In this study, a study on groundwater flow analysis was conducted using hydrochemical and thermal data to find out the flow of groundwater and pollutant behavior in the karst area and to secure countermeasures for problems related to water quality and water resource stability. The flow characteristics were identified using the study area's overall topographic slope and groundwater map. It is more vulnerable to groundwater pollution because it belongs to the discharge stand where groundwater from the west is discharged into the sea. The vertical hydraulic gradient was measured to confirm the direction of recharge and discharge of groundwater and surface water, and it can be seen that the inflow and outflow of groundwater-surface water is active. In both Gyogokcheon (Gyogok-ri) and Sohancheon (Hamaengbang-ri), the recharge of groundwater tends to be more dominant, and in the case of Sohancheon located in Hamangbang-ri, the recharge of groundwater in summer and winter was more active than in spring and fall. In addition, the residence time of groundwater and the recharge and mixing of surface water according to the flow of groundwater and the behavior of pollutants were analyzed using hydrochemical data. There was a distinct difference in radon concentration values between Gyogokcheon (gneiss-based rock) and Sohancheon (limestone-based rock). In the case of Hamaengbang-ri, radon concentration values were not significantly divided according to surface water, groundwater-surface water mixing section (hyporheic zone), and cave water. In the case of Gyogok-ri, radon concentration was used as one of the indicators to estimate the mixing ratio of groundwater and surface water in the hyporheic zone. This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant numbers 2019R1I1A2A01057002 and 2019R1A6A1A03033167). This subject is supported by Korea Ministry of Environment as "The SS(Surface Soil conservation and management) projects; 2019002820004.

How to cite: Ryu, H.-S. and Kim, H.: A Study on the analysis of groundwater flow using thermal and hydrochemical data of groundwater and surface water in the karst area of Samcheok, Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14397, https://doi.org/10.5194/egusphere-egu24-14397, 2024.

Understanding the relationship between flow (Q) and pressure drop (ΔP) for porous media is a long-standing challenge affecting a wide variety of environmental, societal and industrial issues, from soil remediation to enhanced oil recovery. While for homogeneous media such dependence is well represented by the Kozeny-Carman formula,  the fundamental nature of such a relationship (Q vs ΔP) within heterogeneous systems, characterized by a broad range of pore sizes, is still not understood. We design a set of controlled and complex porous structures that we use to conduct microfluidics experiments to measure their intrinsic permeability. We synthesize the results upon deriving an analytical formulation relating the overall intrinsic permeability and key features of the porous structure. We propose to embed the spatial variability of pore sizes into the medium permeability by upscaling the flow through each pore, via the Hagen Poiseuille Law. Our prediction fits well the collected data, highlighting the role played by the micro-structure on the overall medium permeability. Furthermore, beside the theoretical understanding of this important relationship, we also extend our set-up to novel experiments focusing on the paradigmatic case study of biofilm growth that affects the system permeability by obstructing the pore spaces.

How to cite: Jiao, W., Scheidweiler, D., Delouche, N., Guadagnini, A., and de Anna, P.: Intrinsic permeability of porous systems: models and microfludiic experiments for heterogeneous structures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12432, https://doi.org/10.5194/egusphere-egu24-12432, 2024.

Immiscible fluid displacement in rough geological fractures plays a crucial role in various subsurface processes, such as enhanced oil recovery and geological carbon sequestration. In horizontal settings, this displacement is governed by capillary and viscous forces, resulting in the emergence of various displacement patterns as a less viscous fluid displaces a more viscous one (drainage). The macroscopic variables quantifying the flow process differ substantially between the two limit unstable regimes, namely capillary and viscous fingering, for very low and very large capillary numbers, respectively. While there has been extensive investigation of such phenomena in the context of porous media, studies on rough fractures are relatively scarce. In this study, we perform Direct Numerical Simulation (DNS) to analyze the process of drainage by solving the Navier–Stokes equations within the fracture pore space, employing the Volume of Fluid (VOF) method to track the evolution of the fluid-fluid interface. We consider a wide range of Capillary numbers (10^-5 – 10^-2) encompassing both the viscous and capillary dominated regimes, as well as three distinct viscosity ratios (0.8, 0.05 and 0.01), and address realistic synthetic fracture geometries characterized by their Hurst exponent, the ratio of the roughness amplitude to the mean aperture (denoted as the fracture closure), and the correlation scale L_c (i.e., the scale above which the two fracture walls are identical) of the investigated fracture domain. The fracture closure is varied between 0.1 and 1, and L_c between L/32 (aperture field with spatial correlations only at small scales) and L (self-affine aperture field), where L denotes the length of the domain. Starting from the invasion morphologies of the fluid-fluid interface, we examine various pore-scale and macroscopic flow observables, allowing us to systematically characterize the displacement processes of the two-phase system at the hydrodynamic scale. Additionally, flow observables, such as the residual saturation of the displaced fluid and the interfacial area, can be utilized to define the parameter functions of a continuum scale two-phase flow model towards upscaling.

How to cite: Neuweiler, I., Krishna, R., Yang, Z., and Yves, M.: Direct Numerical Simulation of Immiscible Two-phase Flow in Rough Fractures from Viscous to Capillary Fingering – Impact of Flow regime and Structure of the Aperture Field , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9743, https://doi.org/10.5194/egusphere-egu24-9743, 2024.

Carbon-based nanoparticles (CNPs) are increasingly used for environmental and industrial applications such as in pharmaceuticals, energy production, and water and wastewater treatment. Thus, it is crucial to understand their interactions and transport in porous media. Here, we examine the impact of CNP hydrophobicity and porous medium surface area on their transport. We use CNPs that are synthesized from citric acid and ethanolamine and are fluorescent. They exhibit synthesis-temperature-dependent hydrophobicity and were synthesized at four temperatures: 190 °C, 210 °C, 230 °C, and 250 °C. The experiments were conducted by flowing these CNPs in sand-packed columns under saturated and unsaturated conditions. To examine the impact of the surface area of sand on CNP transport, the sands packed in the columns had three surface areas. In addition, a particle transport model in HYDRUS 1D was used to model the transport.

Together, our experimental and modeling noted four important observations. The first observation indicated the importance of hydrophobicity on CNP transport. There was a 55% difference between the recovery of CNPs synthesized at 190 °C compared to those synthesized at 250 °C. Second, a five-fold increase in surface area yielded a 17% decrease in the recovery of CNPs, suggesting the role of sand surface area on CNP recovery. Third, due to the small size of CNPs relative to the water film on the sand surface, there were no significant differences in the mass recovery of CNPs under unsaturated and saturated conditions. Fourth, the particle transport model with a Langmuirian site blocking term successfully simulated the transport of CNPs. There was approximately a 10-fold increase in the adsorption coefficients for hydrophobic CNPs compared to hydrophilic ones. In sum, our observations and modeling demonstrated that hydrophobicity was a major factor that impacted the transport of CNPs.

How to cite: Hassanpour, B., May, D., SinClair, L., Steenhuis, T., and Cathles, L.: Effect of Hydrophobicity on the Transport of Carbon Nanoparticles in Saturated and Unsaturated Porous Media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2723, https://doi.org/10.5194/egusphere-egu24-2723, 2024.

The soil aqueous phase contains a multitude of dissolved as well as colloidal substances, e.g., organic colloids and clay minerals. Due to their ability to facilitate co-transport, colloids significantly contribute to the fluxes of carbon, nutrients, and contaminants, which renders a thorough consideration of colloids and their mobility a prerequisite for an understanding of soil matter exchange. However, a comprehensive assessment of colloidal transport is often hampered by the heterogeneity of reactions at soil mineral interfaces and the compositional and functional diversity of organic matter in natural soil suspensions. We addressed this challenge by using tailored organic polymers based on poly(ethylene glycol) (PEG) with high reactivity towards clay minerals. Hence, the polymers may be immobilized when clays are exposed on pore walls or mobilized when clay minerals form a colloidal suspension that permits a co-transport of clays and polymers. To unravel the competition between these mechanisms, we investigated the separate and combined transport of PEG and bentonite in column experiments using natural limestone as substrate. Here, PEG was strongly retarded due to adsorption on clay mineral surfaces that were exposed following limestone weathering. In contrast, PEG was highly mobile when transported simultaneously with bentonite and the observed PEG breakthrough resembled that of bentonite, indicating PEG was co-transported. This demonstrates that the application of PEG is promising in the disentanglement of complex transport phenomena in natural porous media, particularly if competition between adsorption sites is decisive for the fate of organic matter.

How to cite: Kwarkye, N., Ritschel, T., and Totsche, K.: Tracing colloidal co-transport in porous media with tailor-made polymers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14733, https://doi.org/10.5194/egusphere-egu24-14733, 2024.

The deep geological disposal method is a prominent approach for the management of high-level radioactive waste, and understanding the behavior of uranium under various geochemical conditions is essential for this purpose. To predict the behavior of uranium in the field, it is necessary to evaluate not only the transport of uranium but also the reactions between host rock and groundwater at the field site. In this regard, we evaluated the behavior of uranium in the underground environment by analyzing the temporal and spatial changes in uranium geochemistry in response to water-rock reactions. This was achieved through column experiments using rocks containing uranium ore bodies and groundwater from a natural analogue study site in Korea. Two columns (NA-PJ1 and NA-PJ2) were prepared by collecting coaly slate materials containing uranium minerals sourced from the Okcheon Metamorphic Belt in Korea. NA-PJ1 was filled with coaly slate (0.025 ~ 2 mm grain size) collected from the study area, while NA-PJ2 included a mixture of coaly slate and limestone (10 wt%) to provide pH buffering. The input solutions to the columns were artificial groundwater manufactured with a chemistry similar to that of the groundwater at the study site. The artificial groundwater was purged with Ar gas before the experiment to minimize the ingress of dissolved oxygen (DO) from the atmosphere. To observe spatial and temporal changes in geochemistry resulting from the interactions between the artificial groundwater and the reactive materials inside the columns, water samplings were performed at 0, 5, 10, 15, 20, 25, 30, 35, and 40 cm from the column influent. The results consistently showed low and stable DO concentrations in both columns. The pH in NA-PJ1 initially exhibited the highest value at 0 cm but gradually decreased to below 4.5. This was attributed to the insufficient carbonate buffering capacity to neutralize hydrogen ions generated by the oxidation of iron sulfide in coaly slate. In NA-PJ2, in contrast, the pH remained around 8. Uranium concentration in NA-PJ1 increased gradually with distance. It was determined that uranium was released through the dissolution of uranium minerals (i.e., uraninite and ekanite). Subsequently, the released uranium formed uranium aqueous complexes with dissolved F or SO₄ induced by iron sulfide oxidation. Furthermore, it was shown that uranium in NA-PJ1 formed UO₂CO₃(aq) complexes closer to the column influent, while it formed more UO₂SO₄(aq) complexes with increasing distance. This study contributes to understanding the transport and reaction characteristics of uranium in groundwater, ultimately aiding in the management of high-level radioactive waste in a deep geological disposal site.

How to cite: Lim, S., Cho, H., Noh, S., and Jeen, S.-W.: Evaluating the Behavior of Uranium Through Column Experiments Using Artificial Groundwater and Coaly Slate from a Natural Analogue Study Site in Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5012, https://doi.org/10.5194/egusphere-egu24-5012, 2024.

The Single-Well Push-Pull (SWPP) test is a cost-effective tracer test that has been widely used for aquifer characterization. There is an advantage in concurrently utilizing heat and solute tracers for a comprehensive understanding of the hydraulic and thermal characteristics of the aquifer. However, the application of both tracers in SWPP tests has yet to be commonly used due to their particularity in setting experimental conditions such as drift time and the use of chaser. In this research, dual-tracer SWPP tests were conducted in a laboratory scale using sand (d₅₀ = 0.84 mm, U = 2.06) under six different seepage velocities (v_s = 17.5 ― 59.7 m/d), with relative drift time as the variable. As tracers, a sodium chloride solution with a concentration of 1000 ppm and a temperature difference of approximately 6℃ from the background water temperature was employed. Obtained EC and temperature time series data were analyzed by several analytical models. The estimates from analytical models (seepage velocity, porosity, volumetric heat capacity) were compared to those from measurements to evaluate the applicability of a single analytical model on dual-tracer SWPP test. Preliminary experimental results showed that slower velocities and shorter drift times resulted in higher recovery rates but also led to larger error rates in estimates for the solute tracer. Building upon a solute tracer, more accurate analytical models suitable for the current experimental setup were identified, and subsequently extended to the heat tracer for further analysis. Based on the interpretation of both tracers, appropriate test conditions for dual-tracer SWPP tests will be proposed. We anticipate to offer a deeper understanding of the benefits and considerations associated with the combined use of heat and solute tracers for the thorough evaluation of aquifer characteristics during push-pull tests.

Keywords: Single-well push-pull test, Laboratory experiments, Heat tracer, Solute tracer

Acknowledgements : This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2022R1A2C1006696). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MSIT) (No. 2022R1A5A1085103). This work was also supported by the Nuclear Research and Development Program of the National Research Foundation of Korea (NRF-2021M2E1A1085200).

How to cite: Lee, N.-R., Baek, J.-Y., and Lee, K.-K.: The advantages and considerations of applying dual tracers in SWPP tests , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6871, https://doi.org/10.5194/egusphere-egu24-6871, 2024.

Arsenic (As) pollution in soil from various anthropogenic sources potentially threatens groundwater by migrating downward through a vadose zone. As goes through complex biogeochemical reactions such as sorption, desorption, and/or redox transformation, which affects its retention in this zone. A retardation factor is a critical solute-transport parameter to quantitatively assess the retention of As in this zone, and eventually to predict the potential risk of groundwater contamination. Despite its importance, however, there is still limited information to quantify the retardation factor in a vadose zone, compared to in the saturated condition. This study aimed to assess the retardation factor of As using twenty-two unsaturated soil columns coupled with the non-equilibrium solute-transport modeling. We employed a multiple linear regression approach to develop a prediction model for the retardation factor based on the soil properties. Soil columns with 3-cm inner diameter and 45-cm height were packed with six different field soils at various bulk densities. Distilled water was infiltrated into each column at a constant flowrate, until a steady-state unsaturated condition was achieved. The distilled water was replaced with a solution containing As and a conservative tracer (chloride, Cl), to obtain their breakthrough curves. The retardation factor of As was determined by inversely fitting the breakthrough data of As and Cl with Mobile-Immobile model integrated in HYDRUS 1-D software. The derived retardation factors of As in the mobile and immobile zones ranged 1.58–6.93 and 1.44–25.48, respectively. These showed high degree of dependence on soil properties. In the mobile water zone, iron content and organic matter content emerged as the two most influential properties affecting As transport, impeding As mobility. Conversely, in the immobile water zone, coefficient of uniformity and bulk density were identified as the most influential factors, enhancing As retention. Based on the results, empirical equations were derived to predict the retardation factors of As in a vadose zone based on the aforementioned soil properties.

How to cite: Kim, S. H., Tran, T. H. H., Chung, J., and Lee, S.: Prediction of As behavior in a vadose zone using an empirical relationship between As retardation factor and the soil properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14769, https://doi.org/10.5194/egusphere-egu24-14769, 2024.

The effects of global warming have already been recorded in many decorated caves located in karst systems, and some prehistoric paintings are already deteriorating. Modeling the microclimate of caves under various climate change scenarios will enable to adapt the conservation strategy for rock art heritage.

The first step in this modeling approach is to simulate heat transfer from the surface to the cave through the soil/epikarst/karst system. The rock characteristics in the model are calibrated using sensor data taken at various depths in the soil and in the karst over a few years, and in the cave thanks to long-term monitoring. To provide long-term climate forcing, a transfer function is established between meteorological data measured at a height of 2 meters by Météo France and the temperature measured at the ground surface.

Then, this heat transfer model is fed with projections from regional climate downscaling models. This modeling approach, which integrates both current data and climate projections, will be a significant step towards the effective management and conservation of decorated caves, which are not only geological wonders but also hold critical historical and archaeological significance.

How to cite: Artigue, C. and Mugler, C.:  Heat transfer modeling in karst environments to study the impact of climate change on the future of decorated caves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9577, https://doi.org/10.5194/egusphere-egu24-9577, 2024.

Fluid stretching plays an important role in controlling mixing dynamics in porous media. Recent advances have shown that stretching at pore scale in 3D porous media is chaotic, leading to exponential elongation of mixing interfaces [e.g. 1,2]. Yet, it is not known how the associated stretching rate depend on the pore scale velocity heterogeneity. In this study, we perform particle tracking simulations in a periodic flow fields to investigate how flow heterogeneity control the transient evolution of the stretching rate as well as the asymptotic stretching rate (Lyapunov exponent). Our results reveal that rare low velocity events have a significant impact on the Lyapunov exponent, while these regions are numerically more difficult to treat and thus sometimes excluded from statistics [1]. Moreover, we discuss conceptual difficulties associated to velocity pdf with heavy tails towards low velocities: Ensemble averages of the deformation gradient tensor do not converge under these conditions when taken them at equal advective distances, as opposed to at equal times. As a consequence, the meaning of the steady state stretching rate must be discussed in the context of long memories. Using Continuous Time Random Walks (CTRW) we derive analytical expressions for the averages and discuss low velocity cutoffs to guarantee convergence. We further discuss the nature of the pre-asymptotic stretching kinematics, which can have a dominant effect on mixing processes. We show that the strength of the transient is controlled by the typical shear rate while the duration is determined by the Lyapunov exponent. Weaker chaotic stretching are associated to a longer lasting transient regime.

[1]: Turuban et al. (2019) In: JFM 
[2]: Heyman et al. (2020) In: PNAS

How to cite: Maeritz, M., Heyman, J., Le Borgne, T., and Dentz, M.: Effect of velocity fluctuations on pore scale stretching kinematics in 3D porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17262, https://doi.org/10.5194/egusphere-egu24-17262, 2024.

Random walk particle tracking (RWPT) methods employ a Lagrangian discretization of solute plumes into point particles to numerically solve the advection-dispersion equation. Their recognized advantages over more traditional grid-based Eulerian methods regarding numerical stability and numerical dispersion make them ideal candidates to simulate complex reactive fronts in heterogeneous media. However, handling nontrivial boundary conditions remains a challenge, restricting the range of interface processes that can be simulated. We derive and validate a new collision-based approach to implement a broad class of generalized Robin-type boundary conditions, representing the balance between diffusive fluxes and an arbitrary nonlinear function of the transported and surface reactant concentrations. This formulation allows for modeling arbitrary coupled sets of nonlinear surface reactions within the classical RWPT framework, thus opening new opportunities for simulating pore-scale reactive transport in the subsurface. The collision-based nature of the proposed technique allows for estimating surface reaction rates based on single-particle collisions with the reactive interface. Thus, it does not require concentration field reconstructions or multi-particle searches. We verify the method for a coupled set of nonlinear mass-action reactions under pure diffusion and for nonlinear kinetics representing calcite dissolution in a model porous medium.

How to cite: Aquino, T.: Simulating pore-scale nonlinear reactions at the fluid-solid interface using random walk particle tracking, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5519, https://doi.org/10.5194/egusphere-egu24-5519, 2024.

The origin and the fate of organic carbon and nitrogen compounds in groundwater play an important role in the global biogeochemical cycling of carbon and nutrients and have implications for drinking water production. While the input of these compounds into the subsurface is strongly driven by land use, their fate in subsurface environments such as fractured aquifers is controlled by a complex interplay between hydrological and biogeochemical processes at different temporal and spatial scales and is poorly understood yet. Determining the fate of these organic compounds in fractured aquifers is additionally challenging due to spatial heterogeneities at various scales down to centimeter scales, leading to a multitude of flow paths of different lengths and residence times.  This causes an overlap of solute residence times for compounds moving from the surface through the subsurface to surface waters or groundwater observation wells, stretching from days to many years, thus affecting the dynamics of the biogeochemical processes and the quantitative assessment of compound fluxes. To address this issue, a travel time-based modeling approach is employed to simulate the fate of carbon and nitrogen compounds in groundwater along a hill slope transect of the Hainich Critical Zone Exploratory (CZE), located northwest of Thuringia (central Germany). This transect is set up under the Collaborative Research Center AQUADIVA. It is subject to an intensive surface and subsurface monitoring program providing groundwater quality and quantity data. Travel time distributions obtained from a numerical groundwater flow model of the transect and its vicinity are combined with a set of numerical 1D simulations describing the biogeochemical transformations of carbon and nitrogen. The simulated complex reaction network describes the transformation of carbon and nitrogen along individual groundwater flow paths, which considers varying microbial functional groups such as aerobes and anaerobes, as well as key microbial life processes under different redox conditions, including aerobic, nitrate-reducing, ammonia-oxidizing, and sulfate-reducing conditions.  The model-predicted concentrations of reactive species at various observation wells are compared to measured concentrations to validate the approach. The results show that processes on the surface strongly shape the dynamics of resulting recharge zones represented by different land use areas, which have an impact on observed concentrations at wells. Travel time distributions combined with simulations of the biogeochemical transformation along a flow path can provide a model-based interpretation of measured observations and the factors controlling them. This allows predicting fluxes of chemical species through the entire sub-catchment and their dependency on the dynamics of surface conditions.

How to cite: Duong, T. Q., Hildebrandt, A., and Thullner, M.: Unraveling biogeochemical transformation of organic carbon and nitrogen compounds in groundwater along a hill slope transect, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5705, https://doi.org/10.5194/egusphere-egu24-5705, 2024.

Biofilms in porous media host microbial communities that play a central role in the degradation of nutrients and Contaminants of Emerging Concern. Their importance for promoting contaminants removal in the context of Natural Based Solutions is acknowledged, but we still lack a complete understanding and quantification of biofilm growth dynamics in porous media, and their impact on flow and transport behavior.

In this context, we aim to investigate the effects of sharp interfaces on the spatial and temporal distribution of biofilms growth and their subsequent role in the evolution of flow and transport properties. For this purpose, we conduct flow-through experiments in sand-packed columns characterized by two homogeneous porous media separated by a sharp interface. We inject electron acceptor and electron donor solutions sequentially and multiple times. This creates multiple reactive mixing zones that flow and evolve through the system, depending on the porous medium. The high-resolution monitoring system enables the quantification of biofilm activity, as well as changes in hydraulic conductivity over time and at different sections of the column. Additionally, image analysis allows for the evaluation of the spatial distribution of biofilm growth over time, while breakthrough curve concentrations derived from several tracer tests provide further insights into overall transport parameter changes.

How to cite: Trabucchi, M., Rodriguez Escales, P., Sanchez Vila, X., Carrera, J., and Fernandez Garcia, D.: Impact of Sharp Interfaces on Biofilm Growth: Insights from Mixing Processes in a Flow-Through Column Experiment., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10397, https://doi.org/10.5194/egusphere-egu24-10397, 2024.