•HFE-Diagram and GIS tools to know status of coastal aquifer at one point.•Major ion chemistry changes can be read as space/time variations of marine intrusion.•The new method could help to improve ...management of water resources in coastal areas.
A new method has been developed to recognize and understand the temporal and spatial evolution of seawater intrusion in a coastal alluvial aquifer. The study takes into account that seawater intrusion is a dynamic process, and that seasonal and inter-annual variations in the balance of the aquifer cause changes in groundwater chemistry.
Analysis of the main processes, by means of the Hydrochemical Facies Evolution Diagram (HFE-Diagram), provides essential knowledge about the main hydrochemical processes. Subsequently, analysis of the spatial distribution of hydrochemical facies using heatmaps helps to identify the general state of the aquifer with respect to seawater intrusion during different sampling periods.
This methodology has been applied to the pilot area of the Vinaroz Plain, on the Mediterranean coast of Spain. The results appear to be very successful for differentiating variations through time in the salinization processes caused by seawater intrusion into the aquifer, distinguishing the phase of seawater intrusion from the phase of recovery, and their respective evolutions. The method shows that hydrochemical variations can be read in terms of the pattern of seawater intrusion, groundwater quality status, aquifer behaviour and hydrodynamic conditions. This leads to a better general understanding of the aquifers and a potential for improvement in the way they are managed.
This paper analyzes the results of a theoretical simulation of sea water intrusion and its dynamics. The assignment of hydrochemical facies identifies whether the aquifer is in the phase of sea water ...intrusion or freshening, indicating the status of the aquifer in terms of the advance or regression of the saline front. A new multi-rectangular diagram is proposed that aids interpretation of these important processes through the representation and evolution of hydrochemical facies (hydrochemical facies evolution diagram, HFE-D). As an example, the HEF-D is applied to an alluvial aquifer in the Vinaroz-Peñíscola Plain (Spain), where Ca-Cl facies characterize the sea water intrusion phase, while Na-MixHCO₃/MixSO₄ facies characterize a freshening stage.
A hydrochemical facies evolution diagram (HFE‐D) is a multirectangular diagram, which is a useful tool in the interpretation of sea water intrusion processes. This method note describes a simple ...method for generating an HFE‐D plot using the spreadsheet software package, Microsoft Excel. The code was applied to groundwater from the alluvial coastal plain of Grosseto (Tuscany, Italy), which is characterized by a complex salinization process in which sea water mixes with sulfate or bicarbonate recharge water.
A set of analytical data from the Espadán-Calderona Triassic Domain aquifers was processed using hierarchical agglomerative cluster analysis (HCA) and principal component analysis (PCA), to achieve a ...quantitative and independent approach to investigate the characteristics of groundwater composition and possible differences between groundwater flows from Triassic aquifers from the Espadán-Calderona Triassic Domain (Spain). Mineralization in the Triassic series has led to the presence of several metals and metalloids in groundwater, including As, Mn, Fe and U. These are associated with fresher bicarbonate groundwaters, characterized by lower Sr/Ba ratios. Levels containing sulfate evaporitic salt, which are interbedded through the Triassic series, seem to exert a strong influence on the chemistry of several groundwaters, characterized by calcium sulfate facies with high Sr concentration and high Sr/Ba ratios. The application of multivariate statistical techniques to the interpretation of analytical results allows the differentiation of groundwater types occurring in the Triassic aquifers and identification of the role of a number of minor or trace elements and their ratios that can be treated as hydrogeochemical tracers. With them it was possible to correlate the different recharge waters with the tectonic morphology of the Espadán-Calderona Triassic Domain.
Naturally occurring arsenic in groundwater exceeding the limit for potability has been reported along the southern edge of the Cenozoic Duero Basin (CDB) near its contact with the Spanish Central ...System (SCS). In this area, spatial variability of arsenic is high, peaking at 241μg/L. Forty-seven percent of samples collected contained arsenic above the maximum allowable concentration for drinking water (10μg/L).
Correlations of As with other hydrochemical variables were investigated using multivariate statistical analysis (Hierarchical Cluster Analysis, HCA and Principal Component Analysis, PCA). It was found that As, V, Cr and pH are closely related and that there were also close correlations with temperature and Na+. The highest concentrations of arsenic and other associated Potentially Toxic Geogenic Trace Elements (PTGTE) are linked to alkaline NaHCO3 waters (pH≈9), moderate oxic conditions and temperatures of around 18°C–19°C. The most plausible hypothesis to explain the high arsenic concentrations is the contribution of deeper regional flows with a significant hydrothermal component (cold-hydrothermal waters), flowing through faults in the basement rock. Water mixing and water-rock interactions occur both in the fissured aquifer media (igneous and metasedimentary bedrock) and in the sedimentary environment of the CDB, where agricultural pollution phenomena are also active.
A combination of multivariate statistical tools and hydrochemical analysis enabled the distribution pattern of dissolved As and other PTGTE in groundwaters in the study area to be interpreted, and their most likely origin to be established. This methodology could be applied to other sedimentary areas with similar characteristics and problems.
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•High-As groundwaters are identified in the contact area of the Duero Basin-Spanish Central System.•Structural control of As distribution in groundwaters of this area is marked.•Cold-hydrothermal NaHCO3 waters linked to the deep confined aquifer were identified.•Alkaline NaHCO3 waters are recognized as the primary source of As, V, Cr, (and U).
In the southern part of the Cenozoic Duero Basin (Spain), naturally occurring arsenic and uranium in groundwater sometimes occur in concentrations exceeding the limits for potable water. Usually, ...concentrations of these elements are only slightly above the limit, but this is sufficient to invalidate its use as drinking water.
Hydrogeotoxic risk or hydrogeotoxicity (HGT) is defined as the quotient between the observed concentration of an element and the limit set by health regulations (such as by the World Health Organization, WHO). Areas at risk of HGT from a given Potentially Toxic Geogenic Trace Element (PTGTE) are defined a quotient of >1.
Hydrogeotoxicity of arsenic and uranium (HGTAs and HGTU) were calculated for water samples and 34% returned HGTAs above 1. For uranium, different HGT indexes were considered against a variety of thresholds for drinking water established by different countries and organizations (10μg/L, Germany; 15μg/L, WHO, 2004; 30μg/L, WHO, 2011/US-EPA, 2011): 48% samples returned HGTU10>1; 29% samples, HGTU15>1 and 7% had HGTU30>1. In the water samples analyzed, the highest arsenic content were usually associated with the highest uranium concentrations. However sometimes these two hydrogeotoxicities do not coincide and the HGTAs and HGTU10 distributions show different patterns.
Hydrogeotoxicity due to more than one element (HGTAs and HGTU10) was also considered; 17% samples showed a potentially hydrogeotoxic risk linked to both PTGTEs, leading to the delimitation of these zones as especially vulnerable to a combined hydrogeotoxic hazard.
The linear distribution of HGTAs seems to be related to the structure of the Cenozoic Duero Basin and to deep water inflows that are enriched in As and U, which are associated with its fissured basement. The HGTU can be partly linked to these deep flows with a significant hydrothermal component, but they are also linked to secondary processes occurring in the sedimentary basin, which could explain the scattered distribution of HGTU in some areas.
As well as the HGT values, which are based on total concentrations, bioavailability of arsenic and uranium species was also considered in order to provide a comprehensive assessment of hydrogeotoxic risk over the study area. In all samples with HGTAs>1, arsenic was present as As(V) inorganic form. Likewise, in samples with HGTU10>1, uranium appears as U(VI). This hydrogeotoxic anomaly must be related to both the chemical and radiological hazards.
•HydroGeoToxicity by As and U were calculated in the south edge of the Duero Basin.•The distribution of HGTAs seems to be related to the structure of the basin basement.•The HGTU seems partly linked to structural factors but also to secondary processes.•HGTAs>1 is related with As(V) speciation, whilst HGTU>1 with U(VI).•HGTU>1 must be associated to chemical and radiological hazards.
The Water Framework Directive (WFD) requires EU member states to assess the chemical status of groundwater bodies, a status defined according to threshold values for harmful elements and based on/the ...natural background level (NBL). The NBL is defined as the expected value of the concentration of elements naturally present in the environment. The aim of this study is to propose a methodology that will be broadly applicable to a wide range of conditions at the regional and national scale. Using a statistical approach, the methodology seeks to determine NBLs for SO4, As, Cd, Cr, Cu, Ni, Zn, and F based on the lithology of aquifers from which groundwater monitoring data were collected. The methodology was applied in six EU countries to demonstrate validity for a wide range of European regions. An average concentration was calculated for each parameter and chosen water point and linked to a lithology. Based on the dataset created, significant differences between lithologies and pressure categories (urban, agricultural, industrial, and mining) were tested using a nonparametric test. For each parameter, 90th percentiles were calculated to provide an estimation of the maximum natural concentrations possible for each lithology.
Groundwater from springs and boreholes on the southern edge of the Cenozoic Duero Basin (DB) of Spain has concentrations of arsenic (As) which are commonly above the EC drinking-water limit of ...10 μg/L and reach observed values up to 241 μg/L. Groundwater compositions within the sedimentary aquifer vary from Ca–HCO₃ type, variably affected by evaporation and agricultural pollution at shallow levels, to Na–HCO₃ compositions in deeper boreholes of the basin. Groundwater conditions are mainly oxidising, but reducing groundwaters exist in sub-basins within the aquifer, localised flow paths likely being influenced by basement structure. Arsenic concentrations are spatially variable, reaching up to 38 μg/L in springs of the Spanish Central System (SCS) basement aquifer and up to 62 μg/L in springs from the DB. Highest As concentrations are associated with the Na–HCO₃ compositions in deep boreholes (200–450 m depth) within the DB. These have high pH values (up to 9.6) which can give rise to associated elevated concentrations of V and U (up to 64 and 30 μg/L, respectively). In the deep borehole waters of the DB, oxidising flows derived from the mineralised igneous–metamorphic basement and discharging via major faults, and are considered the origin of the higher concentrations. Compositions are consistent with desorption of As and other anionic species from metal oxyhydroxides in an oxic environment. Under locally reducing conditions prevalent in some low-flow parts of the DB, an absence of detectable dissolved As is coincident with low or undetectable SO₄ concentrations, and consistent with loss via formation of authigenic sulphide minerals. Mitigation measures are needed urgently in this semi-arid region where provision of alternative sources of safe drinking water is logistically difficult and expensive.
Several coastal plains of the Elba Island (Marina di Campo, Portoferraio, Schiopparello, Mola, Porto Azzurro and Barbarossa plains) in Tuscany (Italy) were studied to determine the causes of decline ...in groundwater quality, using major ion chemistry to establish the causes of groundwater salinization. The study demonstrates that salinization of coastal plain alluvial aquifers is not simply linked to seawater intrusion but is also intimately related to inflows from adjacent aquifers. Ionic ratios, correlation graphs and distribution value maps were employed as the means to understand the hydrochemistry of the study areas. The Mg/Cl ratio in particular can be considered a good tracer to distinguish the main salinization processes that control groundwater chemistry. Seawater intrusion only partly determines the chemistry of some groundwaters, which generally belong to a chloride facies where the salinity is derived principally from freshwater-seawater mixing and the participation of cation exchange. Proceeding inland groundwater quality seems to be principally determined by the inflow of Mg, Ca-HCO₃ or Ca, Na-HCO₃ waters formed from the weathering of silicate minerals in adjoining aquifers. Hydrolysis of these minerals is of prime importance in controlling groundwater chemistry in adjacent alluvial plains. The lateral recharge flows introduce water with a different chemical composition and this variable of freshwater recharge changes the hydrochemistry as a result of mixing between two or more waters types. This situation is further complicated when seawater and base exchange reactions participate, due to seawater intrusion.
A study has been performed to explore the origin, spatiotemporal behaviour and mobilisation mechanism of the elevated arsenic (As) concentrations found in ground water and drinking ponds of the ...Doñana National Park, Southern Spain. At a larger scale, 13 piezometers and surface water samples of about 50 artificial drinking ponds and freshwater lagoons throughout the National Park were collected and analysed for major ions, metals and trace elements. At a smaller scale, 5 locations were equipped with piezometers and groundwater was sampled up to 4 times for ambient parameters, major ions, metals, trace elements and iron (Fe) speciation. As was analysed for inorganic and organic speciation. Undisturbed sediment samples were analysed for physical parameters, mineralogy, geochemistry as well as As species. Sediment analyses yielded total As between 0.1 and 18mg/kg and are not correlated with As concentration in water. Results of the surface- and groundwater sampling revealed elevated concentration of As up to 302μg/L within a restricted area of the National Park. Results of groundwater sampling reveals strong correlation of As with Fe2+ pointing to As mobilisation due to reductive dissolution of hydroferric oxides (HFO) in areas of locally elevated amounts of organic matter within the sediments. High As concentrations in surface water ponds are correlated with elevated alkalinity and pH attributed to algae metabolism, leading to As desorption from HFO. The algae metabolism is responsible for the presence of methylated arsenic species in surface water, in contrast to ground water in which only inorganic As species was found. Temporal variations in surface water and groundwater are also related to changes in pH and alkalinity as a result of enhanced algae metabolism in surface water or related to changes in the redox level in the case of groundwater.
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•High pH and alkalinity due to algae metabolism leading to arsenic mobilisation.•Detection of organic As species in surface water.•As mobilisation by reductive dissolution of HFO and competitive sorption on HFO surfaces.
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