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Fluoride in high concentration in groundwater has been reported from many parts of India. However, a systematic study is required to understand the behavior of fluoride in natural water in terms of local hydrogeological setting, climatic conditions, and agricultural practices. The present study is an attempt to assess hydrogeochemistry of groundwater in parts of Palar river basin pertaining to Kancheepuram district Tamil Nadu to understand the fluoride abundance in groundwater and to deduce the chemical parameters responsible for the dissolution activity of fluoride. The study area is geologically occupied by partly sedimentary and partly crystalline formations. A total of 50 dug cum borewell-water samples, representing an area of 2,628.92 km2. The results of the chemical analyses in September 2009 show fluoride abundance in the range of 1 to 3.24 mg/l with 86% of the samples in excess of the permissible limit of 1.5 mg/l. Presence of fluoride-bearing minerals in the host rock, chemical properties like decomposition, dissociation, and dissolution, and their interaction with water are considered to be the main causes for fluoride in groundwater. Chemical weathering with relatively high alkalinity favors high concentration of fluoride in groundwater. Villagers who consume nonpotable high fluoride water may suffer from yellow, cracked teeth; joint pains; and crippled limbs and also age rapidly.

Remote sensing and geographical information system (GIS) has become one of the leading tools in the field of groundwater research, which helps in assessing, monitoring, and conserving groundwater resources. This paper mainly deals with the integrated approach of remote sensing and GIS to delineate groundwater potential zones in hard rock terrain. Digitized vector maps pertaining to chosen parameters, viz. geomorphology, geology, land use/land cover, lineament, relief, and drainage, were converted to raster data using 23 m×23 m grid cell size. Moreover, curvature of the study area was also considered while manipulating the spatial data. The raster maps of these parameters were assigned to their respective theme weight and class weights. The individual theme weight was multiplied by its respective class weight and then all the raster thematic layers were aggregated in a linear combination equation in Arc Map GIS Raster Calculator module. Moreover, the weighted layers were statistically modeled to get the areal extent of groundwater prospects with respect to each thematic layer. The final result depicts the favorable prospective zones in the study area and can be helpful in better planning and management of groundwater resources especially in hard rock terrains.

Fluoride (F−) is essential for normal bone growth, but higher concentration in the drinking water causes health problems which are reported in many states of India. Andhra Pradesh is one of the states which suffer from excess fluoride in groundwater particularly in the hard rock terrain. In this context, a study was conducted in Andhra Pradesh based on chemical analysis of water samples from hydrograph net work stations (dug wells) and exploratory bore wells. The concentration of fluoride in groundwaters ranges from traces to 9.75 mg/l. The occurrence of fluoride is mostly sporadic, uneven and varies with depth. The highly affected districts include Nalgonda and Warangal in Telangana region, Prakasam in coastal region, Anantapur and Kurnool in Rayalaseema region. In certain areas of Nalgonda district, 85% of wells have fluoride more than permissible limit (> 1.5 mg/l) for drinking water. High F− is present in all the geological formations, predominantly in granitic aquifers, compared to the other formations. The average value of fluoride is high in the deeper zone (1.10 mg/L), compared to the shallow zone (0.69 mg/L). The fluoride-rich minerals present are the main sources for fluoride concentrations in groundwater. Residence time, evapotranspiration and weathering processes are some of the other supplementary factors for high fluoride concentrations in groundwater. Long-term data of hydrograph net work stations (dug wells) reveal that fluoride concentrations do not show any marked change of trend with respect to time. The concentration of fluoride is found to increase with increase of Na+and HCO3−, and decrease with increase of Ca2+. Sodium bicarbonate waters are more effective in releasing fluoride from minerals into groundwater. High fluoride waters are of Na+ type. The paper presents a brief account of the study and its results.