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.     

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 levels in the groundwater of the south-eastern part of Ranga Reddy district,Andhra Pradesh,India

The fluoride level in groundwater is controlled by the distribution of Ca²⁺ and SO₄^2?, ionic strength and the presence of complex ions in its composition. In the study area, situated in the Ranga Reddy district, Andhra Pradesh, India, the concentrations of fluoride in the groundwater vary from 0.7 to 4.80 mg/l and from 0.4 to 4.20 mg/l during the pre- and post-monsoon seasons respectively. From the correlation coefficient studies, it is observed that fluoride is inversely related with Ca²⁺ and positively related with HCO₃^?, whereas the correlation coefficient between fluoride and other ions is very poor during both seasons. The difference in F^? concentrations between pre- and post-monsoon seasons could be because the ionic concentrations in the groundwater during the post-monsoon period were generally less than their counterparts during the pre-monsoon period, because of dilution by rainwater. By contrast, the fluoride concentration in many places was relatively high during the post-monsoon period. This indicates contamination of groundwater from surface pollutants.     

Hydrogeochemical parameters for assessment of groundwater quality in the upper Gunjanaeru River basin,Cuddapah District,Andhra Pradesh,South India

In the management of water resources, quality of water is just as important as its quantity. In order to know the quality and/or suitability of groundwater for domestic and irrigation in upper Gunjanaeru River basin, 51 water samples in post-monsoon and 46 in pre-monsoon seasons were collected and analyzed for various parameters. Geological units are alluvium, shale and quartzite. Based on the analytical results, chemical indices like percent sodium, sodium adsorption ratio, residual sodium carbonate, permeability index (PI) and chloroalkaline indices were calculated. The pre-monsoon waters have low sodium hazard as compared to post-monsoon season. Residual sodium carbonate values revealed that one sample is not suitable in both the seasons for irrigation purposes due the occurrence of alkaline white patches and low permeability of the soil. PI values of both seasons revealed that the ground waters are generally suitable for irrigation. The positive values of Chloroalkaline indices in post-monsoon (80%) and in pre-monsoon (59%) water samples indicate absence of base-exchange reaction (chloroalkaline disequilibrium), and remaining samples of negative values of the ratios indicate base-exchange reaction (chloroalkaline equilibrium). Chadha rectangular diagram for geochemical classification and hydrochemical processes of groundwater for both seasons indicates that most of waters are Ca–Mg–HCO₃ type. Assessment of water samples from various methods indicated that majority of the water samples in both seasons are suitable for different purposes except at Yanadipalle (sample no. 8) that requires precautionary measures. The overall quality of groundwater in post-monsoon season in all chemical constituents is on the higher side due to dissolution of surface pollutants during the infiltration and percolation of rainwater and at few places due to agricultural and domestic activities.     

Assessment of impact of ash ponds on groundwater quality: a case study from Koradi in Central India

The present study assesses the impact of the ash ponds on the groundwater quality in the sub-watershed surrounding the ash ponds in the vicinity of Koradi near Nagpur in Maharashtra, India. Observation wells have been set up for monitoring of water level and groundwater quality for major cations, anions and trace elements. Samples (23 nos.) have been collected in pre-monsoon and post-monsoon seasons during 2008 and 2009, and analysis indicates that the sulphate concentration is very high (>1,000 mg/L) in samples close to the ash pond and in its downstream direction. The fluoride concentration exceeds the BIS limits in one sample.     

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.     

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.     

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.     

Identification of major sources controlling groundwater chemistry from a hard rock terrain — A case study from Mettur taluk,Salem district,Tamil Nadu,India

The study area Mettur forms an important industrial town situated NW of Salem district. The geology of the area is mainly composed of Archean crystalline metamorphic complexes. To identify the major process activated for controlling the groundwater chemistry an attempt has been made by collecting a total of 46 groundwater samples for two different seasons, viz., pre-monsoon and post-monsoon. The groundwater chemistry is dominated by silicate weathering and (Na + Mg) and (Cl + SO₄) accounts of about 90% of cations and anions. The contribution of (Ca + Mg) and (Na + K) to total cations and HCO₃ indicates the domination of silicate weathering as major sources for cations. The plot for Na to Cl indicates higher Cl in both seasons, derived from Anthropogenic (human) sources from fertilizer, road salt, human and animal waste, and industrial applications, minor representations of Na also indicates source from weathering of silicate-bearing minerals. The plot for Na/Cl to EC indicates Na released from silicate weathering process which is also supported by higher HCO₃ values in both the seasons. Ion exchange process is also activated in the study area which is indicated by shifting to right in plot for Ca + Mg to SO₄ + HCO₃. The plot of Na-Cl to Ca + Mg-HCO₃-SO₄ confirms that Ca, Mg and Na concentrations in groundwater are derived from aquifer materials. Thermodynamic plot indicates that groundwater is in equilibrium with kaolinite, muscovite and chlorite minerals. Saturation index of silicate and carbonate minerals indicate oversaturation during pre-monsoon and undersaturation during post-monsoon, conforming dissolution and dilution process. In general, water chemistry is guided by complex weathering process, ion exchange along with influence of Cl ions from anthropogenic impact.     

Hydrogeochemistry and microbial contamination of groundwater from Lower Ponnaiyar Basin, Cuddalore District, Tamil Nadu, India

Groundwater is the major source of fresh water in regions where there is inadequate surface water resources. Forty-seven groundwater samples were collected from Lower Ponnaiyar basin, Cuddalore District, south India, during the premonsoon (PRM) and postmonsoon (POM) seasons of 2005. Out of 47 groundwater samples, 15 samples showing higher nitrate concentration were those collected during PRM 2005. Microbial analysis of these samples was carried out by employing 16S rRNA gene sequence tool. Detailed analysis was conducted to determine the hydrogeochemical processes and microbial contamination responsible for deterioration of quality. The abundance of the ions during PRM and POM are in the following order: Na?>?Ca?>?Mg?>?K?=?Cl?>?HCO₃?>?SO₄?>?CO₃. The dominant water types in PRM are in the order of NaCl?>?CaMgCl?>?mixed CaNaHCO₃, whereas during POM NaCl?>?CaMgCl?>?mixed CaNaHCO₃, and CaHCO₃. However, NaCl and CaMgCl are major water types in the study area. The quality of groundwater in the study area is mainly impaired by surface contamination sources, mineral dissolution, ion exchange and evaporation. Groundwater chemistry was used to assess quality to ensure its suitability for drinking and irrigation, based on BIS and WHO standards. Suitability for irrigation was determined on the basis of the diagram of US Salinity Laboratory (USSL), sodium absorption ratio (SAR), residual sodium carbonate (RSC), and Na%. According to SAR and USSL classification, 27.66% (PRM) and 40.43% (POM) of samples fall under C3S2 category, indicating high salinity and medium sodium hazard, which restrict its suitability for irrigation. Microbiological analysis and its effects on the water quality were also addressed. The 16S rRNA gene sequences of 11 bacterial contaminants exhibited five groups with 11 operational taxonomic units with aerobic and facultatively anaerobic organisms. The presence of aerobic organisms in the groundwater samples reflects the active conversion of ammonia to nitrite by Nitrosomonas sp. which is further converted to nitrates by other organisms. Further the presence of nitrate reducers could also play a role in the process of conversion of nitrate to ammonia and nitrate to molecular nitrogen.     

A Statistical appraisal to hydrogeochemistry of fluoride contaminated ground water in Nayagarh district, Odisha

Seasonal variation of ground water in Nayagarh district, Odisha is determined by analysing both pre and post monsoon water samples. The high fluoride content is an endemic problem in the area and special attention was attached to the point. The chemical compositions of the ground water of the area are dominated by CaCl, NaCl and mixed CaMgCl types in pre-monsoon and CaHCO₃-mixed CaMgCl type in post-monsoon. This is largely due to chemical weathering of Eastern Ghats Mobile Belt rock types. Increasing alkalinity vis-a-vis F concentration in pre-monsoon is associated with sodium-bicarbonate water types having high pH (>7) and low calcium and magnesium contents. The percentage of total high fluoride containing water samples is nearly double in pre-monsoon than in post-monsoon. During both the seasons, pH values indicate mildly alkaline to weakly acidic nature of the water samples. Fluoride concentration has good correlation with pH in pre-monsoon whereas in post-monsoon it shows good correlation with Fe. Facies analysis indicates that water is becoming predominantly Ca-Na cation and Cl-SO₄-HCO₃ anion type in premonsoon than Ca-Mg type and HCO₃-Cl-SO₄ type in post-monsoon. The seasonal variations in concentrations of anthropogenic components demonstrate that the groundwater system is very less liable to pollution by human activities.     

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.     

Temporal variations in arsenic concentration in the groundwater of Murshidabad District,West Bengal,India

Systematic investigations on seasonal variations in arsenic (As) concentrations in groundwater in both space and time are scarce for most parts of West Bengal (India). Hence, this study has been undertaken to investigate the extent of As pollution and its temporal variability in parts of Murshidabad district (West Bengal, India). Water samples from 35 wells were collected during pre-monsoon, monsoon and post-monsoon seasons and analyzed for various elements. Based on the Indian permissible limit for As (50 μg/L) in the drinking water, water samples were classified into contaminated and uncontaminated category. 18 wells were reported as uncontaminated (on average 12 μg/L As) and 12 wells were found contaminated (129 μg/L As) throughout the year, while 5 wells could be classified as either contaminated or uncontaminated depending on when they were sampled. Although the number of wells that alternate between the contaminated and uncontaminated classification is relatively small (14%), distinct seasonal variation in As concentrations occur in all wells. This suggests that investigations conducted within the study area for the purpose of assessing the health risk posed by As in groundwater should not rely on a single round of water samples. In comparison to other areas, As is mainly released to the groundwater due to reductive dissolution of Fe-oxyhydroxides, a process, which is probably enhanced by anthropogenic input of organic carbon. The seasonal variation in As concentrations appear to be caused mainly by dilution effects during monsoon and post-monsoon. The relatively high concentrations of Mn (mean 0.9 mg/L), well above the WHO limit (0.4 mg/L), also cause great concern and necessitate further investigations.     

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.     

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.     

Statistical interpretation on seasonal variations of groundwater quality in Ramanathapuram coastal tract,Tamil Nadu,India

Groundwater availability depends on its accessibility, as well as on its quality. Factor analysis (FA) has been used to analyze quality problems and provide strategies for water resources exploitation. The present study demonstrated the use of factor analysis to evaluate temporal variations in groundwater quality and find latent sources of water pollution in coastal areas of Ramanathapuram District, Tamil Nadu, India. The data set included data of eleven water quality parameters viz., pH, electrical conductivity, salinity, total dissolved solids, total alkalinity, calcium hardness, magnesium hardness, total hardness, chloride and fluoride for two different seasons (pre- and post-monsoon) in 2012. FA of the two seasons resulted in two latent factors accounting for 80.38 % of total variance for pre-monsoon (summer) and 73.03 % for post-monsoon (winter) in the water quality data sets. The results obtained from FA prove that the groundwater quality in winter is better than that of summer. Langelier Saturation Index was used to find out scaling and corrosive tendency of the groundwater samples for the study area. Karl Pearson correlation matrix was used to study the correlation between the studied water quality parameters. Hence, the analysis suggests that FA techniques are useful tools for identification of influence of various quality parameters on overall nature of the groundwater.     

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.     

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.     

Development of Water Quality Index (WQI) model for the groundwater in Tirupur district, South India

Groundwater quality of the Tiruppur district in Tamil Nadu was investigated in this study to develop a Water Quality Index (WQI) model. Hydrochemical parameters showed tremendous variation in certain location over the seasons. Ionic chemistry of groundwater suggested that textile industries and rock-water interaction are major threats to the water quality. Analysis of Na and Ca concentration indicates that direct as well as the inverse cation exchange controls the natural cation chemistry. NO3 concentration shows that the pre-monsoon samples were affected by the fertilizer usage in agricultural fields. Na-Cl type of the water was dominant throughout the study area except few locations. WQI showed that 55% of the pre-monsoon samples and the 47% of the post monsoon samples were classified as poor/very poor/unsuitable for drinking category. Leaching of the textile waste and their transport to the downstream was well observed during the post-monsoon season. The specific contribution of river Noyyal in the transport of the solutes to the discharge zones was proved by the hydrochemistry of the samples.     

Spatio-temporal variation in radon concentration in groundwater with respect to rock types: A case study from Chitradurga district,Karnataka

An attempt was made in the present study to delineate how the radon concentrations vary with respect to different geological formations and to evaluate annual effective dose exposure due to ingestion of radon. A total of 60 groundwater samples were collected from layered sequential aquifers in Chitradurga district having major rock types such as Bababudan Group, Charnockite, Chitradurga Group, Closepet granite, migmatites and granodiorite — tonalitic gneisses and Sargur Schist complex during pre-monsoon and post-season of the year 2011. Radon measurement was made using Durridge RAD-7 radon-in-air monitor, connected to RAD H₂O accessory with closed loop aeration concept. In the present study, the radon activity ranged from 0 to 186.6 Bq/L and 0 to 150.6 Bq/L during pre- and post-monsoon seasons of the year 2011, with 56.67 % (17 samples) of samples during both the seasons exceeding the EPA’s MCL value of 11.1 Bq/L. The annual mean radon activity in the groundwater was higher in the area having Chitradurga rock group formations (78.1 Bq/L) followed by Sargur-Satyamangalam schist complex group (56.8 bq/L), migmatites and granodiorite — tonalitic Gneisses group (56.3 Bq/L), Closepet granite (42.7 Bq/L), Charnonkite (29.1 Bq/L) and Bababudan Group (22.2 Bq/L). It is inferred that radon concentration found to depend on the tectonic structure, geology of the area and on the presence of uranium minerals in these rocks. The annual effective dose resulting from radon in groundwater in the Chitradurga district were significantly lower than UNSCEAR and WHO recommended limit of 1 mSv/y.