Chemical Evolution Of Groundwater Research Articles

Impact of anthropogenic and natural processes on the evolution of groundwater chemistry in a rapidly urbanized coastal area, South China

The moving of manufacturing industry from developed countries to Dongguan, China, promoted the semi-urbanization and rural industrialization in this area. It is urgent to acquire the impact of the enhanced anthropogenic pressure on the evolution of groundwater chemistry in this area. The objectives, in this study, were to understand the evolution of groundwater chemistry in Dongguan area based on the comparison of hydrochemical data variations and land use changes during the urbanization, to distinguish the impact of natural processes and anthropogenic activities on the groundwater chemistry by using principal components analysis (PCA) and hierarchical cluster analysis (HCA), and to discuss the origins of trace elements in groundwater. Eighteen physico-chemical parameters were investigated at 73 groundwater sites during July 2006. By analyzing the hydrochemical data, it shows that lateral flow from rivers and agricultural irrigation are the mechanisms controlling the groundwater chemistry in the river network area where the cation exchange of Na+ in sediments taken up by the exchanger Ca2+ occurs. Seawater intrusion is the mechanism controlling the groundwater chemistry in the coast area where the cation exchange of Ca2+ in sediments taken up by the exchanger Na+ occurs. The ion exchange reaction for fissured aquifer is weak in the study area. In addition, the comparison of hydrochemical data between in 2006 and in 1980 shows that anthropogenic activities such as excessive application of agricultural fertilizers, inappropriate emissions of domestic sewage and excessive emissions of SO2 are responsible for the occurrences of groundwater with NO3−, SO42− and Mg2+ types. Four principal components (PCs) were extracted from PCA, which explain 80.86% of the total parameters in water chemistry: PC1, the seawater intrusion and As contamination; PC2, the water–rock interaction, surface water recharge and acidic precipitation; PC3, heavy metal pollution from industry; and PC4, agricultural pollution and sewage intrusion. Four clusters were generated from HCA: cluster 1 is mainly influenced by the industrialization; cluster 2 is mainly affected by the water–rock interaction and the irrigation and lateral flow of river water; cluster 3 is mainly influenced by the seawater intrusion; and cluster 4 is mainly influenced by the sewage intrusion and agricultural pollution. The results show that both natural processes such as seawater intrusion, water–rock interaction and lateral flow of river water and anthropogenic activities such as industrialization, sewage intrusion and agricultural pollution are the two major factors for the evolution of groundwater chemistry in Dongguan area.

Geochemical and isotopic evolution of groundwater in the Wadi Watir watershed, Sinai Peninsula, Egypt

The Wadi Watir delta in the Wadi Watir watershed is a tourist area in the arid southeastern part of the Sinai Peninsula, Egypt, where development and growth of the community on the delta are constrained by the amount of groundwater that can be withdrawn sustainably. To effectively manage groundwater resources in the Wadi Watir delta, the origin of groundwater recharge, groundwater age, and changes in groundwater chemistry in the watershed needs to be understood. Mineral identification, rock chemistry, water chemistry, and the isotopes of hydrogen, oxygen, and carbon in groundwater were used to identify the sources, mixing, and ages of groundwater in the watershed and the chemical evolution of groundwater as it flows from the upland areas in the watershed to the developed areas at the Wadi Watir delta. Groundwater in the Wadi Watir watershed is primarily from recent recharge while groundwater salinity is controlled by mixing of chemically different waters and dissolution of minerals and salts in the aquifers. The El Shiekh Attia and Wadi El Ain areas in the upper Wadi Watir watershed have different recharge sources, either from recharge from other areas or from different storm events. The downgradient Main Channel area receives groundwater flow primarily from the El Shiekh Attia area. Groundwater in the Main Channel area is the primary source of groundwater supplying the aquifers of the Wadi Watir delta.

Influence of the natural oxidation of the leachate organic fraction from a landfill on groundwater quality, Belo Horizonte: Minas Gerais, south-eastern Brazil

The objective of this work was to evaluate the influence of the natural degradation of the leachate organic fraction from the Belo Horizonte landfill on groundwater chemical evolution. The work focused on the modifications introduced by redox reactions in the presence of terminal electron acceptors. Twenty-one sampling points distributed along 13 monitoring wells were selected for the analysis of the chemical indicators of interest (TDS, SO4−2, Fe+2, Ba, pH and Eh). The behaviour of the variables involved in the alteration of the water quality was assessed by the spatial distribution of target parameters, elaboration of redox diagrams and chemical modelling that focused on the determination of mineral saturation indexes. The study showed a trend toward pyrite precipitation, which leads to the removal of chemical species such as divalent iron and sulphur as sulphide from the system. This removal disturbs the chemical equilibrium, typically by moving the reactions to replenish the sulphate concentration present in the groundwater. This process occurs primarily through the dissolution of compounds that have sulphate in their chemical composition, such as barite, suggesting that part of the barium concentration in the subsurface can be of geogenic origin. This study demonstrated the importance of knowing the nature of the geochemical processes in groundwater contaminated by urban solid waste.

Contributions of Chemical and Isotopic Tools for Understanding the Groundwater Modes Recharge and Flow in the Lower Cretaceous Aquifer in the Moroccan Sahara

The present work was conducted in the basin of Laayoun-Dakhla (South Morocco) to: 1) identify the recharge and flow characteristics of the Lower Cretaceous aquifer (LC); and 2) provide information about the mineralization of aquifer’s water. Isotopic and hydrochemical compositions combined with the geological and hydrogeological settings were used for this purpose. The principal changes in chemical composition of LC groundwater result from mixing with water of deeper circulation. Closer analysis of available chemical data reveals the importance of dissolution/precipitation processes in evolution of groundwater chemistry. Piezometric levels, as well as chemical and isotopic composition of groundwaters, confirm hydraulic connection between the LC and the others aquifers. Overlap of some major characteristics (δ18O, δ2H, Cl-) in this aquifer suggests that mixing processes considerably influence the hydrochemical evolution of water. The surface electrical resistivity does not indicate any freshwater-saltwater interface in the coastal aquifer and the relationship between 18O and Cl allows us to reject the hypothesis of a seawater intrusion.

The chemical evolution of groundwater in the Kerman plain aquifer, Iran

A comprehensive hydrogeochemical study was carried out in the Kerman Plain Aquifer, Iran. Groundwater samples were collected from 58 sites. Groundwater was analysed for major constituents (Na+, K+, Ca2+, Mg2+, Cl–, SO42– HCO3–. Different methods including composite diagrams, saturation indices and multivariate statistical methods were employed in assessing groundwater quality. The results show that the main hydrochemical facies of the aquifer (Na+, K+– Cl– SO42–) represents 73% of the total wells. Calcite, dolomite, and gypsum solubilities were assessed in terms of the saturation index indicating supersaturation with respect to calcite and dolomite and undersaturation with respect to gypsum. Groundwater samples were classified into three distinctive groups using cluster analysis. The results of factor analysis indicate that four factors explain about 88.9% of the total sample variance. The variables underlying the first and the most important factor are mainly controlled by halite dissolution. Dissolution of gypsum is the second important source of salinity.

Groundwater Chemical Evolution in the Essaouira Aquifer Basin—NW Morocco

The sustainability of groundwater resources for drinking water supplies, agriculture, and industry a prime concern in countries dominated by arid and semi-arid climates such as Morocco. The growing demand for groundwater coupled with impacts from land use and climate change make sustainability an even more important water management goal. In order to make sound decisions about water use and protection of water quality, managers and policy makers must have a sound understanding of such factors as the location and amount of groundwater recharge and groundwater ages. Due to the population growth and climate change (causing long periods of drought) in the world, many countries have intensively increased their use of water sources for supplying potable water to population and for their agricultural (irrigation) and industrial developments. Due to the lack of surface waters, people exploit mainly underground water reservoirs. So, it is necessary to study and characterize these water reservoirs to avoid any excess of exploitation. The water resources of the Essaouira basin are characteristic of a semi-arid climate, and are severely impacted by the climate (quantity and quality). Considering the importance of the Essaouira aquifer in the groundwater supply of the region, a study was conducted in order to comprehend this aquifer groundwater evolution. It is an aquifer located on the Atlantic coastline, southern (Morocco), corresponding to a sedimentary basin with an area of near200 km2. Covering the Palaeozoic bedrock, the sedimentary series range from the Triassic to the Quaternary. The geological structures delineate a syncline bordered by the Tidzi diapir of Triassic age which outcrops to the East and South. In the Essaouira basin a multi-aquifer was identified constituted by detrital deposits of the Plioquaternary and dolomitic limestones of the Turonian. The Plioquaternary is unconfined below the Senonian marls. However, in some places it can be in direct contact with the other Cretaceous and Triassic units. The Plioquaternary is generally up to60 mthick. The Turonian is confined by the Senonian marls and in direct contact with the Plioquaternary on the edges of the syncline structure. The main flow direction is from SE to NW towards theAtlantic Ocean, being the recharge area located near the Tidzi diapir. In the Essouaira basin, in spite of the occurrence of calcareous and dolomitic levels, all waters are of Na-Cl-type. The chemical signature of these waters should be the result of the preferential recharge area that is located in the Tidzi diapir. Using a simple mass balance model through the PHREEQC program this scenario was tested. The reaction path was assumed to be such that waters observed at shallow depths evolved to more mineralized waters. It was possible to notice that these waters have an important contribution of water-rock interaction in groundwater mineralization, corroborating the influence of the preferential recharge area located in the Tidzi diaper in the waters signature.

Investigation of the hydrogeochemical processes in an alluvial channel aquifer located in a typical Karoo Basin of Southern Africa

An investigation was conducted to assess the hydrogeochemical processes of an alluvial channel aquifer located in a typical Karoo Basin of Southern Africa. The investigation was aimed at identifying and describing the groundwater chemistry evolution and its contribution to the overall groundwater quality. X-ray fluorescent spectrometry (XRF) and X-ray diffractometry (XRD) analyses were performed on geological samples to identify and quantify the major element oxides and minerals. The study utilises the conventional Piper diagram, bivariate plots and PHREEQC hydrogeochemical model to analyse groundwater chemistry data obtained during the wet (February and May) and dry seasons (August and December) of 2011. The XRF and XRD results show that the channel deposits are dominated by SiO2 element oxides and quartz minerals, thus elevated concentrations of silicon (Si4+) were found in the groundwater. Dolomite and calcite minerals were also detected in the unconsolidated aquifer sediments. The detailed study of the alluvial aquifer system has shown that dissolution of dolomite and calcite minerals and ion exchange are the dominant hydrogeochemical processes influencing the groundwater quality. The groundwater evolves from Ca2+–Mg2+–HCO3 − recharge water that goes through ion exchange with Na+ in the clay-silt sediment to give a Na+–HCO3 − water type. The groundwater is supersaturated with respect to quartz, dolomite and calcite minerals. The study shows the potential usefulness of simple bivariate plots as a complimentary tool to the conventional methods for analyzing groundwater hydrogeochemical processes.

Groundwater recharge and hydrogeochemical evolution in the Ejina Basin, northwest China

Groundwater plays a dominant role in the eco-environmental protection of arid/semi-arid areas. Understanding sources and mechanisms of groundwater recharge in the Ejina Basin, an arid inland river basin in northwest China, is important for water resource planning in this ecologically sensitive area. In this study, 90 water samples were collected from rainfall, rivers and lakes, and springs and pumping wells in 2009. Analysis of the aquifer system and hydrological conditions, together with hydrogeochemical and isotope techniques were used to investigate groundwater sources and their associated recharge processes. Our results show that shallow phreatic and deep confined groundwater differ greatly in their compositions, with a distinct spatial heterogeneity of phreatic groundwater TDS (from 365 mg/L to 5833 mg/L), which increase along the shallow groundwater flow paths. Groundwater chemical evolution is mainly controlled by rock dominance and the evaporation-crystallization process, and the dominant anion species change systematically from HCO3 to SO4 to Cl, and the dissolved ions within the groundwater system from Na- and K-rich minerals and sulfate phases also contribute significantly to the groundwater composition. The stable isotope levels (delta O-18 and delta H-2) of the surface water and the shallow phreatic groundwater confirm that the Heihe River and Badain Jaran Desert groundwater are the main sources recharging the phreatic aquifer in the Ejina Basin. Thus, river infiltration and desert front recharge should be considered as the two main recharge mechanisms of the Ejina aquifer. However, recharge from the Badain Jaran Desert aquifer to the Ejina Basin has occurred at a lower rate due to acidification since the middle Holocene. For this reason, the sustainable improvement of the ecological environment should be based on the shallow groundwater recharge of the phreatic aquifer in the Ejina Delta, which mainly takes place via seepage through the riverbed and direct infiltration during periods of environmental flow control. (C) 2012 Elsevier B.V. All rights reserved.

Recharge processes and groundwater evolution of multiple aquifers, Beijing, China

A geological and hydrogeological survey was performed in the upper alluvial and proluvial fan and the northern mountain area of the Chaobai River in Beijing. Samples of local precipitation, surface water and groundwater (including spring discharges, groundwater from the fractured bedrock, and shallow and deep groundwater of the alluvium) were collected and analysed to assemble hydrochemical and isotopic data. Q-mode hierarchical cluster analysis (HCA) was used to classify the groundwater samples from multiple aquifers into objective groups. Two groups and six subgroups with distinct groundwater recharge sources, flowpath histories and geochemical evolution histories were identified. Inverse geochemical modelling was adopted to study the deep groundwater chemical evolution. Hydrochemical data and isotopic data on 2H, 3H and 18O were used to evaluate groundwater recharge, flowpath histories and geochemical evolution, and 87Sr was used to provide further insight into groundwater recharge sources and flow directions. It was found that particularly in areas of groundwater cones of depression, the deep alluvial groundwater may be partly derived from the groundwater of the underlying fractured bedrock. The phreatic, or unconfined, groundwater within the northern area of the alluvial and proluvial fan is sustained mainly by the lateral flow of groundwater from the piedmont regions and by recharge from surface water bodies such as the Miyun reservoir. The shallow alluvial groundwater within the central and southern areas of the alluvial and proluvial fan is recharged primarily by the local precipitation and agricultural irrigation. The deep alluvial groundwater within the central and southern areas of the fan is sustained chiefly by the flow of groundwater from the northern area of the fan or from the underlying fractured bedrock. Methodologies adopted in this work may be useful to future investigation of groundwater in multiple aquifer systems similar to this area.

Use of Hydrochemistry and Stable Isotopes as Tools for Groundwater Evolution and Contamination Investigations

Hydrochemical and isotopic studies in groundwater was attempted in a basin to gain knowledge on geochemical evolution and water quality status. The results of the chemical analysis indicate the sources of ions into the groundwater are from dissolution and leaching from source rocks, cation exchange and anthropogenic activities. The saturation index calculated specify oversaturation of carbonate species and undersaturation of amorphous silica indicating groundwater chemical evolution controlled by water rock interactions. Water type alters from Ca-HCO<SUB>3</SUB> to Na-Cl indicating groundwater chemistry controlled by rock-water interaction and anthropogenic activities. The plots of various ionic ratios point out groundwater chemistry affected by ion exchange process, silicate and carbonate weathering along with anthropogenic activities. The isotopes of δ<SUP>2</SUP>H versus δ<SUP>18</SUP>O signify ionic concentration increases along the groundwater flow direction along lower elevations. The water type’s classification designate 5 distinct groups ranging from low EC and highly depleted isotopes to very high EC with enriched stable isotopic composition indicating longer residence time of groundwater.

The hydro-geochemistry of groundwater resources in an area with prevailing saline groundwater, lower Shire Valley, Malawi

The area considered in this study lies within the western section of the East African Rift System (EARS) and saline groundwater occurs in some parts of the valley plain. Hydrochemical groundwater types were classified into three groups (G1–G3), indicating different stages of groundwater chemical evolution. An overall incongruent weathering of aluminosilicate minerals causes the groundwater solution to generally be in equilibrium with montmorillonite. Ca–(Mg)–HCO3 groundwater (G1), with relatively low TDS (average TDS=548mg/L), are mainly found in areas with Karoo basalt and Precambrian basement complex rocks. This water type is mainly governed by aluminosilicate weathering. Towards the middle of the valley, Na- and mixed cation-HCO3 groundwater (G2; average TDS=1061mg/L) predominates. This water type results from a combination of aluminosilicate mineral weathering, cation exchange and precipitation of clays and carbonates. The increase in ionic strength of G2 samples, in comparison with G1 samples, is attributed to mixing with high TDS groundwater in G3. Brackish and saline groundwaters (G3; average TDS=3457mg/L) are dominated by sodium, chloride and sulphate ions, which is attributable to dissolution of Cl− and SO42- evaporative salts. These are found in clusters and in aquifers with low recharge capacity (low transmissivity) and are attributable to intrusion of mineralised groundwater probably through fault zones from mainly sedimentary Karoo and Cretaceous Lupata formations. Evaporation plays a role in brackish/saline groundwaters found in areas with shallow water table along the Shire River.

Groundwater Flow Patterns and Hydrochemical Facies Distribution Using Geographical Information System (GIS) in Damaturu, Northeast Nigeria

The present study attempts to define the relationship between groundwater flow systems and the distribution of chemical facies with the aid of Geographical Information System (GIS). The study also identifies the different geochemical processes responsible for the chemical evolution of groundwater chemistry. Analytical results of 23 groundwater samples reveal mean values of cations as Na+ (84.2 mg/l), K+ (4.2 mg/l), Ca2+ (27 mg/l), Mg2+ (11.5 mg/l) and Fe2+ (0.6 mg/l). The anion mean values are HCO3– (4.5 mg/l), SO42– (3.7 mg/l), Cl– (22.5 mg/l) and NO3– (2.2 mg/l). Based on mean values, the cations are in order of abundance as Na+ > Ca2+> Mg2+ > K+ > Fe2+ while the anions reveal order of abundance as Cl– > HCO3– > SO42– > NO3– . The geographical information system (GIS) using Inverse Distance Weighted (IDW) delineate two groundwater zones into: Ca-Mg-SO4-Cl and Na-SO4-Cl water types. The Ca-Mg-SO4-Cl constitutes about 35% of the chemical facies and its evolutionary trend is due to simple hydrochemical mixing between Ca-Mg-HCO3 and Na-SO4-Cl facies and reverse cation exchange. The Na-SO4-Cl facies constitutes about 65% of the chemical facies and represents fossil groundwater. The Ca-Mg-SO4-Cl facies is dominant in the recharge areas while Na-SO4-Cl facies prevails in discharge areas. Rock-water interaction diagrams indicate precipitation induced chemical weathering along with dissolution of rock-forming minerals. The scattered plots among ions revealed geochemical processes as carbonate weathering, silicate weathering, cation exchange and sulphate reduction. HCA identified effects of rock-water interaction and anthropogenic effects as responsible for the modification of groundwater chemistry in the area.

Investigation for Assessment of Physico-chemical Water Quality with Modification Parameters in Ghaemabad and Nogan Rural of Iran of Gharghab River, Specially about Langlier's Index

In Ghaemabad and Nogan towns, groundwater and well water is the chief water source for agricultural and domestic use and understanding of the chemical evolution of groundwater provides an insight into the interaction of water with environment and contributes to better management of sources. Water quality in rural areas is still poor. The present research work reports on the results of water quality in rural areas of Ghaemabad and Noghan that is situated near the Kharghab river. Nine water samples from 4 sites of the river at the 2 rural (each rural is 2 sites) were collected. The physico–chemical parameters, trace heavy metals like manganese, calcium, zinc chromium, cadmium, lead, copper, iron, nickel were determined by employing standard methods (APHA, 1976 [1] Trivedy and Goel 1986 [2]. More of anions, COD, TDS, Alkalinity, DO were determined by Trivedy and Goel, 1986 [3].

Hydrochemical analysis and evaluation of groundwater quality of a Mio-Plio-Quaternary aquifer system in an arid regions: case of El Hancha, Djebeniana and El Amra regions, Tunisia

A hydrogeochemical approach has been carried out in the Mio-Plio-Quaternary aquifer system of northern Sfax to investigate the geochemical evolution, the origin of groundwaters and their circulation patterns. The groundwater samples collected from different wells seem to be dominated by sodium chloride type to sulphate chloride type. Detail analysis of chemical data including the thermodynamic calculations was used to assess that the chemical evolution of groundwater is primarily controlled by water–rock interactions. The values of sodium absorption ratio and electrical conductivity of the groundwater were plotted in the US Salinity Laboratory diagram for irrigation water. Most of the water samples in northern Sfax fall in the fields of C4S1, C4S2 and C4S3 indicating very high salinity and medium to high sodium alkalinity hazard. Thus, groundwater quality is ranging between doubtful to unsuitable for irrigation uses under normal condition, and further action for salinity control is required in remediating such problem. Principal component analysis of geochemical data used in conjunction with bivariate diagrams of major elements indicates that groundwater mineralization is mainly controlled by (1) water–rock interaction processes, (2) anthropogenic process in relation with return flow of NO3-rich irrigation waters and (3) domestic discharges.

Anthropogenic impact assessment of Niangziguan karst water

As the biggest karst spring system in northern China, the Niangziguan karst water system is the major source of water supply for Yangquan city, one of the most important bases of coal production in China. In this study, the chemical composition of karst groundwater was investigated with particular emphasis on identifying the sources of chemical variation. The results show significant geographic variation in chemical constituents through the karst groundwater system and also indicate that human activity is responsible for much of the observed hydrochemical variation. The addition of SO42−, Cl− and NO3− from human activities causes the groundwater hydrochemistry to vary from the HCO3-Ca-Mg or HCO3-SO4-Ca-Mg type to the SO4-HCO3-Ca, Cl-SO4-HCO3-Ca, SO4-Ca or SO4-Cl-Ca type. Results from factor analysis indicate that abnormally high levels of SO42− and Na+ are from sources related to coal mining activity, which is widely distributed in the study area. High concentrations of Cl− and NO3− result from sources related to human activities such as agriculture and mining wastewaters and sewage discharge. The results of cluster analysis in combination with hydrogeochemical analysis indicate that natural and anthropogenic processes jointly control the evolution of groundwater chemistry in regional groundwater systems like Niangziguan.

Hydrochemical Characteristics and Sodification of Groundwater in the Shirin Sou, Hamedan, Western Iran

Salinity and sodicity of groundwater are the principal water quality concerns in irrigated areas of arid and semi-arid regions. The hydrochemical characteristics and sodicity of groundwater in the Shirin Sou area, western Iran were investigated in this study by chemical analyses of groundwater samples from 49 wells. Chemical analysis of the groundwater showed that the mean concentration of the cations was in the order: Na+ > Ca2+ > Mg2+ > K+, while that for anions was SO32− > Cl− > HCO3− > NO3−. The most prevalent water type is Na–SO4 followed by water types Na–Cl and Ca–SO4. The chemical evolution of groundwater is primarily controlled by water–rock interactions: mainly weathering of aluminosilicates, dissolution of sulfate minerals, and cation exchange reactions. Sulfate dissolution and pyrite weathering may both contribute to the SO42− load of the groundwater. High Na+ concentrations in groundwater participate in ion-exchange processes, resulting in the displacement of base cations into solution and raised concentrations in groundwater. The principal component analysis (PCA) performed on groundwater identified three principal components controlling variability of groundwater chemistry. Electrical conductivity, Ca2+, Mg2+, Na+, SO42−, and Cl− content were associated in the same component (PC1) (salinity), most likely linked to anthropogenic activities.

Modelling the baseline geochemistry of groundwater in a Chalk aquifer considering solid solutions for carbonate phases

The Chalk aquifer of Champagne (France) baseline geochemistry has been determined using a solid solution approach for the modelling of calcite dissolution. The water–rock interactions are modelled by the speciation code CHESS from field data and Ca, Mg and Sr aqueous concentrations in groundwater. The stoichiometries of solid solutions are defined in each stratigraphic unit of the Chalk aquifer from bulk geochemistry and Chalk mineralogy of samples taken from boreholes. The initial mineralisation of water at the bottom of the unsaturated zone and the characterisation of the theoretical evolution of groundwater chemistry along the flow lines associated with incongruent calcite dissolution are calculated from this approach.

Hydrogeochemistry of groundwaters in a semi-arid region. El Ma El Abiod aquifer, Eastern Algeria

In this work, we present results of the hydrogeochemical and isotopic studies on groundwater samples from the El Ma El Abiod Sandstone aquifer, in Tebessa, Algeria. Chemical and environmental isotope data are presented and discussed in order to identify the geochemical processes and their relation with groundwater quality as well as to get an insight into the hydrochemical evaluation, in space and time, of groundwater and of the origin of dissolved species. A combined hydrogeologic and isotopic investigation have been carried out using chemical and isotopic data to deduce a hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies, and factors controlling groundwater quality. All of the investigated groundwaters are categorized into two chemical types: low mineralized water type and relatively high mineralized water type. Interpretation of chemical data, based on thermodynamic calculations and geochemical reaction models of selected water groups constructed using PHREEQC, suggest that the chemical evolution of groundwater is primarily controlled by water–rock interactions, involving (1) acidic weathering of aluminosilicates, (2) dissolution of secondary carbonate minerals, and (3) cation exchange of Na+ for Ca2+. However, the original composition of groundwater may have been modified by further secondary processes such as mixing of chemically different water masses. The combined use of SI and mass-balance modeling has shown to be a useful approach in interpreting groundwater hydrochemistry in an area where large uncertainties exist in the understanding of the groundwater flow system. Interpretation of 18O and 2H, suggest that the recharge of the investigated groundwaters may result from different mechanisms.

A new groundwater radiocarbon correction approach accounting for palaeoclimate conditions during recharge and hydrochemical evolution: The Ledo-Paniselian Aquifer, Belgium

The particular objective of the present work is the development of a new radiocarbon correction approach accounting for palaeoclimate conditions at recharge and hydrochemical evolution. Relevant climate conditions at recharge are atmospheric pCO2 and infiltration temperatures, influencing C isotope concentrations in recharge waters. The new method is applied to the Ledo-Paniselian Aquifer in Belgium. This is a typical freshening aquifer where recharge takes place through the semi-confining cover of the Bartonian Clay. Besides cation exchange which is the major influencing process for the evolution of groundwater chemistry (particularly in the Bartonian Clay), also mixing with the original porewater solution (fossil seawater) occurs in the aquifer. Recharge temperatures were based on noble gas measurements. Potential infiltration water compositions, for a range of possible pCO2, temperature and calcite dissolution system conditions, were calculated by means of PHREEQC. Then the sampled groundwaters were modelled starting from these infiltration waters, using the computer code NETPATH and considering a wide range of geochemical processes. Fitting models were selected on the basis of correspondence of calculated δ13C with measured δ13C. The 14C modelling resulted in residence times ranging from Holocene to Pleistocene (few hundred years to over 40 ka) and yielded consistent results within the uncertainty estimation. Comparison was made with the δ13C and Fontes and Garnier correction models, that do not take climate conditions at recharge into account. To date these are considered as the most representative process-oriented existing models, yet differences in calculated residence times of mostly several thousands of years (up to 19 ka) are revealed with the newly calculated ages being mostly (though not always) younger. Not accounting for climate conditions at recharge (pCO2 and temperature) is thus producing substantial error on deduced residence times. The derived 14C model ages are correlated with He concentrations measured in the groundwater of the aquifer. The obtained residence times show a gap between about 14 and 21 ka indicating possible permafrost conditions which inhibited any groundwater recharge.

Conservative behavior of arsenic and other oxyanion-forming trace elements in an oxic groundwater flow system

Summary Groundwater samples were collected along a flow path in a shallow, fractured tuffaceous aquifer from the Oasis Valley–Beatty Wash region of southern Nevada, USA, and analyzed for a number of oxyanion-forming trace elements including arsenic (As), antimony (Sb), selenium (Se), molybdenum (Mo), and tungsten (W). In addition, ancillary geochemical parameters, including pH, major solute compositions, dissolved silica, dissolved oxygen, and iron and manganese concentrations were quantified in the groundwaters. Arsenic concentrations range from ∼70 nmol/kg up to 316 nmol/kg in groundwaters of the Oasis Valley–Beatty Wash flow system, and generally exhibit increasing concentrations with flow down-gradient along the flow path. Antimony, W, and to a lesser extent, Mo, exhibit similar increasing concentration trends with flow down-gradient in the aquifer, albeit, at lower concentrations levels (e.g., mean ± SD for Sb, W, and Mo are 2.3 ± 0.9 nmol/kg, 7.4 ± 3.7 nmol/kg, and 101 ± 19 nmol/kg, respectively). Selenium concentration, which range between ∼4 and 11 nmol/kg, generally decrease in groundwaters with flow down-gradients in the Oasis Valley–Beatty Wash groundwater flow systems. Inverse modeling of groundwater chemistry evolution from the lower reaches of the Oasis Valley flow path using PHREEQC indicate that the groundwater composition is consistent with mixing of nearly equal proportions of groundwater from upper reaches of Oasis Valley and Beatty Wash groundwater, along with dissolution of volcanic glass, potassium feldspar, and gypsum, followed by calcite precipitation, and formation of secondary zeolites (analcime), clay minerals (Ca-montmorillonite), and cristobalite. The geochemical modeling indicates that the concentrations of As and the other oxyanion-forming trace elements are controlled by dissolution of volcanic glass, water–rock interaction with mineralized zones within the aquifer (i.e., sulfide oxidation), desorption from aquifer surface sites, and mixing of Oasis Valley and Beatty Wash groundwaters.