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High fluoride in groundwater has been reported from many parts of India. However, a systematic study is required to understand the behaviour of fluoride in natural water in terms of local hydrogeological setting, climatic conditions and agricultural practices. Present study is an attempt to assess hydrogeochemistry of groundwater in Ajmer district in Rajasthan to understand the fluoride abundance in groundwater and to deduce the chemical parameters responsible for the dissolution activity of fluoride. Ajmer district falls in the semi-arid tract of central Rajasthan and is geologically occupied by Precambrian rocks (granites, pegmatites, gneisses, schists etc) where groundwater occurs under unconfined condition. A total of 153 well-water samples, representing an area of 8481 km 2 (further subdivided into eight blocks), were collected and chemically analyzed. The results of chemical analyses (pre-monsoon 2004) show fluoride abundance in the range of 0.12 to 16.9 mg/l with 66% of the samples in excess of permissible limit of 1.5 mg/l.Presence of fluoride bearing minerals in the host rock, the chemical properties like decomposition, dissociation and dissolution and their interaction with water is considered to be the main cause for fluoride in groundwater. Chemical weathering under arid to semi-arid conditions with relatively high alkalinity favours high concentration of fluoride in groundwater. Dental and skeletal fluorosis are prevalent in the study area which can be related to the usage of high fluoride groundwater for drinking. The suggested remedial measures to reduce fluoride pollution in groundwater include dilution by blending, artificial recharge, efficient irrigation practices and well construction.

A direct approach to designing MODFLOW finite difference model is tedious and less intuitive, specifically for complex boundary and initial conditions. Therefore, a MODFLOW model can be developed either using a grid or conceptual model approach. The conceptual model is created using Geographic Information System (GIS) objects including points, arcs and polygons so that it can more accurately represent real world condition. It is a simplified representation of the site to be modelled including the model domain, boundary conditions, sources, sinks and material zones. Advantage of conceptual model is that most of the input can be in terms of physical objects, such as wells, lakes, recharge zones etc which can then be converted to a grid based mathematical model with the help of preprocessor software.This paper presents the results of a mathematical groundwater model developed for the northern part of Mendha sub-basin in the semi arid region of northeastern Rajasthan, employing conceptual groundwater modelling approach. For this purpose, Groundwater Modelling Software (GMS) was used which supports the MODFLOW-2000 code. For the purpose of modelling the Source/ Sink Coverage, Recharge Coverage, Extraction Coverage, Return Flow Coverage and Soil Coverage were considered. The model was calibrated against the historical and observed water level data for periods 1998 to 2003 and 2003 to 2005 respectively.The model was calibrated using observed water level data collected during the study period, so that model is capable to producing field measured heads and flow. For the present study historical data of water level is divided into two parts, in the first part of data from year 1998 to 2003 were used for the calibration purpose. In the second part the available field data during year 2003 to 2005 were used for model verification.The model was run to generate groundwater scenario for a 15 year period from 2006 to 2020 considering the existing rate of groundwater draft and recharge. The water budget predictions indicate a decrease from 349.50 to 222.90 MCM in the groundwater storage system, whereas groundwater abstraction shows an increase from 258.69 to 358.74 MCM per annum. The predicted water table contour maps for the years 2007, 2015 and 2020 have also been generated.

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The physical and chemical characteristics of pond water was investigated during Monsoon Season, Post-monsoon, winter season and Pre-monsoon (2012-13).The studied ponds relocated near about an integrated steel and power plant at Mandir Hasoud, Raipur, India. The eleven water quality parameters like pH, TDS, alkalinity, total hardness, chloride, iron, fluoride, sulphate, nitrate, calcium and magnesium were analyzed in this study. The pH, TDS, Total Hardness, Alkalinity, Chloride, Sulphate, Nitrate, calcium and magnesium were found well within the norms as prescribed by BIS. Fluoride concentration in sample SW1, SW2 and SW4 was found to be slightly higher than desired limit but under permissible limit as prescribed by BIS. Iron concentration was found higher than permissible limit in all the samples. The higher concentration of iron may be due to deposition of iron content mixed suspended particulate matter from atmosphere to surface that is emitted from nearest an integrated steel and power plant. The maximum iron concentration found in the Serikheri pond which is situated in the down wind direction with respect to the plant where dispersion of air pollutants is greater than other location.