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[EN] Fully 3D and multidimensional geological models are key for energy, mining and water resources assessment and management, which has a great economic impact. 3D geological models provide critical information regarding geometric properties of the geological bodies of interest, such as ore deposits or reservoirs, allowing inference of volumes and availability to be exploited. However, defining a useful methodology to create a fully digital 3D geological model of volcanic islands is still very challenging due to the intrinsic complexity observed in the structure of volcanic systems. Two-dimensional geological maps, associated vertical geological cross-sectional diagrams and borehole and water-mining tunnels (galleries) logs were examined on El Hierro Island. A geological modelling procedure using the software GeoModeller obtained the first 3D geological model of El Hierro volcanic island, as a basis for volcanic formation definitions and geometric analysis. Surface, volume and center of mass estimations of the differentiated sub-units allowed a better understanding of the spatial distribution and evolution of the volcanic cycles of El Hierro Island over time. The 3D model provided geometry information correlatable with volcanic activity cycles and lava/pyroclast deposition mechanisms that ultimately defines the geometry of the volcanic units. This information provides new variables valuable for the investigation of the existing relationships between rift zones and giant lateral collapses. In addition, the obtained 3D geological model of a volcanic island will support the building of the first hydrogeological and geothermal model of El Hierro Island, allowing advancement of sustainability of isolated systems.

[EN] Freshwater in coastal and island aquifers is a valuable resource whose availability is strongly conditioned by heterogeneity. More than 80 % of the Earth's surface is of volcanic origin, but the effect of volcanic dykes on the geometry of the saline interface that separates freshwater from seawater is still underexplored. This paper analyzes the impact of volcanic dykes on the depth of the saline interface in coastal and island aquifers and, subsequently, on the availability of fresh groundwater. Hydrogeological and hydrochemical data from a gallery, perpendicularly crossing several tens of dykes, were integrated with numerical modeling on the volcanic island of El Hierro (Canary Islands, Spain). Measured hydraulic heads demonstrated that the presence of dykes increased the hydraulic gradient by more than an order of magnitude, with respect to an adjacent area not affected by dykes. Numerical assessment confirmed that the lower the hydraulic conductivity of the dykes, the greater the depth of the saline interface inland. This impact led to fresh groundwater reserves increasing inland, relative to a hypothetical case without dykes. Numerical simulations also demonstrated that dykes can prevent salinization of production wells in coastal and island aquifers, if they are correctly located. Locating production wells far enough inland in an area affected by dykes allowed a higher freshwater extraction rate than if dykes did not exist; near the coastline, the effect tended to be the opposite. These results will be key to improving the management of fresh groundwater resources in coastal volcanic aquifers, and especially on volcanic islands such as the Hawaiian Islands or the Macaronesian archipelagos.

[EN] Contaminated groundwater is a serious problem in developed countries. The abandonment of industrial waste may lead to acid drainage affecting groundwater and severely impacting the environment and urban infrastructure. We examined the hydrogeology and hydrochemistry of an urban area in Almozara (Zaragoza, Spain); built over an old industrial zone, with pyrite roasting waste deposits, there were acid drainage problems in underground car parks. Drilling and piezometer construction, and groundwater samples revealed the existence of a perched aquifer within old sulfide mill tailings, where the building basements interrupted groundwater flow, leading to a water stagnation zone that reached extreme acidity values (pH < 2). A groundwater flow reactive transport model was developed using PHAST to reproduce flow and groundwater chemistry, in order to be used as a predictive tool for guiding remediation actions. The model reproduced the measured groundwater chemistry by simulating the kinetically controlled pyrite and portlandite dissolution. The model predicts that an extreme acidity front (pH < 2), coincident with the Fe (III) pyrite oxidation mechanism taking dominance, is propagating by 30 m/year if constant flow is assumed. The incomplete dissolution of residual pyrite (up to 18 % dissolved) predicted by the model indicates that the acid drainage is limited by the flow regime rather than sulfide availability. The installation of additional water collectors between the recharge source and the stagnation zone has been proposed, together with periodic pumping of the stagnation zone. The study findings are expected to serve as a useful background for the assessment of acid drainage in urban areas, since urbanization of old industrial land is rapidly increasing worldwide.

Coastal zones are increasingly demanded spots for human settlements and economic development, which subject alluvial coastal aquifers to the threat of seawater intrusion (SWI). But they are also strategic areas for the chemical exchange between the continent and marine ecosystems, providing a source of nutrients from the submarine groundwater discharge (SGD) from the aquifer. Furthermore, in these contexts, the characteristics of the freshwater-seawater interface (FW-SWI) and its dynamics are strongly conditioned by the lithology and, among others, the typology of the discharge, density contrasts and tides. The proper management of such enclaves requires full understanding of the SWI-SGD system, which can only be achieved through a multidisciplinary and multi-scale characterization of the considered aquifer. For that purpose, we have developed an experimental field site in a coastal alluvial aquifer close to the mouth of a temporary stream in the Maresme coast line (Barcelona, Spain). The aquifer is formed by unconsolidated heterogeneous and polygenic alluvial sediments ranging from very fine to very coarse grained sand with discontinuous interfingering lenses of gravel and silt. All these sediments have around 20 m thickness and are overlying a weathered granitic basement. Several boreholes were drilled perpendicular and parallel to the shoreline, at various depths to reach different hydraulic conductivity areas along the mixing zone. Geophysical techniques including electrical resistivity tomography, fiber optics and different types of logging (induction, spectral gamma ray and magnetic susceptibility) have been performed to characterize the salinity gradient and distinguish sedimentary bodies. Moreover, a fully hydrochemical investigation was carried out to define the initial groundwater composition using TOC/DOC measurements, mayor and minor elements analysis and radium and radon isotopes quantifications. Also lithological description, sedimentological correlati

In western Mediterranean areas, seawater intrusion (SWI) used to be a major issue during the 1970’s decade due to the agricultural exploitation of the fertile lands located near to the coast. Proper pumping management nearly solved the problem, but the later economic development carried out by industries and tourism added an extra pressure to these sensitive systems, reactivating SWI in some cases. A good example of this situation can be found in the northeastern coast of Spain. In this area, the topographic configuration is controlled by medium reliefs and sloped piedmonts that discharge precipitation through ephemeral streams towards the sea. These torrential flows have a groundwater component that generates a coeval submarine groundwater discharge (SGD) with the intrusion of seawater. SGD strongly determines the health of marine environments, reason why is classically neglected in SWI research: in this area, SGD has been characterized measuring natural radioactive tracers (223Ra, 224Ra, 226Ra, 228Ra) in open sea campaigns, but the impact of mixing of this seaward flow and SWI within the aquifer remains unknown. The presence of different lithologies also determines the kind of geochemical reactions that modify the conservative behavior of the tracers used to measure SGD, as well as the localization of preferential flowpaths, making hard to quantify and predict both types of reciprocal flows (SGD and SWI). To be able to understand these interactions, a detailed characterization of the solid and liquid phase of the aquifer at different scales has been performed. To do so, we built a dedicated experimental site in a coastal alluvial aquifer in the Maresme coast line (Barcelona, Spain): the Argentona experimental site. Different types of geophysical logging (induction, spectral gamma ray and magnetic susceptibility) were deployed in the drilled wells to characterize the salinity gradient and distinguish sedimentary bodies. Also, the lithology and the geochemistry of d

The steady increase of geothermal systems using groundwater is compromising the renewability of the geothermal resources in shallow urban aquifers. To ensure sustainability, scientifically-based criteria are required to prevent potential thermal interferences between geothermal systems. In this work, a management indicator (balanced sustainability index, BSI) applicable to groundwater heat pump systems is defined to assign a quantitative value of sustainability to each system, based on their intrinsic potential to produce thermal interference. The BSI indicator relies on the net heat balance transferred to the terrain throughout the year and the maximum seasonal thermal load associated. To define this indicator, 75 heating-cooling scenarios based in 23 real systems were established to cover all possible different operational conditions. The scenarios were simulated in a standard numerical model, adopted as a reference framework, and thermal impacts were evaluated. Two polynomial regression models were used for the interpolation of thermal impacts, thus allowing the direct calculation of the sustainability indicator developed as a function of heating-cooling ratios and maximum seasonal thermal loads. The BSI indicator could provide authorities and technicians with scientifically-based criteria to establish geothermal monitoring programs, which are critical to maintain the implementation rates and renewability of these systems in the cities. © 2018 Elsevier Ltd

The Salar de Atacama is one of the most well-known saline endorheic basins in the world. It accumulates the world main lithium reserves and contains very sensitive ecosystems. The objective of this work is to characterize the hydrodynamics of the Salar de Atacama, and to quantify its complex water balance prior to the intense brine extraction. The methodology and results can be extrapolated to the groundwater flow and recharge of other salt flats. A three-dimensional groundwater flow model using low computational effort was calibrated against hundreds of hydraulic head measurements. The water infiltrated from the mountains ascends as a vertical flux through the saline interface (mixing zone) produced by the density contrast between the recharged freshwater and the evaporated brine of the salt flat nucleus. This water discharges and is largely evaporated from lakes or directly from the shallow water table. On the other hand, the very low hydraulic gradients, coupled with the presence of the mixing zone that operates as barrier, leads the salt flat nucleus to act as a hydrodynamically quasi-isolated area. The computed water table shows the lowest hydraulic head in the salt flat nucleus near the discharge at the mixing zone. The groundwater balance of the Salar de Atacama in its natural regime was quantified resulting in an inflow/outflow of 14.9 m3·s−1. This balance considers the basin as an endorheic system. The very low infiltration values that are generally assumed for hyperarid basins are not consistent with the hydrogeology of the Salar de Atacama. Indeed, very high infiltration rates (up to 85% of rainfall) occur because of the high degree of fracturing of rocks and the scarce vegetation. This high infiltration is consistent with the light isotopic composition of the water from the recharge area (Altiplano). Therefore, the existence of additional inflows outside the basin is unlikely. © 2018

The Salar de Atacama is used as a case study to analyse and quantify coupled natural (evaporation and recharge) and anthropogenic processes (pumping of lithium-rich brine) to abstract their patterns to other salt flats using a three-dimensional groundwater flow model. Important changes in the dynamics of the water table between the pre-operational period (1986–1994) and operational period (1994–2015) are observed. The water table exhibited a gradual drawdown during the pre-operational period because the evaporation was greater than the recharge for most of these periods. This negative balance was counteracted by some sharp rises that were produced by direct rainfall events on the salt flat. The deep lateral recharge that arrived from the mountains did not produce abrupt changes in the water table because the rainfall events in the mountains were damped by the distance of the recharge zone and great thickness of the unsaturated zone. The natural evolution of the water table was modified by the intensive brine pumping that was performed in the south-western Salar de Atacama during the operational period. As evaporation depends on the water table depth, the pumping caused a drawdown of the water table, resulting in an evaporation rate reduction that partially compensated for the pumped brine in the water balance of the basin. This effect is defined as the damping capacity of salt flats. Thus, salt flats have a high capacity for dampening oscillations in their water table in response to both natural and anthropogenic disturbances which is of great importance for the management of lake and wetland ecosystems and brine exploitation. The limit of the dampening capacity of salt flats is defined by the evaporation extinction depth, which is in the range of 0.5–2 m. © 2018 Elsevier B.V.

Pleistocene detrital deposits in the central Ebro Basin frequently show deformation features due mainly to karstification in the underlying Neogene evaporites. In 123 cases, estimation of parameters of shape and minimum volume of materials involved was accomplished. Six of them were analysed in more detail to establish the main processes involved in their genesis and the succession of events. All the deformation features in the selected sites are synsedimentary. To achieve the objectives, intense fieldwork was made applying methods of sedimentology and structural geology. Usually, a complex evolutionary pattern was observed, with evidences of dissolution, sagging, collapse, gravity flow, suffosion, and plastic flow. In a schematic way, three main situations, independent of the age of the analysed deposits, can be distinguished: (a) slow subsidence, (b) collapse, and (c) temporal overlapping of both processes. In the first 2 scenarios, basins with smooth or abrupt borders, respectively, were generated on the land surface. In the third one, slow subsidence was followed by a collapse, located in the area of maximum flexure. These patterns are also observed in present-day dolines. Comparison of direct and indirect parameters between paleodolines and present-day dolines indicates a bigger size of the latter, probably caused by the different conditions of observation. This study helps to know the possibilities in the evolution of mantled karst features, to estimate the volume of material affected by karstification and to improve the knowledge of present-day dolines behaviour. Consequently, study of paleodolines must be considered to achieve a better urban planning in active karstic areas. Copyright © 2018 John Wiley & Sons, Ltd.