Hydrogeochemical Modeling Research Articles

Hydrogeochemical Modeling to Identify Potential Risks of Underground Hydrogen Storage in Depleted Gas Fields

Underground hydrogen storage is a potential way to balance seasonal fluctuations in energy production from renewable energies. The risks of hydrogen storage in depleted gas fields include the conversion of hydrogen to CH4(g) and H2S(g) due to microbial activity, gas–water–rock interactions in the reservoir and cap rock, which are connected with porosity changes, and the loss of aqueous hydrogen by diffusion through the cap rock brine. These risks lead to loss of hydrogen and thus to a loss of energy. A hydrogeochemical modeling approach is developed to analyze these risks and to understand the basic hydrogeochemical mechanisms of hydrogen storage over storage times at the reservoir scale. The one-dimensional diffusive mass transport model is based on equilibrium reactions for gas–water–rock interactions and kinetic reactions for sulfate reduction and methanogenesis. The modeling code is PHREEQC (pH-REdox-EQuilibrium written in the C programming language). The parameters that influence the hydrogen loss are identified. Crucial parameters are the amount of available electron acceptors, the storage time, and the kinetic rate constants. Hydrogen storage causes a slight decrease in porosity of the reservoir rock. Loss of aqueous hydrogen by diffusion is minimal. A wide range of conditions for optimized hydrogen storage in depleted gas fields is identified.

Validation of hydrogeochemical databases for problems in deep geothermal energy

Hydrogeochemical modelling has become an important tool for the exploration and optimisation of deep hydrogeothermal energy resources. However, well-established software and model concepts are often run outside of its temperature, pressure, and salinity ranges. The core of the model codes are thermodynamic databases which contain a more or less complete subset of mineral phases, dissolved species, and gases occurring in geothermal systems. Although very carefully compiled, they should not be taken for granted at extreme conditions but checked prior to application. This study compares the performance of four commonly used geochemical databases, phreeqc.dat, llnl.dat, pitzer.dat, and slop16.dat. The parameter files phreeqc.dat, pitzer.dat, and llnl.dat are distributed with PHREEQC and implement extended Debye–Hückel and Pitzer equations. Thermodynamic data in slop16.dat represent an implementation of the revised Helgeson–Kirkham–Flowers formalism and were converted to be used with the Gibbs Energy Minimizer ChemApp for this work. Test calculations focussed on the solubility for some of the most common scale-forming mineral phases (barite, celestite, calcite, siderite, and dolomite). The databases provided with PHREEQC performed comparatively well, as long as the range of validity was respected for which the corresponding database was developed. While it is obvious to use pitzer.dat at high salinities instead of phreeqc.dat, the range of validity for high temperature is usually not given in the database and has to be checked manually. The results also revealed outdated equilibrium constants for celestite in slop16.dat and llnl.dat and the lack of adequate temperature functions for the solubility constants of siderite and dolomite in all databases. For those two minerals, new thermodynamic data are available. There is, however, a lack of experimental thermodynamic data for scale-forming minerals in low-enthalpy geothermal settings, which has to be addressed for successful modelling.

Reactive transport of arsenic-enriched geothermal spring water into a sedimentary aquifer

The movement of high-arsenic (As)-concentration Beitou geothermal spring water up to 4600μg/L from the upstream area may affect the downstream Guandu plain and Guandu wetland. The major As pathway is via the subsurface flow. The study assesses the fate and transport of As-enriched geothermal spring water in the Beitou-Guandu area. The groundwater head and flow field velocity are first simulated by using HYDROGEOCHEM-fluid flow model. The steady state flow field is well-calibrated with root mean square error 1.73m and R2 = 0.992. The spatial-temporal distributions of As in the Beitou-Guandu area are simulated by the HYDROGEOCHEM reactive transport model using the calibrated steady state flow field. The results show that high As concentration (250μg/L) in groundwater of Guandu plain was caused by the movement of high As concentration from the Beitou geothermal spring water. In contrast, the low As concentration (5-50μg/L) in Guandu wetland was mitigated by the tidal water dilution. The simulated As concentrations increase in the first 3years, and then gradually decrease due to the adsorption of As on the iron oxide minerals ferrihydrite and iron sulfide minerals pyrite. Furthermore, the hydrogeochemical transport model is applied to assess the effect of bioaccumulation of As by the mangrove plants of Guandu wetland. The dominant mangrove plants, Kandelia obovata, can reduce about 5-30μg/L As concentration in groundwater. It may be one of sinks of As in Guandu wetland. The inclusion of K. obovata can uptake the aqueous As and allow the simulated As concentration further close to the field measurement in the Guandu wetland. The study successfully models the reactive chemical transport of As by considering both geochemical reactions and biochemical uptakes in the Beitou-Guandu area. The result demonstrates that the complex biogeochemical transport can be quantified by the sophisticated HYDROGEOCHEM model. Moreover, the salient features of the biogeochemical reactions can be recovered and elucidated through a series of systematic simulation.

Negative pH values in an open-air radical environment affected by acid mine drainage. Characterization and proposal of a hydrogeochemical model

This paper presents the finding of a singular environment polluted by acid mine drainage in the Iberian Pyrite Belt. This situation is regulated by particular conditions, thus the analysed values can be considered as extreme, not only because of the high concentrations of toxic elements, but also due to the extreme low pH, reaching an average negative pH of −1.56, never found before in open-air environments contaminated by acid mine drainage. Concentrations up to 59 g/L of Fe, 2.4 g/L of Al, 740 mg/L of As, 4.3 mg/L of Co, 5.3 mg/L of Ge, 4.8 mg/L of Sb, inter alia, can be found dissolved in these polluted waters. The main aims of the present work are the physicochemical characterization and the toxicity assessment of these radical polluted waters. In addition, a hydrogeochemical model of the system will be proposed, which justifies the extreme pH value and the extraordinarily high concentrations of toxic elements, even for acid mine drainage polluted environments. Extreme acidity and metal and sulphate concentrations in the Radical Environment are due to several processes of different nature, mainly driven by the geochemistry of the minerals presents in the endorheic character of the basin. The extremely acidic nature of these waters control the Fe species present in them, being FeHSO4+ the mainly Fe specie representing 94% of total. High toxicity of these waters has been detected due to the absence of any diatoms species.

Hydrogeochemical Modeling of the Shallow Thermal Water Evolution in Yangbajing Geothermal Field, Tibet

The exploitation of thermal water and the mix of cold water changed the properties of geofluid in shallow reservoir, which altered the concentration of the chemical constitutes and continuously built new water-rock reaction. This paper deduced reservoir pressure and temperature variation tendency from 2004 to 2013, analyzed the change of some components in the shallow reservoir water, and finally obtained the evolution of the shallow geothermal water with hydrogeochemical model. The results show the reservoir pressure decreased significantly compared with the slight decline of reservoir temperature, and much cold groundwater infiltrated into the shallow reservoir, which affected the solubility of SiO2 and led to precipitation, the increased CO2 in shallow reservoir promoted the dissolution of aluminosilicate. Calcite and kaolinite precipitation zone has extended to the north in the field, which influenced the porosity of the reservoir rock.

Natural and anthropic processes controlling groundwater hydrogeochemistry in a tourist destination in northeastern Brazil.

The objective of this study was to analyze spatial-seasonal changes to identify the natural and anthropic processes that control groundwater hydrogeochemistry in urban aquifers in municipality of Lençóis (Bahia). Tourism is the main activity of this municipality, which is an important tourist destination in northeastern Brazil and which maintains its tourism infrastructure by using groundwater. Two field campaigns were conducted (dry and rainy seasons) in order to collect groundwater samples extracted from 15 tubular wells distributed over the urban area of the municipality. The Piper diagram, multivariate statistical analyses, and artificial neural networks indicated that there are two types of water (Na-Cl and Na-[Formula: see text]-), which were divided into five different clusters. Seasonal variation was observed to significantly alter groundwater hydrogeochemistry. According to the Gibbs diagram, groundwater within the urban area of Lençóis belonged to the rainfall dominance, demonstrating low water-rock interaction. Hydrogeochemical modeling results suggested hydrolysis as the main natural factors controlling process. However, mineral dissolution also occurred in one of the clusters. Human-originated trace contamination by nitrate, chloride, and sulfate occurred in a zone of the urban area. This contamination was observed regardless of climate seasonality, indicating that the main controlling process for groundwater hydrochemistry in this region is wastewater mobilization (indirect artificial recharge).

Analysis of the Erosion Law of Karst Groundwater Using Hydrogeochemical Theory in Liulin Spring Area, North China

The comprehensive geological, hydrogeological and hydrogeochemical model of the Liulin karstic spring area in the eastern limb of the Ordos syncline was established by a combination of chemical thermodynamics, chemical kinetics and hydrogeology. The study area was divided into four zones based on the saturation indices of calcite, dolomite and gypsum, which were computed by the groundwater-chemical simulation software PHREEQC (a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations), with consideration of the geological and hydrogeological conditions and hydro-geochemical reactions. The weight and volume modulus of carbonate rocks and sulphate rocks in each zone were calculated by the method of correlation analysis to evaluate the dissolution law of karst groundwater. The results showed that in the zone I (saturation index of calcite βc ≤ 1) the dissolution of calcite was the major geochemical reaction, the weight modulus of calcite was higher than that of dolomite and gypsum, and the pore space generated by the dissolution of calcite was one order of magnitude larger than that of dolomite and gypsum. In zone II (saturation index of calcite βc > 1 to saturation index of dolomite βd ≤ 1) the corrosion moduli were all smaller than that in zone I, the solubility of dolomite and gypsum increased, and calcite reached saturation. The space occupied by the calcite sediment was less than that dissolved by dolomite and gypsum. In zone III (saturation index of dolomite βd > 1 to saturation index of gypsum βg ≤ 1), calcite and dolomite had reached saturation, accompanied by dedolomitization, and the amount of gypsum dissolution increased obviously. The conclusions indicate that the hydrogeochemical environment plays an important role in mineral dissolution.

Water-Rock Interaction Effect on Evolution of Total Hardness in Groundwater in Urban

Groundwater is the most important source of water supply in Beijing city. However, groundwater has undergone intensive total hardness pollution caused by water-rock interaction and by human activities. Analysis of monitoring data of 30 years shows that the high concentration of total hardness is relationship with carbonate mineral dissolution and cation exchange. But speciation calculations of two flow path using the hydrogeochemical modeling code PHREEQC indicated that the annual contribution of carbonate dissolution and cation exchange to concentration of Ca2+ and Mg2+ is less than 1 mg∙L-1, which was far less than that observed. The results illustrated that carbonate mineral dissolution and cation exchange in aquifers play a small role in the contribution of groundwater chemical evolution, and also imply other anthropogenic sources exist indirectly.

Hydrogeochemical Model and Water Quality of Groundwater in the Granito-Basaltic Fractured Rock Aquiferous Formations in Bafoussam, West Region-Cameroon

This study determined the hydrogeochemical model of groundwater and groundwater domestic-agro-industrial quality in Bafoussam using hydrogeochemical tools and physicochemical parameters: Ionic ratios, Gibbs diagrams, Piper diagrams, Durov diagrams and water quality indices. From physicochemical parameters; pH ranged from, 4.47 - 7.84; EC, 10 - 820 μS/cm; Temperature, 22.3°C - 29.5°C and TDS, 6.7 - 549.4 mg/L. The major ions fell below WHO acceptable limits. The sequences of major ionic abundance are: Ca2+ > Mg2+ > K+ > Na+ > NH+4, HCO-3 > Cl- > SO2-4 > NO3 > HPO2-4. Recharge by atmospheric precipitation, ion-exchange and simple dissolution processes are responsible for groundwater character, ionic content resulted from ion exchange and rock-weathering. Water types are Ca-HCO3 and Ca-Cl Hydrogeochemical facies are Ca-Mg-Cl-SO4 and Ca-Mg-HCO3. Domestic water quality was determined by use of pH, electrical Conductivity EC, total dissolved solids TDS, total Hardness HT and water quality index WQI. WQI values ranged from 0 - 42.09 and HT 67.89 - 339.01 indicating that water is of good domestic quality. Agro-industrial suitability of groundwater was determined using, sodium adsorption ratio SAR, permeability index PI, Magnesium adsorption ratio MAR, percent sodium %Na, Kelly’s ratio KR and Residual sodium carbonate RSC and Wilcox diagram; From irrigational water suitability parameters, SAR values ranged from 0.01 - 0 05; %Na 3.69 - 15.50; KR 0.005 - 0.023; PI 1.04 - 67.98; MAR 2.89 - 55.27; RSC -5.22 to -0.44 and Wilcox diagram indicate that inorganic groundwater content in the study area is excellent-good for irrigation; this is of significance since Bafoussam a major agroindustrial zone in Cameroon and Central Africa is in the process of developing large scaled irrigation based agricultural projects dependent on use of surface and groundwater. Recharge from precipitation exchanges ions with the weathered country rocks and mixes with regional flow in a generally south-east north-westerly direction by piston flow in the granito-basaltic aquiferous formations in Bafoussam. There is need for detailed studies to determine aquifer characteristics: permeability, transmissivity and storativity, vertical-lateral regional extent of aquifer boundaries, groundwater pollution potentials for biological, organic and trace metals.

Multivariate statistics and hydrogeochemical modeling for source identification of major elements and heavy metals in the groundwater of Qareh-Ziaeddin plain, NW Iran

The present study aims to evaluate the possible source of major and some minor elements and heavy metals in the groundwater of Qareh-Ziaeddin plain, NW Iran with respect to chemical elements, saturation index, and multivariate statistics including correlation coefficient, cluster analysis, and factor analysis. Groundwater samples were collected in Jun 2016 and measured with respect to EC, pH, major and some minor elements and heavy metals including Fe, Mn, Zn, Cr, Pb, Cd, Al, and As. Among all the measured parameters, some of the samples exceed the World Health Organization (WHO) guideline value for EC, Na, Mg, HCO3, SO4, Cl, NO3, F, As, Zn, and Pb. The results of correlation analysis show that weathering and dissolution of minerals especially evaporites and silicates, water-rock interaction, and cation exchange are dominant occurred processes in the groundwater of the study area. Also, denitrification process is occurred in the groundwater system. Cluster analysis categorizes the samples into three distinct groups which are different based on their EC and dependent variables, e.g., Na, Ca, Cl, SO4 and pH, Pb, Cd, and As. It can be found that volcanic, evaporite, and clay formations have the least impact on the chemistry of the cluster 1 samples while clay and evaporite formations have the highest impact on the cluster 3 and also calcareous formations on cluster 2. Factor analysis shows that five factors, with total variance of 83%, are effective in the release of heavy metals and groundwater chemistry which are mostly geogenic.

Influence of the paleogeographic evolution on the groundwater salinity in a coastal aquifer. Cabo de Gata aquifer, SE Spain

The groundwater of the Cabo de Gata detritic aquifer, in southeastern Spain, exhibit salinities of between 70–726 mmol/L of Cl− (brackish-salt to hypersaline waters). We have investigated the causes of the high salinity anomaly, which at certain points exceeds that of present-day seawater (600 mmol/L). Two hypotheses are considered as possible sources for the saline water: (1) The deeper, more saline groundwater date back to an old marine intrusion that occurred at the end of the last Ice Age (14–17 ka), when seawater salinity was higher than in the present day. This hypothesis is supported by the values of 14C measured in this water (∼6–10 pmc), which indicate old water of up to 17 ka. However, the values of 18O and 2H are lower than would be expected. (2) The water is the result of mixing between fresh groundwater and seawater. The latter explanation agrees well with the low values of 18O and 2H. This mixture is later subject to evaporation, explaining its high salinity. Hydrogeochemical modelling was carried out for the most saline samples, assuming such mixing between freshwater and seawater followed by evaporation, and the results show a very good agreement between the measured and simulated values. According to the model calculation, the original mixture contained approximately 60% seawater and its volume subsequently was reduced through evaporation by around 30%. This mixing and evaporation could occur during the Flandrian Transgression (6000–8000 y), when this area accommodated a coastal lagoon.

천부대수층 내 이산화탄소 주입에 의한 물-암석-CO2 반응에 대한 수리지구화학적 모델링

천부대수층 내 이산화탄소 주입에 의한 물-암석-CO2 반응에 대한 수리지구화학적 모델링

Hydrogeochemical modeling (KIRMAT) of spring and deep borehole water compositions in the small granitic Ringelbach catchment (Vosges Mountains, France)

This study presents the results of the coupled hydrogeochemical modeling of the geochemical compositions of spring and borehole waters from the Ringelbach catchment, which is located in the Vosges Mountains (France). This site has been equipped with 150-m-deep boreholes, facilitating the sampling of both rock and groundwater in the granitic bedrock. The data point to very contrasting chemical compositions between spring and borehole waters, which are discussed and explained in this study by the application of the coupled hydrogeochemical code KIRMAT. Using hydrological and geochemical data, simulations were performed through two different water pathways, which crossed different types of rocks within the Ringelbach massif: a subsurface and fast (>2.5 mH2O.yr−1) water flow, which is more or less parallel to the slope, for waters supplying the springs, and a rather vertical and slower flow (0.5–0.1 mH2O.yr−1) for the borehole waters. The KIRMAT simulations make it possible to account for not only the geochemical differences between the spring and borehole waters but also the geochemical variations observed in waters in both contexts. For borehole waters, the model confirms the importance of the dissolution of minor mineralogical phases that are present in the granite (here, carbonates/dolomites) on the chemical budget of waters. It also shows that the chemical differences between the waters collected in the two studied boreholes result from differences in the water flow in the granitic bedrock, i.e., the difference between water flow in a regular porous medium and water flow in a porous medium crossed by a fracture. This result likely highlights the role of geological inheritance on the hydrodynamical rock properties and the chemical compositions of waters circulating within the granitic bedrock. For spring waters, this model enabled us to constrain the nature of the rock in the pathway, which is neither saprolite nor fresh granite but is instead weathered granite with a weathering age of several tens of thousands of years. Spatial and seasonal variations in the chemical compositions of spring water can be explained as the result of the same circulation pattern for which the water-rock interaction time is determined by the length of the pathway and the water velocity. Especially in cases in which this interaction time is long enough, the precipitation of clay phases is enabled, which plays a major role in determining the chemical composition of the water. Despite the only one-dimensional approach and the uncertainties linked to the geochemical complexity and the associated kinetic data, the results obtained in this study demonstrate the effectiveness of using coupled hydrogeochemical modeling to better understand and quantify the weathering processes and the coupling that exists between water circulation dynamics and water-rock interactions at the catchment scale.

Assessment of the influence of temperature and pressure on the prediction of the precipitation of minerals during the desalination process

The results of research designed to examine the influence of the temperature of geothermal water and transmembrane pressure on the precipitation of selected minerals during the desalination process are presented. The geothermal water used in tests was characterised by a high conductivity value, high total hardness and elevated concentrations of sulphates, silicates, calcium, magnesium, and macro and micronutrients, which can cause scaling phenomena to occur. Based on the physicochemical composition of the water, an estimate was made of the extent of the scaling phenomena for all the processes examined. For these analyses, two parameters of the desalination process: 1) the temperature of feed water (T) and 2) the transmembrane pressure (p) were chosen and tested in different value ranges. The research results demonstrate the existence of reactions determined both by hydrogeochemical modelling and from the results obtained during real laboratory tests. It was found that in the case of carbonate (aragonite and calcite) and all silicate minerals, an increase in the pressure value to 40bar slightly decreases the Saturation Index for each mineral. A reverse relationship was reported with gypsum. Increasing transmembrane pressure to 40bar increases the tendency of the mineral form studied to precipitate.

A conceptual model for groundwater flow and geochemical evolution of thermal fluids at the Kızılcahamam geothermal area, Galatian volcanic Province

Kızılcahamam geothermal area is one of the most important geothermal fields in the Galatean Volcanic Province northern Central Anatolia of Turkey. Kızılcahamam geothermal field is liquid-dominated system that have been developed in the rugged terrain, and usually consists of a geothermal systems that occur commonly associated with terrestrial volcanism. This field is characterized by thermal and mineralized springs, travertine, with wide alteration zones. Thermal waters are issue through the faults and fracture zones of the volcanics. The temperatures of the wells in the Kızılcahamam town center varies between 42 and 81°C, whereas the temperature of thermal and mineralized water springs in the area of Acısu Stream and Seyhamam varies between 23 and 43°C. Electrical conductivity values for thermal waters are between 1029 and 3700μS/cm. Thermal waters in Kızılcahamam area are mainly Na-HCO3-Cl and Na-Ca-HCO3 type, with high salinity, while cold groundwater is mostly of Ca (Na, Mg)-HCO3 type, with lower salinity. Both waters of Kızılcahamam town center and Acısu Stream appear to be derived from a deeper reservoir fluid, whereas Seyhamam thermal waters are compatible with shallow cold waters heated by steam absorbing high temperatures. High contents of some minor elements in thermal waters, such as F, B, Li, Rb, Sr and Cs probably derive from enhanced water–rock interaction.The isotopic values of thermal water (δ18O, δ2H, δ3H) indicates their deep-circulating meteoric origin and allow estimation of infilitration altitude ranging between 1350 and 1750m.a.s.l.This datum, supported by structural data, suggests the Işıkdağ and Aluçdağ Mountains as the recharge area of the system. As frequently observed in many geothermal systems positive I8O shifts of Kızılcahamam thermal waters relative to the local meteoric line were considered to be primarily due to interaction with host rocks at elevated temperature (T >150°C) and from CO2 exsolution of thermal and mineral springs. In this system, geothermal waters are heating by an intrusive-cupola and geothermal gradient, followed by the waters rising to the surface along faults and fractures that act as hydrothermal conduits. A conceptual hydrogeochemical model was developed for a hydrogeological flow system in the Kızılcahamam Region.

Subaqueous hot springs in Köyceğiz Lake, Dalyan Channel and Fethiye-Göcek Bay (SW Turkey): Locations, chemistry and origins

In this study, horizontal temperature measurements along organized grids have been used to detect subaqueous hot springs. The study area, located in the southwest of Turkey and comprised of Köyceğiz Lake, Dalyan Channel and Fethiye-Göcek Bay, was scanned by measuring temperatures horizontally, 2–3m above the bottom of the lake or sea. After analyzing the temperature data along the grids, the locations with anomalous temperature values were detected, and divers headed here for further verification. Accordingly, among these anomalies, the divers confirmed seven of them as subaqueous hot springs. Three of these hot springs are located in the Köyceğiz Lake, three of them are located in the Dalyan Channel and one hot spring is located in the Fethiye-Göcek Bay. At the locations where temperature anomalies were detected, the divers collected samples directly from the subaqueous hot spring using a syringe-type sampler. We evaluated these water samples together with samples collected from hot and cold springs on land and from local rivers, lakes and the sea, with an aim to generate a conceptual hydrogeochemical model of the geothermal system in the study area. This model predicts that rainwater precipitating in the highlands percolates through fractures and faults into the deeper parts of the Earth's crust, here it is heated and ascends through the sea bottom via buried faults. Pervious carbonate nappes that are underlain and overlain by impervious rocks create a confined aquifer. The southern boundary of the Carbonate-Marmaris nappes is buried under alluvium and/or sea/lake water bodies and this phenomenon determines whether hot springs occur on land or subaqueous. The chemical and isotopic properties of the hot springs point to seawater mixing at deep levels. Thus, the mixing most probably occurs while the water is ascending through the faults and fractures. The gas geochemistry results reveal that the lowest mantle He contributions occur in the samples from Köycegiz Lake, whereas the highest ones are found in samples from the Dalaman plain. For the first time, we made use of the micro-XRF sediment core scanning (ITRAX Scanner) for exploring the relation between subaqueous geothermal occurrence and chemical properties of the surrounding sediments. The spatial elemental distribution of sea/lake bottom sediments suggests that depending on the surrounding rock units and the temperature of the hot spring, the sediments around the spring can be enriched with certain elements.

Combined hydrogeological and nitrate modelling to manage water resources of the Middle Soummam Aquifer, Northeast of Algeria

Water management is one of the most challenges in Algeria, a semi-arid Mediterranean country confronted to a serious water stress. The country will have to endure, beyond 2025, a situation of chronic water penury, adding an excessive pollution of the majority of groundwater reservoirs. The management of water resources by combined approach using hydrogeological model and nitrates evolution model was experimented in the Middle Soummam valley. The alluvial aquifer, offering good hydrodynamic and geometrical characteristics, is over-exploited, providing in drinking water Akbou and Tazmalt cities and irrigation perimeters. If exploitation continues at these steady paces, the depletion of the water resource and the hydrochemical imbalance will be inevitable. On the one hand, the results of hydrodynamic model, based on an increase of the water takings and simulated needs from 24.71 Mm3/year in 2015 into 39.69 Mm3/year in 2030, show a critical withdrawal. The aquifer budget expresses the inversion of flow between the wadi and the aquifer where the wadi feeds the groundwater reservoir. This hydrodynamic inversion was attributed to simulated pumping rates which increased and exceeded 100,000 m3/day, but the aquifer was partially relieved by the weight of the exploitation through Tichy Haf dam. The water management strategy adopted in this study was based on management measures promoting zones, which have been delimited between Tazmalt and Akbou, and containing important water quantities available in the axis of the valley. However, according to the depleted in isotopes of 18O and 2H, which could be explained by the influence of a paleoclimatic effect and suggested that the aquifer recharge would have largely been made under a colder climate, pumped groundwater could be old, and the implementation of new pumping sites has been studied minutely. On the other hand, the hydrogeochemical modelling allowed following nitrates concentrations in order to project their evolution. Four wells on 25 react in face to the imposed conditions in each scenario simulated until 2030, showing inertia of pollution, and confirmed after three series of tests. This inertia would be related to the hydraulic gradients and hydraulic conductivities, aquifer thickness and recharge. The low hydraulic gradients lead to a rather slow flow velocity and thus to an inertia in the dispersion of nitrates, with a mass transport weakened by the hydrodynamic conditions. It is also related to the aquifer thickness; when the aquifer is powerful (65–85 m), the stock of water would be important and allows a dilution process. The reverse is true for the simulated boreholes where the concentrations remain invariant; the aquifer is less powerful (32–37 m). Finally, the recharge effect through the rain was evoked; the aquifer is unconfined, and the rain water and pollution that reached the piezometric level can remain in position in slow hydrodynamic conditions. The methodology was demonstrated through a combination of monitoring and modelling for both water quantity and quality and the importance to use numerical models to support water resources management strategy in the Mediterranean aquifers.

Uraniferous dolomite: a natural source of high groundwater uranium concentrations in northern Bavaria, Germany?

Naturally high uranium (U) concentrations occur in the groundwater of northern Bavaria (southeastern Germany) although the source(s) and geochemical processes controlling its occurrence are poorly understood. An earlier study identified the weathering of uraniferous apatite as responsible for elevated groundwater U in a part of the region. This present study focuses on a uraniferous dolomite facies in the Triassic sandstone aquifer of northern Bavaria as a potential source of dissolved uranium in the regional groundwater. Hydrogeochemical and mineralogical analytical methods (INAA, ICP-OES, SEP, XRD, C/S measurements), in conjunction with existing hydro- and geochemical datasets, as well as hydrogeochemical modeling approaches indicate a strong connection between groundwater U and the dolomitic facies. Highest groundwater concentrations (max 58.3 µg L−1) occur under slightly alkaline and oxic to slightly reducing conditions. Uranium speciation is dominated by mobile U(VI), predominantly in the form of uranyl-carbonate complexes. Groundwater is undersaturated with respect to U mineral phases. In addition, high values in the dolomite extraction step (SEP) and a positive correlation of dolomite (XRD) and Ca with U (INAA) support the assumption of mobilization from the uraniferous dolomite as a potential source for elevated U concentrations, and hence one of the causes for the geogenic groundwater U problem in this region.

Identifying and quantifying geochemical and mixing processes in the Matanza-Riachuelo Aquifer System, Argentina

The Matanza-Riachuelo River Basin, in the Northeast of the Buenos Aires Province, is one of the most industrialized and populated region in Argentina and it is worldwide known for its alarming environmental degradation. In order to prevent further damages, the aquifer system, which consists of two overlaid aquifers, is being monitored from 2008 by the river basin authority, Autoridad de la Cuenca Matanza-Riachuelo. The groundwater chemical baseline has been established in a previous paper (Zabala et al., 2016), and this one is devoted to the identification of the main physical and hydrogeochemical processes that control groundwater chemistry and its areal distribution. Thirty five representative groundwater samples from the Upper Aquifer and thirty four from the deep Puelche Aquifer have been studied with a multi-tool approach to understand the origin of their chemical and isotopic values. The resulting conceptual model has been validated though hydrogeochemical modeling. Most of the aquifer system has fresh groundwater, but some areas have brackish and salt groundwater. Water recharging the Upper Aquifer is of the Ca-HCO3 type as a result of soil CO2 and carbonate dissolution. Evapotranspiration plays a great role concentrating recharge water. After recharge, groundwater becomes Na-HCO3, mostly due to cation exchange with Na release and Ca uptake, which induces calcite dissolution. Saline groundwaters exist in the lower and upper sectors of the basin as a result of Na-HCO3 water mixing with marine water of different origins. In the upper reaches, besides mixing with connate sea water other sources of SO4 exist, most probably gypsum and/or sulfides. This work highlights the relevance of performing detailed studies to understand the processes controlling groundwater chemistry at regional scale. Moreover, it is a step forward in the knowledge of the aquifer system, and provides a sound scientific basis to design effective management programs and recovery plans.

Geothermal potential evaluation and development prioritization based on geochemistry of geothermal waters from Kangding area, western Sichuan, China

Kangding geothermal area is located in the western Sichuan, belonging to southeastern margin of Tibetan Plateau. Similar to world-renowned south Tibetan and western Yunnan geothermal belt, western Sichuan has intensive surface thermal manifestations including boiling and hot springs. The emerging temperature of thermal waters ranges from 47 to 79 °C with total dissolved solids lying between 899 and 2550 mg/L. δ2H–δ18O isotopes indicate a meteoric source for the thermal waters and a significant positive oxygen-18 shift in the southern region. It is suggested that southern thermal waters experienced stronger water–rock interaction and are closer to thermodynamic equilibrium, which is also proved by the water type classification. The reservoir temperature calculated by empirical and theoretical chemical thermometry is 180–225 °C for the north and 225–310 °C for the south. Evidences of hydrogeochemistry, stable isotopes, geothermometry and radiocarbon dating indicate that southern region of Kangding area shows greater geothermal potential than the northern region. In addition, based on the hydrogeochemical modeling of mineral saturation, underlying problem of scaling is likely to occur in the study area. According to the results of reservoir temperature, south Kangding sub-district has greater potential in geothermal power generation and development than northern Kangding. Therefore, further exploration and drilling work should give priority to the south Kangding area.