Geochemistry of fluoride rich groundwater in Kolar and Tumkur Districts of Karnataka

Groundwater is a significant water resource in India for domestic, irrigation, and industrial needs. By far the most serious natural groundwater-quality problem in India, in terms of public health, derives from high fluoride, arsenic, and iron concentrations. Hydrogeochemical investigation of fluoride contaminated groundwater samples from Kolar and Tumkur Districts in Karnataka are undertaken to understand the quality and potability of groundwater from the study area, the level of fluoride contamination, the origin and geochemical mechanisms driving the fluoride enrichment. Majority of the groundwater samples did not meet the potable water criteria as they contained excess (>1.5 mg/L) fluoride, dissolved salts (>500 mg/L) and total hardness (75–924 mg/L). Hydrogeochemical facies of the groundwater samples suggest that rock weathering and evaporation–crystallization control the groundwater composition in the study area with 50–67% of samples belonging to the Ca–HCO₃ type and the remaining falling into the mixed Ca–Na–HCO₃ or Ca–Mg–Cl type. The saturation index values indicated that the groundwater in the study area is oversaturated with respect to calcite and under-saturated with respect to fluorite. The deficiency of calcium ion concentration in the groundwater from calcite precipitation favors fluorite dissolution leading to excess fluoride concentration.     

Geochemistry, genesis, and health implications of fluoriferous groundwaters in the upper regions of Ghana

 The most appropriate and widely used source of drinking water for the populations of the upper regions of Ghana is groundwater. In general, groundwater quality is acceptable except for some parts of the Bolgatanga and Bongo Districts, where there are occurrences of elevated levels of natural groundwater fluoride. Concentrations of groundwater fluoride in excess of the World Health Organization (WHO) maximum guideline value (1.5 mg/l) in the Bongo area have been known since 1978. However, the effect of fluoride on people ingesting the water did not receive public and medical attention until October 1993, when health personnel were asked to investigate the cause of stained teeth in school children. The investigation established that 62% of the total population of school children in the Bongo area had dental fluorosis. Against this background, a study was initiated to understand the geochemistry, genesis, and distribution of fluoride in relation to the geology of the area. Groundwater fluoride in the upper regions ranges from 0.11 to 4.60 ppm, with the highest concentrations associated with the fluorine-enriched Bongo coarse-grained hornblende granite and syenite suite. The source of groundwater fluoride within the Bongo granitoids is dissolution of the mineral fluorite and dissolution of and anion exchange with micaceous minerals and their clay products. Applying the WHO recommended guideline values for fluoride in drinking water reveals that 49% of wells in the area deliver water below the optimum level of 0.5 mg/l F^–; these populations are thus prone to dental caries. Twenty-eight percent of the wells fall within the optimum interval for good dental health (0.5–1.5 mg/l F^–). Twenty-three percent of the wells have concentrations above the recommended maximum guideline limit of 1.5 mg/l F^–; this population is susceptible to dental and possibly skeletal fluorosis. Climatic conditions of the area suggest that the individual water consumption is in the order of 3 to 4 l which is higher than the WHO estimate of 2 l/adult/day. In addition, dietary intake for the upper region population is probably higher than WHO baseline values (0.2–0.5 mg/day). This implies that a much higher population is susceptible to developing dental and skeletal fluorosis than originally suspected. Geochemical symbol plot maps help geochemists understand factors controlling the distribution and uptake of fluoride in the upper regions, but they are of minimal value to health officials responsible for planning epidemiological studies and dental health education programs in the region. By casting fluoride data into contoured 'geochemical health-risk maps' using intake interval guidelines more closely aligned to regional climatic and dietary conditions, health officals can better judge the impacts (regional and population based) of fluoride on segments of the population, such as various sex and age groups. Received: 11 March 1997 · Accepted: 17 June 1997     

Geochemical characteristics of fluoride in groundwater of Gimcheon, Korea: lithogenic and agricultural origins

The occurrence of fluoride in groundwaters can be influenced by many factors. In Korea, the fluoride-rich groundwaters are normally associated with rock types, especially granite and gneiss. In Gimcheon, high-fluoride groundwaters (up to a maximum of 2.15 mg/L) were observed with bimodal distribution of concentrations. The groundwater in this area showed relatively high concentrations of anthropogenic chemicals such as nitrate, chloride, and sulfate. Statistical analysis showed that fluoride is positively correlated with pH, alkalinity, sodium, and lithium, indicating that the interaction with granite is the main cause enriching its concentration. In Gimcheon, δ¹⁸O data of groundwater showed a negative correlation with nitrate and can be used as an indicator of groundwater age. The four samples of fluoride-rich groundwater were plotted in the light δD and δ¹⁸O region, showing that they were the result of long water–rock reaction. However, other groundwater with a low-fluoride concentration was evenly distributed throughout all δD and δ¹⁸O ranges and did not show a statistically significant correlation with nitrate, indicating possible mixing with another source of fluoride. Considering the influence from the surface on the geochemical characteristics of groundwater in this area, anthropogenic sources including phosphate fertilizer containing fluoride and pesticides may also have partly contributed to the concentrations of fluoride in the low-fluoride groundwater. The scattered distribution of fluoride-rich groundwater and the significant correlation with lithium suggest that pegmatite is the main rock type increasing fluoride concentration in this area.     

Groundwater quality,nitrate pollution and irrigation environmental management in the Neogene sediments of an agricultural region in central Thessaly (Greece)

The degradation of groundwater quality, which has been noted in the recent years, is closely connected to the intensification of agriculture, the unreasonable use of chemical fertilizers and the excess consumption of large volumes of irrigation water. In the hilly region of central Thessaly in Greece, which suffers the consequences of intense agricultural use, a hydrogeological study is carried out, taking groundwater samples from springs and boreholes in the Neogene aquifers. The aim of this study is the investigation of irrigation management, water quality and suitability for various uses (water supply, irrigation), the degradation degree and the spatial distribution of pollutants using GIS. The following hydrochemical types prevail in the groundwater of the study area: Ca–Mg–HCO₃, Mg–Ca–Na–HCO₃ and Na–HCO₃. In the above shallow aquifers, especially high values of NO₃ ⁻ (31.7–299.0), NH₄ ⁺ (0.12–1.11), NO₂ ⁻ (0.018–0.109), PO₄ ³⁻ (0.07–0.55), SO₄ ²⁻ (47.5–146.5) and Cl⁻ (24.8–146.5) are found, particularly near inhabited areas (values are in mg L⁻¹). The water of shallow aquifers is considered unsuitable for human use due to their high polluting load, while the water of the deeper aquifers is suitable for human consumption. Regarding water suitability for irrigation, the evaluation of SAR (0.153–7.397) and EC (481–1,680 μS cm⁻¹) resulted in classification category ‘C3S1’, indicating high salinity and low sodium water which can be used for irrigation in most soils and crops with little to medium danger of development of exchangeable sodium and salinity. The statistical data analysis, the factor analysis and the GIS application have brought out the vulnerable-problematic zones in chemical compounds of nitrogen and phosphates. The groundwater quality degradation is localized and related exclusively to human activities. Based on 2005 and 2008 estimates, the annual safe yield of the region’s aquifers were nearly 41.95 MCM. However, the existing situation is that 6.37 MCM of water is over extracted from these aquifers.     

An assessment of the origin and variation of groundwater salinity in southeastern Ghana

Groundwater from the major aquifers in southeastern part of Ghana was sampled to determine the main controls on groundwater salinity in the area. This paper uses multivariate statistical methods, conventional graphical methods and stable isotope data to determine spatial relationships among groundwaters from the different hydrogeologic units in the area on the basis of salinity. Q-mode hierarchical cluster analysis (HCA) was used to spatially classify the samples, whilst R-mode factor analysis was used to reduce the dataset into two major principal components representing the sources of variation in the hydrochemistry. Analysis of the major chemical parameters suggests that the principal component responsible for salinity increment in the area is the weathering of minerals in the aquifers. This factor is especially more significant in the upland areas away from the coast. The second factor responsible for salinity in the area is the combined effects of seawater intrusion, and anthropogenic activities. This study finds that four major spatial groundwater groups exist in the area: low salinity, acidic groundwaters which are mainly derived from the Birimian and Togo Series aquifers; low salinity, moderate to neutral pH groundwaters which are mainly from the Voltaian, Buem and Cape Coast granitoids; very high salinity waters which are not suitable for most domestic and irrigation purposes and are mainly from the Keta aquifers; and intermediate salinity groundwaters comprising groundwater from the Keta basin aquifers with minor contributions from the other major terrains. The major water type identified in this study is the Ca–Mg–HCO₃ type, which degrades into predominantly Na–Cl–SO₄ more saline groundwaters toward the coast. Stable isotope data analyses suggest that groundwater in the Voltaian aquifers is largely of recent meteoric origin. The Birimian and Togo aquifers receive a component of recharge from the tributaries of the Densu and Volta Rivers, after the waters have undergone evaporative enrichment of the heavier isotopes. In the Keta basin, recharge is mainly from precipitation but an observed enrichment of ²H and ¹⁸O isotopes is probably due to seawater and evaporative effects since the water table there is very shallow. An analysis of the irrigation quality of groundwater from the six aquifers in the study area using sodium adsorption ratio and electrical conductivity suggests that most of the aquifers supply groundwater of acceptable quality for irrigation. The only exception is the Keta Basin area, where extremely high salinities and SAR values render groundwater from this basin unsuitable for irrigation purposes.     

Groundwater classification using multivariate statistical methods: Southern Ghana

This study demonstrates the strength of R-mode factor analysis and Q-mode hierarchical cluster analysis in determining spatial groundwater salinity groups in southeastern Ghana. Three hundred and eighty three (383) groundwater samples were taken from six hydrogeological terrains and surface water bodies and analyzed for the concentrations of the major ions, electrical conductivity and pH. Q-mode hierarchical cluster analysis and R-mode factor analysis were respectively used to spatially classify groundwater samples and determine the probable sources of variation in groundwater salinity. The quality of groundwater for irrigation was then determined using three major indices. The analyses revealed two major sources of variation in groundwater salinity: silicate mineral weathering on one hand, and seawater intrusion and anthropogenic contamination on the other. A plot of the factor scores for the two major sources of variation in the salinity revealed trends which can be used in hydrogeological mapping and assist in drilling potable water boreholes in southeastern Ghana. This study also revealed four major spatial groundwater groups: low salinity, acidic groundwaters which are mainly derived from the Birimian and Togo Series aquifers; low salinity, moderate to neutral pH groundwaters which draw membership mainly from samples of the Voltaian, Buem and Cape Coast granitoids; very high salinity waters which are not suitable for most domestic and irrigation purposes and are mainly from the Keta Basin aquifers; and intermediate salinity groundwaters consisting of groundwater from the Keta basin aquifers with minor contributions from the other major terrains. The major water type identified in this study is the Ca–Mg–HCO₃ type, which degrades into predominantly Na–Cl–SO₄ more saline groundwaters towards the coast.     

Alternative water resources in granitic rock: a case study from Kinmen Island,Taiwan

Kinmen Island is a small, tectonically stable, granitic island that has been suffering from a scarcity of fresh water resources due to excessive annual evapotranspiration over annual precipitation. Recent studies further indicate that shallow (0–70 m) sedimentary aquifers, the major sources of groundwater supply, have already been over-exploited. Therefore, this preliminary study is to investigate the existence of exploitable water resources that can balance the shortage of fresh water on this island. Site characterization data are obtained from island-wide geophysical surveys as well as small-scale tests performed in a study area formed by three deep (maximum depth to 560 m) vertical boreholes installed in mid-east Kinmen northeast to Taiwu Mountain. Vertical fracture frequency data indicate that the rock body is fractured with a spatially correlated pattern, from which three major fracture zones (depths 0–70, 330–360, and below 450 m) can be identified. Geologic investigations indicate that the deepest fracture zone is caused by the large-scale, steeply dipping Taiwushan fault. This fault may have caused a laterally extensive low-resistivity zone, a potential fractured aquifer, near Taiwu Mountain. The middle fracture zone is induced by the Taiwushan fault and intersects the fault approximately 21 m southeast of the study area below a depth of 350 m. Slug testing results yield fracture transmissivity varying from 4.8 × 10⁻⁷ to 2.2 × 10⁻⁴ m²/s. Cross-hole tests have confirmed that hydraulic connectivity of the deeper rock body is controlled by the Taiwushan fault and the middle fracture zone. This connectivity may extend vertically to the sedimentary aquifers through high-angle joint sets. Despite the presence of a flow barrier formed by doleritic dike at about 300 m depth, the existence of fresh as well as meteoric water in the deeper rock body manifests that certain flow paths must exist through which the deeper fractured aquifers can be connected to the upper rock body. Therefore, groundwater stored within the Taiwushan fault and the associated low-resistivity zone can be considered as additional fresh water resources for future exploitation.     

Hydrochemical assessment of groundwater from shallow aquifers in parts of Wadi Al Hamad,Madinah, Saudi Arabia

The present study was carried out in the Mulaylih area which forms a part of Wadi Al Hamad in the Madinah Province of Saudi Arabia. Thirty groundwater samples from agricultural farms were collected and analyzed for various physio-chemical parameters including trace elements. The area is occupied by the Quaternary alluvium deposits which form shallow unconfined aquifers. Evaporation and ion exchange are the major processes which control the major ion chemistry of the area. The extreme aridity has results in high total dissolved solid values (average of 9793.47 mg/l). Trace element concentrations are low and are mainly attributed to geogenic sources (silicate weathering). Na-Cl groundwater type is the main hydrochemical facies found in the area. The waters are found to be oversaturated with calcite/aragonite and dolomite. The average nitrate concentration was found to be 134.10 mg/l and is much higher than the WHO recommended limit of 50 mg/l in drinking water. Their high values are mainly associated with the application of N-fertilizers on the agricultural farms. The average fluoride concentration in the study was found to be 1.54 mg/l. The relation between F and Cl and Cl and Na reveals that the fluoride concentrations are mainly attributed to geogenic sources. A comparison of the groundwater quality with the Saudi drinking water standards shows that the water is unfit for drinking. The high salinity and sodicity of the groundwater make it unfit for irrigation. Principal component analysis resulted in extraction of four principal components accounting for 79.5% of the total data variability and supports the fact that the natural hydrochemical processes (evaporation and ion exchange) control the overall groundwater chemistry.     

Groundwater quality of Yemen volcanic terrain and their geological and geochemical controls

One hundred thirty boreholes of volcanic aquifers in rural Yemen Highland Groundwaters (YHGs) were chemically investigated to assess the suitability of water for drinking. Focus is to identify inorganic constituents of significant risk to health that occur in groundwaters of this area. Results showed that a number of boreholes contain, apart from fluoride, levels of nitrate, some heavy metals, total dissolved solids, and sulfates that could pose a health risk for consumers. The lateral variations of major ions with depth varied within the same aquifer based on the dynamic equilibrium of groundwater and hydrogeological conditions. The main inorganic groundwater contaminant in volcanic YHG is fluoride which is attributed to groundwater lithology and water type. Fluoride appears high in Ca-poor groundwater and where cation exchanges of Ca for Na are dominant. High F concentration in YHG is an extension of East African fluoride-rich groundwater. Majority of tube wells show that Fe concentration exceeds WHO guideline many folds. Much of the iron and manganese in groundwaters are naturally occurring, since the source rocks are enriched in ferromagnesian minerals. NO ₃ ^? and Cl^? concentrations that have been detected in some wells may indicate sewage and/or agricultural runoff. Elevated concentration of chemical constituents in groundwater is a sign of groundwater degradation.     

Factors controlling fluoride contents of groundwater in north-central and northwestern Sri Lanka

Chemical characterization has been made of groundwater bodies at 294 locations in four village districts in north-central and northwestern Sri Lanka, with special focus on fluorine contamination. High fluoride contents in groundwater are becoming a major problem in the dry zone of Sri Lanka, and dental fluorosis and renal failures are widespread. Field measurements of temperature, pH, and electrical conductivity were made during sampling. Chemical analyses of the water samples were later made using atomic absorption spectroscopy, spectrophotometry, and titration. Fluoride concentrations in the study area vary from 0.01 to 4.34 mg/l, and depend on pH and the concentrations of Na, Ca, and HCO₃ ⁻. Basement rocks including hornblende biotite gneiss, biotite gneiss, and granitic gneiss seem to have contributed to the anomalous concentrations of fluoride in the groundwater. Longer residence time in aquifers within fractured crystalline bedrocks may enhance fluoride levels in the groundwater in these areas. In addition, elevated fluoride concentrations in shallow groundwater in intensive agricultural areas appear to be related to the leaching of fluoride from soils due to successive irrigation.     

Processes affecting geochemistry and contaminant movement in the middle Claiborne aquifer of the Mississippi embayment aquifer system

Groundwater chemistry and tracer-based age data were used to assess contaminant movement and geochemical processes in the middle Claiborne aquifer (MCA) of the Mississippi embayment aquifer system. Water samples were collected from 30 drinking-water wells (mostly domestic and public supply) and analyzed for nutrients, major ions, pesticides, volatile organic compounds (VOCs), and transient age tracers (chlorofluorocarbons, tritium and helium-3, and sulfur hexafluoride). Redox conditions are highly variable throughout the MCA. However, mostly oxic groundwater with low dissolved solids is more vulnerable to nitrate contamination in the outcrop areas east of the Mississippi River in Mississippi and west Tennessee than in mostly anoxic groundwater in downgradient areas in western parts of the study area. Groundwater in the outcrop area was relatively young (apparent age of less than 40 years) with significantly (p < 0.05) higher dissolved oxygen and nitrate–N concentrations and higher detections of pesticides and VOCs compared to water samples from wells in downgradient areas. Oxygen reduction and denitrification rates were low compared to other aquifers in the United States (zero order rate constants for oxygen reduction and denitrification were 4.7 and 5–10 μmol/L/year, respectively). Elevated concentrations of nitrate–N, and detections of pesticides and VOCs in some deep public supply wells (>50 m depth) indicated contaminant movement from shallow parts of the aquifer into deeper oxic zones. Given the persistence of nitrate in young oxic groundwater that was recharged several decades ago, and the lack of a confining unit, the downward movement of young contaminated water may result in higher nitrate concentrations over time in deeper parts of the aquifer containing older oxic water.     

Hydrochemistry of groundwater in the Savelugu–Nanton District, Northern Ghana

Calcite (CaCO₃), dolomite [CaMg(CO₃)₂], silicate dissolution, ion-exchange and reverse ion-exchange reactions are the predominant processes influencing groundwater quality in the Savelugu?CNanton District. The main objective of this study is to characterize groundwater and delineate water?Crock interactions responsible for the chemical evolution of groundwater in the District. Eighty-one (81) boreholes were sampled for quality assessment. Results showed that, the pH of the boreholes are slightly acidic to basic ranging from 6.1?C8.3?pH units. Conductivity values are low to high ranging from 147?C23,200???S/cm with, 23.5?% of groundwater within the study area being either brackish (1,500?C5,000???S/cm) or saline (>5,000???S/cm) and therefore, unsuitable for potable purposes. TDS values in groundwater varied widely, ranging from 62?C11,900?mg/L. 61.7?% of groundwater within the study area are fresh (TDS?<?500?mg/L). The chemical constituents generally, have low concentrations and are within the WHO (Guidelines for drinking water quality. Revision of the 1993 Guidelines. Final Task Group Meeting. Geneva, 2004) Guideline values. The relative abundance of cations and anions in the groundwater are in the order: Ca²⁺?>?Na⁺?>?Mg²⁺?>?K⁺ and HCO₃ ^??>?Cl^??>?SO₄ ^2??>?NO₃ ^? respectively. Multivariate statistical analysis showed expected process-based relationship derived mainly from the geochemical and biochemical processes within the aquifer. Hydrochemical facies using piper plot of major ions showed one major hydrochemical water type. The Ca?CMg?CHCO₃ water type. Due to the high cost of drilling of boreholes coupled with the high percentage (×1?%) of people without access to potable water in the Northern Region, it is recommended that the Government of Ghana and other stakeholders within the Water Sector take immediate measures to reduce (to recommended limits for potable uses) the levels of dissolved solids either by installing Reverse Osmosis equipments on such boreholes or employ other relatively known cheaper methods to reduce the dissolved solids to recommended limits. High yielding boreholes with hydrochemical parameters within WHO guideline limits in the Savelugu?CNanton District could also be mechanized to serve a wider area.     

The influence of marine inflows on the chemical composition of groundwater in small islands: the example of the Cyclades (Greece)

 Marine contamination of groundwater may be caused by seawater intrusion and by salt spray. The role of both processes was studied in the Cyclades archipelago on four small islands (45–195 km²) whose aquifers consist essentially of fractured, weathered metamorphic rocks. Annual rainfall ranges from 400 to 650 mm and precipitation has high total dissolved solids contents of 45–223 mg l^–1. The chemical characteristics of the groundwater, whose salinity is from 0.4 to 22 g l^–1, are strongly influenced by seawater intrusion. However, the effect of atmospheric input is shown in certain water sampling locations on high ground elevation where the dissolved chloride contents may attain 200 mg l^–1. Received: 14 November 1995 · Accepted: 9 September 1996     

Temporal variations of fluoride concentration in Isparta public water system and health impact assessment (SW-Turkey)

Water–rock interaction is one of the prime factors affecting the fluoride contents of surface and groundwater. If fluoride concentration of drinking water has been neglected, excess fluoride can cause serious dental and medical problems on human health, which is well known at Golcuk-Isparta region. In the research area, Egirdir lake, Golcuk lake and surrounding springs have been utilized as drinking water sources. Golcuk lake water and surrounding groundwaters have high fluoride content (1.4–4.6 mg/l), which is above the WHO standards. Fluoride is predominantly supplied by dissolution of fluoride within the fluormicas of volcanics during the circulation of water. Fluoride concentrations of waters have shown variations for dry and rainy seasons depending on the degree of interaction between groundwater and volcanic rocks. It tends to decrease in rainy seasons and increase in dry seasons for all years. In this study, temporal variations and spatial distribution of fluoride concentration in public water system of Isparta were investigated to get benefit using GIS techniques from1990 to 2003 years. Extremely fluoride concentrations were measured in the public water system in 1990 at almost every district of the city. In 2003, fluoride content of the public water system decreased in some district of city due to drinking water has started obtaining from Egirdir lake in 1995. The fluoride contents of Isparta drinking water ought to be modified with suitable mixture of lake waters and groundwater point of view to health impact.     

Groundwater availability in the shallow aquifers of the southern voltaian system: a simulation and chemical analysis

A steady state groundwater flow simulation model was developed using available well data and general hydrogeological and geological information, for the Afram Plains area, Ghana. The hydrochemistry of groundwater from wells in the area was then evaluated to determine its suitability for irrigation and domestic uses. The assessment of the irrigation quality of groundwater from this area was based on salinity (EC) and sodium adsorption ratios (SAR), residual sodium carbonate (RSC), and permeability indices (PI). The simulation model reveals that groundwater in the Afram Plains area generally flows from the midsections in the neighborhood of Tease and surrounding areas, where significant recharge takes place, to the outer regions and discharges into the Volta Lake in the southern and eastern sections of the area. Flow magnitude and piezometric maps suggest that there is probably of less potential for groundwater extraction for sustainable irrigation in the central regions of the area, when compared to the other discharge areas. This study reveals that more than 70% of the samples analyzed fall within the C2–S1 category, referring to the medium level salinity and low sodium. Medium salinity waters may be used for irrigation on coarse textured soils with good permeability. About 15% of the data fall within the C3–S2 category, referring to water of high salinity and medium sodicity. High salinity, medium sodicity irrigation water cannot be used on fine-grained soils where drainage is restricted. This is because restricted flow is likely to result in the accumulation of salts in the root zones of crops, leading to salinity and soil clogging crisis. About 3% falls within the C3–S3 (high salinity, high sodicity) category. This category requires special soil management including improved drainage, heavy leaching and the use of chemical amendments on the water. Only one point plots within the extreme salinity–sodicity range. Concentrations of fluoride, arsenic and other natural elements in the area generally fall well within the world health standards for domestic water.     

Hydrochemical appraisal of groundwater and its suitability in the intensive agricultural area of Muzaffarnagar district,Uttar Pradesh,India

Muzaffarnagar is an economically rich district situated in the most fertile plains of two great rivers Ganga and Yamuna in the Indo-gangetic plains, with agricultural land irrigated by both surface water as well as groundwater. An investigation has been carried out to understand the hydrochemistry of the groundwater and its suitability for irrigation uses. Groundwater in the study area is neutral to moderately alkaline in nature. Chemistry of groundwater suggests that alkaline earths (Ca + Mg) significantly exceed the alkalis (Na + K) and weak acids exceed the strong acids (Cl + SO₄), suggesting the dominance of carbonate weathering followed by silicate weathering. Majority of the groundwater samples (62%) posses Ca–Mg–HCO₃ type of hydrochemical species, followed by Ca–Na–Mg–HCO₃, Na–Ca–Mg–HCO₃, Ca–Mg–Na–HCO₃–Cl and Na–Ca–HCO₃–SO₄ types. A positive high correlation (r ² = 0.928) between Na and Cl suggests that the salinity of groundwater is due to intermixing of two or more groundwater bodies with different hydrochemical compositions. Barring a few locations, most of the groundwater samples are suitable for irrigation uses. Chemical fertilizers, sugar factories and anthropogenic activities are contributing to the sulphate and chloride concentrations in the groundwater of the study area. Overexploitation of aquifers induced multi componential mixing of groundwater with agricultural return flow waters is responsible for generating groundwater of various compositions in its lateral extent.     

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.     

Enrichment of fluoride in groundwater under the impact of saline water intrusion at the salt lake area of Yuncheng basin,northern China

Long-term intake of high-fluoride groundwater causes endemic fluorosis. This study, for the first time, discovered that the salt lake water intrusion into neighboring shallow aquifers might result in elevation of fluoride content of the groundwater. Two cross-sections along the groundwater flow paths were selected to study the geochemical processes controlling fluoride concentration in Yuncheng basin, northern China. There are two major reasons for the observed elevation of fluoride content: one is the direct contribution of the saline water; the other is the undersaturation of the groundwater with respect to fluorite due to salt water intrusion, which appears to be more important reason. The processes of the fluorine activity reduction and the change of Na/Ca ratio in groundwater induced by the intrusion of saline water favor further dissolution of fluorine-bearing mineral, and it was modeled using PHREEQC. With the increase in Na concentration (by adding NaCl or Na₂SO₄ as Na source, calcium content kept invariable), the increase of NaF concentration was rapid at first and then became slower; and the concentrations of HF, HF₂⁻, CaF⁺, and MgF⁺ were continuously decreasing. The geochemical conditions in the study area are advantageous to the complexation of F⁻ with Na⁺ and the decline of saturation index of CaF₂, regardless of the water type (Cl–Na or SO₄–Na type water).     

Hydrogeochemical genesis of groundwaters with abnormal fluoride concentrations from Zhongxiang City,Hubei Province,central China

The groundwaters from Zhongxiang City, Hubei Province of central China, have high fluoride concentration up to 3.67 mg/L, and cases of dental fluorosis have been found in this region. To delineate the nature and extent of high fluoride groundwaters and to assess the major geochemical factors controlling the fluoride enrichment in groundwater, 14 groundwater samples and 5 Quaternary sediment samples were collected and their chemistry were determined in this study. Some water samples from fissured hard rock aquifers and Quaternary aquifers have high fluoride concentrations, whereas all karst water samples contain fluoride less than 1.5 mg/L due to their high Ca/Na ratios. For the high fluoride groundwaters in the fissured hard rocks, high HCO₃ ⁻ concentration and alkaline condition favor dissolution of fluorite and anion exchange between OH⁻ in groundwater and exchangeable F⁻ in some fluoride-bearing minerals. For fluoride enrichment in groundwaters of Quaternary aquifers, high contents of fluoride in the aquifer sediments and evapotranspiration are important controls.     

Association of hydrogeological factors in temporal variations of fluoride concentration in a crystalline aquifer in India

The major part of groundwater in India is found in granitic aquifers. Fluoride in groundwater from a crystalline aquifer in a semi-arid region of granitic rocks in India, known as Maheshwaram watershed, was analyzed for spatial and temporal variability during 1999–2002 to assess the effect of hydrogeological factors on fluoride concentration. Samples were collected from 32 representative wells in the area for the pre- and post-monsoon seasons and analyzed for F content. The CHESS computer program was used to calculate ionic activities of aqueous species and the mineral saturation index (SI) for calcite and fluorite. The GARDENIA computer program was used to calculate the recharge values in the study area. The influences of dissolution kinetics of fluoride minerals and recharge from rainfall on fluoride concentration were of interest and results clearly indicate that fluoride content in groundwater depends on the interaction period of groundwater with host rock. Results could also be utilized for designing remedial measures particularly with dilution method in an optimal way.