport models were developed and CO2 leakage processes were simulated in the shallow groundwater aquifer. Throughout a series of numerical simulations, it was revealed that the movement of leaked CO2 was primarily governed by local flow fields within the shallow potable aquifer. The induced low-pH plume caused dissolution of aquifer minerals and sequentially increased permeabilities of the aquifer; in particular, the most drastic increase in permeability appeared at the rear margin of CO2 plume where two different types of groundwater mixed. The distribution of total arsenic (∑As) plume was similar to the one for the arsenopyrite dissolution. The breakthrough curve of ∑As monitored at the municipal well was utilized to quantify the human health risk. In addition, sensitivity studies were conducted with different sorption rates of arsenic species, CO2 leakage rates, and horizontal permeability in the aquifer. In conclusion, the human health risk was influenced by the shape of ∑As plume, which was, in turn, affected by the characteristics of CO2 plume behavior such as horizontal permeability and CO2 leakage rate