HS8.2.7

Coastal areas around the Mediterranean basin concentrate population, multi-sector economic activities and agricultural activities. This induces an important need in fresh water and high solicitation of coastal aquifers, which can lead to salt water intrusion. This issue, added to contaminated surface water percolating towards the aquifer, and along with climate change show the urge for innovative groundwater management, especially in coastal areas. The PRIMA Sustain-COAST European project aims at exploring innovative governance for sustainable coastal groundwater management and pollution reduction in the context of a changing climate by involving researchers, local populations, water stakeholders and policy makers.

The Arborea plain in Sardinia (Italy) is characterized by an intense agricultural activity based on dairy cattle farming (approximately 31.000 livestock units in the district). The area, reclaimed from a lagoon in the 1920s, is intensely used for fodder crops to feed the cattle. Thus, an important drainage network has been developed to maintain the soil in suitable conditions for agriculture. Heterogeneous nitrates contamination of the aquifer system has been highlighted through soil sampling and groundwater monitoring in the Arborea plain in previous studies and the zone is classified as a Nitrates Vulnerable Zone (following Directive 91/676/CEE). The hydrogeology of the study site is characterized by two main aquifers: the upper one, unconfined, hosted in a sandy unit (SHU), separated from the second aquifer, hosted in an alluvial formation (AHU), by lagoon deposits aquitard.

In the present study, we show the individual work steps to get from the existing 3D hydrogeological model to a 3D numerical groundwater model using the interactive finite-element simulation system Feflow 7.4. The developed partially unstructured steady-state flow model takes into account the recharge of the aquifer system by surface water, the drainage and irrigation network and the seasonal variation of water volumes drained and spread on the land. Also accounted for are water pumped by farms for technical use and livestock, groundwater flow between the different units and interactions with seawater. Results show the influence of groundwater management, especially for agricultural activities, and interaction with surface water, which is highly impacted by anthropic networks (irrigation and drainage). Ongoing research is aimed at quantifying the spatio-temporal distribution of nitrate in the SHU aquifer under transient groundwater flow conditions to compare different water management, climate change and contamination scenarios.

References

The project is funded by the General Secretariat for Research and Technology of the Ministry of Development and Investments under the PRIMA Programme. PRIMA is an Art.185 initiative supported and co-funded under Horizon 2020, the European Union’s Programme for Research and Innovation. We also acknowledge funding from the Italian Ministry of University and Research CUP no. J84D18000180005.

How to cite: Lincker, M., Sessini, A., Carletti, A., Roggero, P. P., Karatzas, G., and Schäfer, G.: A 3D numerical groundwater model for sustainable groundwater management of the coastal aquifer system of the Arborea plain, Sardinia (Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3648, https://doi.org/10.5194/egusphere-egu22-3648, 2022.

Groundwater-surface water interaction controls the exchange of contaminants, solutes and energy between aquifers and surface water resources. In particular, groundwater contamination and solute transport time is prolonged due to the impact induced by hyporheic fluxes within the streambed sediment. The retention of contaminants and solutes in streambed sediment influence the ecology and biodiversity of hyporheic zone. In this research, a numerical groundwater model was developed and supported with hydrologic and hydrogeological observations of the Krycklan catchment, Sweden, to investigate the impacts of hyporheic flows on the regional groundwater flow direction and discharge areas at the groundwater-surface water interface along stream networks. The applied method involved a multiscale modelling framework where the regional groundwater and hyporheic flows were analyzed via numerical modelling and exact solutions, respectively; and then superimposed to obtain the subsurface flow field. The regional groundwater flow was analyzed in presence and absence of the hyporheic flow and significant changes in groundwater flow trajectories and size of discharge areas were found upon adding the hyporheic flow fields. In particular, the upward groundwater flow was strongly contracted near the streambed surface due to the impact of hyporheic flow, which led to groundwater funneling and an acceleration of groundwater discharge velocities into streams. Consequently, the size of groundwater coherent discharge areas were substantially reduced leading to significantly fragmentation of groundwater discharge zones due to the impact of hyporheic fluxes.

How to cite: Mojarrad, B. B., Wörman, A., and Riml, J.: Regional groundwater funneling within the hyporheic zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8607, https://doi.org/10.5194/egusphere-egu22-8607, 2022.

Groundwater is the main component of river discharge during low-flow periods. The aquifer response to recharge typically depends on the catchment hydro-geological characteristics, such as the hydraulic conductivity, the storage coefficient and the aquifer dimensions. Moreover, such a response time is key to buffer drought propagation during dry periods. As a consequence, it is of paramount importance to evaluate how fast an aquifer will react to an external perturbation. Here, we apply a spectral approach to evaluate the aquifer response time. At the regional scale, the aquifer behaves as a low-pass filter, which modifies the input signal (e.g., the recharge) in the output signal (e.g., the baseflow) according to its properties. For instance, the groundwater response will be faster when the aquifer transmissivity is high or the storage is low. We tested our method across a wide range of German catchments using stream flow datasets. Spectral analysis across catchments of different sizes can provide insight into the spatial aggregation of groundwater response, thereby indicating the scaling rule in large heterogeneous catchments. This approach can help to evaluate the response time in humid regions, which are characterized by frequent interruptions of recession periods. Moreover, response time can serve to quantify the effect of possible external perturbations (climate, irrigation or land management changes) on aquifer resilience.

How to cite: Di Dato, M., Houben, T., and Attinger, S.: Inferring groundwater response time at regional scale by following a spectral approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11849, https://doi.org/10.5194/egusphere-egu22-11849, 2022.

Fluid-solid reactions play a key role in a wide range of biogeochemical processes. Transport limitations at the pore scale limit the amount of solute available for reaction, so that reaction rates measured under well-mixed conditions tend to strongly overestimate rates occurring in natural and engineered systems. Although different models have been proposed to capture this phenomenon, linking pore-scale structure, flow heterogeneity, and local reaction kinetics to upscaled effective kinetics remains a challenging problem.

We present a new theoretical framework to upscale these dynamics based on the chemical continuous time random walk framework. The approach is based on the concept of inter-reaction times, which incur delays compared to well-mixed conditions due to the times between contacts of transported reactants with the solid phase. We consider a simple chemical reaction in order to focus on the effects of transport limitations and medium structure, namely a second-order degradation reaction between a fluid-phase reactant and a solid-phase reactant distributed uniformly over the fluid-solid interface, where only the fluid reactant is consumed. Our formulation quantifies the global kinetics of fluid-reactant mass as it undergoes advection, diffusion, and reaction. Predictions are in agreement with numerical simulations of transport in stratified channel flows and Stokes flow through a beadpack. The theory captures the decrease of effective reaction rates compared to the well-mixed prediction with increasing Damköhler number due to transport limitations.

How to cite: Aquino, T. and Le Borgne, T.: Upscaling the impact of transport limitations in fluid-solid reactions using a chemical continuous time random walk, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4518, https://doi.org/10.5194/egusphere-egu22-4518, 2022.

The rapid growth of agricultural and industrial sectors has led to inappropriate disposal of pesticides and effluents thereby causing massive ammonium contamination of soil and groundwater resources. Contaminant transport is governed by the adsorption mechanism, which varies as the contaminant migrates through different types of soils. It is important to determine the model that best defines the adsorption mechanism of ammonium ions and the factors influencing it to predict and mitigate their contamination. This work focuses on studying the effects of clay content present in the soil on the adsorption and eventually on the retardation of ammonium ions transport through soil media using single- and dual-porosity models. The movement of ammonium ions was analyzed for three soil types with different clay proportions, by column and batch experiments. The experimental results were verified by simulating ammonium migration by numerical modeling using HYDRUS-2D software. It was observed that the ammonium ions adsorption increases with the increase in the clay content of the soil. Therefore, greater content of clay in the soil enhances the attenuation of ammonium migration in the soil media. Further, the dual-porosity model was found to be a significant factor in analyzing ammonium migration where the presence of an immobile phase in the system contributes to the transport and sorption mechanism of ammonium ions into the porous medium.

Keywords: Clay content, Ammonium ions, Single-porosity, Dual-porosity, Adsorption.

How to cite: Agarwal, P. and Sharma, P. K.: Analyzing the effects of clay content on ammonium migration in soil using single- and dual-porosity models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-255, https://doi.org/10.5194/egusphere-egu22-255, 2022.

According to previous studies, the spatial distribution accuracy of hydrogeological parameters will directly affect the geological assessment and prediction of solute transport in aquifers. In order to describe the heterogeneity of aquifers, Hydraulic conductivity (K) and the specific storage coefficient (S_s) are among the essential hydrogeological parameters as the traditional sampling method consumes construction cost and time. Therefore, the purpose of this study is to design a multi-stage concentric well pipe, which can measure the water level at different depths in a single well pipe. To thoroughly evaluate the delicate characteristics of heterogeneous aquifers, a three-dimensional (3-D) sandbox model will be used to simulate the real underground environment for pumping experiments, and the distribution field of hydrogeological parameters will be estimated by hydraulic tomography (HT). Finally, simulation of the pollution flow direction at the heterogeneous underground field is constructed by VSAFT3. Our study highlights the importance of analyzing the characteristics of groundwater geology parameters by vertical and horizontal. And through the numerical simulation and the real field fitting of the sand box. It is proved that the partitioning well pipe can accurately estimate the 3-D field of hydrogeological parameters and can effectively predict solute transport. This research will significantly contribute to the future analysis of changes in regional flow fields, groundwater replenishment patterns, and control of the diffusion of underground pollution.

How to cite: Lee, B.-S., Li, J.-D., Lin, H.-R., and Wen, J.-C.: The invention of partitioning well pipe to observe solute transport in aquifers: Laboratory sandbox and synthetic studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6908, https://doi.org/10.5194/egusphere-egu22-6908, 2022.

Background

Evolving In situ methods are showing results for sustainable and efficient plume remediation of groundwater contaminations. By injecting reactive components such as oxidation agents, zero valent iron, substrate and/or bacteria, a treatment zone (TZ) is established. In the TZ, the contamination degrades into harmless components by chemical and/or biological processes. Successful in situ remediation depends on contact between injectants and contamination. Yet, monitoring the spreading of the injectant is difficult by point sampling. The cross-borehole geophysical method DCIP (Direct Current, Induced Polarisation) allows for detailed spatial information on subsurface electrical resistivity and induced polarisation properties. The information can be used to assess the success of the injection and the development over time. Furthermore, the IP properties can be used to infer spatial information on hydraulic conductivity, which can be used in planning of the in situ remediation and in quantification of contaminant mass discharge (CMD) at the site. The objective of this study is to develop a cost-efficient method for detailed spatial and temporal monitoring of in situ remediation and to develop better tools to retrieve spatial subsurface information, able to assist and improve CMD based monitoring.

Approach

A TZ in a plume of chlorinated ethenes was established by injecting the micro zerovalent iron product and a bacterial culture into the groundwater. A network of 9 geophysical and 16 monitoring wells was established. Cross-borehole DCIP measurements and water samples were taken before and shortly after injection and during the following year. Soil cores were sampled for chemical analysis of iron shortly after injection, and slug tests and grain size analysis. Data from water samples, soil cores and hydraulic tests were compared to the geophysical measurements to assess correlation between water chemistry and electrical resistivity from cross-borehole DCIP. The hydraulic properties inferred from hydraulic tests and cross-borehole DCIP were compared. The hydraulic properties with uncertainties and the contamination data were used to estimate the CMD through the TZ.

Results

The changes in electrical conductivity and specific water quality parameters caused by the injection, showed a strong correlation with the geophysical model. The observed correlation enabled a coherent, detailed understanding of both spatial and temporal spreading of the injected components, resulting in a re-injection. Hydraulic tests and hydraulic properties inferred from cross borehole DCIP showed a very good correlation, and applying the hydraulic properties inferred from cross borehole DCIP reduced the uncertainty of the CMD estimate before and after injection. In conclusion, cross borehole DCIP has the potential to improve planning and monitoring of in situ groundwater remediation and to reduce uncertainty of CMD estimation and thereby strengthen CMD as a metric in risk assessment.

How to cite: Thalund-Hansen, R., Levy, L., Christiansen, A. V., Bording, T., Rügge, K., Dreyer, M., Brabæk Ildvedsen, L., Troldborg, M., Hag, M., Tuxen, N., and Bjerg, P. L.: Cross-borehole resistivity tomography: Can it be used to plan and monitor in situ remediation and assist risk assessment?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9697, https://doi.org/10.5194/egusphere-egu22-9697, 2022.

Cable bacteria are multicellular microorganisms that are capable of long distance electron transport (LDET) along their length. This electron transport is the result of oxidation of hydrogen Sulfide (H2S) in the sulfidic sediment layer where electrons are conducted up through cable filament aided by cell-to-cell transfer in the oxic layer thus reducing oxygen by gaining electrons. Cable bacteria behave as dipoles where anaerobic zones interfere with oxic zones for example oil/tar pollution site and can generate enough natural SP fields as a function of redox mechanism that can be measured on the surface. This study focuses on the theoretical analysis of Self-Potential (SP) signals resulting due to the presence of dipole current source under different conductivity structures in the subsurface. To investigate the behavior of SP signals, four different types of forward models are synthesized by varying resistivity of subsurface layers and changing the depth of the dipole beneath the surface. The dipole has a default current density of 20 mA/m². In the first model, a rectangular pollution patch carrying a dipole of the same shape is placed between two homogeneous layers where the top layer resistivity is swept from 10-1000 ohm-m while keeping the resistivity of bottom layer constant. In the second model, the pollution patch is placed between an inhomogeneous layer with low, intermediate, and high resistivity contrasts and a homogeneous layer. In this model, half of the patch lies in lower conducting region whereas the other part is in the high conductivity region. The third model is an extension of the second one, where the inhomogeneous layer is sandwiched between two homogeneous layers. In the last model, the pollution patch was moved beneath the surface to a depth where the SP signal cannot be observed at the surface. In this model, the depth is observed for three different pollution sources with current density values equal to 2, 20 and 200 mA/m² respectively. The results showed that SP anomaly caused by the patch when the conductivity of upper layer is high is smaller as compared to the anomaly due to the less conducting upper layer. Next two models with inhomogeneous layer, correlate well with the first model showing high SP anomaly caused by dipole when it is present in the lower conducting region and low values when in high conducting region. Fourth model demonstrates when the depth of pollution patch is increased beneath the surface, SP signal decreases and is not observed beneath a depth of around 10 m, even when the source has current density value as high as 200 mA/m². This study explicitly demonstrates the behavior of SP anomaly and will help in improved interpretation of SP technique where inhomogeneity will be present beneath the surface.

How to cite: Upadhyay, A., Madsen, L. M., Christiansen, A. V., and Damgaard, L. R.: Analysis of Self-Potential signals due to cable bacteria over different conductivity structures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13452, https://doi.org/10.5194/egusphere-egu22-13452, 2022.

In the recent times, simulation-optimization (S/O) models are used to design the optimal in-situ bioremediation system for groundwater problems with constant hydraulic gradient. In such problems, the main objective is to achieve the maximum allowable contaminant concentration within a selected remediation period at a minimum cost. At a relatively higher hydraulic gradient, the contaminant moves faster towards the monitoring wells near the aquifer boundaries, therefore, in-situ bioremediation cost increases to eliminate the contaminant within the same remediation time. Here, the effect of different hydraulic gradients on the in-situ bioremediation cost of a hypothetical case study is systematically studied. The S/O model linking meshless element-free Galerkin method (EFGM) based BIOEFGM model with the particle swarm optimization (PSO) algorithm, known as BIOEFGM-PSO, is applied to estimate the optimized in-situ bioremediation cost. In this study, the different hydraulic conditions are created by changing the head values at the downstream boundary. The different combinations of injection and extraction wells are also tested to satisfy the water quality constraints for different gradient conditions.  The results of the above S/O model showed that in-situ bioremediation cost increases with an increase in hydraulic gradient, and more wells are required for remediation within the same duration under a higher hydraulic gradient.

How to cite: Pathania, T. and Eldho, T. I.: Effect of hydraulic gradient on the optimal cost of in-situ groundwater bioremediation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5385, https://doi.org/10.5194/egusphere-egu22-5385, 2022.

Radionuclide migration through saturated fractured chalk was studied in the context of predicting potential risks to groundwater in the vicinity of nuclear repositories. The aim of the present study was to examine the effect of salinity changes which might result from a sudden rainstorm leading to freshwater infiltration on the mobility of radionuclides in fractured carbonate rocks. A tracer mixture, simulating radioactive contaminants related to spent fuel (SF), including U, Sr, Ce (simulant for redox active actinides) and Re (simulant for Tc) was injected into a naturally fractured chalk rock in the laboratory. Uranine, a fluorescent dye, served as a conservative tracer. Two sets of experiments were carried out in which tracers were added to solutions of different ionic strength (IS) represented by total dissolved solid (TDS) values (Cl^- and HCO₃^- as major anions): (1) low IS artificial rainwater (TDS of ca. 10² mg/L,); and (2) high IS artificial groundwater (TDS of ca. 10⁴ mg/L). In both sets of experiments, the tracer mixture was introduced into a fractured chalk core, followed by the injection of tracer-free solution at the same IS. Next, the opposite (low/high IS) tracer free solution was introduced into the core to induce salinity variation. The behavior of the simulants was investigated under swift changes in background (BG) solution salinity. In all cases, Re breakthrough curves (BTCs) were unaffected by the change in BG solution and exhibit conservative behavior in comparison to that of the Uranine. Cerium was transported as intrinsic colloidal carbonate complexes, in agreement with previous studies, and remained unaffected by the abrupt change in BG solution. Uranium and Strontium BTCs were influenced by the abrupt change in IS, as their recovery significantly increased when high IS solution was injected into the core and reduced when low IS solution is introduced, regardless of the injection order. This indicates that U and Sr sorption to fractured surfaces is enhanced at low salinity, a phenomenon attributed to the replacement of Sr and U ions by Ca and Na at the adsorption sites at elevated IS conditions. The variable mobility of radionuclides found in this study should be considered in the design of natural and engineered barriers for SF disposal, especially in regions where seasonal rains or flooding may cause abrupt changes to groundwater ionic strength.

How to cite: Roded, S., Klein-BenDavid, O., Turkeltaub, T., Tran, E. L., Geller, Y., Gerara, Y., Teutsch, N., and Weisbrod, N.: Radionuclide transport through fractured chalk under abrupt variations in ionic strength, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6305, https://doi.org/10.5194/egusphere-egu22-6305, 2022.