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This study focuses on assessing hydrochemical characteristics and non-carcinogenic health risks associated with fluoride contamination in groundwater within the Palacode and Pennagaram taluks of Dharmapuri district. The presence of fluoride in drinking water is a significant concern due to its potential health impacts on both adults and children. We collected a total of 158 groundwater samples during both the summer (SUM) and monsoon (MON) seasons in 2021 to evaluate the suitability of water for drinking purposes in this region. During the SUM season, groundwater exhibits alkaline characteristics with a pH range of 6.70 to 8.73 and a mean value of 7.43, while the MON season falls within the neutral pH range with values ranging from 6.60 to 7.60 and a mean of 7.00. Hydrogeochemical analysis reveals that fluoride concentrations during the SUM season range from 0.13 to 2.7 mg/L, with a mean of 0.82 mg/L, whereas the MON season exhibits concentrations ranging from 0.08 to 1.6 mg/L, with a mean of 0.5 mg/L. Spatial distribution analysis indicates a gradual increase in fluoride concentrations from the northeast to the central and southern parts of the study area during both seasons. Residents in these areas have been exposed to high fluoride levels for an extended period, leading to health issues related to fluorosis. Our hydrogeochemical analysis attributes fluoride dominance to the Cl - -SO 4 2- water type in both seasons. Furthermore, the relationship between fluoride and pH, HCO 3 - suggests the influence of geological factors in fluoride dissolution under alkaline conditions, while a reverse cation exchange process and increasing calcium concentration inhibit fluoride concentration. Saturation indices indicate that the unsaturated state of gypsum dissolution contributes to elevated fluoride levels in groundwater. Additionally, Gibbs plots highlight rock-water interactions as a significant factor influencing groundwater chemistry in the study area. Based on our hazard quotient (HQ) investigation, children are at a higher risk during both seasons compared to adults, with the central and northern regions showing alarming HQ values. These findings underscore the urgent need for enhanced groundwater quality monitoring and a comprehensive assessment of health risks, providing valuable insights for groundwater safety management in vulnerable areas of this region.2+ , and Na + suggests the influence of geological factors in fluoride dissolution under alkaline conditions, while a reverse cation exchange process and increasing calcium concentration inhibit fluoride concentration. Saturation indices indicate that the unsaturated state of gypsum dissolution contributes to elevated fluoride levels in groundwater. Additionally, Gibbs plots highlight rock-water interactions as a significant factor influencing groundwater chemistry in the study area. Based on our hazard quotient (HQ) investigation, children are at a higher risk during both seasons compared to adults, with the central and northern regions showing alarming HQ values. These findings underscore the urgent need for enhanced groundwater quality monitoring and a comprehensive assessment of health risks, providing valuable insights for groundwater safety management in vulnerable areas of this region., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

A thorough understanding of the evolution of coastal brine-bearing groundwater systems under the influence of human activities contributes to the sustainable use of coastal groundwater resources. Therefore, this study comprehensively investigated the processes associated with hydrochemical changes in groundwater during brine exploitation based on long-term monitoring data. The dataset comprised 102 samples (including groundwater, seawater, rain and river samples) collected from 1966 to 2021 to capture the hydrochemical variability. Significant changes in the brine water table and concentration between the pre-overexploitation period (1965-2000) and the exploitation period (2000-2021) are observed. From the relationship between stable isotope (δ 18 O and δ 2 H) values and Cl - contents, shallow saline water (SSW) near the drawdown cone (with δ 18 O and δ 2 H values of -4.66 ‰ ~ -3.57 ‰ and - 42.1 ‰ ~ -32.8 ‰, respectively) is similar geochemically to the brine inside the drawdown cone (with values of -4.30 ‰ ~ -3.10 ‰ and - 39.0 ‰ ~ -32.3 ‰, respectively), indicating that the SSW has a recharge effect on the underground brine. The delta values of major cations were calculated to analyze the hydrochemical processes at different water quality interfaces (saline/freshwater interface, salinewater/brine interface). The results demonstrated that the SSW and deep saline water (DSW) at the offshore brine/saline water interface undergo seawater intrusion, where SSW undergoes a salinization process with cation exchange (Na + is exchanged for Ca 2+ and Mg 2+ in clay), while DSW undergoes a freshening process. The SSW at the saline/freshwater interface is affected by freshwater pumping, and the DSW undergoes a salinization process influenced by brine intrusion presenting the common salinization process with cation exchange. The hydrochemical model shows that the brine concentration recovered during the restricted exploitation stage due to the dissolution of gypsum and halite. If no measures are taken to restrict exploitation, then brine will eventually be replaced by saline water., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled “Hydrochemical evolution processes of multiple-water quality interfaces (fresh/saline water, saline water/brine) on muddy coast under pumping conditions”., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Sustainable management of groundwater resources in geological transition zones (GTZ) is essential due to their complex geology, increasing population, industrialization, and climate change. Groundwater quality monitoring and assessment represent a viable panacea to this problem. Therefore, there is a great need to investigate groundwater resources in terms of their chemistry and pollution to ascertain their quality and implement robust pollution abatement strategies. This study focused on the characterization of groundwater in a typical geological transition zone in northeastern Nigeria. Eighty-seven (87) groundwater samples were collected from dug wells and boreholes during the 2017 dry season. pH, conductivity, and total dissolved solids (TDS) were measured in situ using a multiparameter probe, while major cations and anions were measured using atomic absorption spectrometry and ion chromatography, respectively. Data were analyzed using descriptive statistics, principal component analysis (PCA), water quality index, and standard hydrochemical plots. TDS ranged between 95 and 1154 mg L -1 in basement terrains and between 49 and 1105 in sedimentary areas. pH ranged between 6.8 and 7.7 mg L -1 in basement terrains and between 5.0 and 6.5 in sedimentary areas, suggesting a moderately acidic to alkaline low mineralized groundwater. Calcium (2.6-128.0 mg L -1 ) was the dominant cation in the basement areas, suggesting silicate weathering/dissolution, while sodium (1.9-106.0 mg L -1 ) dominated the sedimentary zones due to base exchange reactions. The PCA analysis suggests that mineral dissolution (mostly silicate weathering) controls the hydrochemistry of the basement aquifers, while ion exchange and albite weathering, with some influence of anthropogenic factor, control the sedimentary aquifers. The water quality index revealed that the basement setting was predominated by poor to unsuitable groundwater, while the sedimentary terrain was characterized by potable groundwater. The dominant hydrochemical facie in the basement areas was Ca 2+ -(Mg 2+ )-HCO 3 - characteristic of recharge meteoric water. The Na + - (K + facie characterized the sedimentary zones, indicative of cation exchange reactions, while the mixed water facie typifies the geological contact zones. The shallow nature of the basement groundwaters makes them more susceptible to geogenic and anthropogenic pollution compared to the sandstone aquifers. However, the basement aquifers have better irrigation indices (Kelly ratio and soluble sodium percent) as compared to the sandstone aquifers, which exhibit poor Kelly ratios (< 1) and soluble sodium percent (> 50) ratings. Results from the study clearly highlight the poor-unsuitable groundwater quality in parts of the studied GTZ and can be very instrumental to the policymakers in implementing sustainable water treatment strategies and cleaner production technologies in GTZ to forestall the incidence of water-related diseases.3 - facie characterized the sedimentary zones, indicative of cation exchange reactions, while the mixed water facie typifies the geological contact zones. The shallow nature of the basement groundwaters makes them more susceptible to geogenic and anthropogenic pollution compared to the sandstone aquifers. However, the basement aquifers have better irrigation indices (Kelly ratio and soluble sodium percent) as compared to the sandstone aquifers, which exhibit poor Kelly ratios (< 1) and soluble sodium percent (> 50) ratings. Results from the study clearly highlight the poor-unsuitable groundwater quality in parts of the studied GTZ and can be very instrumental to the policymakers in implementing sustainable water treatment strategies and cleaner production technologies in GTZ to forestall the incidence of water-related diseases., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Chemical weathering in a groundwater basin is a key to understanding global climate change for a long-term scale due to its association with carbon sequestration. The present study aims to characterize and to quantify silicate weathering rate (SWR), carbon dioxide consumption rate and carbonate weathering rate (CWR) in hard rock terrain aided by major ion chemistry. The proposed study area Shanmuganadhi is marked with superior rainfall, oscillating temperature and runoff with litho-units encompassing charnockite and hornblende-biotite gneiss. Groundwater samples (n = 60) were collected from diverse locations and analysed for major chemical constituents. Groundwater geochemistry seems to be influenced by geochemical reactions combining dissolution and precipitation of solids, cation exchange and adsorption along with minor contribution from anthropogenic activities. The SWR calculated for charnockite and hornblende-biotite gneiss was 3.07 tons km -2  year -1 and 5.12 tons km -2  year -1 , respectively. The calculated CWR of charnockite and hornblende-biotite gneiss was 0.079 tons km -2  year -1 and 0.74 tons km -2  year -1 , respectively. The calculated CO 2 consumption rates via silicate weathering were 1.4 × 10 3  mol km -2  year -1 for charnockite and 5.8 × 10 3  mol km -2  year -1 for hornblende-biotite gneiss. Lithology, climate and relief were the key factors isolated to control weathering and CO 2 consumption rates.

The hydrogeological and hydrogeochemical data of 75 groundwater samples and Landsat 8 OLI satellite data were used to identify the source and mechanism of groundwater and soil salinization in Femenin-Ghahavand aquifer (FGA) in Hamadan area, Iran. Generally, the EC values range from 350 to 7556 μS/cm with a mean value of 1785 μS/cm. The salinity value increases in the groundwater along the flow direction from southeast to northwest. The water samples are categorized into two water types of HCO 3 -Ca and Ca 2+ -Mg 2+ -Cl - . The water samples are super-saturated with calcite and dolomite due to dissolution of carbonate rocks through the flow path from recharge to discharge zones and under-saturated with respect to gypsum and halite. The most probable source of salinity is dissolution of interlayer of halite and gypsum in Miocene Marl and Qom formation in the bedrock of FGA. Also, the ion exchange is another major process that affects the deep groundwater quality in FGA. The water samples of FGA were divided into two groups based on the HFE diagram. About 71% of the samples are plotted below the mixing line, indicating intrusion process with reverse ion exchange and the rest (29%) is under freshening process with direct ion exchange. Consequently, the source of salinity in FGA groundwater is dissolution of halite and gypsum in deep saline groundwater which is likely upconing and mixing with fresh groundwater during overexploitation. The result of soil investigation using NDS index based on Landsat 8 OLI satellite data shows severe increase in salinization from 2013 to 2019. The areas with saline groundwater have saline soil too, indicating same source of groundwater and soil salinization. However, the main cause of soil salinization would be land use change and irrigation by saline groundwater and high evaporation in the region.

Winter deicing salt application has led to water quality impairment as stormwater carries salt ions (Na + and Cl - ) through watersheds. Green infrastructure (GI) is a promising urban stormwater management practice, but its efficacy in managing salt is unknown. GI is not yet designed to remove salt, but may have potential to mitigate its loading to surface waters. Two roadside infiltration-based GI practices in Northern Virginia (bioretention and bioswale) were monitored year-round over 28 precipitation events to investigate the transport of salt through modern stormwater infrastructure. Stormwater runoff volumes and concentrations of salt ions entering and exiting each GI were monitored to determine reductions of salt ions. Both the bioretention and bioswale significantly reduced effluent surface loads of Cl - and Na + (76% to 82%), displaying ability to temporarily retain and infiltrate salts and delay their release to surface waters. Changes in bioretention soil chemistry revealed a small percentage of Na + was stored long-term by ion exchange, but no long-term Cl - storage was observed. Limited soil storage along with groundwater observations suggest the majority of salt removed from stormwater by the bioretention infiltrates into groundwater. Infiltration GI can buffer surface waters from salt, but are also an avenue for groundwater salt loading., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A comprehensive understanding of the hydrochemical evolution and spatial patterns of shallow groundwater systems is essential for water resource management and wetland ecological restoration. The Baiyangdian Wetland is one of the most concerning areas because of the development of the Xiong'an New Area. The spatial characteristics of groundwater hydrochemistry and potential controlling factors associated with hydrochemical evolution remain unclear. In this study, hydrogeochemistry together with the hierarchical cluster analysis were used to elucidate the hydrochemical processes and hydrological zoning patterns of shallow groundwater systems in the Baiyangdian Wetland, North China Plain. The results showed that hydrochemical compositions of shallow groundwater had considerable spatial variations, which was closely related to the inflow rivers hydrochemistry and the dynamics of groundwater–surface water interactions. A significant increase in SO42− concentration occurring at the cone of the depression was related to extensive pumping caused by anthropogenic activities. Anthropogenic activities were also a major factor controlling the spatial distribution patterns of shallow groundwater hydrochemistry. Ca2+, Mg2+, and SO42− in the wetland and shallow groundwater were primarily derived from carbonate and gypsum dissolution, while Na+ and Cl− originated from halite and silicate dissolution. Rock weathering predominated the geochemical evolution of shallow groundwater in conjunction with carbonate precipitation and cation exchange. The hydrochemistry of the shallow groundwater system presented distinct spatial zonation patterns that were classified into four clusters corresponding to seven subzones. In Zones I–IV, water‐rock interaction was the dominant factor controlling shallow groundwater chemistry, which was driven by the positive groundwater–surface water exchange. The coupled effects of anthropogenic activities and river infiltration and mixing caused the high levels of dissolved components in Zones V–VII. This study contributes to have a better understanding of the water cycle and hydraulic connections among different bodies, and will benefit the rational evaluation of hydrochemical evolution and wetland ecological restoration in the Baiyangdian Wetland. [ABSTRACT FROM AUTHOR]

To trace Critical Zone processes and to quantify Li fluxes from one Critical Zone compartment into another, we investigated the Li concentration and isotopic composition (δ7Li) of time-series water samples (including subsurface flow, groundwater and creek water), vegetation, bedrock (including separated minerals from bedrock), and regolith (including exchangeable fraction and clay-sized fraction of regolith) in a temperate forested headwater catchment in the Black Forest, Conventwald, Germany. Our estimation of the Li budget shows that atmospheric deposition and biological processes played minor roles in the Li cycle relative to chemical weathering. All water samples (δ 7Li value of 6.5 to 20.4 ‰) were enriched in 7Li compared to bedrock (-1.3 ‰) and regolith (∼-1.7 ‰), but δ7Li differed between water pathways: δ7Li variations in subsurface flow, creek water and groundwater were controlled by conservative mixing, exchangeable pool buffering and Li incorporation/adsorption, respectively. Fractionated heavy Li isotopes in water samples resulted from the formation of secondary solids which preferentially incorporated 6Li, with the separated clay-sized fraction of the regolith exhibiting more negative δ7Li values (-5.4 to −3.5 ‰) than the bulk regolith (∼-1.7 ‰). However, Li in secondary solids only accounted for 8 ± 6 % of the total Li hosted in bulk regolith, and consequently δ7Li in soil did not differ significantly from δ 7Li in bedrock. This is unexpected considering water is continuously removing 7Li in preference over 6Li from regolith. Mass balance calculations applied at the catchment scale point to an irreconcilable imbalance with our data. On one hand, the regolith's δ7Li values are not negative enough to balance the 7Li export by river water, and on the other hand Li in the riverine dissolved load only accounts for ∼ 30 % of the Li solubilized from regolith. Therefore, we suggest that there might be a "hidden export pathway" for Li at our site, possibly subsurface removal of fine particles enriched in 6Li. In light of increasingly frequent observations of such isotopic imbalances in the Critical Zone this phenomenon deserves increased attention. [ABSTRACT FROM AUTHOR]

The western U.S. is experiencing shifts in recharge due to climate change, and it is currently unclear how hydrologic shifts will impact geochemical weathering and stream concentration–discharge (C–Q) patterns. Hydrologists often use C–Q analyses to assess feedbacks between stream discharge and geochemistry, given abundant stream discharge and chemistry data. Chemostasis is commonly observed, indicating that geochemical controls, rather than changes in discharge, are shaping stream C–Q patterns. However, few C–Q studies investigate how geochemical reactions evolve along groundwater flowpaths before groundwater contributes to streamflow, resulting in potential omission of important C–Q controls such as coupled mineral dissolution and clay precipitation and subsequent cation exchange. Here, we use field observations—including groundwater age, stream discharge, and stream and groundwater chemistry—to analyse C–Q relations in the Manitou Experimental Forest in the Colorado Front Range, USA, a site where chemostasis is observed. We combine field data with laboratory analyses of whole rock and clay x‐ray diffraction and soil cation‐extraction experiments to investigate the role that clays play in influencing stream chemistry. We use Geochemist's Workbench to identify geochemical reactions driving stream chemistry and subsequently suggest how climate change will impact stream C–Q trends. We show that as groundwater age increases, C–Q slope and stream solute response are not impacted. Instead, primary mineral dissolution and subsequent clay precipitation drive strong chemostasis for silica and aluminium and enable cation exchange that buffers calcium and magnesium concentrations, leading to weak chemostatic behaviour for divalent cations. The influence of clays on stream C–Q highlights the importance of delineating geochemical controls along flowpaths, as upgradient mineral dissolution and clay precipitation enable downgradient cation exchange. Our results suggest that geochemical reactions will not be impacted by future decreasing flows, and thus where chemostasis currently exists, it will continue to persist despite changes in recharge. [ABSTRACT FROM AUTHOR]

Cation mole precents (XCa, XMg, and XNa) on clay minerals in a siliciclastic coastal aquifer calculated from groundwater compositions, can aid in distinguishing fluvial from marine sediments and locate the fluvial/marine transition zone. The clay‐cation compositions of two clay‐rich siliciclastic coastal aquifers calculated from the composition of the groundwater were compared to the location of fluvial, fluvial‐marine transition and marine environments identified by traditional core, well log and paleontological analyses. The traditionally defined fluvial depositional environment is distinguished by clays with low XNa < 8% (for 92% of the samples) and high XCa from 55% to 98% with the remainder XMg. In comparison, the traditionally defined marine depositional environment is distinguished by clays with higher XNa > 8.0% (for 86% of the samples) and lower XCa ranging from 5% to 39% with the remainder XMg. The traditionally defined fluvial/marine transition zone has values overlapping the fluvial and marine end members, with 59% with XNa < 8% (fluvial) and 41% with XNa > 8% (marine), and XCa ranging from 45% to 98% with the remainder XMg. Calculations support that the excess Na (XNa > 8%) on marine clays can be retained for 10s of millions of years despite flushing with meteoric water, because of the high clay content in marine sediments. The calculated cation composition of clays deposited from river water are XNa < 8%. In contrast XNa 8%–54% is possible for seawater equilibrated clays supporting that the values found in the different depositional zones are possible. Calculated cation compositions might supplement traditional stratigraphic interpretations in distinguishing fluvial/marine depositional environments. Key Points: Mole % Na, Ca, and Mg on the clay exchange site can be used to differentiate marine versus fluvial deposited claysGroundwater chemistry used to calculate clay‐cation compositions are much easier to obtain than the traditional stratigraphic analysesMarine clays are shown to retain their depositionally derived elevated Na for millions of years [ABSTRACT FROM AUTHOR]

Abstract Cation mole precents (XCa, XMg, and XNa) on clay minerals in a siliciclastic coastal aquifer calculated from groundwater compositions, can aid in distinguishing fluvial from marine sediments and locate the fluvial/marine transition zone. The clay‐cation compositions of two clay‐rich siliciclastic coastal aquifers calculated from the composition of the groundwater were compared to the location of fluvial, fluvial‐marine transition and marine environments identified by traditional core, well log and paleontological analyses. The traditionally defined fluvial depositional environment is distinguished by clays with low XNa < 8% (for 92% of the samples) and high XCa from 55% to 98% with the remainder XMg. In comparison, the traditionally defined marine depositional environment is distinguished by clays with higher XNa > 8.0% (for 86% of the samples) and lower XCa ranging from 5% to 39% with the remainder XMg. The traditionally defined fluvial/marine transition zone has values overlapping the fluvial and marine end members, with 59% with XNa < 8% (fluvial) and 41% with XNa > 8% (marine), and XCa ranging from 45% to 98% with the remainder XMg. Calculations support that the excess Na (XNa > 8%) on marine clays can be retained for 10s of millions of years despite flushing with meteoric water, because of the high clay content in marine sediments. The calculated cation composition of clays deposited from river water are XNa < 8%. In contrast XNa 8%–54% is possible for seawater equilibrated clays supporting that the values found in the different depositional zones are possible. Calculated cation compositions might supplement traditional stratigraphic interpretations in distinguishing fluvial/marine depositional environments.

Lithium (Li) isotopes have shown large potential in tracing weathering in various water bodies, but there is limited study on Li isotopes in subsurface conditions where CO 2 has been largely consumed. In this study, we use a thick sandstone aquifer in the Ordos Basin, NW China, as a natural setting to investigate the behaviors of Li isotopes in hydrogeochemical conditions with different concentrations of dissolved CO 2. For young groundwater in the recharge area (group R) where CO 2 is abundant (mean P CO2 = 10-2.5 atm), clay formation accompanying with weathering leads to the enrichment of 7Li in groundwater. The four deep samples in the recharge area have uniform Li/Na ratios (with a mean of 2.52 μmol/mmol) and δ7Li (with a mean of 25.0‰), corresponding to a mean Li removal rate of 81.2% compared with the sandstone leachate. For groundwater in the shallow part of the discharge area (group D1), Li was firstly removed by clay formation during weathering in the recharge area and was later removed by physisorption when CO 2 becomes much lower (mean P CO2 = 10-3.1 atm). Different degrees of weathering lead to a wide range of δ7Li varying from 19.7‰ in the deepest well to 33.0‰ in the shallowest well. The proportion of Li removal caused by physisorption is found to increase with groundwater age. After the stage of Li removal by adsorption, Li was released in the deeper part of the discharge area (group D2), and the positive correlation of δ7Li versus Li/Na is explained by a ternary mixing model. The endmember of water brought by cation exchange is inferred to have a heavier δ7Li than sandstone leachate, demonstrating that cation exchange could cause an enrichment of 7Li in water. This study enhances our understanding of the controlling factors of Li isotopes in deep groundwater with low dissolved CO 2 , which have implications for the application of Li isotopes in subsurface water. [ABSTRACT FROM AUTHOR]

The Linta Basin, located in the Southwestern Madagascar, is a semi-arid area where groundwater in fractured media bedrock aquifer constitutes the main source of water supply. In the last two decades, highly mineralized groundwater was identified in this area; however, the origin of the salinity was not clear. The purpose of the study was to clarify the origin of salinity and to identify hotspots with groundwater unsuitable for water supply. Groundwater quality in this basin was investigated by hydrogeochemical and isotopic methods accompanied by mineralogical study. In total, 32 groundwater samples were collected and analyzed. The results showed that groundwater temperature varied from 25.2 °C to 31.7 °C. Values of pH and TDS varied from 6.55 to 8.24 and 221 to 5612 mg/L, respectively. The aquifer, which is mainly fractured, showed 7 groundwater types, namely Mg–HCO 3 ,Na–HCO 3 and also Na–C1, Mg–Cl, Na–Cl–HCO 3 , Mg–Cl–HCO 3 -, and Ca–Mg–HCO 3. Two groups of variables have been identified by factor analysis; the factor F1 comprises EC, Ca2+, Mg2+, SO 4 2−, and Cl− whereas the factor F2 comprises HCO 3 −, K+, and Na+, and they were interpreted in terms of hydrogeochemical processes. Values of saturation indices (SI) for carbonate minerals were generally positive, indicating their possible precipitation. Based on the Gibbs diagram and factor analysis, groundwater mineralization is affected by water-rock interactions and evaporation, respectively. The important role of evaporation is confirmed by enrichment of stable isotopes with δ18O values up to 1.2 ‰. Processes such as base ionic exchange process and reverse ionic exchange process may also be important locally. The main origin of groundwater mineralization is the hydrolysis of silicate minerals such as feldspars and micas coupled with evaporation. In several wells, salinity is too high for water supply and nitrate concentration is above the WHO limit for drinking water. Results of the study highlighted groundwater chemistry formation processes and are applicable in other African countries with bedrock aquifers. • Groundwater chemistry in bedrock aquifer in SW Madagascar was investigated. • Mineralization increases in flow direction and dominant groundwater types are Mg– HCO 3 and Na–HCO 3. • Principal processes affecting groundwater chemistry are dissolution of silicates and evaporation. • Hotspots with high salinity and nitrate concentration were identified. [ABSTRACT FROM AUTHOR]

Abstract Groundwater quality assessment is essential for groundwater resource management, especially as it concerns the health of those that consume it. Consequently, we assembled resistivity and hydrogeochemical data to assess the adverse effect of anthropogenic sources on groundwater quality in Ogbe-Ijoh, a coastal area of the western Niger Delta. Geoelectrical data showed no evidence of quality degradation as reflected by high resistivity values that ranged from 29.3 to 349.9 Ωm. Aquiclude of adequate thickness capping aquifers was uncovered in most areas assessed, with the exception of areas near the bank of the river. The delineated clay sedimentary horizon probably enhanced groundwater quality sustainability by acting as a barrier to migrating contaminants, especially from leachate and septic tanks. The physical properties of groundwater sampled indicated moderate pH, TDS and EC magnitudes, with a majority having magnitudes lesser than the requisite standards. The geochemistry of groundwater revealed cations and anions with magnitudes that are distinctively lesser than the desired ranges. Piper plot revealed two different water types: NaCl− and Ca2+ + Mg2+ + Cl− + SO4, which implied that cation exchange has a weighty effect on quality of groundwater. Overall, the hydrogeochemical results are consistent with resistivity data and revealed the efficacy of the pairs in groundwater quality assessment in the absence of lithologic information. The groundwater condition is relatively safe for consumption; nevertheless, due to health implications we recommend that pH should be increased to the required standard before drinking.

Chemical weathering in a groundwater basin is a key to understanding global climate change for a long-term scale due to its association with carbon sequestration. The present study aims to characterize and to quantify silicate weathering rate (SWR), carbon dioxide consumption rate and carbonate weathering rate (CWR) in hard rock terrain aided by major ion chemistry. The proposed study area Shanmuganadhi is marked with superior rainfall, oscillating temperature and runoff with litho-units encompassing charnockite and hornblende–biotite gneiss. Groundwater samples (n = 60) were collected from diverse locations and analysed for major chemical constituents. Groundwater geochemistry seems to be influenced by geochemical reactions combining dissolution and precipitation of solids, cation exchange and adsorption along with minor contribution from anthropogenic activities. The SWR calculated for charnockite and hornblende–biotite gneiss was 3.07 tons km−2 year−1 and 5.12 tons km−2 year−1, respectively. The calculated CWR of charnockite and hornblende–biotite gneiss was 0.079 tons km−2 year−1 and 0.74 tons km−2 year−1, respectively. The calculated CO2 consumption rates via silicate weathering were 1.4 × 103 mol km−2 year−1 for charnockite and 5.8 × 103 mol km−2 year−1 for hornblende–biotite gneiss. Lithology, climate and relief were the key factors isolated to control weathering and CO2 consumption rates. [ABSTRACT FROM AUTHOR]

The transport characteristics of manganese was investigated by soil columns experiments and provide essential data for aquifer remediation and groundwater protection in Yinchuan City. Soil column experiments involved a solution of manganese chloride in which the chloride ion was the chemical tracer. In the two column experiments, the breakthrough curve (BTC) for Cl– revealed the average linear flow velocity (2.937 and 3.921 cm/h) and longitudinal dispersivity (8.52 and 40.09 cm) of the sediment. The BTC of Mn2+ showed a significant delay compared to Cl–. The adsorptive equilibrium isotherm experiments showed that Ca2+ was the main desorption cation in the cation exchange process. The nonlinear retardation factor Rf (RfTM-1 = 13.97, RfTS-1 = 12.89) of Mn2+ is derived from thermodynamic principles. [ABSTRACT FROM AUTHOR]

Kumamoto is known as the largest groundwater city in Japan. Geochemical modeling (saturation indices and mineral stability diagram) was applied in this area for better understanding a hydrogeochemical evolution in volcanic aquifers in regional scale with additional constraint from stable isotopic dataset. Geochemical evolutionary model was interpreted along the water flow dynamics. In total 136 water samples were collected from wells, springs, and rivers in and around the major groundwater flow lines for geochemical analyses. Our results indicated that plagioclase is the major weathering reactant in aquifers with secondary important weathering minerals of pyroxenes. These reactions facilitate current hydrochemical signatures and produce secondary minerals of kaolinite or halloysite and smectite in later stage. Observed hydrogeochemical processes can be distinguished into two distinct criteria along flow regime. The first processes are material loads from the surface (mixing of contaminants and river waters) and initial stage of silicate weathering, resulting in the formation of Ca-HCO3, Ca-NO3–HCO3, and Ca–Mg–Na-HCO3 type waters. These processes prevail in aquifers at the recharge to lateral flow zones with relatively shorter residence time of < ca. 40 years. The second processes are the precipitation of clay minerals, i.e., smectite, and cation exchange reaction of Ca2+ and Mg2+ to Na+ in downslope aquifers (Na-HCO3 type) with relatively longer groundwater residence time of > 55 years. Microbiological reduction reactions dominate over these areas and salinization occurs at the coast that changes aquifer waters to be Na-Cl type. Proposed models and approach shown in this study may be useful and applicable in interpreting systems in other volcanic aquifer systems at similar climate conditions and for sustainable water resources management. [ABSTRACT FROM AUTHOR]

Groundwater quality assessment is essential for groundwater resource management, especially as it concerns the health of those that consume it. Consequently, we assembled resistivity and hydrogeochemical data to assess the adverse effect of anthropogenic sources on groundwater quality in Ogbe-Ijoh, a coastal area of the western Niger Delta. Geoelectrical data showed no evidence of quality degradation as reflected by high resistivity values that ranged from 29.3 to 349.9 Ωm. Aquiclude of adequate thickness capping aquifers was uncovered in most areas assessed, with the exception of areas near the bank of the river. The delineated clay sedimentary horizon probably enhanced groundwater quality sustainability by acting as a barrier to migrating contaminants, especially from leachate and septic tanks. The physical properties of groundwater sampled indicated moderate pH, TDS and EC magnitudes, with a majority having magnitudes lesser than the requisite standards. The geochemistry of groundwater revealed cations and anions with magnitudes that are distinctively lesser than the desired ranges. Piper plot revealed two different water types: NaCl− and Ca2+ + Mg2+ + Cl− + SO4, which implied that cation exchange has a weighty effect on quality of groundwater. Overall, the hydrogeochemical results are consistent with resistivity data and revealed the efficacy of the pairs in groundwater quality assessment in the absence of lithologic information. The groundwater condition is relatively safe for consumption; nevertheless, due to health implications we recommend that pH should be increased to the required standard before drinking. [ABSTRACT FROM AUTHOR]

The study dealt with seawater intrusion process in a coastal aquifer system in the Mahanadi river delta region in the east coast of India along the Bay of Bengal. The aquifers of Mahanadi delta are characterized as shallow aquifers (< 50 m) and deeper aquifers (> 50 m). Electrical conductivity (EC) of groundwater varied from a fresh of 146 μS/cm (NW of the Mahanadi delta) to a saline of 33,900 μS/cm (close to sea coast) with cation dominance in the order Na+ > Ca2+ > Mg2+ > K+ and anion dominance of Cl− > HCO 3 - > SO 4 2 - . The hydrochemical facies changed from Ca–Mg–Na–HCO3 type to Na–Cl type along the groundwater flow direction due to ion exchange processes. A strong positive correlation (r > 0.9) between Cl− with EC, Na+, Mg2+, Ca2+, SO 4 2 - and K+ was observed, which indicated the influence of seawater on coastal aquifer. The ionic ratios (Na+/Cl−, HCO 3 - /Cl−, Mg2+/Ca2+, SO 4 2 - /Cl−, Ca2+/( HCO 3 - / SO 4 2 - )) also suggested that the groundwater is affected by seawater intrusion. Stable isotope compositions (δ18O and δ2H) varied from − 1.86 to − 6.87 ‰ for δ18O and from − 10.79 to − 45.42 ‰ for δ2H, implying the mixing of saline water and fresh groundwater in the coastal region of the Mahanadi delta. The proportion of seawater in groundwater was estimated to vary from 0% in the upper-delta formation to 72% in the lower-delta formation of the Mahanadi delta (close to seacoast), which was due to inland intrusion of seawater. In a first ever study on this coastal aquifer along the Bay of Bengal, where a large population is dependent on agriculture, seawater intrusion into the fresh groundwater has been quantified. The issue of seawater intrusion into the coastal aquifer in this region may become a serious disaster, if appropriate management strategies are not implemented in time. [ABSTRACT FROM AUTHOR]

A geological repository for low and intermediate radioactive waste (bottom at −130 m a.s.l.) was constructed from 2008 to 2014 in the southeastern coastal area in Korea. This research aimed to evaluate the hydrogeochemistry in this area during the construction period and to determine the characteristics that should be monitored during the operational period. During construction, the groundwater level decreased up to 136 m and the upper groundwater flow in the southeastern area reversed. After the groundwater level dropped below the sea level, the electrical conductivity (EC) in several wells along the coastal line started to increase; 23.2% of the measured water was classified as brackish water and the highest EC observed in groundwater was 18.9 mS/cm, nearly 38% of EC in seawater. The response time of the groundwater chemistry differs depending on the depth, even in wells, because of fracture networks. Among locations that showed drastic changes in EC, only the shallow depth of GM-4 showed a peak pattern in EC, but other locations showed increasing EC patterns or patterns with initial increase and sustained high till the end of the construction period. Based on the Cl/Br ratio, the source of the groundwater salinity was seawater intrusion, and ion exchange played an important role. Compared to Cl concentration, sodium was depleted and calcium was in excess in brackish water; however, the SO 4 /Cl ratio remained constant at a level similar to seawater. Ca and Fe concentrations showed distinguishable characteristics depending on the location, suggesting differences in geological media. During the operational period, periodical evaluation of the groundwater chemistry in the mixing zone and continuous monitoring of EC patterns and seawater fractions are required. [ABSTRACT FROM AUTHOR]

The exploitation of groundwater resources is of high importance and has become very crucial in the last decades, especially in coastal areas of arid and semi-arid regions. The coastal aquifers in these regions are particularly at risk due to intrusion of salty marine water. One example is the case of Tripoli city at the Mediterranean coast of Jifarah Plain, North West Libya. Libya has experienced progressive seawater intrusion in the coastal aquifers since the 1930s because of its ever increasing water demand from underground water resources. Tripoli city is a typical area where the contamination of the aquifer in the form of saltwater intrusion is very developed. Sixty-four groundwater samples were collected from the study area and analyzed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters Electrical Conductivity, Na+, K+, Mg2+, Cl- and SO42-, which can be attributed to seawater intrusion, where Cl- is the major pollutant of the aquifer. The water types according to the Stuyfzand groundwater classification are mostly CaCl, NaCl and Ca/MgMix. These water types indicate that groundwater chemistry is changed by cation exchange reactions during the mixing process between freshwater and seawater. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 25 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high NO3- concentration in the region. [ABSTRACT FROM AUTHOR]

Bentonites are considered as an engineered barrier for a high-level radioactive waste (HLRW) repository. The Czech product Bentonite 75 is a potential candidate material to be used as a buffer and a backfill. The bentonite barrier is supposed to undergo alteration and transformation processes due to reaction with groundwater and heating originated from radionuclide decay. Detailed knowledge of the bentonite-water interaction is a crucial issue for the evaluation of the long-term stability of the bentonite barrier. This study presents the results of a laboratory experiment in which the repository conditions, hydration, and heating of the bentonite were simulated. Bentonite 75 reacted in a closed system with demineralised water and groundwater at 90 °C for 2 years. Bentonite material (solid phase) and aqueous extracts were analysed over time with respect to the mineralogical and chemical changes. The results indicate that montmorillonite alteration, particularly illitization, could be excluded in this system due to the low concentration of K + in the solution. In addition, cation exchange capacity measurements did not indicate any transformation process of montmorillonite. Slight modifications of montmorillonite basal reflection profiles in PXRD patterns were attributed to cation exchange reactions. The most reactive minerals included siderite, Fe-dolomite/ankerite, and calcite/Mg-calcite. Dissolution/precipitation of these minerals controlled the composition of the aqueous phase that affected the distribution of the exchangeable cations in the montmorillonite interlayer. The most significant change was the dissolution of siderite that induced partial dissolution of calcite, which resulted in the replacement of Na + and Mg 2 + by Ca 2 + . The overall evolution of the water chemical composition could be predominantly explained by mineral phase equilibria. The initial water composition did not affect the geochemical processes, which took place in the bentonite-water system due to the strong buffering bentonite capacity. [ABSTRACT FROM AUTHOR]

Major ion concentrations were measured in 22 groundwater samples collected from a coal bearing aquifer in Zhuxianzhuang coal mine, northern Anhui Province, and the ion source and geochemical characteristics were discussed by the methods such as traditional graphic and multivariate statistic analysis. The results showed the presence of three water types, i.e., HCO3-Na, Cl-Na and SO4-Na. The surrounding rock weathering and evaporation, both controlled the chemical characteristics of groundwater, evidenced by the Gibb's diagrams. In detail, the features of ion ratios such as Ca/Na, HCO3/Na and Mg/Na show that the evaporate dissolution and silicate weathering were the dominant water-rock interactions. Multivariate analysis, such as correlation analysis, cluster analysis and FA analysis were also conducted to reveal the ion source in groundwater, and the Ca2+ and Mg2+ were mainly released from the dissolution of gypsum and/or magnesium and/or anorthite; while the Na+ is influenced by the weathering of feldspar and halite, with the cation exchange in a certain extent. In contrast, the Cl-, HCO3 - and SO42- are also controlled by the halite dissolution, silicate mineral weathering and sulphate mineral dissolution, respectively. In addition, the SO42- in groundwater could be influenced by the oxidation of pyrite, which is abundant in the coal bearing aquifers. [ABSTRACT FROM AUTHOR]

This study presents the hydrogeochemical analysis in coastal groundwater mixing zone of a sandy aquifer, Ting Kok, Hong Kong. Groundwater samples collected along a sampling transection that covers the salinity transition zone were analyzed for spatial and temporal distribution of major ions (Cl − , SO 4 2− , Na + , K + , Mg 2+ , and Ca 2+ ) and ancillary parameters such as salinity, pH, temperature, and total alkalinity. The seawater-freshwater interface (SFI) based on different ions, ionic delta of major ions, PHREEQC based saturation index (SI) of minerals are used to systematically investigate geochemical processes such as cation exchange, precipitation/dissolution of minerals, and sulfate reduction under the effect of seasonal hydrologic variation. Compared to Cl − -based SFI, the landward movements of cation-based SFI and seaward movement of SO 4 2- -based SFI indicate that the coastal aquifer serves as the source of cations and sink of SO 4 2− for groundwater. The SFI is sensitive to seasonal hydrologic variation due to the variation of land-sea hydraulic gradient. The cation exchange and precipitation/dissolution of minerals are dynamic and complex in coastal groundwater mixing zone. The simultaneous enrichment of all cations is found in the aquifer due to external input of a specific cation. The sulfate reduction is responsible for SO 4 2− depletion and also the enrichment of total alkalinity in coastal groundwater mixing zone because gypsum precipitation does not occur according to mineral SI analysis. The cation exchange is very sensitive to the seasonal hydrologic variation while the sulfate reduction is not obviously influenced. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the water quality status (especially, salinity problems) and hydrogeochemical processes of an alluvial aquifer in a floodplain of the Red River delta, Vietnam, based on the hydrochemical and isotopic data of groundwater samples (n = 23) from the Kien Xuong district of the Thai Binh province. Following the historical inundation by paleo-seawater during coastal progradation, the aquifer has been undergone progressive freshening and land reclamation to enable settlements and farming. The hydrochemical data of water samples showed a broad hydrochemical change, from Na-Cl through Na-HCO 3 to Ca-HCO 3 types, suggesting that groundwater was overall evolved through the freshening process accompanying cation exchange. The principal component analysis (PCA) of the hydrochemical data indicates the occurrence of three major hydrogeochemical processes occurring in an aquifer, namely: 1) progressive freshening of remaining paleo-seawater, 2) water-rock interaction (i.e., dissolution of silicates), and 3) redox process including sulfate reduction, as indicated by heavy sulfur and oxygen isotope compositions of sulfate. To quantitatively assess the hydrogeochemical processes, the end-member mixing analysis (EMMA) and the forward mixing modeling using PHREEQC code were conducted. The EMMA results show that the hydrochemical model with the two-dimensional mixing space composed of PC 1 and PC 2 best explains the mixing in the study area; therefore, we consider that the groundwater chemistry mainly evolved by mixing among three end-members (i.e., paleo-seawater, infiltrating rain, and the K-rich groundwater). The distinct depletion of sulfate in groundwater, likely due to bacterial sulfate reduction, can also be explained by EMMA. The evaluation of mass balances using geochemical modeling supports the explanation that the freshening process accompanying direct cation exchange occurs through mixing among three end-members involving the K-rich groundwater. This study shows that the multiple end-members mixing model is useful to more successfully assess complex hydrogeochemical processes occurring in a salinized aquifer under freshening, as compared to the conventional interpretation using the theoretical mixing line based on only two end-members (i.e., seawater and rainwater). [ABSTRACT FROM AUTHOR]

The desert of eastern Libya forms one of the most arid regions of the Sahara. Libya suffers from a shortage in water resources due to its arid climate. On the other hand, Libya has large resources of good-quality groundwater distributed in six basin systems beneath the Sahara. In order to deal with the shortage of water in most coastal cities, the Libyan government established the Great Man-Made River Project to transport millions of cubic meters of water a day from desert wellfields to the coastal cities, where over 80% of the population lives. In this paper, a hydrogeochemical study is presented for the Nubian Sandstone Aquifer in Tazerbo Wellfield, SE Libya, based on chemical analyses and physical parameters for 108 wells. Samples were collected from 108 borewells of the Nubian Aquifer (Akakus Formation) from depth range between 280 m in the north and 500 m in the south. This study is the first hydrochemical investigation in Tazerbo and also in the whole Sahara, which introduces the importance of considering the end members and the synsedimentary influence for the interpretation of the groundwater hydrochemistry. The results of the analyses indicate soft to moderately hard, lowly mineralized, slightly alkaline groundwater, with Mg as the main cation and HCO as the main anion. The major hydrogeochemical processes that affect the quality of water in sediments of the Nubian system at Tazerbo have been identified; the water type is mostly fresh MgHCO while NaHCO and KHCO are also found for some wells. These water types indicate that groundwater chemistry is changed by cation exchange reactions during flushing of the aquifer by freshwater from the south. [ABSTRACT FROM AUTHOR]

This paper first time reports the geochemical processes that are controlling fluoride enrichment in the groundwater of western Kumamoto area, Japan. Fifty (50) groundwater samples were collected and analyzed for the study where fluoride (F) concentration ranges from 0.1 to 1.57 mg/L. About 58 % of the shallow groundwater and 26 % of the deep groundwater samples contain fluoride concentration beyond the Japanese drinking water permissible limit (0.8 mg/L). High F is largely accumulated in the stagnant zone of the Kumamoto Plain area and associated with Na-HCO-type groundwater. High pH, high HCO, low Ca, and high Na are the major characteristics of high-F groundwater. Hydrolysis of F-bearing minerals and desorption of F from hydrous metal oxides are considered to be the primary sources of fluoride in groundwater. A positive correlation between F and Na/Ca ratio ( r = 0.53) indicates that major ion chemistry plays a significant role in fluoride mobilization. Weakly alkaline nature of groundwater with high pH (7.05-9.45) expedites the leaching process of exchangeable F from F-bearing minerals as well as favors desorption of F from metal oxide surfaces. High HCO and high PO in the groundwater facilitate desorption process as competing anions, while high Na/Ca ratio largely control this process by decreasing positive-charge density of the metal-oxide surfaces. High Na/Ca ratio is attributed due to the cation-exchange process, while high pH and HCO are the result of both silicate hydrolysis and microbial reduction processes. In addition, calcite and fluorite seem to have a control on groundwater fluoride geochemistry. [ABSTRACT FROM AUTHOR]

An improved procedure was developed using cation exchange enrichment and solid-phase extraction to determine Sr in groundwater. Sr desorption from cation exchange column and sorption on Sr-resin column were carried out at the same time by stacking two cartridges in tandem and rinse with concentrated nitric acid, based on the fact that both the two operations are performed under high acid conditions. Some steps such as evaporating the eluate and dissolving again for Sr transfer, necessary in some standard methods, were skipped. The improved procedure was successfully applied to Sr analysis in true monitor well water. [ABSTRACT FROM AUTHOR]

This paper provides insight into the quality of groundwater used for public water supply on the territory of Kikinda municipality (Vojvodina, Serbia) and main processes which control it. The following parameters were measured: color, turbidity, pH, KMnO consumption, TDS, EC, NH, Cl, NO, NO, Fe, Mn, total hardness, Ca, Mg, SO, HCO, K, Na, As. The correlations and ratios among parameters that define the chemical composition were determined aiming to identify main processes that control the formation of the chemical composition of the analyzed waters. Groundwater from 11 analyzed sources is Na-HCO type. Intense color and elevated organic matter content of these waters originate from humic substances. The importance of organic matter decay is assumed by positive correlation between organic matter content and TDS, HCO content. There is no evidence that groundwater chemistry is determined by the depth of captured aquifer interval. The main processes that control the chemistry of all analyzed water are cation exchange and feldspar weathering. [ABSTRACT FROM AUTHOR]

Groundwaters from the intermediate aquifer of Sfax basin have been investigated using chemical tracers and environmental isotopes to reveal the hydrogeological features of this system and characterize the dynamics of groundwater salinization in this sector. The origin of salinity in the studied aquifer was investigated based on the chemical analyses of 30 groundwater samples. Groundwater is characterized by Na-Cl and Na-SO water types. The saturation indices for calcite and gypsum, and binary diagrams of different ions showed that the main hydrogeochemical processes were the dissolution of carbonates (mainly calcite scattered through the reservoir rocks), the dissolution of evaporites (halite, gypsum and anhydrite) and the cation exchange processes. The isotopic composition investigation allowed the definition of two groups. The first group is represented by groundwater with the highest oxygen-18 content (δO ranges between −5.36 and −4.22 ‰, and δH ranges between −39.2 and −36 ‰). The high δO values in this group can be attributed to the evaporation effect. The second group includes the most depleted waters (δO varies between −6.84 and −5.79 ‰, and δH varies between −42.4 and −36.5 ‰). The combined analyses of stable isotopes and major ions (Cl) showed that mixing between old and recent water and evaporation were the main processes explaining the variation of salinity of the intermediate aquifer of the Sfax basin. [ABSTRACT FROM AUTHOR]

People in the southwestern (SW) coastal part of Bangladesh are suffering from a severe freshwater crisis due to saline groundwater at a shallow depth. Fresh groundwater below a 200 m depth is an option, but it is costly to construct deep tubewells for the local inhabitants. The processes of salinization and freshening were previously identified using conventional methods. In this study, we brought new insight into these processes by analyzing existing datasets using multivariate statistics to identify the factors affecting groundwater chemistry. Cluster analysis (CA) revealed three major clusters. Cluster A corresponded to saline (NaCl-type) water. Cluster B was also saline (NaCl-type) water but showed mixing effects. Cluster C was fresh groundwater (NaHCO3-type) and isolated. The hydrochemical characteristics of clusters A, B and C compared remarkably well with the groundwaters from the upper shallow aquifer (USA), lower shallow aquifer (LSA) and deep aquifer (DA), respectively. Factor analysis (FA) showed that 75% of the total variance was influenced by evaporate dissolution, carbonate dissolution/precipitation, cation exchange and anthropogenic pollution to some extent. Therefore, the integrated approach showed the validity of applying multivariate statistical techniques to infer the dominant hydrochemistry and to characterize and understand a complicated hydrogeological system. [ABSTRACT FROM AUTHOR]

The groundwater of the Korba plain represents major water resources in Tunisia. The Plio-Quaternary unconfined aquifer of the Cap-Bon (north-east Tunisia) is subject to the intensive agricultural activities and high groundwater pumping rates due to the increasing of the groundwater extraction. The degradation of the groundwater quality is characterized by the salinization phenomena. Groundwater were sampled and analysed for physic-chemical parameters: Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-, NO3-, pH, electrical conductivity (EC), and the temperature (T°). The hydrochemical analysis is coupled with the calculation of the saturation indexes (SI gypsum, SI halite, SI calcite and SI dolomite), ionic derivation and with the ion correlations compared to chloride concentrations: Na+/ Cl-, Ca2+/ Cl- and Mg2+/ Cl- ratios. Seawater fractions in the groundwater were calculated using the chloride concentration. Those processes can be used as indicators of seawater intrusion progression. EC methods were also conducted to obtain new informations on the spatial scales and dynamics of the fresh water-seawater interface of coastal groundwater exchange. The mixing zone between freshwater and saltwater was clearly observed from the EC profile in the investigated area where a strong increase in EC with depth was observed, corresponding to the freshwater and saltwater interface. Results of hydrochemical study revealed the presence of direct cation exchange linked to seawater intrusion and dissolution processes associated with cations exchange. These results, together with EC investigation, indicated that the groundwater is affected by seawater intrusion and is still major actor as a source of salinization of the groundwater in Korba coastal plain. Further isotopic and hydrological investigations will be necessary to identify and more understood the underlying mechanisms. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hydrochemical and environmental isotope tracers have been used to identify the geochemical processes that affect groundwater masses in the aquifer system of Grombalia (northeastern Tunisia). The study area presents a multilayer aquifer system logged in the Quaternary and Miocene sandstones. Multi-tracer results show that the dissolution of evaporite minerals as well as the evaporation and the irrigation return flow are the main processes controlling groundwater quality. The isotopic data proves the origin of different groundwater masses as well as the natural and anthropogenic processes that control their mineralization. [ABSTRACT FROM AUTHOR]

Abstract: A series of laboratory-scale studies was conducted by preconcentrating 226Ra from spiked water test samples using Purolite ion-exchange resin to evaluate the adsorption efficiency of the resin under varying conditions. After removing the resin from the columns, it was sealed in gas-tight containers and measured via gamma spectrometry. The Purolite resin showed high radium uptake and retention from natural waters in the presence of high iron and total dissolved solids (TDS). This procedure allowed us to process a large number of high TDS samples at a typical rate of 15 samples/day using three germanium detectors. Quality assurance and method validation have been achieved by analyzing selected groundwater samples, with different 226Ra activities and high TDS values, and comparing the results to those using alpha spectrometry with a 133Ba yield tracer. There was very good agreement between the obtained 226Ra activities by both methods. [Copyright &y& Elsevier]

The chemistry of soil solutions can be altered by human activities, due to the intense agricultural and husbandry, leading to leaching of nutrients and subsequently elevating ground water levels. Multivariate statistical and inverse geochemical modeling techniques were used to determine the main factors controlling soil solution chemistry of calcareous soils. In this research, a total of 21 calcareous soils was characterized and assessed for soil solution using soil column. The major cations in the studied soil solutions were in the decreasing order as Ca > Mg > Na > K. The anions were also arranged in decreasing order as HCO $$ _{3}^{ - } $$ > Cl $$ ^{ - } $$ > SO $$ _{4}^{2 - } $$ > NO $$ _{3}^{ - } $$. Concentrations of NO $$ _{3}^{ - } $$, P, and K in soil solutions were in the range of 6.8-307.5 mg l (mean 63.2 mg l), 5.0-10.4 mg l (mean 5.9 mg l), and 2.8-54.6 mg l (mean 11.3 mg l), respectively. Results suggest that the concentration of P in the soil solutions could be primarily controlled by the solubility of dicalcium phosphate dihydrate and dicalcium phosphate. Interactions between soil properties and observed solubility of nutrients were described, and put into empirical multivariate formulations. Obtained equations contained electrical conductivity (EC) as a key factor in determining nutrients solubility. Inverse geochemical modeling of soil solution using PHREEQC indicates the dissolution of calcite, anhydrite, halite, CO (g), N (g), and hydroxyapatite, and precipitation of sulfur. Cation exchange between Ca, Mg, K and Na occurred with Mg and K into the solution, and Ca and Na out of the solution. Determination of soil solution will improve soil management in the area, and preventing groundwater deterioration. [ABSTRACT FROM AUTHOR]

Summary: This article describes the post audit and inverse modeling of a 1-D forward reactive transport model. The model simulates the changes in water quality following artificial recharge of pre-treated water from the river Rhine in the Amsterdam Water Supply Dunes using the PHREEQC-2 numerical code. One observation dataset is used for model calibration, and another dataset for validation of model predictions. The total simulation time of the model is 50years, from 1957 to 2007, with recharge composition varying on a monthly basis and the post audit is performed 26years after the former model simulation period. The post audit revealed that the original model could reasonably predict conservative transport and kinetic redox reactions (oxygen and nitrate reduction coupled to the oxidation of soil organic carbon), but showed discrepancies in the simulation of cation exchange. Conceptualizations of the former model were inadequate to accurately simulate water quality changes controlled by cation exchange, especially concerning the breakthrough of potassium and magnesium fronts. Changes in conceptualization and model design, including the addition of five flow paths, to a total of six, and the use of parameter estimation software (PEST), resulted in a better model to measurement fit and system representation. No unique parameter set could be found for the model, primarily due to high parameter correlations, and an assessment of the predictive error was made using a calibration constrained Monte-Carlo method, and evaluated against field observations. The predictive error was found to be low for Na+ and Ca2+, except for greater travel times, while the K+ and Mg2+ error was restricted to the exchange fronts at some of the flow paths. Optimized cation exchange coefficients were relatively high, especially for potassium, but still within the observed range in literature. The exchange coefficient for potassium agrees with strong fixation on illite, a main clay mineral in the area. Optimized CEC values were systematically lower than clay and organic matter contents indicated, possibly reflecting preferential flow of groundwater through the more permeable but less reactive aquifer parts. Whereas the artificial recharge initially acted as an intrusion of relatively saline water triggering Na+ for Ca2+ exchange, further increasing total hardness of the recharged water, the gradual long-term reduction in salinity of the river Rhine since the mid 1970s has shifted to an intrusion of fresher water causing Ca2+ for Na+ exchange. As a result, seasonal and longer term reversal of the initial cation exchange processes was observed adding to the general long-term reduction in total hardness of the recharged Rhine water. [Copyright &y& Elsevier]

Abstract: Subsurface iron removal (SIR), or in-situ iron removal, is an established treatment technology to remove soluble iron (Fe2+) from groundwater. Besides the adsorptive-catalytic oxidation theory, it has also been proposed that the injection of O2-rich water onsets the exchange of adsorbed Fe2+ with other cations, such as Ca2+ and Na+. In sand column experiments with synthetic and natural groundwater it was found that cation exchange (Na+–Fe2+) occurs during the injection-abstraction cycles of subsurface iron removal. The Fe2+ exchange increased at higher Na+ concentration in the injection water, but decreased in the presence of other cations in the groundwater. Field results with injection of elevated O2 concentrations (0.55 mM) showed increased Fe removal efficacy; the operational parameter V/Vi (abstraction volume with [Fe]<2 μM divided by the injection volume) increased from an average 7 to 16, indicating that not the exchangeable Fe2+ on the soil material is the limiting factor during injection, but it is the supply of O2 to the available Fe2+. [Copyright &y& Elsevier]

Land reclamation projects and construction of new cities represent one of the Egypt's strategic polices to meet the over increasing population. The Quaternary aquifer represents the main water bearing formation in the study area, which extends from the Rosetta branch in the east to Wadi El-Natrun in the west and from south El-Khattab road at south to El-Nubaria and El-Nasser canals in the north. The present hydrogeological conditions of this area are studied to understand the stresses imposed by these reclamation projects and extensive use of groundwater on heads and quality. The hydraulic head map shows that the aquifer is recharged from the Nile Delta in the east. The present work throws light on the hydrochemistry of the Quaternary aquifer facies in El Sadat City and determines geochemical type, origin, evolution of groundwater and their relation to the prevailing hydrogeological and environmental conditions, and finally evaluates the suitability of ground water for different uses. [ABSTRACT FROM AUTHOR]

Abstract: Finnish spent nuclear fuel is planned to be disposed of deep in the crystalline bedrock of the Olkiluoto island. In such a repository, the role of the bentonite buffer is considered to be central. The initially unsaturated bentonite emplaced around a spent-fuel canister will become fully saturated by the groundwater from the host rock. In order to assess the long-term safety of a deep repository, it is essential to determine how temperature influences the chemical stability of bentonite. The aim of this study was to achieve an improved understanding of the factors governing the thermo-hydro-chemical evolution of the bentonite buffer subject to heat generation from the disposed fuel and in contact with a highly permeable rock fracture intersecting a canister deposition hole. TOUGHREACT was used to model a test known as the long-term test of buffer material adverse-2, which was conducted at the Äspö hard rock laboratory in Sweden. The results on the evolution of cation-exchange equilibria, bentonite porewater chemistry, mineralogy, and saturation of the buffer are presented and discussed. The calculated model results show similarity to the experimental results. In particular, the spatial differences in the saturation and porewater chemistry of the bentonite buffer were clearly visible in the model. [Copyright &y& Elsevier]

Abstract: The Long Term Test of Buffer Material (LOT) project at the Äspö Hard Rock Laboratory, Sweden, is a series of medium-scale field experiments focused on validating models and hypotheses concerning long term processes in the bentonite buffer of a repository for high-level radioactive waste. The test parcels emplaced in crystalline bedrock consist of blocks of compacted MX80 bentonite embedding a Cu-tube equipped with a heater to simulate the heat generation from radionuclide decay. The A2 test parcel had been subjected to elevated temperature (up to 130°C) and hydration by a Na–Ca–Cl type groundwater for almost 6years when it was retrieved to be analysed. The analyses included determinations of chemical composition, cation exchange capacity (CEC), exchangeable cations and mineralogy. Both the bulk bentonite and dialysed, homo-ionic Na-clay (<2μm and <0.2μm fractions) were analysed when relevant. Sulphate was redistributed in the heated part of the buffer under the thermal and hydration gradients that prevailed during the test period. Anhydrite accumulated in the warmer parts, whereas gypsum was dissolved in the peripheral parts of the buffer where water was supplied. Carbonate dissolution increased with temperature in the warmest parts, whereas chloride behaved conservatively in all blocks. Cu was incorporated in the bentonite matrix at the surface of the Cu-tube indicating some corrosion, which may be explained by reactions in an early stage of the test when trapped oxygen existed in the system. Along with the dissolution/precipitation reactions the porewater composition changed, which resulted in replacement of exchangeable sodium by calcium and magnesium in the warmest zone. Also Mg in the clay (<2μm and <0.2μm fractions) displays a clear gradient with peak values at the heater. Because several of the alternative sinks for Mg were eliminated in the sample preparation prior to the chemical analysis (purified clay fractions, removal of carbonates, Na-saturation) the smectite is suggested a candidate sink for Mg. Parallel with the increase in Mg, a loss in Si is indicated and CEC tends to increase in the clay that had been heated at 130°C. A loss in tetrahedral Si that is balanced by Al, and replacement of Al by Mg in the octahedral sheet would imply that the layer charge of the smectite increased, which would be consistent with the higher CEC values of these samples. The changes in CEC are, however, close to the analytical resolution of the CEC method and no effect of the changes in chemical composition can be detected in the XRD-characteristics of the clay. Therefore, supplementary high-resolution analyses are required to verify whether the structure of montmorillonite has altered in the test period. [Copyright &y& Elsevier]

In the Grombalia region, Cap Bon Peninsula, northeastern Tunisia, increasing population and development of agricultural activity during the last few decades have engendered large expansion of groundwater pumping from the shallow, unconfined aquifer. Recently, the water table has displayed some signs of overexploitation such as decline in the water level in boreholes and considerable deterioration of water quality. Hydrochemical and isotopic data were used in conjunction with hydrogeological characteristics to investigate the groundwater composition in this aquifer. It has been demonstrated that groundwaters, recharged mainly in the surrounding foothills, acquire their mineralization principally by water–rock interaction, i.e., dissolution of evaporites and reverse cation exchange, and secondarily by return flow of irrigation waters. The isotopic signature of groundwaters permits identification of two different types. Water with depleted δO and δH contents is interpreted as recharge by non-evaporated rainfall, originating from a mixture of Atlantic and Mediterranean air masses. However, water with relatively enriched δO and δH contents is thought to reflect contamination by return flow of irrigation waters. Tritium contents, ranging between 1.2 and 4.5 TU indicate that groundwaters in an unconfined aquifer derive from post-nuclear recharge or contain a significant component of post-1950s water. The recent origin of these groundwaters is confirmed by the high carbon-14 activities, exceeding sometimes 100%, indicating the existence of a significant fraction of organic C. This younger source of radiocarbon is, however, highlighted by the depleted δC contents, corresponding to a system where CO of C4 plants predominates. [ABSTRACT FROM AUTHOR]

The article presents an experiment of two-stage soil column which includes capillary rise and evaporation to improve understanding of salt and water movement from groundwater to soil surface. It states that the numerical results of the cation distributions in both solid and liquid phase and anions in the liquid phase were relatively in good agreement with the experimental results. Moreover, soil water profile showed a steady behavior around 10 days after the experiments began.

Groundwater is increasingly gaining significance as the main solution to the water supply problems in Ghana, especially in the rural areas. This study was conducted to determine which factors play significant roles in the hydrochemistry of groundwater from the southern Voltaian formation. Conventional graphical and multivariate statistical methods were used. The study reveals three main factors controlling the hydrochemistry. Silicate mineral weathering and reverse cation exchange are the most important processes affecting the hydrochemistry of groundwater at this part of the formation. Interpolation maps created from factor scores suggest that these processes are the most pervasive, recording high scores almost everywhere in the study area. Carbonate mineral weathering is the second most important process in the hydrochemistry. This study finds that carbonate mineral weathering in the area is probably facilitated by carbonic acid rather than sulfuric acid. Chemicals from agricultural activities constitute the third most important process influencing groundwater quality in the area. Eighty samples were used to calculate water quality indices, WQI, which were in turn used to classify groundwater from the study area. Over 98% of the samples fall within the “Excellent” and “Good” categories, suggesting that groundwater from the southern Voltaian formation is generally acceptable for drinking purposes. [ABSTRACT FROM AUTHOR]

Abstract: The fate and transport of commonly used antibiotics in soil and groundwater have attracted renewed studies due to increased sensitivities of analytical instruments and thus frequent detections of these compounds even in treated wastewater. Smectite, an important soil component, has large surface area and high cation exchange capacity, while tetracycline (TC) can exist in different forms and charges under different pH conditions. Thus, the interaction between smectite and TC in aqueous systems is of great importance. This research focused on elucidating the mechanisms of TC uptake by smectite, in terms of TC adsorption, cation desorption, and pH changes associated with TC adsorption by smectite and intercalation in smectite. TC adsorption onto smectite was a relatively fast process even though most of the adsorption sites were in the interlayer position involved in intercalation as confirmed by the expansion of d 001 spacing. The TC adsorption capacity was equivalent to 0.74–1.11 times the cation exchange capacity for three of the four smectite minerals studied. Accompanying TC adsorption was simultaneous adsorption of H+, resulting in protonation of TC on the dimethylamine group. At higher TC input concentrations further adsorption of H+ resulted in the ratio of H+ adsorbed to TC adsorbed greater than one, suggesting that additionally adsorbed H+ could serve as counterions to partially offset the negative charges on the tricarbonyl or phenolic diketone functional groups. The positive correlations between cations desorbed and TC adsorbed, as well as TC adsorbed and H+ adsorbed, provided a first time evidence to confirm cation exchange as the main mechanism of TC uptake, even under neutral pH conditions. [Copyright &y& Elsevier]

Summary: Cation exchange in groundwater is one of the dominant surface reactions that occurs in nature and it carries with it many important environmental implications. The mass transfer of cation exchanging pollutants in groundwater can be described by a series of coupled partial differential equations, involving both aqueous and adsorbed species. The resulting system is mathematically challenging due to the complex nonlinearities that arise, which in turn complicates analytical approaches. While some analytical solutions for simplified problems exist, these typically lack the mechanisms that allow the waters to change their global chemical signature (in terms of total cations present in aqueous form) over time. We propose a methodology to solve the problem of exchanging two homovalent cations by deriving the driving equation for one of the aqueous species. This equation incorporates explicitly a retardation factor and a decay term, both with parameters that can vary in space and time. While the full solution can only be obtained numerically, we provide a solution in terms of a perturbative approach, where the leading terms can be obtained explicitly. The resulting solution provides physical explanations for the possible existence of non-monotonic concentrations for a range of parameters governing cation exchange processes. [Copyright &y& Elsevier]

Groundwater composition in the Kulpawn basin is largely controlled by aluminosilicates dissolution and cation exchange resulting in mainly Ca-Mg-HCO3 and NaHCO3 water types. Principal component analysis, Piper graphical classification, and stable isotope (18O and 2H) of groundwater and surface-water samples were used to delineate geochemical processes and groundwater facies. The groundwater is mildly acid to neutral and low in conductivity. Chemical constituents except HCO3 − and SiO2 have low concentration. No cation shows clear majority, however, the order of relative abundance is Na+ > Ca2+ > Mg2+ > K+. HCO3 − is the predominant anion and the order of abundance is HCO3 − > NO3 concentration is high compared with the major cations. Dissolution of plagioclase, pyroxene and biotite and cation exchange are responsible for groundwater composition. Isotopic data suggest integrative, smooth and rapid recharge from meteoric origin. The groundwater quality is generally good for domestic usage; however, 18 and 47% of boreholes respectively have NO− > SO4 levels outside WHO recommended limits suggesting potential physiological problems in some localities. The groundwater has low sodium absorption ratio and low to moderate salinity hazard but significant magnesium hazard partially limiting its use for irrigation. [ABSTRACT FROM AUTHOR]2− > Cl−. SiO2 concentration is high compared with the major cations. Dissolution of plagioclase, pyroxene and biotite and cation exchange are responsible for groundwater composition. Isotopic data suggest integrative, smooth and rapid recharge from meteoric origin. The groundwater quality is generally good for domestic usage; however, 18 and 47% of boreholes respectively have NO3 − and F− levels outside WHO recommended limits suggesting potential physiological problems in some localities. The groundwater has low sodium absorption ratio and low to moderate salinity hazard but significant magnesium hazard partially limiting its use for irrigation. [ABSTRACT FROM AUTHOR]