Displays

Groundwater dating and travel time distributions are important tools and data for assessment of the vulnerability of water supply wells towards pollution from the surface. Here we present selected results from more than 30 water supply and monitoring wells from major Danish water companies. The wells were recently sampled and investigated using multiple environmental tracers including ⁸⁵Kr, ³⁹Ar, ³H/³He, ¹⁴C, SF₆, CFCs and noble gases and different groundwater modeling techniques. The results demonstrate the value of groundwater dating and travel time estimations for the assessment of the history and fate of contaminants in the subsurface. This information is crucial for the assessment of the efficiency of measures to mitigate pollution of groundwater by harmful substances such as pesticides, nitrate and a large range of emerging contaminants. We demonstrate how groundwater ages and travel time distributions can be used to assess the vulnerability or susceptibility of water supply wells towards pollution, and how level specific sampling in long well screens can provide additional important information for assessment of the vulnerability of deep and shallow parts of a water supply well. Potential applications of the estimated travel time distributions include 1) improved management of well fields 2) development of pumping strategies and well screens minimizing the risk of pollution of drinking water wells, and 3) assessment of the adequacy of regulations established by authorities to protect valuable groundwater resources against pollution.   

How to cite: Hinsby, K., Purtschert, R., Musy, S., Sültenfuss, J., Wachs, D., Aeschbach-Hertig, W., Kidmose, J., Troldborg, L., and Gulbrandsen, M.: Use of multiple tracers and groundwater flow modelling for the estimation of groundwater travel times to water supply wells, vulnerability assessments and improved management of well fields , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20340, https://doi.org/10.5194/egusphere-egu2020-20340, 2020.

The year 2019 marked the 50th anniversary of a pioneering publication in hydrology. Allan Freeze and Richard Harlan published their Blueprint for a physically-based, digitally-simulated hydrologic response model (Freeze and Harlan, 1969) in Journal of Hydrology. Their vision was for a futuristic model that would integrate key processes and compartments in the hydrologic cycle: precipitation, evapotranspiration, overland runoff, infiltration and groundwater exchange (into and out of) surface water bodies, such as rivers and lakes. Today, the original Blueprint is a reality.

We recently published a paper in Journal of Hydrology to commemorate the 50 year anniversary of the original Blueprint paper (Simmons et al., 2019). In this talk, we present an overview of, and highlights from, this paper.

Through personal communications with Allan Freeze, we present the history and genesis of the Blueprint paper. We reflect on the uptake of the Blueprint into modern hydrology, the development of numerical models that enabled this, and the range of challenges being tackled by these models. Finally, we consider challenges and opportunities for the future of this area of modelling and hydrologic science.

Reference

Simmons, C.T., Brunner, P., Therrien, R., and Sudicky, E.A., 2019. Commemorating the 50th anniversary of the Freeze and Harlan (1969) Blueprint for a physically-based, digitally-simulated hydrologic response model, Journal of Hydrology, https://doi.org/10.1016/j.jhydrol.2019.124309  

How to cite: Simmons, C. T., Brunner, P., Therrien, R., and Sudicky, E. A.: Commemorating the 50th anniversary of the Freeze and Harlan (1969) Blueprint for a physically-based, digitally-simulated hydrologic response model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4283, https://doi.org/10.5194/egusphere-egu2020-4283, 2020.

Groundwater quality deterioration by nitrate pollution due to the intensive use of fertilizers in agriculture, release of untreated urban sewage and industrial wastewater, and atmospheric deposition is a worldwide concern. The urbanized and industrialized Monterrey valley has a long record of elevated nitrate concentrations in groundwater with multiple potential pollution sources. This study aimed to fingerprint different sources and transformation processes of nitrate pollution in Monterrey using a suite of chemical and isotopic tracers (δ²H-H₂O, δ¹⁸O-H₂O, δ¹⁵N-NO₃, δ¹⁸O-NO₃) combined with a Bayesian isotope mixing model. The results suggest that soil nitrogen and sewage were the most important nitrate sources. However, the concentrations of nitrate were controlled by denitrification processes in the transition and discharge zones. The approach followed in this study is useful for establishing effective pollution management strategies in contaminated aquifers.

How to cite: Torres-Martinez, J. A., Mora, A., Knappett, P. S. K., Ornelas-Soto, N., and Mahlknecht, J.: Assessment of nitrate sources in groundwater of Monterrey Valley using a multi-tracer approach combined with a probability isotope mixing model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12034, https://doi.org/10.5194/egusphere-egu2020-12034, 2020.

Numerous naturally CO₂-rich mineral water springs, locally called ‘pouhons’, occur in southeast Belgium. These are oversaturated in CO₂ (up to 4g/L) and have attracted economic, touristic and scientific interest for centuries. Water sources occur within Palaeozoic rocks of the Rhenohercynian deformation zone, a fold-and-thrust belt at the north of the Variscan orogeny in central Europe. Many occurrences are concentrated in the Cambro-Ordivician Stavelot-Venn massif. A widely accepted model, supported by H-O isotopic signatures, is that sources are primarily fed by meteoric water, which infiltrates through Quaternary sediments, then reaching Lower Palaeozoic rocks to meet the mineral and CO₂ source at unknown depth.

Different ideas for the origin of CO₂ are grouped in two main hypotheses: a) generation by dissolution of carbonate rocks and/or nodules, and b) volcanic degassing related to the neighbouring Eifel area in Germany. These well-known interpretations are mostly based on geochemical studies that are dispersed and poorly accessible. These have now been gathered in the light of new sampling campaigns, allowing to revisit and compare the views of earlier authors. We also for the first time include the geotectonic setting of the region.

Carbonate rocks in the region are represented by Lower Carboniferous and Middle Devonian limestones. Depending on the assumed structural evolution for this foreland fold-an-thrust belt, these may occur at >2 km depth below the Stavelot-Venn massif. Carbonate nodules are present in other formations, but their limited volume is unlikely to originate high and long-lived quantities of CO₂. Springs enriched in CO₂ are also common in the volcanic Eifel area, with presence of mantle CO₂ well established. The supposed extension of the Eifel plume would allow for a magmatic CO₂ source below the Stavelot-Venn massif from degassing of the plume (>50 km deep), or of an unknown shallower magmatic reservoir. Available stable and noble isotopes point to a mixed carbonate-magmatic origin.

If considering the presence of limestones at depth, meteoric water should infiltrate at least 2 km. Known deep-rooted faults are thought to act as preferential groundwater pathways. However, such deep circulation is incompatible with the low temperatures of springs (~10^oC), unless the ascent is slow enough to fully dissipate heat prior to resurfacing. Another possibility is that meteoric water does not infiltrate as deep, with CO₂ being transported upwards to meet groundwaters at shallower depths. The presence of CO₂ surface leaks, locally called ‘mofettes’, could be evidence of such relatively shallow availability of CO₂.

The evaluation of existing hypotheses highlights complex subsurface processes that involve water infiltration, CO₂ assimilation and water resurfacing in southeast Belgium. As such, this review is an important guide for the newly launched sampling campaigns.

This work is part of two research projects: GeoConnect³d-GeoERA that has received funding by the European Union’s Horizon 2020 research and innovation programme under grant agreement number 731166, and ROSEAU project, as part of the Walloon program «Doctorat en Entreprise», co-funded by the SPW Région Wallonne of Belgium and the company Bru-Chevron S.A. (Spadel group), under grant number 7984.

How to cite: Welkenhuysen, K., Defourny, A., Collignon, A., Jobé, P., Dassargues, A., Piessens, K., and Barros, R.: Naturally CO2-rich water springs in Belgium evidencing complex subsurface interactions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8011, https://doi.org/10.5194/egusphere-egu2020-8011, 2020.

The current study was focused on the characterization of recharge, weathering processes and to check the aptness of groundwater for household and agriculture utility in the Central Gangetic Plain, Uttar Pradesh, India. Arsenic contamination in groundwater recognized as a vital catastrophic problem that affect millions of people across the world and have geogenic as well as anthropogenic sources. In central gangetic, plain, high geogenic arsenic in groundwater is extensively present in Holocene alluvial aquifers. The severity of this problem is further accelerated through in-situ physio-chemical factors in the fluvial environment. In our studied areas, newer alluvium has organic rich clay, which plays an important role in arsenic mobilization by reductive dissolution of Fe-oxyhydroxide. The aim of this paper is to compare and contrast the long-term similarities and differences in arsenic hot spot regions in central gangetic plain with those of other parts of the world and assess the unique socio-cultural factors that determine the human health risks of exposure to arsenic in local groundwater. It documents how the pathways of exposure to this poison have been greatly expanded through intensive application of groundwater in agriculture in the region within the Green Revolution framework.

How to cite: Yadav, S. K. and Ramanathan, A.: Health Risk Assessments of Arsenic and Toxic Heavy Metals Exposure in Drinking Water in Central Gangetic Plain, Uttar Pradesh, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20121, https://doi.org/10.5194/egusphere-egu2020-20121, 2020.

Groundwater is the main source of water supply for the population in the semi-arid zones in Mexico. In this climatic condition, evapotranspiration originated from phreatophytes and evaporation is an important component of the water budget for shallow aquifers. Arsenic and uranium are trace elements generally found naturally in groundwater, as they can originate from the interaction of groundwater with igneous rocks and sediments. Despite their generally different redox properties and transport behavior in groundwater, they show a relationship (a potential common geogenic source).

This research addresses the effect of groundwater evapotranspiration on arsenic and uranium concentrations in different flow systems in Villa de Reyes and Cerritos basins in the Mexican Altiplano. The former is mainly characterized by volcanic rocks and the latter is located in an area dominated by limestone yet connected to felsic, partially mineralized rocks by a complex karst system. According to the Mexican legislation, the permissible limit for arsenic in water for human use and consumption is 25 µg/L; however, it does not consider a permissible limit for uranium. German legislation as well as the World Health Organization (WHO) established 10 µg/L.

The concentrations of arsenic and uranium found in the rocks in the two sites were in the range of 1.8-65 and 0.7-19 mg/kg respectively, in which it is observed that some sites exceed the local background values. The high arsenic and uranium concentrations have been found in felsic intrusive bodies and rhyolites in both sites. This confirmed an earlier study identifying rhyolitic lava flows and rhyolitic glass within the Villa de Reyes Basin as main arsenic and uranium geogenic sources.

The arsenic and uranium concentrations in groundwater at the Villa de Reyes basin showed that 100% of the groundwater samples were within the Mexican Legislation for arsenic but in the case of uranium, 6% of the samples were above the German and WHO regulations. The shallow granular aquifer in the Cerritos Basin, the groundwater values gave different results. Only 74% of the sites were within the Mexican regulation for arsenic and 36% above the critical value. For uranium, 90% of the sites were within the German and WHO regulations.

In addition, isotopic data (environmental stable isotopes from the water molecule ²H and ¹⁸O) showed that shallow groundwater in the Cerritos Basin was fractioned by evapotranspiration processes. These led to the observed high concentrations of especially arsenic as was also supported by geochemical modelling.

Especially as the climatic trend predicted higher temperatures for central to north Mexico, enrichment of arsenic and other potentially toxic elements by evapotranspiration will be encouraged. Increasing population requires a good quality water supply, understanding the behavior of arsenic and uranium in these areas may be useful for similar regions not only in Mexico but also in similar areas around the world.

How to cite: Cauich Kau, D. A., Cardona Benavides, A., Castro Larragoitia, J., and Rüde, T. R.: Understanding co-occurrence and mobility of uranium and arsenic sources in groundwater flow systems in semi-arid zones in the Mexican Altiplano, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-461, https://doi.org/10.5194/egusphere-egu2020-461, 2020.

Positive Matrix Factorization (PMF) is a multivariate analysis aimed at source identification and apportionment, specifically designed to cope with environmental data and manage their uncertainty and distributions. The aim of this work is to test the effectiveness of PMF as a tool to perform data mining and define hydrochemical features of groundwater and surface water and to understand their relationship. Here PMF is applied to a dataset concerning groundwater, springs, rivers and a lake. Factor contributions to the samples are spatially analysed trough GIS approach and their interpretation is supported by considering the land use and hydrogeological features.

The study area is a part of the Oglio River basin (N Italy) and consists in a ~2000 km² area around the Oglio River part that outflows from Lake Iseo until the confluence with Mella River. The available dataset is the result of four field surveys conducted in February 2016, June 2016, September 2016 and March 2017, for a total amount of 270 samples collected on 68 monitoring points.

The first factor represents water with a high content of oxygen, with SO4 and a small content of major ions. In this factor neither nitrate nor trace elements are represented. The profile of this factor overlaps with the characteristics of lake Iseo and surface water bodies directly connected with it. Its spatial variability highlights a contribution of this factor, also in several wells even if they are not close to the river itself. This was related to the channels net collecting water from the Oglio River and spreading it to the nearby fields.

The second factor explains the whole chemical variability of As, Fe, P-tot and NH₄. Furthermore, it has a significant contribution of Mn and it can be associated to the advanced stages of reducing conditions due to degradation of natural organic matter.

The third factor is characterized mainly by Mn and SO₄, with a contribution of the major ions. Based on the profile and on the spatial distribution, it is possible to associate this factor to the early stages of the reducing process.

The fourth factor represents only major ions. Major ion concentration in groundwater is mainly determined by water – rock interactions, which increase the concentrations especially with increasing residence times. This factor shows an increasing trend from north to south, which is the flow direction, confirming its relationship with residence time.

The fifth factor represents the total variability of the variable NO₃ with contributions also in terms of Cl, SO₄, Ca and Mg. Higher NO₃ concentrations in groundwater are mostly related with the use of organic or synthetic fertilizers; recent studies reported that this kind of anthropogenic impact affects also major ions concentrations such as Cl, SO₄, Ca and Mg. Thus, the profile of this fifth factor was associated to the anthropogenic impact related to the agricultural land use, not just in terms of NO₃ but also considering the contribution of different elements.

How to cite: Zanotti, C., Rotiroti, M., Fumagalli, L., Stefania, G., Canonaco, F., Stefenelli, G., Prévôt, A., Leoni, B., and Bonomi, T.: Positive Matrix Factorization and GIS approach to perform data mining on groundwater and surface water quality dataset., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1429, https://doi.org/10.5194/egusphere-egu2020-1429, 2020.

Groundwater flow understanding is a must in any study related to sustainable water management and in preventing or controlling negative environmental responses due to changes in the groundwater regime. Indeed, further developing of methods, terminology, concepts, teaching and research may benefit from considering relevant collective scientific knowledge base. Disregarding psychological and social constraints, several perceptions have been found to prevent reaching to desirable groundwater flow understanding to backup adequate decision making, among them the following three may be stated. Firstly, not all hydrological methodology provides with adequate reference to arrive at the desired groundwater flow understanding. There is a groundwater evaluation method that is usually applied in developed countries based on long periods of daily hydrological data to achieve a reliable water-balance which, however, fails to provide with related processes as groundwater quality changes, soil subsidence, ecosystem functioning, transboundary flow conditions, among others. Disregarding the lack of obtaining reliable and adequate data in time and space in developing countries, the water-balance is the recommended methodology to be applied to seek an understanding of the relation of groundwater with other components of the environment. Secondly, concepts as aquifer (water + rock) provide a further challenge to achieve a groundwater flow understanding due to the quasi-static view it provides for groundwater management. An aquifer is often strongly related to the water-balance concept where natural vertical components of flow are usually neglected. Here, inconsistent terms as overexploitation, scarcity, transmissivity, among others unnecessarily emerge. Thirdly, further education and research is under strong constrains to reach desirable teaching and research to enhance science on Water Security. Existing capacity building in groundwater in top-ranking universities (UK, Canada) has been disappearing or, is under threat, not only directly on groundwater flow systems, but as research in hydrogeology as a subject. Other universities have a latent (France, Spain) capacity building in groundwater flow systems; in many, there is an absence on the topic. It is to note that several universities (Hungary, China) are growing a sound groundwater flow systems capacity building. There are universities (Mexico) where research on groundwater flow systems is carried out by interested hydrogeologists who wait to have institutional support that might even reach government organizations. Groundwater management related government offices required to enhance the acknowledgement of the importance of groundwater remembering that more than 80% of the water supply in many countries is obtained from that source. It should be remembered that groundwater intake of the ecosystem is almost fully related to this source, which needs to be fully understood to achieve a reliable ecological yield.

How to cite: Carrillo-Rivera, J.-J., Hatch-Kuri, G., and Ouysse, S.: Some challenges for reaching a groundwater flow understanding to manage water and environmental responses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12568, https://doi.org/10.5194/egusphere-egu2020-12568, 2020.

Specific storage (S_s) values are important for analyzing the quantity of stored groundwater and for predicting drawdown to ensure sustainable pumping. This research compiled S_s values from multiple available studies based on pore pressure responses to passive stresses, for comparison and discussion with relevant poroelastic theory and groundwater applications. We find that S_s values from pore pressure responses to passive in situ stresses ranged from 1.3x10^-7 to 3.7x10^-5 m^-1 (geomean 2.0x10^-6 m-1, n=64 from 24 studies). This large S_s dataset for confined aquifers included both consolidated and unconsolidated strata by extending two recent literature reviews. The dataset included several passive methods: Individual strains from Earth tides and atmospheric loading, their combined effect, and values derived from soil moisture loading due to rainfall events. The range of S_s values spans approx. 2 orders of magnitude, far less than for hydraulic conductivity, a finding that has important implications for sustainable groundwater management. Both the range of values and maximum S_s values in this large dataset were significantly smaller than S_s values commonly applied including laboratory testing of cores, aquifer pump testing and numerical groundwater modelling. 

Results confirm that S_s is overestimated by assuming incompressible grains, particularly for consolidated rocks. It was also evident that Ss that commonly assumes uniaxial conditions underestimate S_s that accounts for areal or volumetric conditions.  Further research is required to ensure that S_s is not underestimated by assuming instantaneous pore pressure response to strains, particularly in low permeability strata. However, in low permeability strata S_s could also be overestimated if based on total porosity (or moisture content) rather than a smaller free water content, due to water adsorbed by clay minerals. Further evaluation is also required for influences on S_s from monitoring bore construction (ie. screen and casing or grouting), and S_s derived from tidal stresses (undrained or constant mass conditions) that could underestimate S_s applicable to groundwater pumping (drained or changing mass conditions). In summary, poroelastic effects that are often neglected in groundwater studies are clearly important for quantifying water flow and storage in strata with changing hydraulic stress and loading conditions. 

How to cite: Timms, W. A., Chowdhury, M. F., and Rau, G. C.: A review of specific storage values from pore pressure response to passive in situ stresses: Implications for sustainable groundwater management, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11002, https://doi.org/10.5194/egusphere-egu2020-11002, 2020.

Aquifers are heterogeneous systems with limited accessibility for their characterization. Their hydrogeological parameterization is therefore complicated, producing uncertainty in groundwater and solute transport modelling. When numerical models are used to support pump-and-treat (P&T) applications to control the migration of solute plume in heterogeneous aquifers, the uncertainty in the design of the array of boreholes forming the hydraulic barrier and in the calculation of optimal pumping rates (Q) strongly depends on the variability in aquifer properties such as the hydraulic conductivity (K) (e.g. Bayer et al. 2004).

Geological entropy (Bianchi and Pedretti 2017, 2018) is a new approach that combines multiple controls of flow and solute transport in heterogeneous media. Geological entropy relies on the assumption that flow and transport are correlated to the degree of spatial order in the heterogeneous aquifer structure, which is measured by metrics derived from the information entropy concepts. Geological entropy is particularly useful to detect and highlight structural differences in aquifers associated to the presence of extreme connected features, such as fractures (Pedretti and Bianchi, 2019) or connected high-K facies (Bianchi and Pedretti 2017, 2018).

In this work, we present the result of an application of geological entropy to support the optimization of P&T scenarios in heterogeneous aquifers. A numerical case study based on the stochastic analyses by Bayer et al (2004) was reevaluated and extended. Multiple P&T setups considering both hydraulic and physical barriers were evaluated using stochastic geostatistical modeling based on 2D Sequential Gaussian Simulations and particle tracking simulations. The goal of Bayer et al (2004) was to identify the best hydraulic and physical barriers combination minimizing Q that allow for fully controlling a plume migrating in the aquifer.

In our work, we maintained a similar setup and optimization criteria, yet different aquifer structures using Sequential Gaussian and Indicator Simulations and model dimensionality (2D vs 3D simulations) are assessed. By doing this, we tested if the behavior of aquifer structures and connectivity among K clusters plays a role in defining Q, and if geological entropy can be used as the approach to disentangle the differences among the tested scenarios.

The results suggested that optimal pumping rates are very sensitive to the aquifer structures and model dimensionality. In particular, the range of variability of optimal Q is strongly reduced for systems characterized by shorter entropic scales, which means short-scale continuity of the spatial order of K patterns. 3D systems imply more percolation, connection among K clusters, enhancing mixing and homogenizing better the system dynamic properties.

It is thus concluded that the selection of the optimal P&T configuration is strongly sensitive to the tested variables, and that geological entropy provides a potential geologically-based tool to support decision makers when defining the optimal (i.e. cost-effective) implementation of coupled P&T systems.

References:

Bayer P, Finkel M, Teutsch G. 2004. Ground Water, 42(6): 856–867. https://doi.org/10.1111/j.1745-6584.2004.t01-4-.x.

Bianchi M, Pedretti D. 2017. Water Resources Research, 53(6): 4691–4708. https://doi.org/10.1002/2016WR020195.

Bianchi M, Pedretti D. 2018. Water Resources Research, 54(7): 4432–4448. https://doi.org/10.1029/2018WR022827.

Pedretti D, Bianchi M. 2019. Acque Sotterranee - Italian Journal of Groundwater. In press. https://doi.org/10.7343/as-2019-421.

How to cite: Pedretti, D. and Bianchi, M.: Using geological entropy to support the optimization of coupled pump-and-treat systems in contaminated heterogeneous aquifers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20560, https://doi.org/10.5194/egusphere-egu2020-20560, 2020.

The Edendale terrace aquifer in Southland New Zealand has experienced a declining trend of groundwater table over the past two decades. Water abstraction has increased over this time and is associated with farming development, intensification and increased production of local industry. Coincident with an increase of groundwater abstraction is a decrease in annual precipitation. Current granted water allocation is ~55% of the allowable limit of 15% of land surface recharge. Determining the main driver of the declining groundwater table is a first step to improving the sustainability of water use in this area.

In this study, we combined a statistical method and physically based modelling method to analyse the main driving force. In the statistical method, the relationship between precipitation, groundwater abstract, and groundwater table over the past two decades have been analysed and the contributions from decreasing precipitation and increasing groundwater abstract were quantified. In the physically based method, a groundwater model (MODFLOW) was coupled with a hydrologic model (TopNet) to simulate the groundwater flow, and scenarios of groundwater abstract and precipitation were assessed using this coupled hydrologic model and groundwater model.

The modelling result above is used for sustainable water allocation management by the regional government, and this methodology can be used for groundwater management in other regions with declining groundwater table.

How to cite: Yang, J., Rajanayaka, C., and Kees, L.: What drives the decline in groundwater table? A story of Edendale in New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12050, https://doi.org/10.5194/egusphere-egu2020-12050, 2020.

In many parts of the world, groundwater extraction for agriculture is strongly increasing, causing severe stress on groundwater resources and associated ecosystems. Understanding how groundwater flow systems support extractions is therefore essential. However, particularly in developing, rural, tropical regions, monitoring of groundwater levels, chemistry and extractions is poorly regulated, resulting in a lack of data. Hence, alternative approaches are necessary to develop best management practices in these groundwater basins. In this study, catchment-scale groundwater extraction is indirectly estimated by two “soft data” approaches: (1) using local knowledge through a qualitative field survey of groundwater level fluctuations and groundwater withdrawals; and (2) land-use/population data combined with local knowledge on cropping/water use practices. Spatially distributed recharge is simulated on the basis of a monthly water balance model, which requires widely available topographic, soil, land-use and meteorological data. Extractions and recharge force a simple, basin-scale groundwater model for assessment of impact of irrigation practices. Agricultural scenarios are developed and modelling procedures are designed to test the temporal and spatial vulnerability over a 100 yr time span of the groundwater resource. The approaches are tested and applied for the agricultural La Vi River basin, Vietnam, where the livelihood of the local farmers requires development of new agricultural and hydrological techniques. The typical cash-crops are cultivated on sandy soils and irrigated in the dry season from thousands of private shallow wells. The tropical climate and strong seasonal rainfall pattern produces a strong fluctuation in groundwater levels. The modelling shows significant spatio-temporal unmet pumping demand dependent on the agricultural development scenario, indicating the need and opportunity for planning of groundwater based irrigation development. Overall, the multi-method comprehensive approach supports basin-scale sustainable groundwater resource development and only requires relatively easily accessible data.

How to cite: Batelaan, O., Partington, D., Vu, M. H., and Shanafield, M.: Assessment of groundwater resource vulnerability to over-exploitation in a tropical, agricultural basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12951, https://doi.org/10.5194/egusphere-egu2020-12951, 2020.

In the presence of a groundwater monitoring network (GMN) of sensors aimed at measuring the hydraulic head in a given domain, the statistical analysis of time series not only provides insight into the general aquifer behaviour, but it can also return parameters useful to optimize and enhance the GMN’s efficiency.

Several methods to design new GMNs are available, but few of them are useful for optimizing existing networks. This study compares two methods in order to define pros and cons of their applicability and effectiveness.

They are carried out for the case study of the alluvial basin of the Bacchiglione river, near Vicenza (Veneto, Italy). The existing network comprises 92 groundwater data-loggers, installed in wells screening mostly the unconfined aquifer.

The first simple method, here proposed, is based on the Pearson correlation coefficient and the microscale parameter, which shows the time interval in which data are perfectly correlated. The coefficients were calculated between detrended time series. Firstly, based on the correlation coefficient threshold of 0.95, areas of intercorrelated couples are defined. They are characterized by similar hydrological behaviour, therefore it is sufficient to constantly monitor only one location in each area, while other interesting correlated points can be measured manually at longer sampling time. The microscale can be used to estimate this sampling time in order to see the water table trend (between 7 and 78 days in this domain), even if shorter oscillations are obviously missed and some peaks could remain unseen. This way, extra sensors can be moved to other critical areas, in order to improve the system knowledge.

The second method defines the seasonal Mann Kendall (sMK) test for detecting monotonic trends, that are used into Principal Component Analysis (PCA). Finally, a Hierarchical Clustering Analysis is carried out to group sensors with similar factors of the PCA. This method is more articulated than the previous one and entails some informed choices to be made about the distance measure and the clustering algorithm. Thanks to the sMK test and the PCA, a high insight of the system is achieved, however the clustering result may strongly variate depending on the expert’s knowledge and expectation.

The two proposed statistical analyses of hydrogeological data provide integrative decision support to improve representativeness and effectiveness of monitoring networks aimed at both qualitative and quantitative groundwater control.

How to cite: Sottani, A., Meggiorin, M., Ribeiro, L., and Rinaldo, A.: Comparison of two methods for optimizing existing groundwater monitoring networks: application to the Bacchiglione Basin, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8759, https://doi.org/10.5194/egusphere-egu2020-8759, 2020.

Groundwater is the main water resource in arid and semi-arid areas. Its evaluation in terms of recharge, discharge, flow system and change in storage is thus vital for management purposes. However, distributed numerical models which are considered as favourable tools for assessment of groundwater resources are often limited by availability of input data especially in arid and semi-arid areas in developing countries where monitoring networks are scarce. Moreover, in case of transboundary aquifers, political, institutional, cultural, socio-economic differences among countries make management of groundwater even more complex.

Remote sensing is a handy tool for monitoring water resources in data scarce areas. This study entails application of remote sensing data in developing a distributed integrated hydrological model for Stampriet Transboundary Aquifer System using MODFLOW-NWT coupled with the Unsaturated Zone Flow (UZF1) Package.

Stampriet Transboundary Aquifer is a multi-layered aquifer system shared between Namibia, Botswana and South Africa. The aquifer system consists of three aquifers, characterized by low transmissivity and low storage, intercalated by two aquitards. Conceptually, the physical processes taking place in this system are reasonably understood in Namibia and not as much in Botswana and South Africa. However, quantification of water resources and fluxes is still limited.

The aquifer system is mainly exploited in Namibia for socio-economic growth, where abstraction from storage has led to decline in local groundwater level. Water quality constraints have restrained its usage in South Africa, while in Botswana the potential for available resources is likely to be exploited, but there is not enough data for making firm decisions.

A numerical model has been set – up in transient conditions at daily time step and calibrated with groundwater levels as the state variables and satellite rainfall and potential evapotranspiration as the model driving forces. The calibrated model provides spatio-temporal water flux dynamics as well as water balances and hence an understanding of the groundwater-resource dynamics and replenishment. The results are compared to analysis of GRACE data to further constrain the model. This information is useful for proper management of the transboundary water resource as well as for policy making.

How to cite: Kinoti, I., Leblanc, M., Olioso, A., and Lubczynski, M.: Assessment of groundwater flow system for management of Stampriet Transboundary Aquifer System , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19896, https://doi.org/10.5194/egusphere-egu2020-19896, 2020.

Coastal areas worldwide are often highly impacted due to the concurrence of aquifer exploitation for irrigation, human consumption exacerbated during touristic seasons and industrial activities. In order to meet the objectives of the GWD, European groundwater bodies’ status (chemical and quantitative) is evaluated every 6 years. Criteria for good status include chemicals exceeding standards and threshold values, saline intrusion and others. Apulian region features a very high ratio coastline/area (44 m/km², for Italy is 25 m/km²) thus seawater intrusion is a very common phenomenon, due to both natural and anthropogenic drivers.

In this contribution, the first results of the VIOLA project (Natural Background Values for the Apulian groundwater bodies) are presented, supplying a preliminary geochemical characterization of the coastal Murgia groundwater body. This is part of a fractured and karstified calcareous-dolomitic aquifer with groundwater naturally flowing to the Adriatic sea. Exceedances were reported for nitrates, as well as for EC, Cl, SO₄, Fe, Mn. The main objective for this groundwater body is to assess the natural background levels for the aforementioned parameters, and discriminate between the natural and anthropogenic origin of saline intrusion. Four sampling campaigns have been planned, and we present here the result of the first two sampling rounds carried out in spring and fall 2019.

Groundwater sampling was performed at 47 wells with submergible pumps or with a water depth sampler. Field parameters (T, EC, pH, DO, ORP) were measured with a multiparametric probe in a flow through cell. Ammonia, cyanides and nitrites were measured in the field (UV-VIS). Laboratory analysis were performed for major anions, major cations, minor and trace elements, environmental isotopes, DOC and microbial parameters.

Natural background values (NBLs) for the critical parameters have been provisionally assessed using the preselection method. Sampled waters show neutral/weakly alkaline and mostly oxidizing conditions, with conductivity values between about 700 and 20.000 µS/cm. The high salinity detected in some water points (chlorides up to 10 g/L, sulphates up to 1 g/L) is clearly linked to mixing with seawater. On a Piper diagram, the samples show a clear transition from earth alkaline-bicarbonate water towards mean seawater composition. A clear trend from coastline to inland can be recognized, with the most extended contamination in the northern and southern sectors. Trace elements (B, Sr, Ba), show a similar pattern. From spring (beginning of the irrigation season) to fall (end of the irrigation season) only a slight increase in salinity/chloride concentration can be observed. Nitrates are widespread in the study area, as well as the agricultural pressures, with values even higher than 100 mg/L without a specific spatial pattern.

As for the NBLs derivation, classic indicators of anthropogenic contamination (e.g. nitrates, ammonia, NaCl) for the pre-selection of uninfluenced samples failed, due to the extensive distribution of saline groundwaters in the study area. Thus, new solutions, including environmental isotope analysis, for discriminating the anthropogenic and natural origin of the salinity are under evaluation.

How to cite: Parrone, D., Frollini, E., Amalfitano, S., Ghergo, S., Masciale, R., Melita, M., Passarella, G., Vurro, M., Zoppini, A., and Preziosi, E.: The VIOLA project: geochemical characterization and natural background levels in a coastal groundwater body of the Apulia Region (southern Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7561, https://doi.org/10.5194/egusphere-egu2020-7561, 2020.

The vulnerability to salinization is a major issue for coastal aquifers. The resulting rapid modifications of hydro-geochemical characteristics, driven by the different origin of water inputs, can modify the properties of the resident biological communities. The study of structural and functional properties of groundwater microbial community, posed at the base of the heterotrophic food web, assumes an increasing importance to describe the effect of water quality on C-cycling and the resilience of groundwater systems to changes.

Within the framework of the VIOLA project, this study was entailed to explore the groundwater quality and the functional responses of the microbial community across the gradient of salinity in a coastal karst aquifer located in Apulia Region (Southern Italy). The investigated area (1227 km²) is located in a semi-arid climate region with predominantly agricultural vocation. In this area, an excess of withdrawals for irrigation and other uses, often results in a significant decline of the water table, facilitating saline intrusion.

The main physical-chemical parameters of 47 groundwater sampling sites (T, pH, oxidation-reduction potential, electrical conductivity, major anions/cations, trace elements, dissolved oxygen, ammonia, nitrites, cyanides and dissolved organic carbon) were measured, along with microbial community analyses including the total cell abundance, the High Nucleic Acid and Low Nucleic Acid content cell ratio (Flow Cytometry), the total coliform and Escherichia Coli contamination (Colilert-18 assay), the microbial metabolic potential (Biolog EcoPlates), and the microbial respiration (Biolog MT2 MicroPlates). The preliminary results allowed identifying two major groups of waters with different salinity levels and concentrations of Cl, Na, Mg and SO₄. Prokaryotic cell abundance (mean 3.5 x 10⁴ ± 4.6 x 10⁴ cells/ml) showed higher values in saline waters, so as HNA cell percentages and total coliforms. Saline waters were also characterised by relatively higher metabolic potential and respiration values. In conclusion, the observed groundwater quality changes induced the stimulation of the functional microbial properties and the functional diversity. These changes in the metabolic potential of the resident communities could alter the ability to exploit the available resources and modify the related groundwater biogeochemical cycling.

How to cite: Melita, M., Amalfitano, S., Eleonora, F., Stefano, G., Rita, M., Daniele, P., Giuseppe, P., Elisabetta, P., Michele, V., and Annamaria, Z.: The VIOLA Project: Functional responses of groundwater microbial community across the salinity gradient in a coastal karst aquifer , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7630, https://doi.org/10.5194/egusphere-egu2020-7630, 2020.

The European Water Directives (WDs, 2000/60/EC; 2006/118/EC) force Member States to proceed to the characterization of groundwater bodies in order to define their quantitative and chemical status and their environmental objectives. Since the earlier years of this century, the Department of Water Resources Management of the Apulia Region implemented the WDs by setting a wide groundwater monitoring network, delineating regional groundwater bodies and characterizing their status. The groundwater bodies characterization showed that the risk of not achieving a good status was generally related to salt contamination and the exceedance of the threshold values or the quality standards for some parameters (e.g., NO₃, Fe, Mn), as expected for regions with a predominantly agricultural vocation and characterized by extensive coastal development. The main regional aquifers reside in the carbonate bedrock characterized by intense fracturing and karstification.

The groundwater Directive 2006/118/EC allows the evaluation of Natural Background Levels (NBLs) to be taken into account when establishing the relevant threshold values.

During the last years, the IRSA-CNR collaborated with the National Environmental Protection Agency (ISPRA) in defining scientifically based guidelines for the NBLs assessment and clarifying some methodological aspects. These guidelines suggest excluding water samples characterised by high levels of specific markers clearly indicating anthropogenic inputs.

The project "VIOLA - Natural background levels for the groundwater bodies of Apulia Region ", has been funded by the Department of Water Resources Management of the Apulia Region for carrying out the application and validation of the above mentioned methodologies and to develop and test methodologies better tailored for coastal aquifers. In particular, isotopic techniques will be used to discriminate between the anthropogenic and natural origin of the salinization and historical data of groundwater salinization will be processed in order to study its evolution in time. . Finally, the investigation of innovative microbiological techniques is envisaged to evaluate how changes in groundwater quality will affect the resident microbial community properties involved in C-flux.

The VIOLA project will last three years during which the IRSA-CNR will:

• collect and order all the background knowledge relating to the hydro-geo-chemical characteristics of the Apulian groundwater bodies,
• define adequate groundwater sampling procedures and assessment protocols for the NBLs,
• carry out field activities, aimed at sampling groundwater at a specific monitoring network and measuring values of main physico-chemical and microbiological parameters, in the study area of the coastal Murgia groundwater body, and
• produce tools to support the planning and management of groundwater resources integrated in a GIS environment.

This contribution aims at providing an overview at the ongoing activities at the regional scale, illustrating the groundwater bodies setting, the main pressures and the preliminary derivation of NBL using the historical data.

How to cite: Masciale, R., Amalfitano, S., Frollini, E., Ghergo, S., Melita, M., Parrone, D., Preziosi, E., Vurro, M., Zoppini, A., and Passarella, G.: The VIOLA Project: Natural background levels for the groundwater bodies of Apulia Region (Southern Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7716, https://doi.org/10.5194/egusphere-egu2020-7716, 2020.

Increased variability in precipitation and more extreme weather events caused by climate change can lead to more extended periods of droughts and floods, which directly affects the availability of groundwater. The consequent fluctuation of the water table can also affect groundwater quality. Particularly, a higher recharge, and the resultant increase of the piezometric level, can have, as a positive result, the dilution of the contaminants in aquifers and a decrease of the concentrations. On the other side, water that infiltrates can leach pollutants that are present in the unsaturated zone, with an increase of groundwater pollution. Even, the rise of the piezometric level can have negative consequences on groundwater quality, also due to groundwater that leach the capillary fringe and the previously unsaturated zone; if a contaminant is present in these sectors, it can lead to an increase of the aquifer pollution.

The increase or decrease in contaminants levels depend on a complex balance between all the described phenomena, and contaminant behaviour. This study wants to analyse the hydrogeochemical variations in time due to climate variability to define the role of different processes.

Two different hydrogeological environments were chosen as test fields: an alluvial aquifer in the Piedmont Po Plain (NW Italy) and an alluvial-pyroclastic aquifer in the Campanian plain (S Italy).

Piedmont Po plain shows a diffuse nitrate contamination, due to intensive agricultural and livestock activities. A nickel contamination is locally present, due to natural causes, namely the presence of basic and ultrabasic rocks debris in the supply basins, containing high amount of nickel-bearing femic minerals. Consequently, nitrate and nickel fluctuation were analysed and compared with precipitation and piezometric levels.

The hydrogeochemistry of the Campanian plain is influenced by the closeness of volcanic active areas (Phlegrean Fields and Vesuvius), bringing high As and F values, and by the presence of reducing conditions, bringing high Fe and Mn values. Moreover, there is a widespread nitrate contamination, prevalently due to intensive agricultural and livestock activities. The fluctuations of these 5 ions (As, F, Fe, Mn and NO₃) have been observed during almost twenty years and compared with the differences in recharge, sometimes significant due to the climate change.

The monitoring and analyses of the chemical concentrations of ions of anthropogenic and natural origin in a context of climate variability represent a key element to offer a new and different research perspective in the field of groundwater chemistry.

How to cite: Lasagna, M., Ducci, D., Sellerino, M., Mancini, S., and De Luca, D.: Chemical variations in time in a context of climate variability: examples in different hydrogeological settings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8230, https://doi.org/10.5194/egusphere-egu2020-8230, 2020.

Almonte-Marismas is a coastal aquifer situated in Doñana Natural Park (Southwestern of Spain, Huelva). It supports one of the most important wetland areas in Europe due to its biodiversity, size and strategic location. Nowadays, the aquifer suffers serious threats due to the large amount of water extraction that takes place in the area due to the high demand for water that exists for the supply of tourism and irrigation.

There is a flow model of the regional aquifer which is used to support the water management Administration. However, this model does not take into account groundwater interactions with local ponds. Santa Olalla pond is a hypogenic wetland that, on a regional scale, it receives the discharge of the Almonte-Marismas aquifer. This fact allows it to maintain a permanent water regime without suffering a reduction in its volume of water. Despite of that, the intense pumping in the zone could affect it and be a risk in the future.

The objective of this study is the identification of an appropriate model structure to characterize and implement the Santa Olalla Pond in the current steady-state model of the regional aquifer of Doñana employing ModelMuse interface. For this purpose, different boundary conditions (LAKE and DRAIN packages) were contrasted to represent the pond, combined with different local grid refinement (LGR2 package). The contrast criteria to assess the goodness of the numerical representation have been the piezometric heads in the wells situated in the surroundings of the pond and the stage levels and water balance of the pond.

How to cite: Serrano-Hidalgo, C., Heredia Díaz, J., Guardiola-Albert, C., and Elorza Tenreiro, F. J.: Evaluation of pond/aquifer flow exchanges using local discretization and contrasting different boundary condition in MODFLOW. Case of Santa Olalla pond (SW Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8748, https://doi.org/10.5194/egusphere-egu2020-8748, 2020.

Salt flats (salars) are endorheic hydrogeological systems associated with arid to hyperarid climates. The brines of salt flats account the 80 % of the world’s reserves of Li highly demanded by modern industry. About 40 % of the worldwide Li is extracted from the brine that fills the pores and cavities of the Salar de Atacama. However, the origin of the extreme Li-enrichment of these brines is still unknown.

The thick accumulation of salts and brines in salt flats results from the groundwater discharge (phreatic evaporation) near the land surface for thousands to millions of years. The strong evaporation contributes the enrichment in major cations and anions as well as other rare elements (e.g. Li, B, Ba, Sr, Br, I and F) which are very attractive for mining exploitation. However, only evaporation cannot explain by itself the extreme concentrations of some of these elements and the strong decoupling between the most evaporated brines and the most Li-enriched brines in the Salar de Atacama. Several hypotheses have been proposed to explain the extreme Li-enrichment of the salt flat brines: (a) concentrated brines leaking down from salt flats located in the Andean Plateau, (b) leaching of hypothetical ancient salt flats buried among volcanic rocks, and (c) rising of hydrothermal brines from deep reservoirs through faults. However, none of them has been able probed neither validated by a numerical model till the date.

The objective of this work is to discuss the feasibility of the different hypotheses proposed until now to explain the formation of the world's largest lithium reserve. To achieve this objective, two sets of numerical simulations of a 2D vertical cross-section of the entire Salar de Atacama basin are carried out to define (1) the origin and evolution of a salt flat and how climate cycles can affect the location of the most Li-concentrated brines by evaporation and (2) the establishment of the hydro-thermo-haline circulation of a mature salt flat basin.

How to cite: Marazuela, M. A., Ayora, C., Vázquez Suñé, E., Olivella Pastallé, S., and García Gil, A.: A hydro-thermo-haline numerical approach of the groundwater flow to explain the extreme Li-enrichment in the Salar de Atacama (NE Chile), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9524, https://doi.org/10.5194/egusphere-egu2020-9524, 2020.

In the Radovna River valley (NW Slovenia) in fluvioglacial sediments with high permeability and high yield, drainage capture supplies drinking water to over 20,000 inhabitants and extensive tourist facilities in one of the most important Slovenian tourist centers of Bled in the Gorenjska region. Drainage is dug at a depth of 10.0 m to 5.5 m and is 235 m long. It runs parallel to the river at a distance of 30 to 60 m. The total drainage flow ranges from 0.40 to 0.60 m³/s.

The Radovna River valley is a deep glacial valley with karstic plateaus on both sides of the valley. On the plateaus, sinkholes and smaller karst poljes are developed. The thickness of the fluvioglacial sediment in the valley exceeds 140 m. The position of the recharge area is such that it includes water infiltrating through the fluvioglacial sediment from the river and water infiltrating from the karst aquifer through the fluvioglacial sediment. The ratio of drainage water originating from the karst area and the river changes throughout the hydrological season. The proportion of water from the karstic plateau is higher in the high-water condition, and in the low-water conditions, water from the river bed is almost entirely dominant.

The paper presents a numerical model of groundwater flow toward the drainage, modeling both the inflow from the river area and the inflow from the karstic aquifer. The modeling is performed using the MODFLOW numerical model in the FREEWAT modeling environment.

How to cite: Brencic, M., Loboda, J., Germovšek, A., Greiner, C., Jelovčan, M., Krušec, U., Pajnkiher, A., Peulić, K., Rustja, D., and Vidmar, I.: Modeling of mixed karstic and alluvial recharge area for the drainage capture in Radovna River valley, Julian Alps (NW Slovenia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13457, https://doi.org/10.5194/egusphere-egu2020-13457, 2020.

Onset of thermal and haline convection was studied separately by Lapwood (1948) and Wooding (1956) in theoretical models using analytical methods. They established that the buoyancy force caused by difference in temperature (ΔT) or concentration (Δc) can induce natural convection depending on the model properties (e.g. geometry, permeability, etc.). In the course of further numerical simulations, the thermal (Ra_T) and the haline Rayleigh number (Ra_H) proved itself useful to characterise the type, the intensity and the form of the natural convection (e.g. Diersch and Kolditz, 2002). The main purpose of our study was to examine numerically the combined effect of temperature- and salinity-driven natural convection in a two-dimensional homogeneous porous medium.

Two-dimensional finite element base model was set up in agreement with the Elder problem (Wooding, 1956) in order to verify the numerical calculation. First, it was established that (1) the critical Rayleigh numbers are mathematically equivalent in the two separated cases (Ra_Tcr=Ra_Hcr=4π²), and (2) time-dependent thermal or haline natural convections evolve, when the Rayleigh number lies within the range of 300–600. Numerical simulations were accomplished to investigate the interaction of the temperature- and salinity-driven natural convection. Non-dimensional thermal expansion and haline concentration were increased from αΔT=0.01 to 1 and from βΔc=10^-5 to 10^-3, respectively, while the variation of the Darcy flux, the temperature, the concentration, the Nusselt and the Sherwood numbers was computed. The main points of this study were that (1) how the onset of the thermohaline convection is facilitated by the positive interaction of the thermal and haline effects (Ra_THcr); (2) under what conditions time-dependent flow evolves in the theoretical models; (3) whether a new non-dimensional number can be defined instead of the two separated Rayleigh numbers in order to characterise the behaviour of the thermonaline convection. These simulations draw attention to the importance of understanding the physical background of thermohaline convection, for instance, at the margin of confined and unconfined carbonate systems (e.g. Buda Thermal Karst), or in the case of groundwater flow induced by water pumping/injection of deep geothermal power plants.

The project was supported by the ÚNKP-19-3 and ÚNKP-19-4 New National Excellence Program of the Ministry for Innovation and Technology, the Hungarian Research Fund (K 129279) and the János Bolyai Scholarship of the Hungarian Academy of Science. This research is a part of a project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 810980.

References:

Diersch, H.-J.G., Kolditz, O. (2002), Variable-density flow and transport in porous media: approaches and challenges. Advances in Water Resources, 25, 899-944.

Lapwood, E.R. (1948), Convection of a fluid in a porous medium. Mathematical Proceedings of the Cambridge Philosophical Society, 44, 508-521.

Wooding, R.A. (1956), Steady state free thermal convection of liquid in a saturated permeable medium. Journal of Fluid Mechanics, 2, 273-285.

How to cite: Szijártó, M. and Galsa, A.: Interaction of temperature- and salinity-driven natural convection in homogeneous porous media, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9896, https://doi.org/10.5194/egusphere-egu2020-9896, 2020.

In Hungary the drinking water supply is mainly based on groundwater from aquifers characterized by different lithology. Riverbank filtered systems represent 40 % of drinking water supply. According to the EURATOM drinking water directive, there are recent regulations in Hungary regarding the natural radioactivity of drinking waters. Based on this, if gross alpha or gross beta radiation exceeds the limit, nuclide-specific measurements are required to be performed by the relevant waterworks. Since the mobility of uranium and radium is strongly influenced by the geochemical conditions, knowledge on the geochemical parameters of water is required. Therefore hydrogeology has a crucial role in revealing the origin of elevated activity concentrations. This research presents a case study in Hungary where the drinking water supply is provided by bank filtered and karst wells. The main aim of this study is to determine which radionuclides may cause the elevated radioactivity and explain their occurrence using hydrogeological approach, considering also the temporal variation of groundwater/surface water ratio. In most of the wells of the research area the gross alpha values are above the screening level, 0.1 Bq L^-1. The study revealed the correlation between the river water level fluctuation and the uranium content of the wells. Among the investigated radionuclides, the uranium activity concentrations responded the most to the water level changes of the river and showed systematically higher values during low water conditions. In addition the karst wells showed low activity concentrations. This suggests, that uranium is transported by the groundwater component, and possibly sourced from the fluviatile sediments. The results of this study highlighted the transient nature of river bank filtered systems, which should be taken into account in the monitoring and water supply strategy. Nevertheless, the study emphasizes the importance of considering the dynamics of groundwater and associated geochemical environment in addition to geological factors, when investigating the radioactivity of groundwater or other potential contaminants.

This study was supported by the ÚNKP-19-3 New National Excellence Program of the Ministry of Human Capacities. This study is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980.

How to cite: Csondor, K., Baják, P., Izsák, B., Vargha, M., Surbeck, H., Horváth, Á., and Erőss, A.: Transient nature of riverbank filtered drinking water supply systems - a new challenge of natural radioactivity assessment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14554, https://doi.org/10.5194/egusphere-egu2020-14554, 2020.

The Lower Triassic Buntsandstein is an economically important clastic underground reservoir and aquifer unit in the Central European Basin (e.g. for hydrocarbon reservoirs, gas storage, geothermal energy use, drinking water supply). Its quality mainly controls its prospectivity, storage capacity and exploitability. Thus, predictions for the realization of economic intentions depend most notably on a substantial understanding of the parameters that control reservoir quality, such as facies and diagenetic alterations resulting from fluid-rock interaction. Therefore, research of even small-scale relationships between hydraulic heterogeneities and rock properties is necessary.

The study area is the Thuringian Syncline, which is a small sub-basin of the North German Basin located at its southern margin. One of its major aquifers is built from siliciclastic sediments of the Buntsandstein, which are characterized by rapid changes of depositional environments from channel to sandflat to lacustrine depositions resulting in large heterogeneities at a relatively small scale (few to some hundred meters). Furthermore, burial history and subsequent basin inversion and uplift led to only minor depths of 700 to 1000 m in the center of the syncline and an exposure at the surface at syncline margins, which allows for the exploration of the recent impact of meteoric water infiltration vs. former burial evolution on aquifer quality. We combined a petrographic study focusing on mineral composition and diagenesis with a study of depositional facies and linked the results with petrophysical data like permeability and porosity. The corresponding dataset consists of measurements on more than 300 plug samples from 12 wells and additionally more than 400 thin sections.

All in all, the Buntsandstein exhibits a very complex relationship of hydraulic parameters with diagenetic evolution in relation to depositional preconditions. For example, high amounts of channel deposits in the sandstones result in better aquifer qualities. The same holds true for increasing grain sizes. Finally, there is a major influence of telodiagenetic processes and meteoric water infiltrations. Thus, major pathways for fluid flow are not solely controlled by sedimentary facies, but also by present-day cement dissolution and mineral alteration, especially in the vadose zone.

How to cite: Kunkel, C., Aehnelt, M., Pudlo, D., Gaupp, R., and Totsche, K. U.: Relationship of hydraulic parameters with diagenetic evolution and depositional preconditions (Buntsandstein, Central Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17911, https://doi.org/10.5194/egusphere-egu2020-17911, 2020.

Groundwater is depleting across the globe. According to NASA, 33% of the world’s major basins are overexploited. This water shortage could be alleviated by using Managed aquifer recharge (MAR)  techniques. MAR is defined by Gale, 2005 as “Intentional storage and treatment of water in aquifers”. The three most common methods of MAR are a) direct infiltration into the aquifer through wells, b) interception in the river bed, c) indirect infiltration from the land surface (Dillon et al., 2009a). Baluchistan, the largest province of Pakistan by area (44 % of the total area of Pakistan) has hyper-arid to dry climate and is comprised of 18 river basins, 11 of which are suffering from groundwater depletion (2-3 m cumulative decline in watertable) . To solve the issue, 300 delay action dams were constructed but due to high-intensity rainfalls, steep slopes, and lack of vegetative cover, the sediment erosion rate was very high which converted the delay action dams into evaporation ponds and this scheme failed. After the failure of delay action dams, the leaky dam technique along with effective watershed management was applied, this enhanced the percolation and reduced the sedimentation in the reservoir (Asharaf and Sheikh 2017). Leaky dams reduce the energy of flood, initiate the sedimentation of suspended load and release the water downstream through leakage to infiltrate in the riverbed (Gale, 2005). The integrated approach of watershed management, leaky dams, ditches, and furrows positively affected the watertable in the area (Asharaf and Sheikh, 2017). The goals of this research are to revise the development of MAR in Baluchistan (Pakistan), to display a MAR suitability map using INOWAS platform and update of MAR sites in Baluchistan at Global MAR portal. To delineate potential MAR sites, thematic layers such as slope, rainfall, drainage, land cover, and soil characteristics are integrated using GIS multi-criteria decision analysis (based on weighted linear combination method) (Senanayake et al, 2016).  MAR suitability maps are used as a preliminary step to field investigation to decide whether an area is suitable for a particular MAR type and hold the potential to be integrated into sustainable groundwater management plans . This study helps design a suitable groundwater management plan for Baluchistan.

Acknowledgement:

"This work is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980."

References

•  Dillon, P., I. Gale, S. Contreras, P. Pavelic, R. Evans & J. Ward. (2009a), Managing aquifer recharge and discharge to sustain irrigation livelihoods under water scarcity and climate change. IAHS Publication 330, pp.1-12
•  Gale, I. (2005). Strategies for Managed Aquifer Recharge (MAR) in semi-arid areas.UNESCO
•  M.Ashraf and Ashfaq A. Sheikh (2017). Sustainable Groundwater Management in Balochistan. Pakistan Council of Research in Water Resources (PCRWR), pp. 34.
•  Senanayake, I.P., Dissanayake, D.M.D.O.K., Mayadunna, B.B., Weerasekera, W.L.,( 2016). An approach to delineate groundwater recharge potential sites in Ambalantota, Sri Lanka using GIS techniques. Geoscience Frontiers, Special Issue: Progress of Machine Learning in Geosciences 7, 115–124.

How to cite: Hayat, S., Ben Mahrez, H., Szabó, Z., Tóth, Á., and Mádl-Szőnyi, J.: Managed Aquifer Recharge (MAR) in Baluchistan, Pakistan, Present Situation and Future Prospects, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18588, https://doi.org/10.5194/egusphere-egu2020-18588, 2020.

The Transdanubian Range is located in the mid-western part of Hungary and contains Mesozoic, mainly Triassic formations with the total thickness of 1.5-2 km. From 1950 to 1990 coal and bauxite mining took place with different centres in this area, therefor large amount of karst water was extracted for preventative purpose. Thus, the water levels decreased from ten to more than a hundred of meters. Since the mining was stopped in the beginning of the 1990s, the natural recharge exceeded the amount of extraction and the recovery of the karst water began. Since then the system is on the way to return to its original – undisturbed – state. Because of the rising water level, economic and technical engineering problems have occurred, which requires the better understanding of the process.

Water level changes are often predicted with a deterministic approach using different modelling software (e.g. MODFLOW, FEFLOW, etc.). However, stochastic approaches (e.g. trend estimation), which have so far been little used in forecast of groundwater, can also be applied for certain hydrogeological problems. The aims of the research were (i) to find the most accurate trend function describing the recovery process (ii) in order to make a long-term prediction, (iii) and compare the results with the results deterministic modelling. For this purpose, decades of time series from 107 monitoring wells were investigated.

As a result of the research, it was identified that the karst water time series from the Transdanubian Range can be properly estimated (R² > 0.9 in the 82.24% of the cases) by growth and logistic curves, especially by the so-called Richards and “63%” ones. These curves gave the best fit in 57.95% of the cases based on the R² value obtained by fitting the 10 examined models. Both the deterministic approach modelling (MODFLOW) and the stochastic approach trend analysis are suitable for estimating and predicting the water level rise in the karst aquifer, but the results are slightly different. Modelling with the MODFLOW software can be affected by the accuracy of input parameters (infiltration, yield of springs, etc.) and the realness of the conceptual model. First and foremost, more and better-quality water level data series are needed for trend analysis, and based on our prior knowledge, it is essential to provide an accurate expected maximum water level (upper limit). The comparison of the two methods unveiled, that growth and logistic curves can also be successfully used in the prediction of groundwater levels. As a conclusion, the number of methods which may be used for such research can be expanded.

This research is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980.

How to cite: Modrovits, K., Csepregi, A., and Kovács, J.: Long-term prediction of karst water recovery process based on two different approaches in a former mining area, Transdanubian Range, Hungary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18969, https://doi.org/10.5194/egusphere-egu2020-18969, 2020.

The Danube-Tisza Interfluve is one of the largest areas covered by wind-blown sand in Hungary. Two major morphologic region types are the flat-bottomed valleys of the Danube and Tisza rivers and a central elevated ridge region, characterized by sand plains, dunes and deflationary depressions. The area is poor in surface waters, mainly artificial channels can be found. Previously many lakes were present, but most of them dried out due to water abstraction, climate change, forestation and canalization related water level reduction. Water management problems in the broader area have been known for decades, many plans have been made to address water scarcity, but none have materialized (Kovács et al. 2017). These plans usually tried to solve water shortage with large scale engineering solutions, e.g. to pump water up from the Danube River Valley through surface channels to the ridge region (Nagy et al. 2016). This is very expensive, influences the ecological pattern, moreover water can easily infiltrate from the channels and would not reach the higher regions in the required amount (Silva Cisneros, 2019).
The aim of the research was to examine the suitability of Managed Aquifer Recharge methods, then a local scale field research was carried out in order to find local scale solutions. Finally the results were checked by numerical simulation to contribute to the solution of water shortage of this ecologically important area.
Firstly, a MAR surface infiltration suitability map was constructed, that shows areas with favorable hydraulic conductivity at the upper 10 m and low water levels, which means that there is a reservoir in the unsaturated zone to store infiltrated water. Based on suitability mapping, a local research area was selected which showed promising potential. Geophysical measurements (ERT – Electrical Resistivity Tomography, RMT – Radio-magnetotellurics) were performed, shallow wells were surveyed, and additional wells were drilled by hand driller. The results obtained during the field sampling contributed to the preliminary characterization of the area from a geological and hydrogeological point of view. In order to understand the effects of artificial channels and the possible water recharge methods a saturated-unsaturated flow model and different scenario models were built up in 2D.
This local scale case study was a first step towards the further aim of this research, which is to understand the effects of man-made changes on groundwater flow systems in the broader area and suggest appropriate local scale MAR solutions accordingly.

This research is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 810980.

Kovács, A. D., Hoyk, E., Farkas, J. Z. (2017). Homokhátság–A semi-arid region facing with complex problems in the Carpathian Basin. European Countryside, 9(1), 29-50.
Nagy, I., Tombácz, E., László, T., Magyar, E., Mészáros, Sz., Puskás, E., Scheer, M. (2016). Vízvisszatartási mintaprojektek a Homokhátságon: „Nyugati és Keleti” mintaterületek. Hidrológiai Közlöny, 96(4), 42-60.
Silva Cisneros, C. (2019). Identification of suitable zones of Managed Aquifer Recharge (MAR) in Western area of Duna-Tisza Interfluve using Geographic Information System (GIS). MSc thesis. Eötvös Loránd University, 62.

How to cite: Szabó, Z., Szijártó, M., Masetti, M., Pedretti, D., Visnovitz, F., and Mádl-Szőnyi, J.: Managed Aquifer Recharge suitability mapping combined with field examination and numerical simulation in the Danube-Tisza Interfluve, Hungary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19857, https://doi.org/10.5194/egusphere-egu2020-19857, 2020.

It is well known that various kinds of factors are causing the fluctuation of the groundwater level. The influence of earth tide on groundwater is first observed in confined-aquifer, while in unconfined-aquifer, understanding the influence of earth tide on the micro-fluctuation of the water level is crucial for obtaining key geo-hydrological parameters of the aquifer. In this study, the groundwater level of a monitoring well in Kualiangzi Village, Zhongjiang County, Deyang, as well as the data of local earth tides and rainfall were collected. And then the identification of the earth tide’s influences and its main influencing-components on groundwater level were studied by means of spectral analysis, cross-correlation analysis and harmonic analysis. The results show that the local groundwater levels are featured periodic changes of 1-day, 1/2 day and 1/3 day, which are corresponded to the earth tide. Moreover, the amplitude of the groundwater levels are negatively correlated with the earth tide, and there is no obvious hysteresis between them. The main influencing-components of earth tide are K1 diurnal wave and S2 semidiurnal wave.

How to cite: Guo, J., Xu, M., Shi, H., and Ge, J.: Identification of the Earth Tide’s Influences and its Main Influencing-Components on Groundwater Level in an Unconfined-Aquifer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21033, https://doi.org/10.5194/egusphere-egu2020-21033, 2020.

In recent years, deep aquifers (> 50 m below ground level) have become increasingly interesting for the supply of drinking and irrigation water or geothermal use. Understanding the regional flow processes between near-surface and deep aquifer systems is an important criterion for the sustainable management of deep groundwater resources. However, hydrogeological conditions, regional flow rates and aquifer recharge in deep aquifers are largely unknown in many cases. The aims of the present study are therefore to determine (i) groundwater flow velocities in a Cenozoic multi-aquifer system, and (ii) proportion of aquifer recharge into the individual Cenozoic aquifers and timescales to completely replace water in the Cenozoic aquifers (turnover time).  

The numerical study was carried out in three adjacent groundwater catchment areas in the region of Eastern Brandenburg. In a first step, a hydrogeological 3D model of the entire Cenozoic aquifer system (85 km × 73 km and down to a depth of 0.5 km) was developed, which comprises up to 12 unconsolidated sandy aquifers and 10 confining units (glacial tills, silts and clays). In a second step, a steady-state flow modelling was performed including calibration using natural hydraulic head data from both regional main and deep aquifers.

The modeling results show that the average groundwater flow velocities decrease from 20-50 m/a in the near-surface Pleistocene main aquifers to 1-2 m/a in the deep Oligocene aquifers. At the same time, the aquifer recharge in the aquifer system decreases substantially with increasing depth. Depending on the catchment geology, the Pleistocene main aquifers are recharged by 65-70 % of infiltration water, while the aquifer recharge of the deep Oligocene aquifers is only 4.5-9.5 %. The calculations of turnover time indicate that the time periods to completely flush the deep aquifers are very long (approx. between 90 and 4600 years). The results thus allow a first quantification of the flow processes between near-surface and deep aquifers as well as the identification of flow paths to develop a utilization concept for deep groundwater resources in the region of Eastern Brandenburg.

How to cite: Janetz, S., Jahnke, C., Wendland, F., and Voigt, H.-J.: Modeling of groundwater flow velocity and aquifer recharge in a Cenozoic multi-aquifer system – a case study from Eastern Brandenburg (Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21667, https://doi.org/10.5194/egusphere-egu2020-21667, 2020.

Mechanical discontinuities control groundwater flow in fractured aquifers. Bedding plane and sub-vertical discontinuities create fracture networks geometrically organized both horizontally and vertically in areas un-affected by compressional tectonic forces. In this structural setting, we use the Columbia River Basalt aquifer in the Palouse to show how the combination of previous acquired stable isotope data and geological, groundwater, and particle tracking modeling better describes groundwater flow in three dimensions. We present a steady-state flow model simulating backward particle traces from abstraction wells to the recharge boundaries. Backwards particle analysis coupled with the ¹⁴C isotope vertical concentration distribution shows how the aquifer system is characterized by two separate zones. A shallow (<120 mBGL) zone of freshwater circulation is characterized by higher ¹⁴C concentrations and low particle travel times with respect to the deeper (>120 mBGL) aquifer zone. Here, penetration of particles is partially impeded by the low vertical hydraulic conductivity of the volcano-sedimentary layers and recharge preferentially occurs in correspondence of discontinuities related to a geological unconformity. Hence, the outputs of a particle tracking analysis fits stable isotope data either validating a 3D groundwater flow model or aiding detail to conceptualization of a fractured aquifer.

The Columbia River Basalt aquifer is also horizontally anisotropic due to sub-vertical tectonic fractures which are related to gentle folding and faulting. This horizontal anisotropy significantly influences particle tracking analysis in the basin up to 120 mBGL. Well-head protection areas are defined globally by backward particle tracking analyses at shallow depths. Thus, as a consequence of this research we envisage introduction of horizontal anisotropies in groundwater flow models for definition of well capture zones.

How to cite: Medici, G.: A basin-scale groundwater flow model in the Columbia Plateau (Pacific Northwest, USA); insights for management of fractured aquifer-types, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3996, https://doi.org/10.5194/egusphere-egu2020-3996, 2020.

Lake Karla aquifer, with extent of 500 km², is located at the eastern part of the most cultivated region of Greece, Thessaly, where water demanding crops prevail. The last three decades is under a status of quantitative and qualitative degradation because of the long-term intense agricultural activities, the lack of any significant surface water body and of an organized irrigation network. About 80% of the pumped groundwater is used for irrigation. According to Lake Karla recreation project fifty wells have been established at the southern part of the aquifer in order to cover the drinking water needs for the nearby city of Volos. This area is characterized by the greatest depletion of aquifer’s water table and by high values of nitrate concentrations in groundwater resources.  The area is one of the seven vulnerable zones of Greece, with respect to nitrogen pollution from agricultural run-off, according to the requirements of the Nitrates Directive (91/676/EEC).

The study proposes a pump and treat optimization method for nitrates removal from the supply wells area with the use of a simulation-optimization modelling system through two scenarios regarding nitrate fertilization of crops during the remediation period:

The classification of crop types at the study area of aquifer is implemented with the use of a Geographical Information System (GIS). Nitrate leaching to aquifer is achieved through water infiltration from surface to subsurface system and has been estimated to 40% of nitrogen fertilizer application. The simulation-optimization modelling system applied, consists of a groundwater simulation model (MODFLOW), a groundwater transport and a dispersion simulation model (MT3DMS) and a management model (GWM). The optimization problem targets to the minimization of the operation cost of pump and treat wells, subject to plume stabilization through reversing the hydraulic heads slope and to keeping the values of nitrate concentration in the supply wells area lower than the threshold of 25 mg/L introduced by Nitrates Directive. Pump and treat wells are proposed to be located at the boundary of the urban supply wells area, where the plume crosses it.  The historical period is from 1995 to 2007, while the remediation period starts on 2007.

The results indicate that, for the first scenario, the pump and treat wells must operate through the whole remediation period (2007-2017) since great volumes of nitrate pollutants continuously leach to aquifer concluding to high operation costs equal to 372.47 thousands of euros. On the contrary, for the second scenario, the remediation period is decreased to four years resulting to an operational cost lower than the half of the additional of the first scenario equal to 147.09 thousands of euros. These results highlight the importance of the full compliance with Nitrates Directive requirements by the farmers of rural basins, where the groundwater resources are used for potable use; otherwise any remediation design will be costly.

How to cite: Sidiropoulos, P., Mylopoulos, N., Loukas, A., and Vasiliades, L.: Pump and treat optimization schemes for nitrate removal from a rural basin aquifer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3081, https://doi.org/10.5194/egusphere-egu2020-3081, 2020.

Hot springs in the stable Indian shield are non-volcanic in origin. Atri and Tarbalo are two such hot springs in the Eastern Ghats Province (EGP), Eastern India and these are characterized as part of a low enthalpy geothermal system. Stable isotopic, geochemical and geothermometric studies were carried out on these two hot springs as well as on the groundwater of this region to understand the origin and evolution of these non-volcanic hot springs as well as subsurface water system in terms of the source of the dissolved solute in the water, mixing processes and the residence time of the thermal and non-thermal waters. Surface temperature of the slightly alkaline hot spring waters ranges from 45 to 58 °C. Temperature of the cold groundwater, collected from tube and dug well varies between 28 and 32 °C. A distinct hydro-chemical difference can be interpreted from the major ion concentrations of hot waters and non-thermal waters. Hot spring waters have higher concentrations of sodium, potassium and lower calcium, magnesium than cold water. While the hot springs waters are enriched in Cl^- and F^- and cold waters are rich in bicarbonate. The low bicarbonate concentration of thermal waters may indicate that the hot spring reservoirs have no atmospheric effect. Definite geochemical differences between these two types of water suggested that there is no mixing between hot spring water and cold groundwater. Thermodynamic calculations suggest that mineral dissolution is the predominant evolutionary mechanism for the thermal and non-thermal waters and these waters hold a partially equilibrated state with the surrounding rocks. Bivariate plots of the major ions also indicate that silicate weathering is the dominant mechanism controlling solutes concentrations in the cold water whereas evaporite dissolution more likely involves in the evolution of hot spring water. The measured stable isotope ratios (δ²H and δ¹⁸O) of all the hot and most of the cold-water samples plot along the Global Meteoric Water Line (GMWL), indicating their meteoric origin where as some cold waters show evaporation effect which suggests atmospheric influence. Tritium and ¹⁴C ages indicate that the cold waters are relatively modern, while the hot waters have a longer residence time of about 5000 years. Based on the chemical characteristics of the hot waters Na-K thermometer, Na-K-Ca thermometer and silica (quartz) thermometer were used to estimate the reservoir temperatures. Cation and silica geothermometers yield similar estimation of the reservoir temperature between 125 -150 °C for hot spring waters. Results of geochemical (numerical) modelling of water-rock interaction in this region, using PHREEQC, are consistent with hydrochemical analysis. Inverse modelling and saturation indices of minerals indicate that water chemistry in this region is controlled by the dissolution of feldspar and saturated with kaolinite, gibbsite and fluorite. This equilibrium is attained in the thermal waters, which therefore show a more restricted range of composition than the non-thermal, colder waters. The higher fluoride concentration in the thermal water may also be attributed of chemical equilibrium with the enclosing host rock.

How to cite: Maitra, A., Gupta, S., Panigrahi, M. K., and Keesari, T.: Characterization of low enthalpy non-volcanic geothermal systems at Atri and Tarbalo, Eastern Ghats Province, India: An integrated isotope-geochemistry-geothermometry studies and geochemical modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7600, https://doi.org/10.5194/egusphere-egu2020-7600, 2020.

A null‐space Monte‐Carlo (NSMC) approach was applied to assess uncertainty in the calibration of the hydraulic conductivity (K) field for a three‐dimensional groundwater flow model of a major water supply system in Switzerland. Different parameter realizations of the K field are generated by applying the pilot point methodology. Backward particle tracking (PT) was then applied to each calibrated model, and the resulting particles are interpreted as the spatial pathline density distribution of multiple sources. The adopted approach offers advantages over classical PT which does not provide a means for treating uncertainty originating from the incomplete description of the K field. Besides evaluating the effect of uncertainty in the K field on pathline distribution, the importance of the chosen boundary conditions for flow predictions is also investigated by applying a linear uncertainty approach.

Uncertainty in the K field is shown to strongly influence the spatial pathline distribution. Pathline spreading is particularly evident in locations where the information content of the head observations does not sufficiently constrain the estimated parameters. As demonstrated with the linear uncertainty analysis, however, the artificial recharge rates and the pumping well conditions can also significantly affect the model predictions. Explicitly accounting for uncertainty in the boundary conditions is therefore a necessity rather than a choice.

Despite the predictive uncertainty, the pumped drinking water at the study site is most likely dominated by artificially‐infiltrated groundwater originating from the local artificial infiltration canals and ponds. The results suggest that within the well field, the central pumping wells could be extracting regional groundwater, although the probability is relatively low. Nevertheless, a rigorous uncertainty assessment is still required since only a few realizations resulted in flow paths that support the field observations from tracer tests and on-site noble gas measurements to estimate groundwater mixing ratios.

We demonstrate that standard PT approaches without a Monte-Carlo approach will not represent the underlying subsurface uncertainty and will always underestimate well capture zones. While PT based on a single flow simulation can be used as an initial screening tool, model results and hence water resource management decisions should not be based on only one model realization; rather, an uncertainty analysis should be carried out to provide simulations within the range of all likely system states, including uncertainties in the hydraulic K distribution.

How to cite: Moeck, C., Molson, J., and Schirmer, M.: Pathline Density Distributions in a Null‐Space Monte Carlo Approach to estimate Groundwater Pathways for a Major Water Supply System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11265, https://doi.org/10.5194/egusphere-egu2020-11265, 2020.

During the evolutionary stages of sedimentary basins, different processes are active. Secondary migration means the movement from the source area to the trap and it has most likely the tendency to move along with water. Thus, the secondary migration of petroleum is directly affected by the different driving forces which also influence the ambient groundwater (Tóth 1988). In other words, understanding the regional groundwater flow systems and driving forces may support petroleum exploration. In this theoretical framework, a hydrogeological evaluation of the broader environment of Ebes-Hajdúszoboszló area(Eastern Hungary, Pannonian basin) was executed on the interpretation of the coexistence of thermal water and hydrocarbon accumulations in the specific area.

The study is based on the application of two different methods. At first a basin-scale hydrogeological evaluation of the recent fluid flow condition including archive hydraulic, chemical, borehole temperature data interpretation, and regional pressure field evaluation was carried out. These data confirmed the superposition of an over-pressured flow regime driven by tectonic compression and compaction and the upwelling of fluids in the gravity driven-flow system in the upper part (Zentai-Czauner et al., 2018).

The data analysis could provide initial understanding and conceptual framework for 2D numerical evaluation of superposition of the topography differences and overpressure as driving forces It was carried out using the Heat Flow Smoker software version 7.0 developed by (Molson, 2014) which can simulate density-dependent flow and advective-dispersive transport of thermal energy, mass or residence time in three-dimensional porous or fractured media.

The interpretation of the 2D simulation of the cross-section was compared with the results of the data analysis and it can show the relationship between the hydrocarbon accumulations and the existence of thermal water is due to groundwater flow.

The regional data analysis and subsequent 2D simulation could confirm the favorable conditions for hydraulic trapping of hydrocarbons and the heat accumulation in groundwater due to advective heat transport.

This work is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 810980.

Keywords:

Groundwater-flow, thermal water, hydraulic trapping, hydrocarbons, migration, accumulation.

References:

• Szabó Zs., Zentai-Czauner B., Mádl-Szőnyi J., 2018 Hydrogeological evaluation of the broader environment of Ebes concession area for the understanding of recent fluid flow conditions, final report of Vermillion Energy Hungary.
• Toth J., 1988, Groundwater and hydrocarbon migration, in back, W., Rosenshein, J. S., and Seaber, P. R., eds., Hydrogeology: Boulder, Colorado, Geological Society of America, The geology of North America, v. O-2, chap. 48, pp. 485-502.
• John W. Molson, 2019. Heat Flow Smoker, Version 7.0, density-dependent flow and advective-dispersive transport of thermal energy, mass or residence time in three-dimensional porous or fractured porous media, université Laval, University of Waterloo.

How to cite: Ben Mahrez, H., Szabó, Z., Havril, T., Czauner-Zentai, B., and Mádl-Szőnyi, J.: Combination of Basin Scale Data Analysis and Numerical Simulations for the Interpretation of the Coexistence of Thermal Water and Hydrocarbon Accumulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16173, https://doi.org/10.5194/egusphere-egu2020-16173, 2020.

The presented study estimates salt dissolution caused by groundwater around a salt diapir in the Transylvanian Basin, which is facing land-collapse hazards related to historic salt mining activities. Because the amount of salt dissolution is controlled by the concentration gradients and fluxes near vulnerable areas of the salt dome, specific attention has been given to hydrogeological boundary conditions. They include the hydraulic role of possible more permeable fault zones along the salt dome, and the potential access to the salt diapir of over-pressurized subsaturated groundwater within regional scale sandstone layers. A structural three-dimensional (3D) model of the salt diapir, the adjacent basin sediments, and the mining galleries was developed based on existing maps, borehole data, own field observations, and geological publications of the Transylvanian Basin. The salt dissolution potential was simulated with 2D vertical thermohaline flow and transport model scenarios along the southeastern flank of the diapir. Results showed that the following factors increase the salt dissolution capacity along the upper 180 m of the diapir: (1) the presence of more permeable Quaternary alluvial sediments in connection with a fault zone of higher permeability along the diapir, and (2) the presence of more permeable sandstone units within the Miocene sediments in the east of the diapir, which provide freshwater access to the upper parts of the diapir. Thermohaline simulation with viscosity variation of the fluid, instead of a constant viscosity, influences the resulting salt fluxes by up to 50% within studied temperature ranges of 10 to 60°C in the model domain. The range of theoretical dissolution rates along the upper 180 m of the diapir supports the hypothesis that cavern collapse is more likely to occur where cavern side walls have already been mined to almost no remaining side walls of rock salt, which is the case in the southeastern part of the diapir. A past land collapse from 2010, which formed a 70-90 m wide saline lake, has occurred in this area southeast of the diapir appearing to be the more vulnerable to land collapse.

Zechner, E., Dresmann, H., Mocuţa, M., Danchiv, A., Huggenberger, P., Scheidler, S., Wiesmeier, S., Popa, I., Zlibut, A. (2019): Salt dissolution potential estimated from two-dimensional vertical thermohaline flow and transport modeling along a Transylvanian salt diapir, Romania, Hydrogeol. J., 27, 1245-1256, https://doi.org/10.1007/s10040-018-1912-1.

How to cite: Zechner, E., Dresmann, H., Mocuţa, M., Danchiv, A., Huggenberger, P., Scheidler, S., Wiesmeier, S., Popa, I., and Zlibut, A.: Relating thermohaline simulation of salt dissolution to land collapse at a Transylvanian salt diapir, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19529, https://doi.org/10.5194/egusphere-egu2020-19529, 2020.