Delineation of potential fluoride contamination zones in Birbhum,West Bengal,India, using remote sensing and GIS techniques

Birbhum district in West Bengal, India, is one of the most severely affected districts by fluoride-contaminated groundwater. Fluoride content as high as 20.4 mg/L has been reported. Several cases of fluoride-related disorder such as dental fluorosis and skeletal fluorosis have been reported to be endemic in the district. Proper management of groundwater is very crucial. This contribution has been carried out for delineating potential fluoride-contaminated zones (PFCZ) in Birbhum district with the implementation of weighted overlay analysis in GIS environment. Twelve different potentially influential environmental parameters are integrated and evaluated. The final output map was categorised into two subclasses, i.e. ‘low’ and ‘high’, where the low region represents fluoride concentration of 1.5 mg/L and below and the high region represents fluoride concentration above 1.5 mg/L. The outcome reveals that approximately 24.35% of the study area falls under PFCZ, whereas about 75.65% of the study area falls under the safe zone with respect to potential fluoride contamination. On validation of the PFCZ, the reported fluoride contamination data in groundwater shows an overall 87.50% accuracy in prediction via superimposition method and 89.06 and 85.85% success and prediction rates, respectively, when validated with success and prediction rates.     

Delineation of groundwater potential zone in Chhatna Block, Bankura District, West Bengal, India using remote sensing and GIS techniques

Groundwater is one of the most valuable natural resources, which is an immensely important and dependable source of water supply in all climatic regions over the world. Groundwater is in demand in areas where surface water supply is inadequate and nonsexist in the Chhatna Block, Bankura district and is located on the eastern slope of Chotonagpur Plateau, which is mapped on 73 I/15, 73 I/16 and 73 M/3, and falls between latitude 23°10′–23°30′N and longitude 86°47′–87°02′E. It represents plain land and gentle slope, which is responsible for infiltration and groundwater recharge. The groundwater in this region is confined within the fracture zones and weathered residuum. The present investigation is, therefore, undertaken to delineate potential zones for groundwater development with the help of a remote-sensing study. IRS–LISS-III data along with other data sets, e.g., existing toposheets and field observation data, have been utilized to extract information on the hydrogeomorphic features which include valley fills, buried pediment moderate, buried pediment shallow and structural hills, lineament density contour and slope map of this hard rock terrain. The target of this study is to delineate the groundwater potential zones in Chhatna block, Bankura District, West Bengal. Satellite imagery, along with other data sets, has been utilized to extract information on the groundwater controlling features of this study area. Three features (hydrogeomorphology, slope, and lineaments) that influence groundwater occurrences were analyzed and integrated. All the information layers have been integrated through GIS analysis and the groundwater potential zones have been delineated. The weighted index overlay method has been followed to delineate groundwater potential zones. The results indicate that good to excellent groundwater potential zones are available in almost the entire block. The results show that there is good agreement between the predicted groundwater potential map and the existing groundwater borehole databases. The area is characterized by hard rock terrain—still due to the presence of planation surface along valley fills; it became the prospective zone. The area has been categorized into four distinct zones: excellent, good, fair and poor. Excellent groundwater potential zones constitute 30–35 % of the total block area; good groundwater potential zones occupy a majority of the block, covering approximately 55–60 % and the fair potential zones occupy about 10–15 % of the total block. Poor potential zones occupy a very insignificant portion (less than 1 %).     

Delineation of groundwater potential zones in Kakund watershed,Eastern Rajasthan,using remote sensing and GIS techniques

The remotely sensed data provides synoptic viewing and repetitive coverage for thematic mapping of natural resources. In the present study hydrogeomorphological mapping has been carried out in Kakund watershed, Eastern Rajasthan for delineating groundwater potential zones. IRS-1D LISS III Geocoded FCC data in conjunction with Survey of India toposheet (1:50000 scale) and field inputs were used for thematic mapping. Geomorphic units identified through visual interpretation of FCC include: alluvial plain, plateau, valley fills, intermontane valleys, burried pediment, residual hills, and linear ridges. In addition, lineaments were mapped since they act as conduit for groundwater recharge. Majority of the lineaments trends NE-SW and a few along NW-SE directions and are confined to the southern and southeastern parts of the watershed. Based on hydrogeomorphological, geological and lineament mapping the Kakund watershed has qualitatively been categorized into four groundwater potential zones, viz. good to very good, moderate to good, poor to moderate and very poor to poor. The study reveals that only 10.97% of the area has good to very good, 35.41% area with moderate to good, 49.04 % of the area has poor to moderatel, while remaining 4.57% has poor to very poor groundwater potential.     

Identification of suitable sites for groundwater recharge in Awaspi watershed using GIS and remote sensing techniques

Groundwater is a valuable natural resource for drinking, domestic, livestock use, and irrigation, especially in arid and semi-arid regions like the Garmiyan belt in Kurdistan region. The Awaspi watershed is located 50 km east of Kirkuk city, south Kurdistan, Iraq; and covers an area of 2146 km². The paper presents result of a study aimed at: (1) mapping and preparing thematic layers of factors that control groundwater recharge areas, and (2) determination of sites suitable for groundwater recharge. We used available data such as geological map, groundwater depth map, digital elevation model (DEM), Landsat 8 imagery, and tropical rainfall measuring mission (TRMM) data for this study. These data, supplemented by slope features, lithology, land use land cover, rainfall, groundwater depth, drainage density, landform, lineament density, elevation and topographic position index, were utilized to create thematic maps to identify suitable areas of groundwater recharge, using GIS and remote sensing techniques. Analytic hierarchy process (AHP) was applied to weight, rank, and reclassify these maps in the ArcGIS 10.3 environment, to determine the suitable sites for groundwater recharge within the Awaspi watershed. Fifty-five percent of the total area of the watershed was found to be suitable for groundwater recharge; whereas 45% of the area was determined to have poor suitability for groundwater recharge, but can be used for surface water harvesting.     

Delineation of potential sites for groundwater recharge using a GIS-based decision support system

In arid and semi-arid regions without perennial water sources such as rivers or lakes, almost all water supply needs are met by groundwater. Groundwater recharge (GWR) is critical to maintain the abundance of groundwater. This paper presents a methodology based on a decision support system (DSS) that combines remote sensing, field survey and geographic information system techniques to identify suitable GWR areas. The DSS was implemented to obtain suitability maps and to evaluate the existing GWR in the study area. The DSS inputs comprised maps of rainfall surplus, slope, potential runoff coefficient, land cover/use and soil texture. The spatial extents of GWR suitability areas were identified by a hierarchical process analysis that considered five layers. The model generated a GWR map with four categories of suitability: excellent, good, moderate and poor and unsuitable. The spatial distribution of these categories showed that 0.08 and 32.3 % of the study area was classified as excellent and good for GWR, respectively, while 63.2 and 4.42 % of the area was classified as moderate and poor and unsuitable, respectively. Most of the areas with excellent to good suitability have slopes of between 4 and 8 % and are intensively cultivated areas. The major soil type in the excellent to good areas is loam, followed by clay loam, and the rainfall in these areas ranges from 150 to 260 mm. Another suitability model, in which all criteria were assigned equal influence, generated a suitability map in which 0.1 % of the study area was rated as excellent, 10.9 % as good, 82 % as moderate and 7 % as poor and unsuitable. The locations of existing GWR dams were compared with the locations indicated on the generated suitability map using the proximity analysis tool in ArcGIS 10.1. Most (77 %) of the existing GWR structures that were categorised as successful were within the excellent and good areas, followed by moderately suitable (23 %).     

Morphological analysis and channel shifting of the Fulahar river in Malda district,West Bengal,India using remote sensing and GIS techniques

GeoJournal - The present study has been carried out to analyse and interpret the morphological changes and channel shifting along the Fulahar river in the Malda district. Fulahar river is one of...     

Economic significance of colonial invasions in Khejuri-Hijli coastal sector of Purba Medinipur district,West Bengal: A geographical review

Khejuri- Hijili coastal area, now extends over the Khejuri police station, is situated in the southeastern part of the district of Purba Medinipur of West Bengal, on the western bank of the Hugli river. Between 21°47'42"N-22°4'N latitudes and 87°45'4"E-88°18"E longitudes the area covers about 267.97 sq. km. At the confluence of the rivers Bhagirathi-Hugli and the Bay of Bengal, Hijili emerged as an island from the estuarine surroundings around 1400-1500 A.D. afterward the island became covered with natural mangroves. Gradually it became the abode of fishermen. To gather some primary data, household survey by different questionnaire, topographic survey was done. Secondary data are mainly produced by assembling historical charts, maps, literatures for the specified work of the area concerned. Historical records including documents, survey notes, maps and photographs provided valuable information about the study area. Remains of early structures, monuments, and office buildings have been vigilantly watched and written reports and research articles have been carefully studied for sequencing the socio-economic history of the area. Later on accuracy assessment was performed by comparing two sources of information: classification of map derived from old records and maps and the ground truth information. The output obtained by performing the above steps includes land use and other maps and charts. These outputs were then analyzed to detect the historical significance of Khejuri-Hijili sector of the Hugli estuary and its sequential deterioration. These changes in the study area that were identified from classified maps, charts and diagram were tabulated.     

Use of remote sensing, GIS and groundwater monitoring to estimate artificial groundwater recharge in Riyadh, Saudi Arabia

This study aims to estimate artificial recharge of groundwater by using remote sensing technology, geographical information systems, and groundwater surveys. This study is part of the King Fahd project for rainfall and runoff water harvesting, within the premises of Alilb Dam in Diriyah to the west of Riyadh. Digital elevation models were obtained with the help of aerial photography from the year 2007. These models were used to delineate watershed. Average rainfall was calculated using isoheytal method, and the area of each of the storage lakes was measured using SPOT 5 satellite images from 2007. Fluctuations in groundwater levels, evaporation, and infiltration rates were used to determine the water balance for the purpose of estimating of artificial recharge. Artificial recharge rates were found to surpass natural recharge from rainfall. Recharge wells caused a reduction in the effect of evaporation on storage lakes and helped in supplying water to the groundwater reservoir. Moreover, 80% and 86% of the rainwater was found to be available for artificial recharge in Alilb at 2005 and 2007, respectively. The study recommends the establishment of strategic projects for water storage using artificial recharge wells, an increase in the number of monitoring wells around the dams, and the monitoring of hydrochemical changes in groundwater both before and after the artificial recharge. It also recommends the erection of a weather station in the northwest of Wadi Hanifa.     

Identifying potential sites for artificial groundwater recharge in sub-watershed of River Kanhan,India

Groundwater is an important decentralized source of drinking water. Being underground, it is relatively less susceptible to contamination. In addition to domestic needs, it is extensively used for irrigation and industrial purposes. It is therefore necessary to implement groundwater recharge systems by capturing the rainwater runoff. In the present study, GIS-based hydrological assessment of watershed has been used to identify the potential sites for locating the groundwater recharge structures. Based on land use, soil and topography, rainfall runoff modelling was carried out in GIS for a sub-watershed of River Kanhan, in Nagpur District, Maharashtra State, India. Five potential sites with maximum flow accumulation were delineated using the rational method for peak runoff estimation. As the groundwater recharge potential also depends on the geological and geomorphological characteristics of land, analytic hierarchy process (AHP) with expert’s judgement was used for ranking the sites. The criteria considered in AHP were geological features, i.e. lineament density, depth to bedrock and soil cover; geomorphological features, i.e. drainage density, slope, landforms and land use/land cover; and water table level fluctuation. The site P5 with maximum flow accumulation and sandstone rock formation was ranked first. The site P1, where catchment has well-developed drainage and geological formation shows rock with secondary porosity, was ranked second.     

Mapping groundwater recharge potential using GIS approach in Darwha block

Groundwater is the most important source of water in meeting irrigation, drinking, and other needs in India. The assessment of the potential zone for its recharge is critical for sustainable usage, quality management, and food security. This study reports alternative mapping of the groundwater recharge potential of a selected block by including large-scale soil data. Thematic layers of soil, geomorphology, slope, land use land cover, topographical wetness index, and drainage density of Darwha block (District Yavatmal, Maharashtra, India) were generated and integrated in a geographic information system environment. The topographic maps, thematic maps, field data, and satellite image were processed, classified, and weighted using analytical hierarchical process for their contribution to groundwater recharge. The layers were integrated by weighted linear combination method in the GIS environment to generate four groundwater potential zones viz., “poor,” “poor to moderate,” “moderate to high,” and “high.” Based on the generated groundwater potential map, about 9830 ha (12%) of the study area was categorized as high potential for recharge, 25,558 ha (31%) as poor to moderate, 33,398 ha (40%) as moderate to high, and 12,565 ha (15%) as poor potential zone. The zonation corresponds well with the field data on greater well density (0.22/ha) and irrigated crop area (27%) in the high potential zone as against 0.02 wells/ha and only 6% irrigated area in the poor zone. The map is recommended for use in regulating groundwater development decisions and judicious expenditure on drilling new wells by farmers and the state authorities.     

Application of remote sensing and GIS for delineating groundwater recharge potential zones of Kovilpatti Municipality,Tamil Nadu using IF technique

During the last three decades, remotely sensed data (both satellite images and aerial photographs) have been increasingly used in groundwater exploration and management exercises. An integrated approach has been adopted in the present study to delineate groundwater recharge potential zones using RS and GIS techniques. IRS-1C satellite imageries and Survey of India toposheets are used to prepare various thematic layers viz. geology, soil, land-use, slope, lineament and drainage. These layers were then transformed in to raster data using feature to raster converter tool in ArcGIS 9.3 software. The raster maps of these factors are allocated a fixed score and weight computed from Influencing Factor (IF) technique. The weights of factors contributing to the groundwater recharge are derived using aerial photos, geology maps, a land use database, and field verification. Subjective weights are assigned to the respective thematic layers and overlaid in GIS platform for the identification of potential groundwater recharge zones within the study area. Then these potential zones were categories as ‘high’, ‘moderate’, ‘low’, ‘poor’. The resulted map shows that 19 % of the area has highest recharge potential, mainly confined to buried pediplain, agriculture land-use and river terraces (considerable amount of precipitated water percolates into subsurface), 28 % of the area has moderate groundwater recharge potentiality and rest of the area has low to poor recharge potentiality. The residual hills and linear ridges with steep slopes are not suitable for artificial recharge sites. Finally, 13 % of total average annual precipitated water (840 mm) percolates downward and ultimately contributes to recharge the aquifers in the Kovilpatti Municipality area. The paper is an attempt to suggest for maintaining the proper balance between the groundwater quantity and its exploitation.     

Evaluating the impact of artificial groundwater recharge structures using geo-spatial techniques in the hard-rock terrain of Rajasthan,India

Groundwater levels in hard-rock areas in India have shown very large declines in the recent past. The situation is becoming more critical due to a paucity of rainfall, limited surface water resources and an increasing pattern of groundwater extraction in these areas. Consequently, the Ground Water Department with the aid of World Bank has implemented the water structuring programme to mitigate groundwater scarcity and to develop a viable solution for sustainable development in the region. The present study has been undertaken to assess the impact of artificial groundwater recharge structures in the hard-rock area of Rajasthan, India. In this study groundwater level data (pre-monsoon and post-monsoon) of 85 dug-wells are used, spread over an area of 413.59 km². The weathered and fractured gneissic basement rocks act as major aquifer in the area. Spatial maps for pre- and post-monsoon groundwater levels were prepared using the kriging interpolation technique with best fitted semi-variogram models (Spherical, Exponential and Gaussian). The groundwater recharge is calculated spatially using the water level fluctuation method. The entire study period (2004–2011) is divided into pre- (2004–2008) and post-intervention (2009–2011) periods. Based on the identical nature of total monsoon rainfall, two combinations of average (2007 and 2009) and more than average (2006 and 2010) rainfall years are selected from the pre- and post-intervention periods for further comparisons. All of the water harvesting structures are grouped into the following categories: as anicuts (masonry overflow structure); percolation tanks; subsurface barriers; and renovation of earthen ponds/nadis. A buffer of 100 m around the intervention site is taken for assessing the influence of these structures on groundwater recharge. The relationship between the monsoon rainfall and groundwater recharge is fitted by power and exponential functions for the periods of 2004–2008 and 2008–2011 with R ² values of 0.95 and 0.98, respectively. The average groundwater recharge is found to be 18% of total monsoon rainfall prior to intervention and it became 28% during the post-intervention period. About 70.9% (293.43 km²) of the area during average rainfall and more than 95% (396.26 km²) of the area during above-average rainfalls show an increase in groundwater recharge after construction of water harvesting structures. The groundwater recharge pattern indicates a positive impact within the vicinity of intervention sites during both average and above-average rainfall. The anicuts are found to be the most effective recharge structures during periods of above-average rainfall, while subsurface barriers are responded well during average rainfall periods. In the hard-rock terrain, water harvesting structures produce significant increases in groundwater recharge. The geo-spatial techniques that are used are effective for evaluating the response of different artificial groundwater recharge techniques.     

Mapping lithological variations in a river basin of West Bengal,India using electrical resistivity survey: implications for artificial recharge

Groundwater is a treasured earth’s resource and plays an important role in addressing water and environmental sustainability. However, its overexploitation and wide spatial variability within a basin and/or across regions are posing a serious challenge for groundwater sustainability. Some parts of southern West Bengal of India are problematic for groundwater occurrence despite of high rainfall in this region. Characterization of an aquifer in this area is very important for sustainable development of water supply and artificial recharge. Electrical resistivity surveys using 1-D and 2-D arrays were performed at a regular interval from Subarnarekha River at Bhasraghat (south) to Kharagpur (north) to map the lithological variations in this area. Resistivity sounding surveys were carried out at an interval of 2–3 km. Subsurface resistivity variation has been interpreted using very fast simulated annealing (VFSA) global optimization technique. The analysis of the field data indicated that the resistivity variation with depth is suitable in the southern part of the area and corresponds to clayey sand. Interpreted resistivity in the northern part of the area is relatively high and reveals impervious laterite layer. In the southern part of the area resistivity varies between 15 and 40 Ωm at a depth below 30 m. A 2-D resistivity imaging conducted at the most important location in the area is correlated well with the 1-D results. Based on the interpreted resistivity variation with depth at different locations different types of geologic units (laterite, clay, sand, etc.) are classified, and the zone of interests for aquifer has been demarcated. Study reveals that southern part of the area is better for artificial recharge than the northern part. The presence of laterite cover in the northern part of the area restricts the percolation of rainwater to recharge the aquifer at depth. To recharge the aquifer at depth in the northern part of the area, rainwater must be sent artificially at depth by puncturing laterite layers on the top. Such studies in challenging areas will help in understanding the problems and finding its solution.     

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.     

Geostatistical analysis of arsenic concentration in the groundwater of Malda district of West Bengal, India

The problem of arsenic (As) poisoning in the upper deltaic plain of the Ganga-Bhagirathi river system in the Bengal Basin of West Bengal, India is an alarming issue. Four blocks (Kaliachak-1, 2, 3 and English Bazar) of Malda district, West Bengal were critically studied. Geomorphologically, the area exhibits three terraces: the present Youngest terrace (T₀-terrace), the Older Shaugaon Surface (T₁-terrace) and the Oldest Baikunthapur Surface (T₂-terrace). On the basis of numerous measurements, including As-content, pH, DO, specific conductivity and salinity, it was observed that maximum As-content beyond the permissible limit (0.05 mg/L, Indian standard) occurs within a depth range of 10–30 m with a non-linear distribution pattern. Variance test also found that a block effect was highly significant in an As-distribution pattern. Mean arsenic level of Kaliachak block-1 is 0.2253 mg/L, followed by Kaliachak-2 with arsenic level 0.1923, Kaliachak-3 with arsenic level 0.1755 and English Bazar with arsenic level 0.1324. The arsenious belt lies mainly within the Older terrace (T₁). The very recent flood plain deposits of silvery white, fine sands lying very close to the Ganga River margin do not contain significant amounts of As. Elevated As-concentration in the ground water was observed in alluvial sands, grayish white to brownish in color and occurring away from the Ganga margin. The Oldest terrace (T2) further away from the Ganga margin (e.g. English Bazar) and Barind surface contains less arsenic. Barind surface acts as a hard capping with ferruginous sands and lateritic concretions-chocolate, mottled and purple brown in color-occurring northeast of the studied area. Arsenic content of ground water in the same locality within a radius of ∼ 20 m varies within wide limits. Thus, it poses problem to delineate its distribution pattern. Such a patchy occurrence possibly could not be explained satisfactorily solely by geomorphology. Chemical analysis of aquifer clay samples of the cores shows a maximum Ascontent of up to 3 mg/kg, whereas the bulk samples (sandclay mixture) of the cores contain a maximum of 17 mg/kg As-value. Therefore, it is not always true that clay contains elevated As-value.     

Delineation of groundwater zones using lithology and electric tomography in the Khartoum basin, central Sudan

The three towns of Khartoum, Omdurman and Khartoum are located north of the capital of Sudan. This capital has agglomerated to reach more than 7 million inhabitants. The present situation is confronted with a dramatic shortage in freshwater supply. The treatment of surface water from the Nile became costly, particularly in flood season. Thus the authorities turned towards developing groundwater resources. The electric tomography, obtained by the combination of Vertical Electrical Sounding (VES) and well logs, turned out to be very efficient to provide a complete electrical image of the underground from the surface until about 200-m depth. This methodology constitutes a very cheap guide for the evaluation of the quality of groundwater resources in the Khartoum area. To cite this article: M.T. Hussein, H.S. Awad, C. R. Geoscience 338 (2006).     

Delineation of groundwater potential zones in Wadi Saida Watershed of NW-Algeria using remote sensing,geographic information system-based AHP techniques and geostatistical analysis

Sustainable management of groundwater resources has now become an obligation,especially in arid and semi-arid regions given the socio-economic importance of this resource.The optimization in zoning for groundwater exploitation helps in planning and managing groundwater supply works such as boreholes and wells in the catchment.The objective of this study is to use remote sensing and GIS-based Analytical Hierarchy Process(AHP)techniques to evaluate the groundwater potential of Wadi Saida Watershed.Spatial analysis such as geostatistics was also used to validate results and ensure more accuracy.Through the GIS tools and remote sensing technique,earth observation data were converted into thematic layers such as lineament density,geology,drainage density,slope,land use and rainfall,which were combined to delineate groundwater potential zones.Based on their respective impact on groundwater potential,the AHP approach was adopted to assign weights on multi-influencing factors.These results will enable decision-makers to optimize hydrogeological exploration in large-scale catchment areas and map areas.According to the results,the southern part of the Wadi Saida Watershed is characterized as a higher groundwater potential area,where 32%of the total surface area falls in the excellent and good class of groundwater potential.The validation process revealed a 71%agreement between the estimated and actual yield of the existing boreholes in the study area.     

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.     

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

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

GIS based groundwater modeling study to assess the effect of artificial recharge: A case study from Kodaganar river basin,Dindigul district,Tamil Nadu

Groundwater is a dynamic and replenishable natural resource. The numerical modeling techniques serve as a tool to assess the effect of artificial recharge from the water conservation structures and its response with the aquifers under different recharge conditions. The objective of the present study is to identify the suitable sites for artificial recharge structures to augment groundwater resources and assess its performance through the integrated approach of Geographic Information System (GIS) and numerical groundwater modeling techniques using MODFLOW software for the watershed located in the Kodaganar river basin, Dindigul district, Tamil Nadu. Thematic layers such as geology, geomorphology, soil, runoff, land use and slope were integrated to prepare the groundwater prospect and recharge site map. These potential zones were categorized as good (23%), moderate (54%), and poor (23%) zones with respect to the assigned weightage of different thematic layers. The major artificial recharge structures like percolation ponds and check dams were recommended based on the drainage morphology in the watershed. Finally, a threelayer groundwater flow model was developed. The model was calibrated in two stages, which involved steady and transient state condition. The transient calibration was carried out for the time period from January 1989 to December 2008. The groundwater model was validated after model calibration. The prediction scenario was carried out after the transient calibration for the time period of year up to 2013. The results show that there is 15 to 38% increase in groundwater quantity due to artificial recharge. The present study is useful to assess the effect of artificial recharge from the proposed artificial structures by integrating GIS and groundwater model together to arrive at reasonable results.