Search

Riverbank filtration (RBF) consists in forcing surface water to infiltrate and flow through an aquifer by means of a pumping well located near a surface water body. RBF aims to take advantage of the filtration capacity of aquifers to improve the water quality by removing a wide range of pollutants, including contaminants of emerging concern, by combining of physical, chemical and biological processes. However, the efficacy of RBF for eliminating substances that are considered persistent, mobile, and toxic (PMT), or very persistent and very mobile (vPvM), is expected to be low due to the high mobility of these substances. PMT and vPvM compounds, which are accumulated in the water cycle, are harmful to humans and the environment. For this reason, the processes affecting PMT and vPvM substances during RBF processes deserve to be deeply investigated.This study aims at investigating the processes affecting PMT and vPvM substances in a site that behaves similarly to a RBF system. The study site is located in Sant Adriá del Besòs (Barcelona, Spain), where a constant pumping to drain an underground parking lot forces the water from the Besòs river to infiltrate and travel up to 230 m through the aquifer. Groundwater samples were collected from the river, and a set of piezometers aligned along the groundwater flow line between the Besòs river, and the underground parking lot allowed monitoring of the water at different stages after its infiltration. The samples were analysed by liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) and PMT and vPvM were determined by a suspected screening approach.This investigation provides new insights into the processes affecting PMT and vPvM substances and will have tremendous implications for determining groundwater quality in managed aquifer recharge contexts.

Water shortage is expected to exacerbate because of the increase pressure on water resources due to climate change and the growing population. It is deemed necessary to take advantage of all the available freshwater resources to cover the growing demand, especially in urban areas. However, urban aquifers are commonly contaminated by a wide range of organic contaminants of emerging concern (OCECs). OCECs, which comprise natural and synthetic compounds, are potentially hazardous to the environment and human health. Therefore, the processes controlling the behaviour of OCECs must be investigated to determine when and how the urban resources can be used safely and to design remediation strategies against them. The removal rate of OCECs depends on the temperature and redox conditions of groundwater that may be affected by anthropogenic activities like the exploitation of the geothermal potential of aquifers. The behaviour of some OCECs has been investigated in the context of managed aquifer recharge (MAR). However, the water range in MAR is lower than that expected around geothermal exploitations, and the behaviour of OCECs under similar conditions to that found around geothermal facilities should be evaluated. We have investigated the removal of 12 OCECs reported in the aquifers of Barcelona (Spain) by using batch experiments under different redox conditions and temperatures (25°C and 35°C). The results show that the removal rate of OCECs depends on the temperature, suggesting that the impact of geothermal exploitations must be considered when investigating the fate and evolution of OCECs in urban aquifers. Unexpectedly, it was observed that the removal rate could also decrease with the temperature, which may be related to the proliferation of different communities of bacteria depending on the temperature. Overall, this investigation supports the idea that it is possible to design geothermal facilities to promote the removal of OCECs.

Phosphogypsum is a waste that results when fertilizer is obtained from phosphate through a wet chemical process. Phosphogypsum waste can entail negative consequences for the environment and human health since it is enriched in radionuclides from U-decay series and metal impurities. Phosphogypsum wastes are commonly accumulated in large stockpiles that are exposed to weathering processes. These stockpiles are located near the plants where phosphate is processed, which are usually located in coastal areas. This is the case of a phosphogypsum stack on the western side of the Tinto River estuary (Huelva, SW Spain), where the piles were directly settled on the marshland without using any isolation from 1968 to 2010. Here, in addition to the potential environmental impacts, the effect of the phosphogypsum wastes on human health are a source of concern since the piles are located near the city of Huelva (Spain). In this context, it is of paramount importance to assess the phosphogypsum leachate percolation into underlaid aquifer systems and the release of pollutants to the Tinto River.This investigation aims at building a complex coupled hydro-chemical numerical model accounting with variable density to quantify how the pollutants are released to the environment. The first step has consisted in developing the flow numerical model that has been calibrated by fitting the piezometric head oscillations as a result of recharge processes and sea tide oscillations. The good fitting obtained during the calibration process (normalized RMS when comparing simulated and observed piezometric heads is less than the 10%) allows affirming that the estimated hydraulic parameters are accurate, and are consistent with the literature reviewed. Furthermore, the numerically calculated mass balance is consistent with the conceptually estimated one, the differences were as expected. Thus, the model allows simulating the flow processes and modelling predictive scenarios. The next steps will consist in implementing variable density and hydro-chemical, and possibly, hydromechanical processes.This study, which uses numerical modelling, is intended to be useful for future work related to restoration measures and provides new insights into the water balance along with the complex processes occurring at the site.

Most underground constructions, which are needed to improve mobility and increase available space in urban areas, require excavations that are usually deeper than the water table (e.g., for the construction of stations or underground parking lots). A frequently used technique to develop excavations under these conditions consists in combining the cut-and-cover method with a dewatering system based on deep pumping wells. Retaining walls used for the cut-and-cover method allow excavating between vertical walls and minimizes the inflow of groundwater, while deep pumping wells provide dry and stable conditions. Despite this technique is widely used, some aspects related with the presence of groundwater must be considered to avoid accidents. Dewatering systems must be properly designed to guarantee suitable conditions and to minimize the pumping settlements outside of the working area. In addition, it is required to assess the presence of defects in the retaining walls because the flow of groundwater through them may entail negative consequences. This chapter explains procedures (i) to design efficient dewatering systems considering the working conditions, the stability and the impacts generated in the vicinity of the construction, and (ii) to evaluate the state of the retaining walls by using hydrogeological tools.

Groundwater is the main source of freshwater in the European Union, yet freshwaters are polluted by organic contaminants if contaminants are not efficiently removed in wastewater treatment plants. Here we review the occurrence, fate, and risk assessment of organic contaminants included in the surface water watch list of the European groundwater bodies. This list includes 15 compounds: the hormones estrone, 17˗β˗estradiol and 17˗α˗ethinylestradiol; the pesticides methiocarb, metaflumizone, imidacloprid, thiacloprid, thiamethoxam, clothianidin and acetamiprid; and the antibiotics amoxicillin, ciprofloxacin, azithromycin, clarithromycin and erythromycin. We found that while contaminants commonly occur at low levels of few nanograms per L or are not detected in natural waters, there is an increasing number of reports displaying concentrations above 100 ng/L. Surface waters are commonly more contaminated than groundwater, suggesting that contaminants are removed in groundwater aquifers, e.g. by sorption or biodegradation. The estimated risk following water drinking by humans is higher for infants than for adults. Nonetheless, on the average, groundwater consumption does not pose a risk for human health at the reported groundwater concentrations. Risk assessment using fish, plants, algae, and invertebrates shows that only few species are impacted by contaminants, e.g. Americamysis bahia, Mysidopsis bahia, and Daphnia magna by pesticides; and the plant Lemna minor and the algae Microcystis aeruginosa by the antibiotics ciprofloxacin and erythromycin., This research has been supported through the Grant CEX2018-000794-S funded by MCIN/AEI/https://doi.org/10.13039/501100011033. Anna Jurado thanks the Ministry of Science, Innovation and Universities for funding the project INTEGRATE (Ref: PID2019-107945RJ-I00) under the 2019 call of the "Proyectos de I+D Retos Investigación”. Estanislao Pujades gratefully acknowledges the support received through the grant RYC2020-029225-I funded by MCIN/AEI/https://doi.org/10.13039/501100011033 and by “ESF Investing in your future”, and the Award for Scientific Research into Urban Challenges in the City of Barcelona 2020 (20S08708) from the Barcelona city council. M. Silvia Díaz˗Cruz acknowledges the Generalitat de Catalunya (Water and Soil Quality Unit 2017-SGR-1404) and the EU (LIFE20 ENV/ES/000284—LIFE REMAR project).

Estimation of groundwater travel time distribution (TTD) is critical to environmental assessment and successful urban water management. This paper presents a novel analytical approach to account for the groundwater TTD in an unconfined aquifer, considering the impervious urban structure and the modified aquifer hydraulic properties due to consolidation processes. The analytical solution follows the Dupuit-Forchheimer assumption and is verified through comparisons with numerical results. Sensitivity study reveals a potential increase in the mean travel time when the aquifer intersects with an impervious underground structure, while the degree of change depends on the interplay of two mechanisms (i.e., the increase in upgradient groundwater storage and the decrease in pore space of the consolidated zone). Global sensitivity analysis suggests that urban groundwater TTD systems are strongly dependent on both construction-related parameters and aquifer compressibility, indicating that adaptive strategies of groundwater management should be taken for different aquifer types. The proposed analytical model has great implications for the management of water resources in urban areas, the utilization of urban groundwater for human consumption, and the quality of urban aquifers., C. Lu acknowledges the financial support from the the National Key R&D Program of China (2021YFC3200500), the National Natural Science Foundation of China (51879088), and the Fundamental Research Funds for the Central Universities (B200204002). M. Jing acknowledges the financial support from the National Natural Science Foundation of China (52109012) and the China Postdoctoral Science Foundation (2021M690877).

Urban aquifers are a valuable resource of freshwater for cities, however, their quality is degraded due to the presence of organic contaminants of emerging concern (CECs). The effects of organic CECs are largely unknown, but there is evidence that they pose a risk for human health, soil, plants and animals. Organic CECs are naturally degraded in aquifers and their degradation rates depend on the physico-chemical properties, i.e., redox conditions and groundwater temperature. Some anthropogenic activities, like low-enthalpy geothermal energy (LEGE), may modify subsurface physico-chemical conditions altering the behaviour of organic CECs. LEGE is a renewable and carbon-free energy that allows obtaining cooling and heating energy. The utilization of LEGE is currently growing and it is expected that in a near future the density of LEGE systems will increase. LEGE modifies the groundwater temperature and in some situations the redox state (i.e., if the dissolved oxygen increases when groundwater is returned to the aquifer as a result of a poorly design), thus, it is of paramount importance to determine the impact of LEGE related activities on the behaviour of organic CECs. The behaviour of organic CECs under the influence of LEGE is investigated by means of thermo-hydro-chemical numerical modelling. Simulation output shows that LEGE activities have the potential to modify the degradation rates of organic CECs, and thus, their concentrations in aquifers. In the simulated scenario, the concentration of the chosen CEC decreases by the 77 % at the downgradient boundary of the model. The results of this study have significant implications for predicting the behaviour of organic CECs in urban aquifers and suggest specific changes in the design of LEGE facilities aiming to improve the quality of urban groundwater by boosting in-situ attenuation mechanisms., This research has been supported by the Barcelona city council through the Award for Scientific Research into Urban Challenges in the City of Barcelona 2020 (20S08708) and by the grants PID2021-128995OA-I00 funded by MCIN/AEI/10.13039/501100011033T and FEDER “one way to make Europe”, CEX2018-000794-S funded by MCIN/AEI/10.13039/501100011033 and RYC2020-029225-I funded by MCIN/AEI/10.13039/501100011033 and “ESF Investing in your future”.​​​​​​​ We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

A simple data-based advection-reaction (reactive transport) model applicable to both rivers and aquifers monitoring networks is proposed. It is built on (a) available monitoring data, and (b) graph-theoretical concepts, specifically making use of the Laplacian matrix to capture the network topology and the advection process. The method yields useful information regarding the dynamic spatial behavior of the variables monitored, expressed in terms of quantitative parameters like characteristic length, entropy, first-order decay constants, synchronization between sites, and the external inputs/outputs to the system. The model was tested in an unconfined shallow aquifer located in the lower Besòs River (Spain), in which 37 pharmaceutical compounds were monitored at 7 sites, alongside two campaigns (February and May 2021). Characteristic lengths were, on average, of the same order (24.5 m) as the mean distance between consecutive monitoring sites (33.6 m), thus reflecting an adequate monitoring network design. From an estimated mean advection velocity (0.24 m·h-1), first-order decay constants were calculated for each compound and campaign, with mean values of 0.025 h-1 (February) and 0.005 h-1 (May). Whereas entropy was generally slightly larger values in February than in May (mean values of 1.02 and 0.9 entropy units respectively), synchronization showed the opposite trend (mean values of 62.4% and 68.8% respectively). The input/output profiles were generally site-dependent, regardless of the compound, and campaign considered. • A new advection-reaction modeling approach directly based on experimental data obtained from monitoring campaigns together with the network topology is proposed. • The method yields new quantitative information regarding the dynamic behavior of the variables monitored, useful for both research and management purposes., This research has been supported through the grant CEX2018-000794-S funded by MCIN/AEI/ 10.13039/501100011033.

Trabajo presentado en la EGU General Assembly 2022 , celebrada en Viena (Austria), del 22 al 27 de mayo de 2022., Pressure over water resources is increasing rapidly as a result of climate change and growing population. In this context, urban aquifers emerge as a valuable resource of fresh-water for cities. However, the quality of urban groundwater is degraded due to the presence of contaminants of emerging concern (CECs) that reach continuously urban aquifers from different recharge sources. The effects of CECs are largely unknown, but it is expected that they pose a risk for human health, soil, plants and animals. CECs are naturally degraded in aquifers and their degradation rates depend on the physico-chemical conditions (i.e., redox conditions and water temperature) of the groundwater, which may vary as a result of anthropogenic activities. Therefore, it is needed to establish the impact of anthropogenic activities on CECs to determine their behaviour under modified and variable physico-chemical conditions and allow the safely use of urban groundwater. One of these anthropogenic activities that potentially modify the physico-chemical conditions is the use of the subsurface to obtain cooling and heating energy through low-enthalpy geothermal energy (LEGE) systems. LEGE is a renewable and carbon-free energy whose utilization is currently growing. Thus, it is expected that in a near future the density of LEGE systems will increase over most cities. Then, our objective is to determine the impact of LEGE systems on the behaviour of CECs. We have investigated the behaviour of CECs under the influence of LEGE by means of numerical models and considering different representative scenarios. The results show that the physico-chemical variations induced by LEGE systems modify notably the degradation rates of CECs, and thus, their concentrations on the downgradient side. Our results have significant implications for predicting the behaviour of CECs in urban aquifers and suggest the possibility of specifically design LEGE systems to improve in a passive way the quality of urban groundwater by eliminating CECs.

The expected growth of urban areas requires the construction of underground infrastructures, especially for improving transportation and mobility. These new infrastructures are commonly constructed below the water table because they must be deeper than previous underground structures. In addition, many urban areas are located near surface water bodies (i.e., seas, rivers and/or lakes) that induce a shallow water table. The “cut and cover” method combined with dewatering wells is a frequently used procedure under these conditions for the construction of underground infrastructures. The main concerns of this procedure are related to the stability of the excavation bottom, the behavior of the retaining walls and/or the impacts induced by the dewatering actions. These issues must be evaluated, and new solutions must be proposed to improve its weak points. This paper compiles the main publications focused on the construction of underground infrastructures below the water table and in urban areas by using the cut and cover method combined with pumping. This review reveals that, despite many published studies, more research is needed to address some relevant issues such as: (1) the mitigation of dewatering impacts by using artificial recharge, (2) the adaptation of methods for characterizing retaining walls to be used under heterogeneous conditions, (3) the improvement of the prediction of surface settlements produced by pumping, and (4) the consideration of non-Darcy flows in the design of dewatering systems.

Trabajo presentado en la EGU General Assembly 2022 , celebrada en Viena (Austria), del 22 al 27 de mayo de 2022., The widespread development of geothermal energy is deemed to accelerate the transition to a low-carbon future. Hot Sedimentary Aquifers (HSA) provide cost-effective and non-intermittent geothermal resources. However, HSA development has reportedly been associated with seismic events, harming the public perception of exploiting these resources. This work digs deeper into thermo-hydro-mechanical (THM) mechanisms raised by water circulation in a HSA and their control on fault reactivation. We numerically simulate the problem by a 2D plane-strain model. The model consists of a porous and permeable hot aquifer sandwiched between the tight seal and base rocks and laterally bounded by two normal faults, representative of extensional tectonic environments. The horizontal injection-production well pairs are spaced 500 m apart at the middle of the aquifer, and the faults are located on each side of the doublet at a distance of 1 km. We consider two scenarios: low-permeability faults, mimicking a compartmentalized reservoir, and high-permeability faults, across which fluid flow takes place with further ease. We show that the fault permeability governs the hydraulic response of the reservoir. While the pore pressure slightly increases around the injector and decreases around the producer for the case of high-permeability faults, the compartmentalized reservoir experiences a global pore pressure decline. The latter is supported by the fact that the injected cold water is denser than the extracted hot water and occupies less space in the pore system. As soon as the thermal breakthrough occurs, which is after 12 years in the current setting, a more uniform temperature distribution across the doublet is established and the pressure begins to increase in the vicinity of the injector. Provided the high permeability of the reservoir rock, pore pressure and poroelastic stress perturbations impose rapid but minor effects on the fault stability. On the contrary, the cooling front formed around the injector lags much behind the pore pressure front toward the fault. The reservoir cooling contracts the rock and triggers stress reductions. Thermal stresses are transmitted much ahead of the cooled region and destabilize the fault located on the injection side. The fault begins to slip after 18 and 21 years of circulation for the high- and low-permeability scenarios, respectively. The reservoir pressure decrease in the latter case, attenuating the fault slip tendency, feeds into the observed difference in reactivation timings. Although thermal stresses initiate the slip, the static stress transfer jointly contributes to rupture nucleation along the fault. Interestingly, the slip-induced shear stress release, tied to a slip weakening frictional behavior, slows down elastic energy build-up on the other fault closer to the production well and impedes its reactivation. Our findings on the prolonged but dominant role of thermal stresses on the reactivation of distant faults have direct implications for safe and long-term production from geothermal systems.

Les Stations de Transfert d'Energie par Pompage (STEP) representent plus de 97 % des stockages d'energie electrique dans le monde et totalisent environ 170 GW de puissance installee. La France et la Belgique disposent actuellement de 9 STEP d'une puissance totale de 6,3 GW mais il n'existe plus de nouveaux sites acceptables pour des STEP conventionnelles car ces dernieres necessitent le creusement de deux bassins en surface et ne peuvent etre installees que dans des zones au relief marque. Suite a la demande de stockage d'energie engendree par le developpement des energies renouvelables intermittentes, on aborde la possibilite de creer de nouvelles STEP non conventionnelles en utilisant les bassins existants dans des mines ou des carrieres abandonnees ou en voie d'abandon. Il peut s'agir de bassins en surface ou en souterrain, ces derniers donnant acces a la technologie des STEP souterraines ou semi-souterraine (STEP-3S). On decrit ici le potentiel de ces nouvelles technologies de STEP ainsi que les risques et impacts qu'elles sont susceptibles d'engendrer : interactions hydromecaniques et hydrochimiques avec les aquiferes adjacents, mouvements de terrain, emissions de gaz. Il s'agit de risques deja identifies et maitrises dans le cadre d'autres activites du sous-sol.

Underground pumped hydropower storage (UPHS) using abandoned mines is an alternative to store and produce electricity in flat regions. Excess of electricity is stored in form of potential energy by pumping mine water to a surface reservoir. When the demand of electricity increases, water is discharged into the mine (i.e., underground reservoir) through turbines producing electricity. During the complete operational process of UPHS plants, hydrochemical characteristics of water evolve continuously to be in equilibrium successively with the atmosphere (in the surface reservoir) and the surrounding porous medium (in the underground reservoir). It may lead to precipitation and/or dissolution of minerals and their associated consequences, such as pH variations. Induced hydrochemical changes may have an impact on the environment and/or the efficiency (e.g., corrosions and incrustations affect facilities) of UPHS plants. The nature of the hydrochemical changes is controlled by the specific chemical characteristics of the surrounding porous medium. However, the magnitude of the changes also depends on other variables, such as hydraulic parameters. The role of these parameters is established to define screening criteria and improve the selection procedure of abandoned mines for constructing UPHS plants. This work evaluates the role of the main hydrogeological factors for three different chemical composition of the porous medium. Results are obtained by means of numerical reactive transport modeling. Potential impacts on the environment (mainly on groundwater and surface water bodies) and on the efficiency of the UPHS plants vary considerably from a hydraulic parameter to another showing the need for a detailed characterization before choosing locations of future UPHS plants.

Impervious structures below the water table modify the natural groundwater flow in aquifers. They act as barriers, causing heads to rise upgradient and to fall downgradient. We define the barrier effect as the increase in head loss across the barrier with respect to the natural conditions prior to construction. We distinguish between regional (the minimum head loss observed at long distances) and local (the maximum head loss observed close to the structure) barrier effects. We use numerical and analytical methods to derive semi-empirical equations to quantify the two barrier effects for semi-permeable, partially penetrating (or fully penetrating but finite in length), and barriers with a by-pass in confined aquifers. The resulting equations depend on the barrier geometry and on the natural head gradient in the aquifer and they are easy to apply. We test their validity at two construction sites, obtaining excellent agreement between the computed and observed barrier effects.

Estimated and measured settlements caused by pumping rarely agree. Several reasons could explain this mismatch, including the influence of layering, the mechanical parameters used in the predictions, or the relationship between settlements and drawdown. We analyze the influence of the above issues by investigating the mechanical response of pumped elastic porous media under different conditions. A radially symmetric conceptual model is considered and several hydro-mechanical simulations are performed varying the boundary conditions, the size of the modeled domain and the presence or not of an overlying layer. The simplicity of the considered problem allows us to compare our results with existing analytical solutions, to identify the role of each variable on pumping settlements and to generalize the results. The most relevant results are as follows: (1) settlements are proportional to drawdown only outside a circle of radius equal to 0.7 times the thickness of the pumped porous medium; inside, they are virtually constant, which leads to two simple procedures for computing pumping settlements. (2) Poorly conductive layers located above (or below) a pumped porous medium (with higher hydraulic conductivity) reduce and smooth settlements. (3) Boundary constraints affect the local specific storage coefficient and the displacements occurred. (4) The specific storage coefficient evaluated by interpreting pumping tests with the Cooper and Jacob method (1946) leads to overestimation of the actual Young’s Modulus of the soil. The main conclusion is that settlements are less differential than expected near pumping wells. Still, they must always be evaluated acknowledging the nature of layering, the boundary constraints and carefully selecting the mechanical parameters of the soil.

Excavations below the water table are usually undertaken by combining the protection of retaining walls with dewatering by pumping wells. Severe difficulties may arise if the retaining walls have defects. Therefore, their state must be determined and, if needed, the defects repaired or the dewatering system redesigned. The state of underground retaining walls can be evaluated using hydrogeological methods, but these methods are well-established only for linear excavations. The objective of this work is to propose a procedure to evaluate the state of non-linear underground enclosures by analysing the groundwater response to pumping inside the enclosure. The proposed method, which is based on diagnostic plots (derivative of drawdown with respect to the logarithm of time), allows (1) determining if an underground non-linear enclosure has isolated openings or numerous defects and (2) computing its effective conductance or effective hydraulic conductivity. The methodology is tested with data collected during the excavation of a shaft required for the construction of the high speed train (HST) tunnel in Barcelona, Spain. The procedure can be applied using the wells drilled for dewatering. Although a test before the excavation is recommended to evaluate the underground retaining walls (Watertightness Assessment Test), the method can be applied using data collected at the beginning of the dewatering stage.

Underground Pumped Storage Hydropower (UPSH) is a potential alternative to manage electricity production in flat regions. UPSH plants will interact with the surrounding porous medium through exchanges of groundwater. These exchanges may impact the surrounding aquifers, but they may also influence the efficiency of the pumps and turbines because affecting the head difference between the reservoirs. Despite the relevance for an accurate efficiency assessment, the influence of the groundwater exchanges has not been previously addressed.A numerical study of a synthetic case is presented to highlight the importance of considering the groundwater exchanges with the surrounding porous medium. The general methodology is designed in order to be further applied in the decision making of future UPSH plants introducing each case specific complexity. The underground reservoir of a hypothetical UPSH plant, which consists in an open pit mine, is considered and modelled together with the surrounding porous medium. Several scenarios with different characteristics are simulated and their results are compared in terms of (1) head difference between the upper and lower reservoirs and (2) efficiency by considering the theoretical performance curves of a pump and a turbine. The results show that the efficiency is improved when the groundwater exchanges increase. Thus, the highest efficiencies will be reached when (1) the underground reservoir is located in a transmissive porous medium and (2) the walls of the open pit mine do not constrain the groundwater exchanges (they are not waterproofed). However, a compromise must be found because the characteristics that increase the efficiency also increase the environmental impacts. Meaningful and reliable results are computed in relation to the characteristics of the intermittent and expected stops of UPSH plants. The frequency of pumping and injection must be considered to properly configure the pumps and turbines of future UPSH plants. If not, pumps and turbines could operate far from their best efficiency conditions.

Underground pumped hydropower storage (UPHS) using abandoned mines is an alternative to store and produce electricity in flat regions. Excess of electricity is stored in form of potential energy by pumping mine water to a surface reservoir. When the demand of electricity increases, water is discharged into the mine (i.e., underground reservoir) through turbines producing electricity. During the complete operational process of UPHS plants, hydrochemical characteristics of water evolve continuously to be in equilibrium successively with the atmosphere (in the surface reservoir) and the surrounding porous medium (in the underground reservoir). It may lead to precipitation and/or dissolution of minerals and their associated consequences, such as pH variations. Induced hydrochemical changes may have an impact on the environment and/or the efficiency (e.g., corrosions and incrustations affect facilities) of UPHS plants. The nature of the hydrochemical changes is controlled by the specific chemical characteristics of the surrounding porous medium. However, the magnitude of the changes also depends on other variables, such as hydraulic parameters. The role of these parameters is established to define screening criteria and improve the selection procedure of abandoned mines for constructing UPHS plants.This work evaluates the role of the main hydrogeological factors for three different chemical composition of the porous medium. Results are obtained by means of numerical reactive transport modeling. Potential impacts on the environment (mainly on groundwater and surface water bodies) and on the efficiency of the UPHS plants vary considerably from a hydraulic parameter to another showing the need for a detailed characterization before choosing locations of future UPHS plants.

Underground pumped storage hydropower (UPSH) is an alternative energy storage system (ESS) for flat regions, where conventional pumped storage hydropower plants cannot be constructed due to topographical limitations. UPSH plants consist in two reservoirs, the upper one is located at the surface or possibly underground (but at shallow depth) while the lower one is underground. Although the underground reservoir can be drilled, the use of abandoned mines (deep or open pit mines) as underground reservoir is a more efficient alternative that is also beneficial for local communities after the cessation of mining activities. Given that mines are rarely waterproofed, water exchanges between UPSH plants and the underground medium are expected. Water exchanges may have negative consequences for the environment, but also for the feasibility of UPSH plants. The impacts on the environment and the plant efficiency may have hydraulic (changes of the natural piezometric head distribution, effects in the hydraulic head difference between the two reservoirs, etc.) or hydrochemical nature (dissolution and/or precipitation of minerals in the aquifer and in the reservoirs, corrosion of facilities, modification of pH, etc.). At this stage, it is required a sound understanding of all the impacts produced by the water exchanges and evaluate under which circumstances they are mitigated. This assessment will allow ascertaining criteria for the selection of the best places to construct future UPSH plants.

Pumped storage hydropower (PSH) enables the temporary storage of energy, including from intermittent renewable sources, and provides answers to the difficulties related to the mismatch between supply and demand of electrical energy over time. Implementing a PSH station requires two reservoirs at different elevations and with large volumes of water. The idea of using old, flooded open-pit quarries as a lower reservoir has recently emerged. However, quarries cannot be considered as impervious reservoirs, and they are connected to the surrounding aquifers. As a result, PSH activities may entail environmental impacts. The alternation of the pumping–discharge cycles generates rapid and periodic hydraulic head fluctuations in the quarry, which propagate into the surrounding rock media forcing the exchange of water and inducing the aeration of groundwater. This aeration can destabilize the chemical balances between groundwater and minerals in the underground rock media. In this study, two numerical groundwater models based on the chalk quarry of Obourg (Belgium) were developed considering realistic pumping–discharge scenarios. The aim of these models was to investigate the hydrodynamic and hydrochemical impact of PSH activities on water inside the quarry and in the surrounding rock media. Results showed that (1) water exchanges between the quarry and the adjacent rock media have a significant influence on the hydraulic head, (2) the frequency of the pump–discharge scenarios influence the potential environmental impacts, and (3), in the case of chalk formations, the expected impact of PSH on the water chemical composition is relatively limited around the quarry. Results highlight that those hydrogeological and hydrochemical concerns should be assessed when developing a project of a PSH installation using a quarry as a lower reservoir, considering all particularities of the proposed sites., This research was supported by the Public Service of Wallonia, Department of Energy and Sustainable Building in the framework of the SMARTWATER project. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S). E.P. was also funded by the Barcelona City Council through the Award for Scientific Research into Urban Challenges in the City of Barcelona 2020 (20S08708)

Water provision and distribution are subject to conflicts between users worldwide, with agriculture as a major driver of discords. Water sensitive ecosystems and their services are often impaired by man-made water shortage. Nevertheless, they are not sufficiently included in sustainability or risk assessments and neglected when it comes to distribution of available water resources. The herein presented contribution to the Sustainable Development Goals Clean Water and Sanitation (SDG 6) and Life on Land (SDG 15) is the Ecological Sustainability Assessment of Water distribution (ESAW-tool). The ESAW-tool introduces a watershed sustainability assessment that evaluates the sustainability of the water supply-demand ratio on basin level, where domestic water use and the water requirements of ecosystems are considered as most important water users. An ecological risk assessment estimates potential impacts of agricultural depletion of renewable water resources on (ground)water-dependent ecosystems. The ESAW-tool works in standard GIS applications and is applicable in basins worldwide with a set of broadly available input data. The ESAW-tool is tested in the Danube river basin through combination of high-resolution hydro-agroecological model data (hydrological land surface process model PROMET and groundwater model OpenGeoSys) and further freely available data (water use, biodiversity and wetlands maps). Based on the results, measures for more sustainable water management can be deduced, such as increase of rainfed agriculture near vulnerable ecosystems or change of certain crops. The tool can support decision making of authorities from local to national level as well as private enterprises who want to improve the sustainability of their supply chains.

The stormwater infiltration system (SIS) has been recognized as a feasible way to manage stormwater and restore streamflow. As a lumped representation of the flow and transport processes, the groundwater transit time distribution (TTD) is highly relevant to this restoration goal. However, the influence of the SIS on groundwater TTDs has rarely been studied. In this paper, we propose a novel analytical model for groundwater TTDs in regional urban aquifers accounting for the impact of the SIS. This analytical solution is developed for a homogeneous 2-D cross-section of an idealized unconfined aquifer following the Dupuit-Forchheimer assumption. The analytical solution is verified through the comparison with simulated TTDs using the Lagrangian particle tracking algorithm. The global sensitivity analysis reveals that the stormwater infiltration rate, the number of infiltration facilities, the size of the urban area, and the evapotranspiration are the most important factors for groundwater mean transit times (MTTs). Although groundwater discharge and MTT can be restored to the pre-urban one, groundwater TTDs will inevitably deviate from the pre-urban ones due to the alteration from diffuse recharge to infiltration-focused recharge, indicating that the urban groundwater flow regime cannot be fully restored to the pre-urban conditions. Overall, as a first-order approximation of the real-world urban groundwater system, the proposed analytical model provides decision-making support for urban water resources management and the design of the SIS., C. Lu acknowledges the financial support from the National Key R&D Program of China (2021YFC3200500), National Natural Science Foundation of China (51879088) and the Natural Science Foundation of Jiangsu Province (BK20190023). M. Jing acknowledges the financial support from the National Natural Science Foundation of China (52109012).

Underground pumped storage hydropower (UPSH) is an alternative energy storage system (ESS) for flat regions, where conventional pumped storage hydropower plants cannot be constructed due to topographical limitations. UPSH plants consist in two reservoirs, the upper one is located at the surface or possibly underground (but at shallow depth) while the lower one is underground. Although the underground reservoir can be drilled, the use of abandoned mines (deep or open pit mines) as underground reservoir is a more efficient alternative that is also beneficial for local communities after the cessation of mining activities. Given that mines are rarely waterproofed, water exchanges between UPSH plants and the underground medium are expected. Water exchanges may have negative consequences for the environment, but also for the feasibility of UPSH plants. The impacts on the environment and the plant efficiency may have hydraulic (changes of the natural piezometric head distribution, effects in the hydraulic head difference between the two reservoirs, etc.) or hydrochemical nature (dissolution and/or precipitation of minerals in the aquifer and in the reservoirs, corrosion of facilities, modification of pH, etc.). At this stage, it is required a sound understanding of all the impacts produced by the water exchanges and evaluate under which circumstances they are mitigated. This assessment will allow ascertaining criteria for the selection of the best places to construct future UPSH plants.

Underground constructions in urban environments are more and more frequent, and usually, they are undertaken below the water table. The interaction between groundwater and underground constructions is a relevant topic that has to be carefully considered because unforeseen incidents may appear during these constructions. This paper shows the methodology used to design the dewatering system of a large excavation below the water table in a high populated urban area. The excavation was required for the construction of the assembly shaft of the tunnel boring machine that was used to excavate the high speed train tunnel below Barcelona (Spain). This methodology was useful to design an efficient dewatering systems that allowed constructing the assembly shaft in safe conditions and without producing appreciable impacts around the construction site. The most important step of the proposed method was the hydrogeological characterization of the soil because this allowed building a realistic and representative numerical model. This work shows the importance of interdisciplinary approach because the dewatering system was designed combining field work, classical analytical solutions and numerical methods.

Large-scale groundwater models are needed for assessing impacts of global changes, such as the “Global Warming”, and adapt the groundwater management strategies to ensure its availability. However, the construction of these models presents numerous difficulties, among which the lack of data concerning the properties (hydraulic parameters and geometries) of the subsurface is the most problematic. Although it is possible to find data concerning the hydraulic parameters of the soil (hydraulic conductivity and porosity), there is no realistic information about the saturated aquifer thickness which contributes to the active part of the flow regime. This thickness, which can be named “effective thickness”, is of paramount importance to improve the representativeness of large-scale groundwater models.Commonly, a constant “effective thickness” is assumed for global models, which provides not a realistic boundary condition. Here, we propose a new approach based on spectral analyses of the baseflow in combination with hydraulic conductivity values to derive the spatial distribution of “effective thickness”. The calculated “effective thickness” can be used to build 2D groundwater models using a transmissivity field or to constrain the thickness in 3D models. The effectiveness of this approach is tested here by constructing Europe-wide groundwater. The representativeness of the model is improved by coupling off-line a mesoscale hydrological model (mHM), which computes near-surface water processes, and the deep groundwater simulation using the numerical model of OpenGeoSys.We demonstrate the implications of our study in conducting large-scale groundwater simulations across Europe for providing continental scale assessment of the impacts of global changes on groundwater system and discussing about the adaptation of different water management strategies affecting the regional groundwater system.

River stream is the result of several complex processes operating at basin scale. Therefore, the river catchment can be conceptualized as a series of interlinked compartments, which are characterized by their own response time to a rainfall event. Each compartment generates a flow component, such as the direct runoff, the interflow and the baseflow. The latter, typically generating from groundwater, is the slower portion of stream flow and plays a key role in studying the hydrological droughts.In many catchment or large-scale hydrologic models, the groundwater dynamics are typically described by a linear reservoir model, which depends on the state of the reservoir and the parameter, known as recession coefficient or characteristic time. The characteristic time can be considered as the time needed until an aquifer reacts to a certain perturbation. So far, the characteristic time has been estimated by analyzing the slope of the recession (discharge) curve. However, as this method assumes that the recharge is zero within the basin, it may lead to inaccurate estimate when such a hypothesis is not fulfilled in reality.The present work proposes to infer the characteristic time by using a stochastic approach based on spectral analysis. The catchment aquifer can be viewed as a filter, which modifies an input signal (e.g., rainfall or recharge) into an output signal (e.g., the baseflow or the hydraulic head). Since the transfer function, namely the ratio between the spectrum of baseflow and the spectrum of recharge, is dependent on the aquifer characteristics, it can be used to infer the aquifer parameters. In particular, the characteristic time is evaluated by fitting the spectrum and the variance of the measured baseflow with the analytical stochastic solutions for the linear reservoir. We compare six different methods for hydrograph separation, thereby highlighting a systematic uncertainty in determining the characteristic time due to the choice of filter used. To reduce the uncertainty in fitting, we will use the mesoscale Hydrological Model (mHM) (Samaniego et al., 2010; Kumar et al., 2013) to generate realistic time series for recharge. We apply the spectral analysis method to several river basins in Germany, with the goal to define a regionalization rule for characteristic time. References:Samaniego L., R. Kumar, S. Attinger (2010): Multiscale parameter regionalization of a grid-based hydrologic model at the mesoscale. Water Resour. Res., 46, W05523, doi:10.1029/2008WR007327. Kumar, R., L. Samaniego, and S. Attinger (2013): Implications of distributed hydrologic model parameterization on water fluxes at multiple scales and locations, Water Resour. Res., 49, doi:10.1029/2012WR012195

This study investigates the occurrence of greenhouse gases (GHGs) and the role of groundwater as an indirect pathway of GHG emissions into surface waters in a gaining stretch of the Triffoy River agricultural catchment (Belgium). To this end, nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) concentrations, the stable isotopes of nitrate, and major ions were monitored in river and groundwater over 8 months. Results indicated that groundwater was strongly oversaturated in N2O and CO2 with respect to atmospheric equilibrium (50.1 vs. 0.55 μg L−1 for N2O and 14,569 vs. 400 ppm for CO2), but only marginally for CH4 (0.45 vs. 0.056 μg L−1), suggesting that groundwater can be a source of these GHGs to the atmosphere. Nitrification seemed to be the main process for the accumulation of N2O in groundwater. Oxic conditions prevailing in the aquifer were not prone for the accumulation of CH4. In fact, the emissions of CH4 from the river were one to two orders of magnitude higher than the inputs from groundwater, meaning that CH4 emissions from the river were due to CH4 in-situ production in riverbed or riparian zone sediments. For CO2 and N2O, average emissions from groundwater were 1.5 × 105 kg CO2 ha−1 year−1 and 207 kg N2O ha−1 year−1, respectively. Groundwater is probably an important source of N2O and CO2 in gaining streams but when the measures are scaled at catchment scale, these fluxes are probably relatively modest. Nevertheless, their quantification would better constrain nitrogen and carbon budgets in natural systems.

Underground pumped storage hydropower (UPSH) using abandoned mines is an alternative system to manage electricity production in flat regions. Water from an underground reservoir is pumped to a surface reservoir to store electricity in the form of potential energy. Later, water is discharged through turbines into the underground reservoir to produce electricity when demand increases. During this operation, the water hydrochemistry continuously evolves. It varies in order to reach chemical equilibrium with the atmosphere (in the surface reservoir) and with the surrounding porous medium and groundwater (in the underground reservoir). The hydrochemical variations may lead to reactions in the reservoirs and in the surrounding porous medium, causing potentially negative consequences for the environment and the system efficiency, especially when pyrite is present in the surrounding porous medium. In this case, pyrite oxidation leads to a decrease in pH and the precipitation of goethite or schwertmannite in the surface reservoir. The decrease in pH is mitigated when calcite is present in the porous medium. However, other concerns may arise, such as slight increases in pH, the precipitation of ferrihydrite and calcite in the surface reservoir, and the oxidation of pyrite and dissolution of calcite in the surrounding porous medium. Understanding the pH variations and the precipitation/dissolution of minerals is of paramount importance in terms of the environmental impacts and system efficiency. For this reason, this work investigates the main hydrochemical changes and their associated consequences when abandoned deep mines are used for UPSH by means of numerical modelling. The main objective is to highlight the importance of considering hydrochemical aspects when designing future UPSH plants.

The impacts induced by the interaction between underground constructions and groundwater should be minimised by implementing corrective measures. These impacts are twofold, which means that underground constructions affect groundwater, and vice versa. Two common situations resulting from this interaction are the barrier effect (impact of an underground construction on groundwater) and groundwater pressure on the bottom slab (impact of groundwater on an underground construction). In the literature, there are examples and designs of mitigation measures to minimise both impacts. However, to the best of the authors’ knowledge, there are not any designs that combine corrective measures to minimise these simultaneously. This paper proposes an innovative groundwater by-pass design to mitigate the barrier effect and to alleviate the groundwater pressure on the bottom slab. The proposed integrated design was applied to the largest underground infrastructure in Barcelona: the Sagrera railway station. The design was tested and compared numerically with a solution initially designed (not integrated). The numerical comparison was undertaken with three different hydrogeological scenarios. The proposed integrated design mitigated the barrier effect and optimised the bottom slab. It considerably reduced costs and increased safety during the construction phase.

Urban groundwater has often been over-exploited for industrial uses. Now, this usage tends to be reduced or the resource abandoned due to pollution and/or changes in land use. The use and the subsequent disuse of groundwater has resulted in rising water tables that damage underground structures (e.g., building basements and underground car parks and tunnels), leading to the need for additional pumping in urban areas. In the case of the underground parking lot of Sant Adria del Besos (Barcelona, NE Spain), large amounts of urban groundwater are pumped to avoid seepage problems. Can this pumped groundwater be used for other purposes (e.g., drinking water and urban irrigation) instead of wasting this valuable resource? To answer this question, it was necessary to quantify the groundwater recharge and to assess the evolution of groundwater quality. The limiting factor at this study site is the groundwater quality because ammonium and some metals (iron and manganese) are present at high concentrations. Hence, further treatment would be needed to meet drinking water requirements. The pumped groundwater could also be used for supplementing river flow for ecological benefit and/or for mitigating seawater intrusion problems. Currently, only a small amount of this urban groundwater is used for cleaning public areas and watering public gardens. This situation highlighted the urgent need to manage this resource in a responsible and more efficient manner, especially in moments of high water demand such as drought periods.

Underground Pumped Storage Hydropower (UPSH) is a potential alternative to manage electricity production in flat regions. UPSH plants will interact with the surrounding porous medium through exchanges of groundwater. These exchanges may impact the surrounding aquifers, but they may also influence the efficiency of the pumps and turbines because affecting the head difference between the reservoirs. Despite the relevance for an accurate efficiency assessment, the influence of the groundwater exchanges has not been previously addressed. A numerical study of a synthetic case is presented to highlight the importance of considering the groundwater exchanges with the surrounding porous medium. The general methodology is designed in order to be further applied in the decision making of future UPSH plants introducing each case specific complexity. The underground reservoir of a hypothetical UPSH plant, which consists in an open pit mine, is considered and modelled together with the surrounding porous medium. Several scenarios with different characteristics are simulated and their results are compared in terms of (1) head difference between the upper and lower reservoirs and (2) efficiency by considering the theoretical performance curves of a pump and a turbine. The results show that the efficiency is improved when the groundwater exchanges increase. Thus, the highest efficiencies will be reached when (1) the underground reservoir is located in a transmissive porous medium and (2) the walls of the open pit mine do not constrain the groundwater exchanges (they are not waterproofed). However, a compromise must be found because the characteristics that increase the efficiency also increase the environmental impacts. Meaningful and reliable results are computed in relation to the characteristics of the intermittent and expected stops of UPSH plants. The frequency of pumping and injection must be considered to properly configure the pumps and turbines of future UPSH plants. If not, pumps and turbines could operate far from their best efficiency conditions.

Monitoring is required when dewatering underground construction sites to anticipate unexpected events and preserve nearby existing structures and/or buildings. The most accurate and widespread monitoring method to measure displacements is leveling, a point-like surveying technique that typically allows for tens of discrete in situ sub-millimeter measures per squared kilometer. Another emerging technique for mapping soil deformation is the interferometric synthetic aperture radar (InSAR) method, which is based on SAR images acquired from orbiting satellites. This remote sensing technique can provide better spatial point density than leveling, more extensive spatial coverage and lower-cost acquisitions. This paper analyses, compares and discusses leveling and advanced multi-temporal InSAR measurements when they are used to measure the soil deformation induced by the dewatering associated with underground constructions in urban areas. This comparison, which has not been considered in previous works, is of paramount importance to ascertain the most suitable technique (or combination of techniques) in these contexts. To do so, an experiment was performed in the future railway station of La Sagrera, Barcelona (Spain), in which leveling and advanced multi-temporal InSAR were used to quantify ground deformation by dewatering. The results showed that soil displacements measured by leveling and InSAR were not always consistent. In the context of soil deformation measurements produced by dewatering in urban areas, InSAR measurements appear to be more accurate for investigating soil deformation, whereas leveling was more appropriate for quantifying the real impact on the nearby buildings.

In the actual evolving energy context, characterized by an increasing part of intermittent renewable sources, the development of energy storage technologies are required, such as pumped storage hydroelectricity (PSH). While new sites for conventional PSH plants are getting scarce, it is proposed to use abandoned underground mines as lower reservoirs for Underground Pumped Storage Hydroelectricity (UPSH). However, the hydrogeological consequences produced by the cyclic solicitations (continuous pumpings and injections) have been poorly investigated. Therefore, in this work, groundwater interactions with the cyclically fill and empty cavity were numerically studied considering a simplified description of a slate mine. Two pumping/injection scenarios were considered, both for a reference slate rock case and for a sensitivity analysis of variations of aquifer hydraulic conductivity value. Groundwater impacts were assessed in terms of oscillations of piezometric heads and mean drawdown around the cavity. The value of the hydraulic conductivity clearly influences the magnitude of the aquifer response. Studying interactions with the cavity highlighted that seepage into the cavity occurs over time. The volume of seeped water varies depending on the hydraulic conductivity and it could become non-negligible in the UPSH operations. These preliminary results allow finally considering first geological feasibility aspects, which could vary conversely according to the hydraulic conductivity value and to the considered groundwater impacts.

AkvaGIS is a novel, free and open source module included in the FREEWAT plugin for QGIS that supplies a standardized and easy-to-use workflow for the storage, management, visualization and analysis of hydrochemical and hydrogeological data. The main application is devised to simplify the characterization of groundwater bodies for the purpose of building rigorous and data-based environmental conceptual models (as required in Europe by the Water Framework Directive). For data-based groundwater management, AkvaGIS can be used to prepare input files for most groundwater flow numerical models in all of the available formats in QGIS. AkvaGIS is applied in the Walloon Region (Belgium) to demonstrate its functionalities. The results support a better understanding of the hydrochemical relationship among aquifers in the region and can be used as a baseline for the development of new analyses, e.g., further delineation of nitrate vulnerable zones and management of the monitoring network to control chemical spatial and temporal evolution. AkvaGIS can be expanded and adapted for further environmental applications as the FREEWAT community grows. © 2018 The Authors, Funding text This paper is presented within the framework of the project FREEWAT , which received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement n. 642224 . R. Criollo thanks the financial support from the Catalan Industrial Doctorates Plan of the Secretariat for Universities and Research , Ministry of Economy and Knowledge of the Generalitat de Catalunya . A. Jurado and E. Pujades gratefully acknowledge the financial support from the University of Liège and the EU through the Marie Curie BeIPD-COFUND postdoctoral fellowship programme (2015–2017 and 2014–2016 fellows from FP7-MSCA-COFUND , 600405 ).

Water scarcity periods will increase in frequency and magnitude in the near future, especially in Mediterranean regions, and proper groundwater management has been recognized as a key issue to mitigate possible impacts. In this context, numerical models acquire a special relevance to quantify the availability of water resources and predict their behavior under changing climate conditions. This work shows the procedure followed to model a mountainous fractured aquifer located in the northern Apennines (Italy) using an open source code. This aquifer feeds springs with an average discharge of about 96.8 L/s. Even though they are not exploited at the moment, these springs might represent a relevant resource of freshwater for public water supply and are essential for ecosystem sustainment. The main limitation faced to model the aquifer in a realistic way is the lack of data, which hinders the calibration of the model. A nonconventional procedure was followed to obtain information on the hydraulic parameters. The hydraulic conductivity is computed from a steady-state calibration for which a limited number of groundwater head observations are available, whilst information concerning the storage coefficient is obtained analytically from the spring discharge recession curve. Finally, the model is used for predicting the system behavior under different groundwater recharge scenarios. Numerical simulations and analytical approximations reveal that the studied aquifer can provide fresh water under different groundwater recharge conditions and has the capacity to smooth the effects of short drought periods, representing an option for water management strategies in the region.

The aim of this study is to investigate the occurrence of faecal indicator and microbial pathogens (bacteria and virus) in the shallow urban aquifer of the Besòs River Delta (NE Spain). To this end, human adenovirus (HAdV) and Norovirus of genogroups I and II (NoV GI and NoV GII) as well as the faecal indicator bacteria (FIB) Escherichia coli (EC) and faecal enterococci (FE) were monitored in groundwater and in the River Besòs in December 2013 and in July 2104. None of the targeted pathogens were detected in groundwater in December 2013 but contamination of human origin was observed in approximately 50% of the points sampled in July 2014 reaching concentrations up to 99 GC/100 mL for HAdV. Generally, microbial concentrations in river water were higher than those detected in groundwater. This observation indicates that pathogens are naturally attenuated when river water infiltrates and flows through the aquifer, however HAdV were detected at a sampling point located at 380 m from the river in the absence of FIB. The presence of human viral contamination may represent a risk for the use of groundwater as a drinking water source. Further research is needed to understand the dynamics of pathogens in river–groundwater interface over long time periods and a wide range of flow conditions (wet and dry periods) since the urban groundwater of this aquifer might be a valuable drinking water resource in Barcelona especially during drought periods. The methodology followed in this research can be applied to other urban aquifers with similar purposes since the scarcity and contamination of freshwater resources are worldwide issues. © 2019 Elsevier B.V., A. J gratefully acknowledges the financial support from the Excellence Initiative of the German Federal and State Governments through the “Open Topic Postdoc Position Fellow” at the Technische Universität Dresden. The authors would like to thank the European Commission, the Spanish Foundation for Science and Technology (FECYT) and Spanish State Research Agency (AEI) for funding in the frame of the collaborative international consortium (URBANWAT) financed under the 2018 Joint call of the WaterWorks2017 ERA-NET Cofund. This ERA-NET is an integral part of the activities developed by the Water JPI. Additionally authors would also thank the Ministry of Science, Innovation and Universities, for funding the project UNBIASED (Ref: RTI2018-097346-B-I00) under the 2018 call of the “Proyectos de I+D Retos Investigación.