Mapping of fluoride ions in groundwater of Dindigul district, Tamilnadu, India—using GIS technique

The accurate information through water quality analysis, scientific study on F ^? distribution in groundwater and geochemical knowledge with spatial information on geology and climate are necessary to understand the source/cause, type and level of F ^? contamination. The Dindigul district is a hard-rock terrain and marked as one of the fluoride-rich area in Tamilnadu due to occurrence of various rock types including fluoride-bearing minerals. The F ^? content of groundwater can thus originate from the dissolution of fluoride-bearing minerals in the bed rock. Eighty-six representative groundwater samples from Dindigul district was collected during two different seasons. Samples were analysed for F ^?, other major cations and anions. The study area is chiefly composed of hornblende biotite gneiss and charnockite, apart from this untreated tannery effluents also let from many places in the study area. Geographical Information System technique was adopted to study the sources of F ^?, and it was found that F ^? in the study is mainly attributed to geogenic source.     

Geochemical characteristics and controlling factors of chemical composition of groundwater in a part of Guntur district,Andhra Pradesh,India

A survey on quality of groundwater was carried out for assessing the geochemical characteristics and controlling factors of chemical composition of groundwater in a part of Guntur district, Andhra Pradesh, India, where the area is underlain by Peninsular Gneissic Complex. The results of the groundwater chemistry show a variation in pH, EC, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, Cl^?, SO₄ ^2?, NO₃ ^? and F^?. The chemical composition of groundwater is mainly characterized by Na⁺?HCO₃ ^? facies. Hydrogeochemical type transits from Na⁺–Cl^?–HCO₃ ^? to Na⁺–HCO₃ ^?–Cl^? along the flow path. Graphical and binary diagrams, correlation coefficients and saturation indices clearly explain that the chemical composition of groundwater is mainly controlled by geogenic processes (rock weathering, mineral dissolution, ion exchange and evaporation) and anthropogenic sources (irrigation return flow, wastewater, agrochemicals and constructional activities). The principal component (PC) analysis transforms the chemical variables into four PCs, which account for 87% of the total variance of the groundwater chemistry. The PC I has high positive loadings of pH, HCO₃ ^?, NO₃ ^?, K⁺, Mg²⁺ and F^?, attributing to mineral weathering and dissolution, and agrochemicals (nitrogen, phosphate and potash fertilizers). The PC II loadings are highly positive for Na⁺, TDS, Cl^? and F^?, representing the rock weathering, mineral dissolution, ion exchange, evaporation, irrigation return flow and phosphate fertilizers. The PC III shows high loading of Ca²⁺, which is caused by mineral weathering and dissolution, and constructional activities. The PC IV has high positive loading of Mg²⁺ and SO₄ ^2?, measuring the mineral weathering and dissolution, and soil amendments. The spatial distribution of PC scores explains that the geogenic processes are the primary contributors and man-made activities are the secondary factors responsible for modifications of groundwater chemistry. Further, geochemical modeling of groundwater also clearly confirms the water–rock interactions with respect to the phases of calcite, dolomite, fluorite, halite, gypsum, K-feldspar, albite and CO₂, which are the prime factors controlling the chemistry of groundwater, while the rate of reaction and intensity are influenced by climate and anthropogenic activities. The study helps as baseline information to assess the sources of factors controlling the chemical composition of groundwater and also in enhancing the groundwater quality management.     

A study on the status of fluoride ion in groundwater of coastal hard rock aquifers of south India

India has an increasing incidence of fluorosis, dental and skeletal, with nearly about 62 million people at risk. High fluoride groundwaters are present especially in the hard rock areas of the country. This paper analyzes the most extensive database on fluoride and other chemical constituent distribution in the coastal hard rock aquifers of Thoothukudi district. A total of 135 samples were collected and analyzed for major cations and anions to assess the geochemical process. The fluoride concentration in drinking waters varied from BDL to 3.2 mg?l^?1 in the study area. Majority of the samples do not comply with WHO standards for most of the water quality parameters. The saturation index of fluorite saturation index was used to correlate with F^? to identify their relationship to increase of fluoride levels. The correlation between the F^? concentration and the water type was also attempted. Spatial distribution of fluoride in groundwater was studied to understand the influencing factors. The relationship of F^? with HCO^? _3, Na⁺ and pH concentrations were studied and found that HCO^? ₃, has good correlation with F^? than the other parameters.     

Groundwater solute chemistry,hydrogeochemical processes and fluoride contamination in phreatic aquifer of Odisha,India

The work investigates the major solute chemistry of groundwater and fluoride enrichment(F~-) in the shallow phreatic aquifer of Odisha.The study also interprets the hydrogeochemical processes of solute acquisition and the genetic behavior of groundwater F~-contamination.A total of 1105 groundwater samples collected from across the state from different hydro-geomorphic settings have been analyzed for the major solutes and F~-content.Groundwater is alkaline in nature(range of pH: 6.6–8.7; ave.: 7.9) predominated by moderately hard to very hard types.Average cation and anion chemistry stand in the orders of Ca~(2+) Na~+ Mg~(2+) K~+and HCO_3~- Cl~- SO_4~(2-) CO_3~(2-)respectively.The average mineralization is low(319 mg/L).The primary water types are Ca-Mg-HCO_3 and Ca-Mg-Cl~-HCO_3, followed by Na-Cl, Ca-Mg-Cl, and Na-Ca-Mg-HCO_3~-Cl.Silicate-halite dissolution and reverse ion exchange are the significant processes of solute acquisition.Both the geogenic as well as the anthropogenic sources contribute to the groundwater fluoride contamination,etc.The ratio of Na~+/Ca~(2+) 1.0 comprises Na-HCO_3(Cl) water types with F~- 1.0 mg/L(range 1.0–3.5 mg/L)where the F~-bears geogenic source.Positive relations exist between F~-and pH, Na~+, TDS, and HCO_3~-.It also reflects a perfect Na-TDS correlation(0.85).The ratio of Na~+/Ca~(2+) 1.0 segregates the sample population(F~- range: 1.0–4.0 mg/L) with the F derived from anthropogenic sources.Such water types include Ca-Mg-HCO_3(Cl) varieties which are recently recharged meteoritic water types.The F~-levels exhibit poor and negative correlations with the solutes in groundwater.The Na-TDS relation remains poor(0.12).In contrast, the TDS levels show strong correlations with Ca~(2+)(0.91), Mg~(2+)(0.80) and even Cl~-(0.91).The majority of the monitoring points with the anthropogenic sources of groundwater F~-are clustered in the Hirakud Canal Command area in the western parts of the state, indicating the role of irrigation return flow in the F~-contamination.     

Regional appraisal of the fluoride occurrence in groundwaters of Andhra Pradesh

Fluoride (F^?) is essential for normal bone growth, but higher concentration in the drinking water causes health problems which are reported in many states of India. Andhra Pradesh is one of the states which suffer from excess fluoride in groundwater particularly in the hard rock terrain. In this context, a study was conducted in Andhra Pradesh based on chemical analysis of water samples from hydrograph net work stations (dug wells) and exploratory bore wells. The concentration of fluoride in groundwaters ranges from traces to 9.75 mg/l. The occurrence of fluoride is mostly sporadic, uneven and varies with depth. The highly affected districts include Nalgonda and Warangal in Telangana region, Prakasam in coastal region, Anantapur and Kurnool in Rayalaseema region. In certain areas of Nalgonda district, 85% of wells have fluoride more than permissible limit (> 1.5 mg/l) for drinking water. High F^? is present in all the geological formations, predominantly in granitic aquifers, compared to the other formations. The average value of fluoride is high in the deeper zone (1.10 mg/L), compared to the shallow zone (0.69 mg/L). The fluoride-rich minerals present are the main sources for fluoride concentrations in groundwater. Residence time, evapotranspiration and weathering processes are some of the other supplementary factors for high fluoride concentrations in groundwater. Long-term data of hydrograph net work stations (dug wells) reveal that fluoride concentrations do not show any marked change of trend with respect to time. The concentration of fluoride is found to increase with increase of Na⁺and HCO ₃ ^? , and decrease with increase of Ca²⁺. Sodium bicarbonate waters are more effective in releasing fluoride from minerals into groundwater. High fluoride waters are of Na⁺ type. The paper presents a brief account of the study and its results.     

Controlling factors of fluoride in groundwater in a part of South India

Fluoride (F^?) is the most important element for human health. Hydrogeochemical survey was conducted to probe into the controlling factors of F^? in the groundwater of a semi-arid part of South India. The study area comprises of F^?-bearing minerals (hornblende, biotite, and apatite) in the Precambrian rocks, sandstones in the Upper Gondwana rocks, and clays in the Quaternary formations. Forty-seven percent of the total groundwater samples have the higher F^? content than its permissible limit of 1.50 mg/L prescribed for drinking purpose. The chemical data of the groundwater is analyzed to assess the geochemical processes dominating the F^?-bearing groundwater, using Piper and Gibbs diagrams, correlations, saturation indices, ionic ratios, and multivariate analysis. Piper diagram shows that the groundwater quality is characterized by Na⁺-HCO\( {}_3^{-} \) and Na⁺-Cl^?types, while the Gibbs diagrams suggest that the groundwater chemistry is mainly controlled by water-rock interactions and is subsequently modified by human activities. The F^? groundwater is positively correlated with pH, total dissolved solids, Mg²⁺, Na⁺, K⁺, HCO\( {}_3^{-} \), Cl^?, SO\( {}_4^{2-} \), and NO\( {}_3^{-} \) and negatively with Ca²⁺, representing the influences of geogenic and anthropogenic origins on the groundwater system. Geochemical ratios and saturation indices indicate that the processes of mineral dissolution, ion exchange, and evaporation mainly govern the high F^? groundwater, while the chemical fertilizers cause for the enrichment of F^?in the groundwater. Cluster and principal component analyses further support the above findings.     

Hydrogeochemical processes and contaminants enrichment with special emphasis on fluoride in groundwater of Birbhum district,West Bengal,India

The hydrogeochemistry of groundwater in rural parts of Birbhum district, West Bengal, India, has been studied to understand the contaminants and prime processes involved in their enrichment with a focus on F^? concentration. The lithological units consist of Quaternary alluviums with underlying Rajmahal basaltic rocks of Middle Jurassic age. Groundwater occurs in the alluviums, weathered residuum and fracture zone of Rajmahal rocks. Studies show elevated concentration of Cl^?, SiO₂, Fe and F^?; excess Cl^? is attributed to anthropogenic inputs, SiO₂ is ascribed to high degree of weathering of silica rich host rocks, and high Fe is due to the interaction of water with Fe-rich sediments under reducing condition. The F^? concentration is found high (>1.20 mg/L) mainly in water from Rajmahal rocks revealing a lithological control on F^? enrichment. The weathering of silicates and ion exchange are the leading controlling processes for major ions in groundwater. The F^? enrichment is due to the dissolution of F^?-bearing minerals and perhaps also through anion exchange (OH^? for F^?) on clay minerals at high alkaline conditions; precipitation of CaCO₃ favours CaF₂ dissolution leading to elevated F^? concentration. CaHCO₃, the dominant water type, contains low F^? while NaHCO₃ and NaCl types exhibit high F^? concentrations. Among the three spatial associations, Cluster-1 and Cluster-2 are CaHCO₃ type; Cluster-3 shows NaHCO₃ and NaCl waters with low Ca²⁺ and Mg²⁺ and high Na⁺ contents. Cluster-1 and Cluster-2 waters are, in general, drinkable barring the elevated Fe content, while Cluster-3 water is unsafe for drinking due to the high F^? concentration.     

Geochemistry and assessment of hydrogeochemical processes in groundwater in the southern part of Bathinda district of Punjab, northwest India

Hydrogeochemistry of groundwater is important for sustainable development and effective management of the groundwater resource. Fifty-six groundwater samples were collected from shallow tube wells of the intensively cultivated southern part of district Bathinda of Punjab, India, during pre- and post-monsoon seasons. Conventional graphical plots were used to define the geochemical evaluation of aquifer system based on the ionic constituents, water types, hydrochemical facies and factors controlling groundwater quality. Negative values of chloroalkaline indices suggest the prevalence of reverse ion exchange process irrespective of the seasons. A significant effect of monsoon is observed in terms chemical facies as a considerable amount of area with temporary hardness of Ca²⁺–Mg²⁺–HCO₃ ^? type in the pre-monsoon switched to Ca²⁺–Mg²⁺–Cl^? type (18%) followed by Na⁺–HCO₃ ^? type (14%) in the post-monsoon. Evaporation is the major geochemical process controlling the chemistry of groundwater process in pre-monsoon; however, in post-monsoon ion exchange reaction dominates over evaporation. Carbonate weathering is the major hydrogeochemical process operating in this part of the district, irrespective of the season. The abundance of Ca²⁺ + Mg²⁺ in groundwater of Bathinda can be attributed mainly to gypsum and carbonate weathering. Silicate weathering also occurs in a few samples in the post-monsoon in addition to the carbonate dissolution. Water chemistry is deteriorated by land-use activities, especially irrigation return flow and synthetic fertilisers (urea, gypsum, etc.) as indicted by concentrations of nitrate, sulphate and chlorides. Overall, results indicate that different natural hydrogeochemical processes such as simple dissolution, mixing, weathering of carbonate minerals locally known as ‘‘kankar’’ and silicate weathering are the key factors in both seasons.     

Assessment of groundwater quality with special reference to arsenic in Nawalparasi district,Nepal using multivariate statistical techniques

Groundwater is a precious resource for humankind not only in Nepal but also across the globe due to its diverse functions. A total of 48 groundwater samples were collected from three villages of Nawalparasi district, Nepal, during pre-monsoon and monsoon to estimate the overall groundwater quality and to identify the sources of contamination with emphasis on arsenic (As). The average concentrations of all tested groundwater quality parameters (temp., pH, EC, ORP, Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^?, F^?,SO₄ ^2?, PO₄ ^3?, HCO₃ ^?, NO₃ ^?, Cu, Ni, Mn, Cd, Pb, Fe, Zn, Cr, and As) were well within permissible limits of WHO for drinking water, except for Ni, Cd, Pb, Cr, and As. Concentration of As ranged from 60 to 3,100 μg L^?1 and 155 to 1,338 μg L^?1 in pre-monsoon and monsoon, respectively. The Piper diagram of the groundwater chemistry showed groundwater of Nawalparasi belongs to Ca–Mg–HCO₃ and Mg–HCO₃ water type with HCO₃ ^? as dominant ions. As content in the study area was negatively correlated with Fe in pre-monsoon, while it was positively correlated in monsoon. Furthermore, As was negatively correlated with oxidation reduction potential suggesting reducing condition of groundwater. Principal component analysis revealed seven major factors that explained 81.996 and 83.763 % of total variance in water quality in pre-monsoon and monsoon, respectively. The variance of water quality was related mainly with the degree of water–rock interaction, mineralization, and anthropogenic inputs.     

Geochemical processes controlling fluoride-bearing groundwater in the granitic aquifer of a semi-arid region

The aim of the present study is to identify the geochemical processes responsible for higher fluoride (F^–) content in the groundwater of the Yellareddigudem watershed located in Nalgonda district, Andhra Pradesh. The basement rocks in the study area comprise mainly of granites (pink and grey varieties), which contain F-bearing minerals (fluorite, biotite and hornblende). The results of the study area suggest that the groundwater is characterized by Na⁺: HCO facies. The F^– content varies from 0.42 to 7.50 mg/L. In about 68% of the collected groundwater samples, the concentration of F^– exceeds the national drinking water quality limit of 1.5 mg/L. The weathering of the granitic rocks causes the release of Na⁺ and HCO ions, which increase the solubility of ions. Ion exchange between Na+ and Ca²⁺, and precipitation of CaCO₃ reduce the activity of Ca²⁺. This favours dissolution of CaF₂ from the F-bearing minerals present in the host rocks, leading to a higher concentration of F^– in the groundwater. The study further suggests that the spatial variation in the F^– content appears to be caused by difference in the relative occurrence of F-bearing minerals, the degree of rockweathering and fracturing, the residence time of water in the aquifer materials and the associated geochemical processes. The study emphasizes the need for appropriate management measures to mitigate the effect of higher F groundwater on human health.     

Hydrochemical characterization,mechanism of mobilization,and natural background level evaluation of arsenic in the aquifers of upper Gangetic plain,India

Although arsenic (As) contamination has been extensively investigated in the aquifers of the lower and middle Gangetic plains, less attention has been given to the distribution and fate of As in the groundwater of the upper Gangetic plain, India. In the current study, groundwater samples (n = 40) were collected from Moradabad district in the upper Gangetic plain and analyzed for several physicochemical parameters to characterize the groundwater chemistry and evaluate various geogenic and anthropogenic factors controlling the occurrence, mobilization, and fate of As in the plain. Arsenic concentrations in groundwater ranged from 0.17 μg/L to 139 μg/L, with the majority of high-As groundwater associated with high Fe, Mn, and HCO₃⁻ and low NO₃⁻, SO₄²⁻, and negative Eh values, implying that As was released via reductive dissolution of Fe and Mn oxyhydroxides in reducing conditions under the influence of organic matter degradation. Interrelationships between various geochemical variables and the natural background level (NBL) quantification of As suggested the influence of anthropogenic processes on the mobility of As in groundwater. Piper and Gibbs diagrams and various bivariate plots revealed that the majority of groundwater was of the Ca²⁺ − Mg²⁺ − HCO₃⁻ type and that the major ions in groundwater were derived from carbonate and silicate weathering, cation exchange and reverse ion exchange processes, and anthropogenic activities. Moreover, the results of principal component analysis (PCA), and hierarchical cluster analysis (HCA) also suggested geogenic and anthropogenic sources for the ion concentration in groundwater. The health risk assessment showed a higher non-carcinogenic risk for children and a higher carcinogenic risk for adults, respectively, due to the daily intake of As contaminated groundwater. Overall, this study represents the first systematic investigation of the distribution, geochemical behavior, and release process of As in groundwater in the study area and provides a strong base for future research in the alluvial aquifers of the upper Gangetic plain.     

Investigation of fluoride contamination and its mobility in groundwater of Simlapal block of Bankura district,West Bengal,India

The occurrence of dental/skeletal fluorosis among the people in the study area provided the motivation to assess the distribution, severity and impact of fluoride contamination in groundwater of Bankura district at Simlapal block, West Bengal, India. To meet the desired objective, groundwater samples were collected from different locations of Laxmisagar, Machatora and Kusumkanali regions of Simlapal block at different depths of tube wells in both pre- and post-monsoon seasons. Geochemical results reveal that the groundwaters are mostly moderate- to hard-water type. Of total groundwater samples, 37% are situated mainly in relatively higher elevated region containing fluoride above 1.5 mg/L, indicating that host aquifers are severely affected by fluoride contamination. Machatora region is highly affected by fluoride contamination with maximum elevated concentration of 12.2 mg/L. Several symptoms of fluorosis among the different age-groups of people in Laxmisagar and Machatora areas are indicating consumption of fluoridated water for prolonged period. The groundwater samples were mainly Na–Ca–HCO₃ type and rock dominance indicating the dissolution of minerals taking place. Ion exchange between OH^? ion and F^? ion present in fluoride-bearing mineral is the most dominant mechanism of fluoride leaching. High concentration of Na⁺ and HCO₃ ^? increases the alkalinity of the water, providing a favorable condition for fluoride to leach into groundwater from its host rocks and minerals.     

Occurrence and hydrogeochemistry of fluoride in alluvial aquifer of Weihe River,China

Fluoride (F^?) has significant impacts on human health. High fluoride groundwater (up to 1.90 mg/L) has been found in upper confined aquifer underlying the first terrace of Weihe River during a hydrogeological investigation for water supply in 2005. To reveal the occurrence and hydrogeochemistry of high F^? groundwater, hydrogeochemical tools such as saturation index, ionic ratios and correlation analysis were used in this study. The study shows that the concentrations of most physiochemical parameters from phreatic water, influenced by intensive evaporation and anthropogenic activities such as unregulated sewage and excreta disposal and agricultural practices in the area, are higher than those of confined water. The F^? concentration in phreatic water is within the acceptable limits set by China and the World Health Organization (WHO), while that of upper confined water shows a decreasing trend northwestward as the Weihe River approaches, with F^? concentration in the first terrace beyond the national and the WHO standards. High F^? groundwater is observed in alkaline environment associated with high Na⁺, pH, HCO₃ ^? and low Ca²⁺ and Mg²⁺. The enrichment of F^? is controlled by geologic and hydrogeological conditions, fluorine-bearing minerals presented in alluvial formations and their dissolution/precipitation under the alkaline environment along groundwater flow. Ion exchange, human activities and the mixing of different recharge waters may influence the enrichment of F^? as well.     

Major ion chemistry and metal distribution in coal mine pit lake contaminated with industrial effluents: constraints of weathering and anthropogenic inputs

Ion chemistry of mine pit lake water reveals dominance of alkaline earths (Ca²⁺ and Mg²⁺) over total cation strength, while SO₄ ^2? and Cl^? constitute the majority of total anion load. Higher value of Ca²⁺?+?Mg²⁺/Na⁺?+?K⁺ (pre-monsoon 5.986, monsoon 8.866, post-monsoon 7.09) and Ca²⁺?+?Mg²⁺/HCO₃ ^??+?SO ₄ ² (pre-monsoon 7.14, monsoon 9.57, post-monsoon 8.29) is explained by weathering of Ca?CMg silicates and dissolution of Ca²⁺-bearing minerals present in parent rocks and overburden materials. Silicate weathering supposed to be the major geological contributor, in contrast to bicarbonate weathering does a little. Distribution coefficient for dissolved metals and sorbed to surface sediments is in the order of Cd?>?Pb?>?Fe?>?Zn?>?Cu?>?Cr?>?Mn. Speciation study of monitored metals in surface sediments shows that Fe and Mn are dominantly fractionated in exchangeable-acid reducible form, whereas rest of the metals (Cr, Pb, Cd, Zn, and Cu) mostly in residual form. Cd, Pb, and Zn show relatively higher recalcitrant factor that indicates their higher retention in lake sediments. Factor loading of monitored physico-chemical parameters resembles contribution/influences from geological weathering, anthropogenic inputs as well as natural temporal factors. Ionic load/strength of lake water accounted for geochemical process and natural factors, while pollutant load (viz BOD, COD and metals, etc.) is associated with anthropogenic inputs through industrial discharge.     

Fluoride incidence in groundwater in an area of Peninsular India

Groundwater samples were collected from Anantapur District, Andhra Pradesh, India. The district is mainly underlain by Peninsular Gneisses of Archaean age. The samples were analysed for fluoride (F^–) along with other chemical parameters. The results suggest that the main sources of F^– in groundwater in the district are the country rocks, in which fluorine is strongly absorbed in soils consisting of clay minerals. A strong positive correlation between F^– and lithogenic sodium reflects weathering activity. This is responsible for the leaching of F^–, which is also caused by the semi-arid climate and intensive irrigation in the area. An alkaline environment of circulating water in the investigated area mainly facilitates leaching of F^– from the soils, contributing to high F^–-containing groundwater. A longer residence time of water in the aquifer zone, caused by a high rate of evapotranspiration and a weathered zone of low hydraulic conductivity, which promotes the dissolution of fluorine-bearing minerals, is another factor that further increases the F^– content in groundwater. Suggestions are made to improve groundwater quality and, thus, the health status of the population.     

Identification of hydrogeochemical processes and pollution sources of groundwater resources in the Marand plain,northwest of Iran

The main aims of the present study are to identify the major factors affecting hydrogeochemistry of groundwater resources in the Marand plain, NW Iran and to evaluate the potential sources of major and trace elements using multivariate statistical analysis such as hierarchical clustering analysis (HCA) and factor analysis (FA). To achieve these goals, groundwater samples were collected in three sampling periods in September 2013, May 2014 and September 2014 and analyzed with regard to ions (e.g., Ca²⁺, Mg²⁺, Na⁺ and K⁺, HCO₃ ^?, SO₄ ^2?, Cl^?, F^? and NO₃ ^?) and trace metals (e.g., Cr, Pb, Cd, Mn, Fe, Al and As). The piper diagrams show that the majority of samples belong to Na–Cl water type and are followed by Ca–HCO₃ and mixed Ca–Na–HCO₃. Cross-plots show that weathering and dissolution of different rocks and minerals, ion exchange, reverse ion exchange and anthropogenic activities, especially agricultural activities, influence the hydrogeochemistry of the study area. The results of the FA demonstrate that 6 factors with 81.7% of total variance are effective in the overall hydrogeochemistry, which are attributed to geogenic and anthropogenic impacts. The HCA categorizes the samples into two clusters. Samples of cluster C1, which appear to have higher values of some trace metals like Pb and As, are spatially located at the eastern and central parts of the plain, while samples of cluster C2, which express the salinization of the groundwater, are situated mainly westward with few local exceptions.     

Statistical analysis of the hydrogeochemical evolution of groundwater in hard rock coastal aquifers of Thoothukudi district in Tamil Nadu, India

The study of groundwater hydrogeochemistry of a hard rock aquifer system in Thoothukudi district has resulted in a large geochemical data set. A total of 100 water samples representing various lithologies like Hornblende Biotite Gneiss, Alluvium Marine, alluvium Fluvial, Quartzite, Charnockite, Granite and Sandstone were collected for two different seasons and analyzed for major ions like Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, Cl^?, SO₄ ^2?, NO₃ ^?, PO₄ ^?, F^? and H₄SiO₄. Statistical analysis of the data has been attempted to unravel the hidden relationship between ions. Correlation analyses and factor analyses were applied to classify the groundwater samples and to identify the geochemical processes controlling groundwater geochemistry. Factor analysis indicates that sea water intrusion followed by leaching of secondary salts, weathering and anthropogenic impacts are the dominant factors controlling hydrogeochemistry of groundwater in the study area. Factor score overlay indicate major active hydrogeochemical regimes are spread throughout the Eastern, Northwestern and Southeastern parts of the study area. The dominant ions controlling the groundwater chemistry irrespective of season are Cl^?, Na⁺, Mg²⁺, Ca²⁺, SO₄ ^2?, K⁺ and NO₃ ^?. An attempt has also been made to note the seasonal variation of the factor representations in the study area. This study also illustrates the usefulness of statistical analysis to improve the understanding of groundwater systems and estimates of the extent of salinity/salt water intrusion.     

Mechanism of fluoride enrichment in groundwater of hard rock aquifers in Medak,Telangana State,South India

A total of 194 groundwater samples were collected from wells in hard rock aquifers of the Medak district, South India, to assess the distribution of fluoride in groundwater and to determine whether this chemical constituent was likely to be causing adverse health effects on groundwater user in the region. The study revealed that the fluoride concentration in groundwater ranged between 0.2 and 7.4 mg/L with an average concentration of 2.7 mg/L. About 57% of groundwater tested has fluoride concentrations more than the maximum permissible limit of 1.5 mg/L. The highest concentrations of fluoride were measured in groundwater in the north-eastern part of the Medak region especially in the Siddipeta, Chinnakodur, Nanganoor and Dubhaka regions. The areas are underlain by granites which contain fluoride-bearing minerals like apatite and biotite. Due to water–rock interactions, the fluoride has become enriched in groundwater due to the weathering and leaching of fluoride-bearing minerals. The pH and bicarbonate concentrations of the groundwater are varied from 6.6 to 8.8 and 18 to 527 mg/L, respectively. High fluoride concentration in the groundwater of the study area is observed when pH and the bicarbonate concentration are high. Data plotted in Gibbs diagram show that all groundwater samples fall under rock weathering dominance group with a trend towards the evaporation dominance category. An assessment of the chemical composition of groundwater reveals that most of the groundwater samples have compositions of Ca²⁺–Mg²⁺–Cl^? > Ca²⁺–Na⁺–HCO₃ ^? > Ca²⁺–HCO₃ ^? > Na⁺–HCO₃ ^?. This suggests that the characteristics of the groundwater flow regime, long residence time and the extent of groundwater interaction with rocks are the major factors that influence the concentration of fluoride. It is advised not to utilize the groundwater for drinking purpose in the areas delineated, and they should depend on alternate safe source.     

The origin of groundwater arsenic and fluorine in a volcanic sedimentary basin in central Mexico: a hydrochemistry hypothesis

A groundwater sampling campaign was carried out in the summer of 2013 in a low-temperature geothermal system located in Juventino Rosas (JR) municipality, Guanajuato State, Mexico. This groundwater presents high concentrations of As and F^? and high Rn counts, mainly in wells with relatively higher temperature. The chemistry of major elements was interpreted with different methods, like Piper and D’Amore diagrams. These diagrams allowed for classification of four groundwater types located in three hydrogeological environments. The aquifers are hosted mainly in alluvial-lacustrine sediments and volcanic rocks in interaction with fault and fracture systems. The subsidence, faults and fractures observed in the study area can act as preferential channels for recharge and also for the transport of deep fluids to the surface, especially in the basin plain. The formation of a piezometric dome and the observed hydrochemical behavior of groundwater suggest a possible origin of the As and F^?. Geochemical processes occurring during water–rock interaction are related to high concentrations of As and F^?. High temperatures and alteration processes (like rock weathering) induce dissolution of As and F^?-bearing minerals, increasing the content of these elements in groundwater.