Hydrochemistry of groundwater (GW) and surface water (SW) for assessment of fluoride in Chinnaeru river basin,Nalgonda district, (AP) India

Hydrochemical studies were conducted in Chinnaeru river basin of Nalgonda district, Andhra Pradesh, India, to explore the causes of high fluorides in groundwater and surface water causing a widespread incidence of fluorosis in local population. The concentration of fluoride in groundwater ranges from 0.4 to 2.9 and 0.6 to 3.6 mg/l, stream water ranges from 0.9 to 3.5 and 1.4 to 3.2 mg/l, tank water ranges from 0.4 to 2.8 and 0.9 to 2.3 mg/l, for pre- and post-monsoon periods, respectively. The modified Piper diagram reflects that the water belongs to Ca²⁺–Mg²⁺–HCO₃ ^? to Na⁺–HCO₃ ^? facies. Negative chloroalkali indices in both the seasons prove that ion exchange between Na⁺ and K⁺ in aquatic solution took place with Ca²⁺ and Mg²⁺ of host rock. The interpretation of plots for different major ions and molar ratios suggest that weathering of silicate rocks and water–rock interaction is responsible for major ion chemistry of groundwater/surface water. High fluoride content in groundwater was attributed to continuous water–rock interaction during the process of percolation with fluorite bearing country rocks under arid, low precipitation, and high evaporation conditions. The low calcium content in rocks and soils, and the presence of high levels of sodium bicarbonate are important factors favouring high levels of fluoride in waters. The basement rocks provide abundant mineral sources of fluoride in the form of amphibole, biotite, fluorite, mica and apatite.     

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.     

Seasonal disparity in the co-occurrence of arsenic and fluoride in the aquifers of the Brahmaputra flood plains,Northeast India

Arsenic (As) and fluoride (F^?) in groundwater are increasing global water quality and public health concerns. The present study provides a deeper understanding of the impact of seasonal change on the co-occurrence of As and F^?, as both contaminants vary with climatic patterns. Groundwater samples were collected in pre- and post-monsoon seasons (n = 40 in each season) from the Brahmaputra flood plains (BFP) in northeast India to study the effect of season on As and F^? levels. Weathering is a key hydrogeochemical process in the BFP and both silicate and carbonate weathering are enhanced in the post-monsoon season. The increase in carbonate weathering is linked to an elevation in pH during the post-monsoon season. A Piper diagram revealed that bicarbonate-type water, with Na⁺, K⁺, Ca²⁺, and Mg²⁺ cations, is common in both seasons. Correlation between Cl^? and NO₃ ^? (r = 0.74, p = 0.01) in the post-monsoon indicates mobilization of anthropogenic deposits during the rainy season. As was within the 10 µg L^?1 WHO limit for drinking water and F^? was under the 1.5 mg L^?1 limit. A negative correlation between oxidation reduction potential and groundwater As in both seasons (r = ?0.26 and ?0.49, respectively, for pre-monsoon and post-monsoon, p = 0.05) indicates enhanced As levels due to prevailing reducing conditions. Reductive hydrolysis of Fe (hydr)oxides appears to be the predominant process of As release, consistent with a positive correlation between As and Fe in both seasons (r = 0.75 and 0.73 for pre- and post-monsoon seasons, respectively, at p = 0.01). Principal component analysis and hierarchical cluster analysis revealed grouping of Fe and As in both seasons. F^? and sulfate were also clustered during the pre-monsoon season, which could be due to their similar interactions with Fe (hydr)oxides. Higher As levels in the post-monsoon appears driven by the influx of water into the aquifer, which drives out oxygen and creates a more reducing condition suitable for reductive dissolution of Fe (hydr)oxides. An increase in pH promotes desorption of As oxyanions AsO₄ ^3? (arsenate) and AsO₃ ^3? (arsenite) from Fe (hydr)oxide surfaces. Fluoride appears mainly released from F^?-bearing minerals, but Fe (hydr)oxides can be a secondary source of F^?, as suggested by the positive correlation between As and F^? in the pre-monsoon season.     

An appraisal of groundwater quality for drinking and irrigation purposes in southern part of Bathinda district of Punjab, northwest India

Groundwater is being used for drinking and irrigation purposes in the agricultural dominated Indian state of Punjab. Fifty-six groundwater samples were collected from Bathinda, a south-western district of Punjab, during the pre-monsoon (March 2010) and post-monsoon (October 2011) seasons. These samples were tested for major cations, anions and contaminants. Various classification systems were used to study the groundwater quality with respect to drinking as well as irrigation purposes. Total dissolved solids (TDS) and total hardness (TH) are generally used to determine the suitability of groundwater for drinking purpose. Considering TDS as a parameter, 54 and 57 % groundwater samples were found to be unsuitable for use during the pre- and post-monsoon seasons. A wide range of TH values were observed in the pre-monsoon and post-monsoon waters samples (mean 250 and 270 mgL^?1). About 75 % of pre-monsoon and 79 % of post-monsoon samples exceeded the maximum permissible limit (MPL) of TH (150 mg L^?1) proposed by WHO. In terms of contaminant ions, 40 % and 55 % of the pre- and post-monsoon water samples were unfit for drinking purposes w.r.t. fluoride (MPL 1.5 mg F L^?1), 29 and 36 % were unfit w.r.t arsenic (MPL 10 μg L^?1) and 33 and 45 % were unfit w.r.t nitrate (MPL 45 mg NO₃ ^? L^?1), respectively. To determine the suitability of groundwater of Bathinda for irrigation purpose, three classification systems proposed by different research workers were used. The parameters electrical conductivity (EC), sodium adsorption ratio, and residual sodium carbonate (RSC) were calculated on the basis of chemical data. Considering EC and RSC together, 32 % samples collected during pre-monsoon season were fit, 19 % were marginal and 49 % were unfit for use. However, during post-monsoon, samples fit for irrigation decreased to 17 % and samples unfit for irrigation increased to 70 %. Increases in the percentage of unfit samples for irrigation after monsoon indicates addition of salts along with the rain water percolated into the groundwater. The other two classification systems, i.e. US Salinity diagram and Wilcox diagram also showed the similar results.     

Hydrochemical characteristics of groundwater quality with special reference to fluoride concentration in parts of Mulugu-Venkatapur Mandals,Warangal district,Telangana

Hydrochemical studies were carried out in Mulugu-Venkatapur Mandals of Warangal district, Telangana state, India to find out the causes of high fluorides in groundwater and surface water causing a widespread incidence of fluorosis in local population. The fluoride concentration in groundwater ranges from 0.28 to 5.48 mg/l with a mean of 1.26 mg/l in pre-monsoon and 0.21 to 4.43 mg/l with a mean 1.45 mg/l in post-monsoon. About 32% and 34% of samples in pre and post-monsoon containing fluoride concentrations that exceed the permissible limit. The Modified Piper diagram reflects that, water belong to Ca⁺²-Mg⁺²-HCO₃ - to Na⁺-HCO₃ - facies. Negative chloroalkali indices in both the seasons prove that ion exchange took place between Na⁺ & K⁺ with Ca⁺² and Mg⁺² in aquatic solution in host rock. Different plots for major ions and molar ratios suggest that weathering of silicate rocks and water-rock interaction is responsible for major ion chemistry of water. High fluoride content in groundwater attributed to continuous water-rock interaction during the process of percolation with fluorite bearing country rocks under arid, low precipitation, and high evaporation conditions. The low calcium content in rocks and soils, and the presence of high content of sodium bicarbonate in soils and waters are important factors favouring high levels of fluoride in waters. The basement rocks provide abundant mineral sources of fluoride in the form of amphibole, biotite, fluorite, mica and apatite.     

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.     

Principal component and multivariate statistical approach for evaluation of hydrochemical characterization of fluoride-rich groundwater of Shaslar Vagu watershed,Nalgonda District,India

In order to assess the impact of fluoride-rich groundwater of Shasilair Vagu watershed on groundwater regime, more than hundred groundwater samples for pre- and post-monsoon seasons were collected from bore wells/dug wells and analyzed for major ions. Water quality analysis of major ion chemistry shows elevated concentration of fluoride in groundwater samples. The fluoride concentration ranges from 1.4 to 5.9 mg/l and 1.5 to 5.8 mg/l in pre- and post-monsoons, respectively. The result clearly shows that the seasonal variation of fluoride in groundwater is due to recharge of rain water during monsoon. The water quality data was analyzed by hydrochemical facies (Piper diagram), Gibbs plot, and various plots. Plots of Na versus Cl, Ca versus SO₄, and (Na+Cl)-(SO₄+HCO₃) versus (Na+K-Cl) shows positive and negative values, indicating that their source of high concentration are aquifer, evapotranpiration, and other anthropogenic sources. Saturation index of halite and gypsum shows that all groundwater samples were undersaturated and suggests that carbonate minerals influence the concentration. Using multivariate statistical techniques, viz., principal component (factor analysis and cluster analysis), the analysis brought out impact of intensity of excess use of fertilizers and excess withdrawal of groundwater regime. Multivariate statistical techniques are potential tools and provide greater precision for identifying contaminant parameter linkages.     

Determining the genetic origin of nitrate contamination in aquifers of Northern Gujarat,India

Over the past decades, the Gujarat state of India experienced intensive agricultural and industrial activities, fertilizer consumption and abstraction of groundwater, which in turn has degraded the ground water quality. Protection of aquifers from nitrate pollution is a matter of prime concern for the planners and decision-makers. The present study assessed the spatial and temporal variation of groundwater nitrate levels in areas with different land use/land cover activities for both pre- and post-monsoon period. The pre-monsoon nitrate level (1.6–630.7 mg/L) in groundwater was observed to be higher as compared to the post-monsoon level (2.7–131.7 mg/L), possibly due to insufficient recharge and evaporation induced enrichment of agrichemical salts in groundwater. High HCO₃ ^? (200–1,000 mg/L) as well as SO₄ ^2?/Cl^? (0.111–0.992) in post-monsoon period provides a favourable environment for denitrification, and lower the NO₃ levels during the post-monsoon period. The K vs NO₃ scatter plot suggests a common source of these ions when the concentration is <5 mg/L, the relationships between different pollutants and nitrate also suggest that fertilizers and other sources, such as, animal waste, crop residue, septic tanks and effluents from different food processing units present in the area can be attributed to higher nitrate levels in the groundwater. Appropriate agronomic practices such as application of fertilizers based on calibrated soil tests and proper irrigation with respect to crop can minimize the requirement for inorganic fertilizers, which can bring down the cost of cultivation considerably, and also protect groundwater from further degradation.     

Assessment of groundwater quality for drinking and irrigation purposes using hydrochemical studies in Nalbari district of Assam,India

The present work was carried out in Nalbari district of Assam (India) with an objective to assess the quality of groundwater and to check its suitability for drinking and irrigation purposes. Groundwater samples were collected from 50 different locations during pre- and post-monsoon seasons of 2016. Results of chemical analysis revealed that mean concentration of cations varied in the order Ca²⁺?>?Na⁺?>?Mg²⁺?>?K⁺, while for anions the order was HCO₃ ^??>?Cl^??>?SO₄^2??>?NO₃^2??>?F^? during both pre- and post-monsoon seasons. The suitability of groundwater samples for drinking purpose was assessed by comparing the results of physico-chemical analysis of groundwater with Indian Standards. Further, its suitability for irrigation purpose was assessed by evaluating several parameters like sodium adsorption ratio (SAR), sodium percentage (Na%), magnesium ratio, Kelly’s ratio and residual sodium carbonate (RSC). The SAR values obtained for all the samples were plotted against EC values in the US Salinity Laboratory diagram, and it was revealed that the most of the samples fall under water type C2-S1 indicating medium salinity and low SAR. Further, it was found that the majority of the samples belong to Ca–Mg–HCO₃ hydrochemical facies followed by Ca–Mg–Cl–SO₄, whereas only a few samples belong to Na–K–HCO₃ hydrochemical facies.     

Hydrogeochemical processes controlling fluoride enrichment within alluvial and hard rock aquifers in a part of a semi-arid region of Northern India

Rock–water interaction along with mineral dissolution/ precipitation plays a profound role in the control of fluoride ion concentration within the alluvial groundwater in a part of semi-arid northern India. In the premonsoon season, the alluvial region experiences evaporative processes leading to increase in Na⁺ ions which through reverse ion exchange processes are adsorbed onto suitable sites within the aquifer matrix in exchange for Ca²⁺ ion in solution. Increase in Ca²⁺ ions in solution inhibits fluorite mineral dissolution, thereby controlling premonsoon fluoride ion concentration within alluvial groundwaters (1.40?±?0.5 mg/l). In the postmonsoon season, however, higher average fluoride ion concentration within the alluvial aquifer samples (2.33?±?0.80 mg/l) is observed mainly due to increase in silicate weathering of fluoride-bearing rocks and direct ion exchange processes enabling Ca²⁺ ion uptake from solution accompanied with the release of fluoride ions. Combined effect of these processes results in average fluoride ion concentration falling above the WHO drinking water permissible limit (1.5 mg/l). Alternatively, the hard rock aquifer samples within the study area have an average fluoride ion concentration falling below the permissible limit in both the seasons.     

Impact of anthropogenic activities on the chemistry and quality of groundwater: a case study from a terrain near Zarand City, Kerman Province, SE Iran

Groundwater of an aquifer located in the vicinity of a large coal washery near Zarand City, Iran consists of two hydrochemically differing facies, which have been informally designated as groundwater (A) and groundwater (B). Groundwater (A) is native, brackish in composition and is characterized by Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and SO₄ ^2? > HCO₃ ^? > Cl^? > NO₃ ^?. Spearman’s rank correlation coefficient matrices, factor analysis data, and values of chloro-alkaline indices, C ratio and Na⁺/Cl^? molar ratio indicate that in the groundwater (A), the ionic load of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ^2? and HCO₃ ^? is derived essentially from weathering of both carbonates and aluminosilicates and direct cation and reverse cation–anion exchange reactions. Groundwater (B) is the polluted variant of the groundwater (A), brackish to saline in composition, and unlike the groundwater (A), consists of HCO₃ ^? as the dominant anion. In comparison with the groundwater (A), the groundwater (B) contains higher concentrations of all ions, and its average ionic load (av. = 59.74 me/L) is 1.43 times higher than that of the groundwater (A) (av. = 41.54 me/L). Additional concentrations of Ca²⁺, Mg²⁺, K⁺, SO₄ ^2?, Cl^? and HCO₃ ^? in the groundwater (B) are provided mainly by downward infiltrating water from the coal washery tailings pond and reverse cation–anion exchange reaction between tailings pond water and exchanger of the aquifer matrix during non-conservative mixing process of groundwater (A) and tailings pond water. Certain additional concentrations of Na⁺, K⁺ and NO₃ ^? in the groundwater (B) are provided by other anthropogenic sources. Quality wise, both groundwaters are marginally suitable for cultivation of salt-tolerant crops only.     

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.     

Seasonal variation in major ion chemistry of a tropical mountain river,the southern Western Ghats,Kerala, India

A comprehensive and systematic study to understand various geochemical processes as well as process drivers controlling the water quality and patterns of the hydrochemical composition of river water in Muthirapuzha River Basin, MRB (a major tributary of Periyar, the longest river in Kerala, India), was carried out during various seasons, such as monsoon, post-monsoon and pre-monsoon of 2007–2008, based on the data collected at 15 monitoring stations (i.e., 15 × 3 = 45 samples). Ca²⁺ and Mg²⁺ dominate the cations, while Cl^? followed by HCO₃ ^? dominates the anions. In general, major ion chemistry of MRB is jointly controlled by weathering of silicate and carbonate rocks, which is confirmed by relatively larger Ca²⁺ + Mg²⁺/Na⁺ + K⁺ ratios as well as Ca²⁺/Na⁺ vs. Mg²⁺/Na⁺ and Ca²⁺/Na⁺ vs. HCO₃ ^?/Na⁺ scatter plots. The relationship between Cl^? and Na⁺ implies stronger contributions of anthropogenic activities modifying the hydrochemical composition, irrespective of seasons. The water types emerged from this study are transitional waters or waters that changed their chemical character by mixing with waters of geochemically different ionic signatures. However, various ionic ratios, hydrochemical plots and graphical diagrams suggest seasonality over the hydrochemical composition, which is solely controlled by the rainfall pattern. Relatively higher pCO₂ indicates the disequilibrium existing in natural waterbodies vis-à-vis the atmosphere, which is an outcome of both the contribution of groundwater to stream discharge and anthropogenic activities. Hence, continuous monitoring of hydrochemical composition of mountain rivers is essential in the context of climate change, which has serious implications on tropical mountain fluvial-hydro systems.     

Hydrochemical and isotopic characteristics of groundwater in the Ndop plain,northwest Cameroon: resilience to seasonal climatic changes

Shallow groundwater (>30 mbgl) is an essential source of drinking water to rural communities in the Ndop plain, northwest Cameroon. As a contribution to water management, the effect of seasonal variation on the groundwater chemistry, hydrochemical controls, drinking quality and recharge were investigated during the peaks of the dry (January) and rainy (September) seasons. Field measurements of physical parameters were preceded by sampling 58 groundwater samples during both seasons for major ions and stable isotope analyses. The groundwater, which was barely acidic (mean pH of 6) and less mineralised (TDS < 272 mg/l), showed no significant seasonal variation in temperature, pH and TDS during the two seasons. The order of cation abundance (meq/l) was Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ in the dry and rainy seasons, respectively, but that of anions ( \( {\text{HCO}}_{3}^{ - } \)  >  \( {\text{NO}}_{3}^{ - } \)  > Cl^? >  \( {\text{SO}}_{4}^{2 - } \)  > F^?) was similar in both seasons. This suggests a negligible effect of seasonal variations on groundwater chemistry. The groundwater, which was CaMgHCO₃ and NaHCO₃, is chemically evolved rainfall (CaMgSO₄Cl) in the area. Silicate mineral dissolution and cation-exchange were the main controls on groundwater chemistry while there was little anthropogenic influence. The major ions and TDS concentrations classified the water as suitable for human consumption as per WHO guidelines. The narrow cluster of δ¹⁸O and δD of same groundwater from both seasons between the δ¹⁸O and δD values of May–June precipitation along the Ndop Meteoric Water Line indicates meteoric origin, rapid recharge (after precipitation) and timing of recharge between May and June rainfall. Diffuse groundwater recharge mainly occurs at low altitudes (<1,400 m asl) within the plain. Besides major ions and TDS, the similar δ¹⁸O and δD of groundwater from both seasons indicate a consistent groundwater recharge and flow pattern throughout the year and resilience to present day short-term seasonal climatic variations. However, controlled groundwater abstraction is recommended given the increasing demand.     

Assessment of the factors controlling groundwater quality in a coastal aquifer adjacent to the Bay of Bengal,India

A study has been conducted in the heavily populated coastal areas of the Puri district (Odisha, India) with the aim to: (1) identify the factors that influence the major ion composition and concentrations of trace elements in groundwater; (2) determine the spatial distribution of the water-quality parameters and how they vary on a seasonal basis. To do this, groundwater samples were collected from 60 shallow tube wells located along the Puri coast during the pre-monsoon and post-monsoon seasons. Based on their TDS content, 52% of the collected groundwater samples were identified as being brackish-to-saline and unsuitable for drinking purposes in both the pre- and post-monsoon seasons. Significant concentrations of trace elements including Ba, Br, F, Fe, Mn, and Sr were detected in most of the samples. Iron concentrations were found to be higher than the WHO drinking water guideline value (0.3 mg/l) in 92% of the samples irrespective of seasons. Elevated Mn concentrations were observed in 37% and 40% of samples during the pre-monsoon and post-monsoon seasons, respectively. In addition, fluoride concentrations in excess of the WHO limit (1.5 mg/l) were found in 15% of samples during the pre-monsoon and 23% of samples during the post-monsoon season. The concentrations of major and trace elements show wide spatial and minor temporal variations. Large spatial and limited temporal variations in Cl and Na concentrations along with considerable Br and Sr concentrations in groundwater suggest that saltwater intrusion is the dominant process controlling groundwater quality in the study area, although other processes including ion exchange, the precipitation and dissolution of minerals, microbial activity, and the weathering of aquifer material also play roles to some extent in determining the spatial and seasonal distribution of the major and trace elements in coastal groundwater. Grouping of various water-quality parameters related to these processes by principal component analysis and their linking to one cluster in the hierarchical cluster analysis further supports the view that these processes control the groundwater chemistry in the coastal aquifer.     

Fluoride contamination of groundwater and its seasonal variability in parts of Purulia district,West Bengal,India

The contamination of aquifers by fluoride and arsenic is a major cause of concern in several parts of India. A study has thus been conducted to evaluate the extent and severity of fluoride contamination and also its seasonal variability. Two blocks (Purulia-1 and Purulia-2) were considered for this purpose. Twenty groundwater samples (in each season) were collected from tube wells during the pre-monsoon and post-monsoon seasons. In addition to fluoride, groundwater samples were also analyzed for major cations, anions, and other trace elements. The concentration of fluoride shows significant seasonal variation and ranges between 0.94–2.52 and 0.25–1.43 mg/l during the pre-monsoon and post-monsoon seasons, respectively. In pre-monsoon season, more than 40% of the water samples show fluoride concentrations higher than the WHO limit. However, during the post-monsoon season, none of the groundwater sample shows fluoride concentrations higher than the WHO limit. Lesser concentration during the post-monsoon season is attributed to the dilution effect by the percolating rainwater, which has also been reflected in the form of a decrease in concentrations of other elements. The petrographic studies of the rock samples collected from the study area show that the rocks are mainly composed of plagioclase, orthoclase, and quartz with abundant biotite. The weathering and dissolution of biotite plays an important role in controlling the fluoride concentrations in the groundwater of the study area.     

Hydrochemical characteristics and quality assessment of regolith aquifers in Enugu metropolis, southeastern Nigeria

Twenty groundwater samples were collected from Enugu metropolis over two seasonal periods in order to characterize the groundwater and to determine its quality for domestic and irrigation purposes. The results show that groundwater of the area is strongly acidic to slightly alkaline in nature and varied from “soft water” to “moderately hard” water type. The major ionic trend is in the order Cl^? > Na⁺ > HCO₃ ^? > K⁺ > Mg²⁺ > Ca²⁺ > SO₄ ^2?and Mg²⁺ > Cl^? > Na⁺ > K⁺ > Ca²⁺ > HCO ₃ ^?  > SO₄ ^2? in abundance for dry and rainy seasons, respectively. The results also reveal that there is an increase in trend of the ionic concentrations during the dry season, which arises from weathering of the host rocks and anthropogenic activities. Two hydrochemical facies were identified, namely, Na⁺ –K⁺ –Cl^? –SO₄ ^2?and Ca²⁺ –Mg²⁺ –Cl^? –SO₄ ^2? _, with Na⁺ –K⁺ –Cl^? –SO₄ ^2? as the dominant facies for the two seasons. Groundwater quality ranges from “very poor water” to “good water” and “water unsuitable for drinking purposes” to “good water” for the dry season and rainy season investigations, respectively. The groundwater is suitable for irrigation purposes for the two seasons.     

A diagnosis of groundwater quality from a semiarid region in Rajasthan,India

A diagnosis of the groundwater quality of 70 wells sampled during two climatic regimes (dry and raining seasons) from a semiarid area in Rajasthan, India, had been carried out using standard methods. Analysis of the results for various hydrochemical parameters wherein the geological units are alluvium, quartzite and granite gneisses showed that all the parameters did not fall within the World Health Organisation’s acceptable limits for irrigation and drinking water purposes. The order of major cations and anions obtained during the dry and raining seasons are Na⁺ ? Mg²⁺ ? Ca²⁺ ? K⁺ and Cl^?? HCO₃ ^? ? SO₄ ^2?? CO₃ ^?> F^? ? NO₃ ^?, respectively. A maximum value of nitrate of 491.6 mg/l has been examined and its contamination is due to discriminated highly impacted groundwater samples by agricultural activity and small-scale urbanization. Fluoride (F^?) concentration is 6.50 mg/l as a maximum value, whereas values in about 26 % of the samples are more than the permissible limit (1.5 mg/l) for drinking water. The cumulative probability distributions of the selected ions show two individual intersection points with three diverse segments, considered as regional threshold values and highly impacted threshold values for differentiating the samples with the effects of geogenic, anthropogenic and saline water mixing. The first threshold values indicate the background hydrochemical constituents in the study area. The second threshold value of 732 mg/l for bicarbonate indicates that sandy aquifer is being dissolved during wet period, whereas NO₃ ^? concentration of more than the initial threshold value (=75 mg/l) indicates discriminated highly impacted groundwater samples by agricultural activity and urbanization in dry season. Various parameters such as soluble sodium percentage (SSP), salinity (electrical conductivity (EC)), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), Kelley’s ratio (KR), permeability index (PI), residual sodium bicarbonate (RSB) and magnesium absorption ratio (MAR) for the well samples show that, overall, 46 % of groundwater samples are not suitable for irrigation. Further, chloro-alkaline indices (CAIs) were used for distinguishing regional recharge and discharge zones whereas corrosivity ratio (CR) utilized for demarcating areas to use metallic pipes for groundwater supply. In general, groundwater quality is mainly controlled by the chemical weathering of rock-forming minerals. The information obtained represents a base for future work that will help to assess the groundwater condition for periodical monitoring and managing the groundwater from further degradation.     

Geochemical evaluation of nitrate and fluoride contamination in varied hydrogeological environs of Prakasam district,southern India

Hydrogeochemical controlling factors for high rate of groundwater contamination in stressed aquifer of fractured, consolidated rocks belonging to semi-arid watershed are examined. The groundwater in mid-eastern part of Prakasam district confining to Musi-Gundlakamma sub-basins is heavily contaminated with nitrate and fluoride. Distinct water chemistry is noticed among each group of samples segregated based on concentration of these contaminants. The nitrate is as high as 594 mg/l and 57 % of the samples have it in toxic level as per BIS drinking water standards, so also the fluoride which has reached a maximum of 8.96 mq/l and 43 % of samples are not fit for human consumption. Nitrate contamination is high in shallow aquifers and granitic terrains, whereas fluoride is in excess concentration in deeper zones and meta-sediments among the tested wells, and 25 % of samples suffer from both NO₃ ^? and F^? contamination. Na⁺ among cations and HCO₃ ^? among anions are the dominant species followed by Mg²⁺ and Cl^?. The NO₃ ^?-rich groundwater is of Ca²⁺–Mg²⁺–HCO₃ ^?, Ca²⁺–Mg²⁺–Cl^? and Na⁺–HCO₃ ^? type. The F^?-rich groundwater is dominantly of Na⁺–HCO₃ ^? type and few are of Na⁺–SO₄ ^2? type, whereas the safe waters (without any contaminants) are of Ca²⁺–Mg²⁺–HCO₃ ^?– and Na⁺–HCO₃ ^? types. High molecular percentage of Na⁺, Cl^?, SO₄ ^2? and K^? in NO₃ ^? rich groundwater indicates simultaneous contribution of many elements through domestic sewerage and agriculture activity. It is further confirmed by analogous ratios of commonly associated ions viz NO₃ ^?:Cl^?:SO₄ ^2? and NO₃ ^?:K⁺:Cl^? which are 22:56:22 and 42:10:48, respectively. The F^? rich groundwater is unique by having higher content of Na⁺ (183 %) and HCO₃ ^? (28 %) than safe waters. The K⁺:F^?:Ca²⁺ ratio of 10:5:85 and K⁺:F^?: SO₄ ^2? of 16:7:77 support lithological origin of F^? facilitated by precipitation of CaCO₃ which removes Ca²⁺ from solution. The high concentrations of Na⁺, CO₃ ^? and HCO₃ ^? in these waters act as catalyst allowing more fluorite to dissolve into the groundwater. The indices, ratios and scatter plots indicate that the NO₃ ^? rich groundwater has evolved through silicate weathering-anthropogenic activity-evapotranspiration processes, whereas F^? rich groundwater attained its unique chemistry from mineral dissolution-water–rock interaction-ion exchange. Both the waters are subjected to external infusion of certain elements such as Na⁺, Cl^?, NO₃ ^? which are further aggravated by evaporation processes leading to heavy accumulation of contaminants by raising the water density. Presence of NO₃ ^? rich samples within F^? rich groundwater Group and vice versa authenticates the proposed evolution processes.     

Characterisation and quality assessment of groundwater with a special emphasis on irrigation utility: Thirumanimuttar sub-basin, Tamil Nadu, India

Thirumanimuttar sub-basin is of particular importance in the study of groundwater quality due to the release of effluents from industries, agricultural, sewage and urban runoff, brining considerable change in water quality. An investigation was carried out by collecting a total of 194 groundwater samples for two seasons to decipher hydrogeochemistry and groundwater quality for determining its suitability for agricultural purposes. The water is neutral to alkaline in nature with pH ranging from 6.78 to 9.22 with an average of 7.37. Higher electrical conductivity (EC) was noted in NW and mid-downstream parts of the study area. Higher NO ₃ ^? was observed during post-monsoon (POM) due to the action of leaching and anthropogenic process. The piper plot reveals the dominance of Na⁺?CCl^? and Na⁺?CHCO ₃ ^? , mixed Ca²⁺?CNa⁺?CHCO ₃ ^? , mixed Ca²⁺?CMg²⁺?CHCO ₃ ^? and Ca²⁺?CSO ₄ ^? types of hydrogeochemical facies. Higher total hardness in the groundwater is due to the effect of dyeing and bleaching industries discharging effluents affects the quality of water. Residual Sodium Carbonate value indicates 56% of the samples are not suitable for irrigation purposes in both seasons. Higher sodium percentage is noted during PRM indicating the dominance of ion exchange and weathering. Higher sodium adsorption ratio was observed during POM indicating the effect of leaching and dissolution of salts into the aquifer matrix. USSL plot indicates 15% of samples record high salinity to medium sodicity. The Permeability Index indicates water is moderate to good for irrigation purposes. In general, groundwater in the study area is influenced by both natural and anthropogenic activities.