Chemical Evolution Of Groundwater Research Articles

Tracing recharge and groundwater evolution in a glaciated, regional-scale carbonate bedrock aquifer system, southern Ontario, Canada

Where carbonate bedrock aquifers are overlain by glacial sediments, these sediments control the locations and geochemical signatures of recharge to the bedrock groundwater system. In these settings, geochemical and isotopic tracer tools may be rendered ineffective due to geochemical fingerprinting that can develop as groundwater migrates through the sediments and carbonates of the recharge pathway. In this investigation, traditional tracer tools are assessed in an 8000 km2 study area in southern Ontario, Canada, where the Early Silurian carbonate bedrock aquifers are overlain by glacial sediments. These carbonate aquifers contain significant quantities of high-quality groundwater resources and provide the sole drinking water source to many large cities and private residences. The glacial history of the study area is complex, with the advance and retreat of three ice lobes having deposited sediments that vary widely in permeability, mineralogy, and geochemistry. Results show that spatial trends of higher tritium correlate with aerobic redox chemistry in the carbonate groundwater systems underlying areas of thin or permeable sediment cover. Groundwater chemical evolution beyond recharge areas is assessed with general chemistry, redox characteristics and an investigation of water-rock interactions. A comparison of strontium isotope ratios (87Sr/86Sr) in bedrock and groundwater shows that long residence times may be required for the isotopic signature of the carbonate bedrock to imprint on the groundwater, though this does not occur consistently. The isotopic composition of sulphate (δ34SSO4 and δ18OSO4) in groundwater was most informative, showing isotopic evidence of sulphide oxidation in recharge areas, and a Silurian sulphur isotopic signature of the host bedrock in areas of thick and low permeability sediment, downgradient of identified recharge areas. The set of tracer tools deemed most useful in this investigation provides the empirical evidence needed to support a conceptual model of recharge and groundwater evolution and is recommended for use in similar settings elsewhere.

Evolution of groundwater chemistry in coastal aquifers of the Jiangsu, east China: Insights from a multi-isotope (δ2H, δ18O, 87Sr/86Sr, and δ11B) approach

Groundwater salinization is currently a very serious and challenging issue in many parts of the world. With an increasing demographic pressure and remarkable changes of water and land uses over the last decades, the multilayer coastal aquifer system of Jiangsu province, east China, was affected by increasing salinization. In this study, we investigate the groundwater salinization process and the salinity sources of the aquifer system in Nantong area (southern part of the Jiangsu coastal plain) using a multi-isotope (δ2H, δ18O, 87Sr/86Sr, and δ11B) approach. The results show that the TDS (total dissolved solids) values in most deep groundwater samples are generally lower than those of the shallow groundwater samples. The TDS of both shallow and deep groundwater increase from western Nantong (inland) to the eastern coastal region of the Yellow Sea. The chemical types transform from Ca-Mg-HCO3 or Mg-Ca-HCO3 to NaCl. The stable hydrogen and oxygen isotopes signatures of the groundwater samples indicate that local precipitation likely acts as the main recharge source of both the shallow and deep confined groundwater systems. The deep groundwater shows more depleted isotopes, suggesting recharging by the precipitation under a cold climate before the Holocene period. The shallow groundwater features heavier water isotopes, indicating recharging source from recent precipitation under a warm climate. The variations in δ11B and 87Sr/86Sr of groundwater samples can be explained by the changes of solute sources. In the inland region (western Nantong), shallow groundwater with higher TDS is mainly caused by evaporation-induced concentration, whereas in coastal areas, seawater intrusion exerts a major influence on the chemical composition of the shallow groundwater.Our results show that that seawater intrusion mainly occurs in eastern and southeastern Nantong area. We also find that hydraulic connection between shallow and deep groundwater is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points. The mixing between upper saline water and deep freshwater, together with water-rock interactions, likely explain the observed low salinity in deep groundwater in coastal areas. Overall, with growing observations of salty seawater intrusion in the estuary region of the Yangtze River, future efforts are needed to prevent further seawater intrusion as sea level rises and groundwater table declines. In this context, our findings provide key information for groundwater management in other coastal aquifers, east China.

Hydrochemical Evolution of Shallow Groundwater from Sandstone Aquifer in the Chahan Basin, China: Evidences from Chemical and Isotopic Tracers

Geochemical processes controlling hydrochemical evolution of shallow groundwater (<200 m) were studied in the Chahan Lake Basin, China. A combination of chemical and isotopic tracers (δ2H, δ18O, 87Sr/86Sr, 3H and 14C), along with inverse geochemical modeling were applied. Shallow groundwater primarily originates from local precipitation, and has negligible mixture with deep groundwater. Shallow groundwater in the recharge areas and discharge areas were recharged during the Holocene and late Pleistocene, respectively. Groundwater chemistry systematically changes along the flow path from northwest to southeast: water type evolves from Ca.Mg–HCO3 type in the recharge areas through mixed cations-HCO3 type towards Na–HCO3 and Na–HCO3.SO4 type in the discharge areas. Carbonate dissolution and cation exchange are the predominant processes controlling groundwater chemical evolution, which principally occur in the recharge areas and discharge areas, respectively. Furthermore, human activities (e.g. agricultural fertilizer) also significantly affect the chemical compositions of groundwater in the recharge areas, particularly N $${\text{O}}_{3}^{ - }$$ and Cl– contents. Silicate weathering is found to be an insignificant reaction, although the aquifer studied is composed of silicate-dominated sandstone.

Chemical Evolution and Formation Mechanism of Groundwater in Hetao Irrigation Area

Groundwater resources are important sources of water in the arid region of northwestern China, but their overexploitation and utilization has led to a series of ecological and environmental problems. Exploring the characteristics and mechanism of groundwater chemical evolution is important for the rational use of groundwater resources. The characteristics of groundwater chemical evolution were studied in the Yongji Irrigation Area of Hetao Irrigation District and the formation mechanism of the chemical compounds in groundwater were investigated using cluster analysis, factor analysis, and other statistical methods. The influence degree of different factors was calculated. The results showed that the major cations in groundwater in the study area were Na+ and K+, and the major anions were Cl- and HCO3-. Moreover, Na+, K+, and Cl- showed high spatial variability and were the main factors contributing to groundwater salinization. The major chemical compounds in the groundwater in the study area were Cl-Na, HCO3 ·Cl ·SO4-Na, and HCO3-Na. Based on the cluster analysis results, the groundwater was divided into four categories (A1, A2, B1, and B2), of which A1 was highly mineralized by Cl-Na type water, while A2, B1, and B2 were mainly HCO3 ·Cl ·SO4-Na and HCO3-Na type water. Principal component analysis results suggest that groundwater chemistry was mainly affected by salinization, carbonate karstification, and human activities with the influence degrees of 45.976%, 23.853% and 16.678%, respectively. Evaporation, salt rock dissolution, and cation exchange were important sources of Na+ and Cl- accumulation in the irrigation area. Agricultural irrigation (leaching of soil salts) and drought (intense transpiration) were the key drivers of groundwater salinization in the irrigation area.

Investigation of factors influencing groundwater quality in a typical Karoo aquifer in Beaufort West town of South Africa

The study investigates factors that influence the evolution of groundwater chemistry and groundwater quality in a typical Karoo aquifer in South Africa. Groundwater samples were collected from production and monitoring boreholes during spring, summer and autumn seasons. The samples were analysed for inorganic chemistry species. Bivariate plots, stoichiometric analysis and principal component analysis were used as complimentary tools to identify and describe main factors that control the evolution of groundwater chemistry and quality. Groundwater quality was assessed to determine its suitability for domestic and irrigation uses. Three main hydrochemical facies were identified in all seasons; Ca-HCO3, Na-SO4 and mixed water types. The Ca-HCO3 facie evolves from the hydrogeochemical process of calcite dissolution by weak rain carbonic acid and is associated with recently recharged groundwater at higher elevations. The Na in the Na-SO4 facie evolves through cation exchange between calcium and sodium while gypsum dissolution accounts for SO4. Principal component analysis suggests that there is an influence of anthropogenic activities mineralising the groundwater resulting in saline water at lower elevation which negatively affects the groundwater quality. The Ca-HCO3 facie that dominated groundwater at higher elevation is fresher and therefore suitable for both irrigation and domestic uses. The study highlighted the value of using hydrochemical facies, bivariate correlation plots and principal component analysis as complimentary tools to understand hydrogeochemical processes and their influence on groundwater quality.

Hydrochemical Characteristics of Groundwater and Dominant Water–Rock Interactions in the Delingha Area, Qaidam Basin, Northwest China

Groundwater is undoubtedly important for water supplies and eco-environment protection, especially for arid and semi-arid regions. Analyzing the characteristics and evolution of groundwater is significant for the rational management of groundwater resources. This study investigated the hydrogeochemical characteristics and evolutions of groundwater in the Delingha area, northeast of the Qaidam Basin, northwest China, with a total of 123 water samples, including 105 unconfined groundwater samples, 12 confined groundwater samples, and 6 surface water samples. Hydrochemical results showed that the unconfined and confined groundwater presented diversity in ion concentration. Total Dissolved Solids (TDS) of the unconfined groundwater increased from 146.5 to 8954 mg/L along the groundwater flow direction. The groundwater hydrochemical types were HCO3-Ca·Mg and HCO3·SO4-Ca·Mg in the mountain front area, SO4·HCO3-Ca·Mg and SO4·Cl-Ca·Mg types in the alluvial-lacustrine plain, and Cl·SO4-Na and Cl-Na types in the lacustrine plain. The saturation index showed that parts of the groundwater samples were supersaturated with carbonate minerals (calcite and dolomite); however, all the samples were undersaturated with evaporite minerals (halite and gypsum). Groundwater chemical evolution is mainly controlled by evaporite and carbonate mineral dissolutions, aluminosilicates weathering, and cation exchange.

Chemical Evolution of Groundwater in the Tacheng Basin of Xinjiang in the Process of Urbanization

With the development of the local economy, the volume of groundwater production has increased continuously in the past decades in the Tacheng Basin of the Xinjiang Uygur Automous Region. Previous studies have not provided a clear pattern of the chemical composition evolution of groundwater and its driving force in this basin, which makes the future development and utilization of groundwater riskier. This study carried out systematic sampling and analysis of groundwater chemistry in this basin, and the chemical evolution of groundwater in the basin was analyzed by comparison with historical hydrochemical data. The results show that Ca2+ and Na+ are the main cations in the groundwater, HCO3-, SO42- are the main anions in the groundwater, and freshwater is widely distributed. The chemical types of groundwater changed from HCO3-Ca and HCO3·SO4-Ca·Mg in the source zone in front of the mountains to SO4·HCO3-Na·Ca type in the plain area. In comparison with the hydrochemical data of 1979, HCO3 and SO4·HCO3 type groundwater increased significantly. SO4 and Cl type groundwater with high total dissolved solids decreased significantly. However, the Cl- and SO42- concentration and total hardness in the groundwater around the cities and towns increased. Aquifer material and the change of flowing field are the two controlling factors of groundwater chemical change, but the leakage of waste water from city drainage channels also affects the groundwater chemistry drastically.

Geochemical evolution of groundwater in hard-rock aquifers of South India using statistical and modelling techniques

ABSTRACTMultivariate statistical analysis and inverse geochemical modelling techniques were employed to deduce the mechanism of groundwater evolution in the hard-rock terrain of Telangana, South India. Q-mode hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to extract the hydrogeochemical characteristics and classify the groundwater samples into three principal groups. Use of thermodynamic stability diagrams and inverse geochemical modelling in PHREEQC identified the chemical reactions controlling hydrogeochemistry of each of the groups obtained from statistical analysis. The model output showed that a few phases are governing the water chemistry in this area and the geochemical reactions responsible for evolution of groundwater chemistry along the flow path are (i) dissolution of evaporite minerals (dolomite, halite); (ii) dissolution of primary silicate minerals (albite, anorthite, K-feldspar, biotite); (iii) precipitation of secondary silicate minerals (kaolinite, quartz, gibbsite, Ca-montmorillonite) along with anhydrite and calcite; and (iv) reverse ion exchange processes.

Using multivariate statistical techniques and geochemical modelling to identify factors controlling the evolution of groundwater chemistry in a typical transitional area between Taihang Mountains and North China Plain

AbstractIdentifying the key factors controlling groundwater chemical evolution in mountain‐plain transitional areas is crucial for the security of groundwater resources in both headwater basins and downstream plains. In this study, multivariate statistical techniques and geochemical modelling were used to analyse the groundwater chemical data from a typical headwater basin of the North China Plain. Groundwater samples were divided into three groups, which evolved from Group A with low mineralized Ca‐HCO3 water, through Group B with moderate mineralized Ca‐SO4‐HCO3 water, to Group C with highly saline Ca‐SO4 and Ca‐Cl water. Water‐rock interaction and nitrate contamination were mainly responsible for the variation in groundwater chemistry. Groundwater chemical compositions in Group A were mainly influenced by dissolution of carbonates and cation exchange, and suffered less nitrate contamination, closely relating to their locations in woodland and grassland with less pronounced human interference. Chemical evolution of groundwater in Groups B and C was gradually predominated by the dissolution of evaporites, reverse ion exchange, and anthropogenic factors. Additionally, the results of the inverse geochemical model showed that dedolomitization caused by gypsum dissolution, played a key role in the geochemical evolution from Group A to Group B. Heavy nitrate enrichment in most groundwater samples of Groups B and C was closely associated with the land‐use patterns of farmland and residential areas. Apart from the high loads of chemical fertilizers in irrigation return flow as the main source for nitrate contamination, the stagnant zones, flood irrigation pattern, mine drainage, and groundwater‐exploitation reduction program were also important contributors for such high mineralization and heavy NO3− contents in Group C. The important findings of this work not only provide the conceptual framework for the headwater basin but also have important implications for sustainable management of groundwater resources in other headwater basins of the North China Plain.

Hydrogeologic investigations to determine the sources of groundwater recharge of Samalut carbonate aquifer in some wadis, East El Minia, Egypt

ABSTRACT Thirty groundwater samples were collected from wells tapping Samalut fractured carbonate aquifer in the Eastern Desert fringes of the Nile Valley in Minia. The results show a wide variation of groundwater salinity and the graphical presentation of major ion concentrations reflecting variable sources and complex mixing. The inverse evolution modelling shows that the dedolomitization, dissolution of calcite, ion exchange, pyrite and gypsum dissolution are the main mineral–solution interactions controlling the groundwater chemical evolution along flow paths. This study provides evidence on the occurrence of recharge of Samalut aquifer from both the Nile and local floods.

Hydrogeochemical and isotopic characteristics of groundwater in Xinchang preselected site and their implications.

The safety disposal of high-level radioactive waste (HLW) has become an important issue for nuclear energy and environmental protection. Water chemistry and environmental isotope are accepted as feasible ways to trace groundwater circulation; it can effectively reveal the conversion relationship between different groundwater of the disposal site. Geochemical and isotopic tracers were used to constrain origins and chemical evolution of groundwater in the arid fissure system of the Xinchang preselected site for high-level radioactive waste geological disposal in China. Groundwater level, water temperature, and water chemistry information at different depths were obtained by multi-layer groundwater monitoring. The results show that the chemical and isotopic composition of groundwater in this fissure system is mainly controlled by evaporation, the water chemistry type of the shallow groundwater is mainly Na-Cl-SO4 or Na-Ca-Cl-SO4, and the deep groundwater is mainly Na-Cl-SO4. Based on the values of monitoring data in deep borehole, the fluctuation of groundwater level is less than 0.40m with weak hydrodynamic condition, and the geothermal gradient is 1.91°C/100m. The isotope analyses indicate that the groundwater in the system recharged by local atmospheric precipitation, and the deep groundwater recharged capacity of the site is weak and with no deep cycle.

Coupling hydrochemistry and stable isotopes to identify the major factors affecting groundwater geochemical evolution in the Heilongdong Spring Basin, North China

Understanding the interference of natural processes and anthropogenic activities in geochemical evolution of groundwater is vital for groundwater sustainable management in water-stressed regions. This study is devoted to the identification of the main factors controlling the evolution of groundwater chemistry by the combined use of hydrogeochemical indicators along with isotope tracers in the Heilongdong Spring Basin, North China. Thirty-nine groundwater samples and twelve surface water samples were collected, and major ions and stable isotopes were measured during the two campaigns (December 2017 and August 2018). The isotope approach indicates that the groundwater is recharged by precipitation infiltration after evaporation, and interacts with surface water along preferential flow paths in fault zones and karst conduits. Currently, the main chemical facies of groundwater evolve from Ca-HCO3 and Ca-Mg-HCO3 types with low TDS, through Ca-Mg-HCO3-SO4 and Ca-HCO3-SO4 types with moderate TDS, to Ca-SO4, Ca-SO4-Cl and CaCl types with high TDS. Apart from natural processes (involving dissolution/precipitation of minerals, cation exchange, and evaporation) regulating the groundwater quality, the stagnant zones also play a crucial role in the formation of severe localized nitrate contamination. The deterioration in groundwater quality can be attributed to anthropogenic factors (including the change in groundwater exploitation, the leaching of solid waste, and the overuse of agricultural fertilizers). The high loads of agricultural fertilizers in irrigation return flows are likely to be the main contributor of the dissolved nitrate in groundwater. The findings of this work not only have important implications for groundwater sustainable utilization, but also could serve as a template for other rapidly industrialized and water-stressed regions.

Hydrochemical and isotopic characterization of groundwater in the southeastern part of the Plateaux Region, Togo

ABSTRACTHydrochemical, inverse geochemical modelling and isotopic approaches are used to assess the hydrogeochemical evolution of groundwater from the basement aquifers in the southeastern part of the Plateaux Region, Togo. Groundwater originates from present-day rainwater infiltration and is mostly fresh and slightly acidic to neutral. Hydrochemical facies are predominantly mixed cations-HCO3 associated with Ca/Mg-Cl, Na-HCO3 and Na-Cl water types in equilibrium with kaolinite and Ca/Mg-smectites. They are related to silicates hydrolysis, anthropogenic contamination, nitrification/denitrification, mixing along flowpaths and dissolution/precipitation of secondary minerals. The pattern of flow paths is in accordance with an increasing trend in total dissolved solids (TDS) toward the potentiometric depression located in the central and southern parts of the aquifer system. Inverse geochemical modelling using the NETPATH-WIN model showed the relative importance of biotite, plagioclase and amphibole weathering and dissolution of secondary carbonate minerals along the flowpath, suggesting that an abundance of minerals is not necessarily the main factor controlling the groundwater chemistry evolution.

Hydrogeochemical Characterization and Suitability Assessment of Groundwater: A Case Study in Central Sindh, Pakistan.

Groundwater is the most important water resource, on which depends human geo-economic development and survival. Recent environmental changes and anthropogenic activities render groundwater severely vulnerable. Groundwater in Central Sindh, Pakistan, is facing a similar situation. Hydrogeochemical characteristics of the groundwater in the said region were investigated by analyzing 59 groundwater samples via agricultural and drinking indices, using various statistical methods and graphical approaches to identify factors affecting groundwater. Major reactions occurring in the groundwater system were quantified by hydrogeochemical modeling. A statistical summary reveals the abundance of cations is Na+ > Ca2+ > Mg2+ > K+, while the abundance of anions is HCO3− > Cl− > SO42. Groundwater chemistry is mainly of rock dominance. Correlation analysis and graphical relationships between ions reveal that ion exchange and rock weathering such as the dissolution of halite, albite, and dissolution of carbonate minerals are important rock–water interactions, governing the evolution of groundwater chemistry. Hydrochemical facies are predominantly of mixed CaMgCl and Na-Cl type, with few samples of Ca-HCO3 type, which constitutes fresh recharged water. Based on the Water Quality Index (WQI), 28.82% samples were found to be unsuitable for drinking. A United States Salinity Laboratory (USSL) diagram, Wilcox diagram, and other agricultural indices indicate that majority of the groundwater samples fall within the acceptable range for irrigation purposes.

Groundwater quality appraisal by improved set pair analysis with game theory weightage and health risk estimation of contaminants for Xuecha drinking water source in a loess area in Northwest China

The current study was carried out to investigate the hydrochemistry of groundwater in Xuecha drinking water source by statistical analysis and graphical approaches, and to evaluate the groundwater quality using improved set pair analysis (SPA) model with game theory for weight determination. The non-carcinogenic health risks and carcinogenic health risks of nitrate and Cr6+ through oral exposure pathway for adults and children were also estimated, respectively. For this study, 39 groundwater samples were collected from Luohe and Huanhe aquifers in the study area for physicochemical analysis. Groundwater in the Huanhe aquifer shows poorer quality than that in the Luohe aquifer with greater hardness and higher salinity. The Piper diagram and Gibbs diagrams show that the Huanhe groundwater is mainly SO4·Cl–Ca·Mg, HCO3–Na, and HCO3–Ca·Mg types, and rock weathering is the leading factor in groundwater chemistry evolution, and groundwater evaporation is also a noticeable factor. All Luohe groundwater samples are SO4·Cl–Na type and are mainly regulated by the weathering of rocks and water–rock interactions, but less affected by evaporation compared to the Huanhe groundwater. Most of the Huanhe groundwater is of excellent to fair quality, and more than half the Luohe water samples are of poor quality. Children in the area are facing higher health risks. Carcinogenic risks caused by Cr6+ in this study area are higher than the acceptable limit for adult and children, and higher severity is observed in the Huanhe groundwater. For the non-cancer risk, greater threat is from the Luohe groundwater.

Evolution of groundwater chemistry in coastal aquifers of the Northern Dvina basin (NW Russia)

The specific objective of the study is to clarify the sources and characteristics of groundwater chemistry in coastal aquifers of the Northern Dvina basin. It has been established that the chemical composition of fresh water evolves in the direction (Ca-Mg-HCO3) - (Na-HCO3) - (Na-Cl). It is due to successive replacement of the process of calcite dissolution in the recharge area on the watershed i) by the process of hydrolysis of sodium aluminosilicates in the transit zone and ii) by the processes of mixing fresh water with salt water and brines, cation exchange of alkaline earth elements with alkaline elements and dissolution of gypsum near discharge areas at the seashore and in paleovalleys. In the brackish and salty waters the Na/Ca ratio is reduced to 1-4. This indicates that in the aquifers there are other sources of Ca, in addition to the dissolution of gypsum. The most probable process is the hydrolysis of Ca-aluminosilicates, which indicates a significant time of water-rock interaction. The “brackish1” water with TDS 5-6 g·L-1, is particularly distinguished by the degree of modification due to water-rock interaction.

The Influence of Karst Aquifer Mineralogy and Geochemistry on Groundwater Characteristics: West Bank, Palestine

This work reports, for the first time, the mineralogical and geochemical characteristics of karst aquifers in the Central West Bank (CWB) catchment in Palestine. It provides an integrated study approach by correlating the geochemistry of the lithology and hydrochemical data of groundwater samples. Mineralogical analysis showed that all of the samples were dominantly composed of either calcite CaCO3 (5–100 wt. %) or dolomite CaMg(CO3)2 (4–100 wt. %), with minor amounts of quartz and feldspar, which is supported by the inorganic carbon content (9–13 wt. %) and hydrochemical composition of the spring water samples. The whole-rock geochemical data indicated that the samples have low contents of trace elements and transition metals. In contrast, the concentrations of alkaline earth elements (Mg, Ca, Sr, Ba) and Mn were high in the rock and groundwater samples. Generally, the trace elements of rock samples with concentrations &gt;10 ppm included Sr (17–330 ppm), Mn (17–367 ppm), Ba (2–32 ppm), W (5–37 ppm), Cr (3–23 ppm), Zn (1.7–28 ppm), V (4–23 ppm), and Zr (1–22 ppm), while the concentrations of all the other trace elements was below 10 ppm. Ionic ratios and hierarchical cluster analysis (HCA) suggested that the chemical evolution of groundwater was mainly related to the geogenic (rock–water) interaction in the study area. This is clear in the alkaline earth elements (Mg, Ca, Sr, Ba) ratios, especially regarding the Sr values. The calcite rock samples had higher Sr (mean 160 ppm, n = 11) than those of the dolomite rocks (mean 76 ppm, n = 9).

Hydrochemical characteristics and quality evaluation of groundwater in terms of health risks in Luohe aquifer in Wuqi County of the Chinese Loess Plateau, northwest China

Groundwater is the main source of water for domestic and agricultural purposes in Wuqi County on the Loess Plateau. The present study was carried out to assess the hydrochemical characteristics and quality of groundwater in the Luohe aquifer, which is a crucial aquifer for water supply. For this study, 22 groundwater samples and 6 surface water samples were collected for analysis. Hydrochemistry and hydrochemical facies of groundwater were analyzed using statistical analysis and Tri-linear diagram. Gibbs diagram, correlation analysis and bivariate plots were used to investigate the natural evolution mechanisms of groundwater and surface water. Potential health risks of nitrate and Cr6+ through drinking water ingestion for adults and children were estimated. The results show that the major hydrochemical facies is Cl·SO4-Na, mixed Cl·SO4·HCO3-Na and SO4·Cl-Mg·Na types, and high concentration of Na+ is a remarkable feature of groundwater in the study area. Groundwater chemistry evolution is affected by rock weathering and evaporation. The high concentrations of Na+, SO42- and TDS suggest that groundwater is not suitable for irrigation purposes. According to WQI values, above 80% of the groundwater samples are fair quality water. It is also found that the groundwater of the study area is contaminated with nitrate and Cr6+. Children are at higher health risk than adults. Multiple measures such as establishing new centralized water supply sources and inter-basin water transfer projects have also been proposed in this study to guarantee the safety of sustainable groundwater supply.

Conceptual hydrogeochemical characteristics of a calcite and dolomite acid mine drainage neutralised circumneutral groundwater system

This article presents and discusses conceptual hydrogeochemical characteristics of dolomite and calcite acid mine drainage (AMD) neutralised circumneutral groundwater system. The conceptual discussions are based on the consideration of calcite and dolomite AMD buffering hydrogeochemical processes. Using theoretical chemical reaction stoichiometry, predictions are made for molar ratios of associated AMD – calcite and dolomite buffering reaction products (SO42−, Ca2+ and Mg2+). Comparison is made between stoichiometrically predicted molar ratios of SO42−/Ca2+, SO42−/Mg2+, Ca2+/Mg2+ and field data from previous studies in South Africa. There is a close match between stoichiometrically predicted molar ratios of the calcite and dolomite AMD neutralisation reaction products and field data. The results provide basis to improve the conceptual understanding of hydrogeochemical processes associated with dolomite and calcite AMD neutralisation which is important for field investigations related to mine-water quality, water management, remediation and overall environmental protection. Results further demonstrates the potential usefulness of relating ion concentration molar ratios of field measurements to stoichiometric predictions as a tool to identify hydrogeochemical processes controlling the evolution of groundwater chemistry.

Source apportionment and health risk assessment of fluoride in water resources, south of Fars province, Iran: Stable isotopes (δ18O and δD) and geochemical modeling approaches

In this study the key factors influencing fluoride enrichment in water resources, south of Fars province, Iran are investigated. For this purpose, hydrogeochemical, statistical and isotopic studies were conducted on water and dominant rock types. Impact on human health is also considered. The results indicated that fluoride concentrations in water resources range from 0.06 to 4.95 mg/L, while 67.5% of the analysed samples displayed concentrations above the world health organization guidelines for drinking water. Fluoride enrichment is associated with NaCaMgClSO4 water type and the chemical evolution of groundwater along flow path. F/Cl ratio, δ18O and δD results of water samples indicated that evaporation favored F‾ enrichment. Calculated mineral saturation indices and statistical analysis indicated that while the lithological units play a prominent role in fluoride anomalies, anthropogenic sources are negligible. Inverse geochemical modeling and calculated Chloro-Alkaline indices proved the occurrence of reverse ion exchange processes in the groundwater. Conducted leaching tests and X-ray diffraction data on abundant geological formations revealed dolomite and clay minerals as two likely candidates for contributing fluoride to the aquifers. The alkaline nature of water seems to have intensified the F‾ exchange in clay minerals with OH‾ in water. Fluoride exposure risk assessment revealed that children and adults are prone to fluoride-related diseases caused by ingestion of fluoride-rich water. Considering the prevailing climatic conditions and the ongoing geochemical processes, fluoride level in local aquifers will undoubtedly rise with time unless preventive and remediative measures are taken by the responsible authorities.