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This paper presents the results of investigations on groundwater nitrate contamination in the Dharapuram area of Tamil Nadu in south India as a primary step to initiate denitrification. Groundwater samples were collected from 26 selected locations during the pre-monsoon season in July 2010 and analysed for nitrate and other water quality parameters. Two important water types were identified, viz. Ca-Na-HCO 3 and mixed Ca-Mg-Cl. It is found that the majority of samples possess high nitrate concentration; 57 % of samples exceeded the permissible limit of Indian (45 mg/L) and WHO (50 mg/L) drinking water standard. Spatial distribution map of NO 3 suggested that major contamination was observed in the SW and NW parts of the study area. This result was in agreement with the corresponding land-use pattern in this study area. Denitrification process at greater depths was evident from the negative correlation between NO 3 and well depth. The sources and controlling factors of high nitrate were investigated using cross plots of NO 3 with other selected hydrochemical parameters. Positive correlation for NO 3 was observed with EC, K, Cl and SO 4 . This analysis was capable of differentiating the various sources of nitrate in groundwater. The major sources of nitrate contamination are identified as areas of high fertilizer application, sewages and animal waste dumping yards. Regulation of these pollutant sources with appropriate and cost-effective denitrification process can restore the water quality in this area.

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