A study of pH and alkalinity in thirty-nine groundwater locations in the semi-arid region of Central India was carried out with the objective of monitoring and controlling the groundwater pollution seasonally. The study area was Sidhi district bounded by Son river in North, Gopad river in the east, Banas river in the west and Kusmi forest in the south. Geologically, the entire Sidhi district is dissected into Vindhyan, Archean, Dharwar and Permian regions. The study revealed higher alkalinity in the area ranging beyond the standard permissible limit while pH of all locations was well within the permissible limits (8.5). Increased pH and alkalinity were reported in the monsoon. The prevailing hydrochemical processes are water-rock interaction, seepage, percolation and leaching in the Sidhi district.

The systematic and comprehensive geochemical analysis of fluoride (F) in twenty agricultural soil samples was carried out to understand spatial variability, mechanism of retention and release, and the areas of potential risk due to high concentrations of F in soil around Sidhi District, Central India. The spatial variations in physico-chemical parameters revealed significant difference in the methods of cultivation due to geomorphological constraints, availability of surface water and ground water etc., in the study area. The north and small pocket in central Sidhi were rich in fertile soils due to availability of surface and ground water. The southern and eastern Sidhi were rainfed areas, hence, the monocropping system by traditional methods showed less impact on the soil physico-chemical parameters. The soil F varied from 366.94 to 1178 mg/kg and 2-4 times greater than the background soil value (320 mg/kg) of the world. The pollution indexes were > 1 indicating prevalence of elevated soil fluorine.

Geochemical and hydrogeochemical studies were conducted to assess the origin and geochemical mechanisms driving the fluoride enrichment in groundwaters of semiarid regions in Central India. The study region is geologically occupied by Precambrian rocks (granites, pegmatites, gneisses, schists, etc.) where groundwater occurs under unconfined condition. Majority of the groundwater locations did not meet the potable water criteria as they contained excess fluoride (>1.5 mg/l). The greater concentrations of fluoride were recorded in the monsoon followed by post-monsoon and pre-monsoon. Ionic composition and hydrogeochemical facies revealed the dominance of carbonate weathering and alkalinity that favors high dissolved fluoride in groundwaters. The values of dissociation constant showed slow weathering of fluorite and fast weathering of calcite in the study area. Rainfall shifted the unsaturated to saturated values of SI C and SI F in the monsoon. The factor analysis and saturation indices revealed geogenic origin of fluoride, a condition responsible for perennial fluoride problem in the study region.

The systematic and comprehensive geochemical analysis of dissolved fluoride (F -) in thirty-nine groundwater samples were carried out to understand the spatial and temporal variability, areas of potential risk, and mechanism of fluoride precipitation/solubility in Central India. The dissolved ions showed weathering of carbonate minerals in the study area. Fluoride concentrations were beyond the permissible limit ([1.5 mg/l) in the pre-monsoon and monsoon seasons. The fluoride concentrations showed following spatial variations: urban area [ village in agricultural area [ village in forest area. The human population living in village, urban, and forest areas reported skin, mouth, and stomach problems due to high fluoride in the groundwater. Rainfall shifted the unsaturated to saturated values of SI C and SI F in the monsoon season. Strong indicators of alkaline condition were effective-CO 2 pressure (logP CO 2 ) and HCO 3 -/Ca ?2 ratio. The dissolved fluoride showed positive relationship with pH, TDS, and HCO 3 -/Ca ?2 explaining the global variability observed in ground water fluoride.

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