EnviroGeoChimica Acta (2016) 3(1): 63-70 Special Issuee ISSN 2348 -7259 Quality of groundwater and hydrogeochemical processes in hard rock region of Salem taluk, Tamilnadu Venkatesan D • Suresh Gandhi M • Thivya C Received: 12 January 2016 / Accepted: 05 March 2016 ©EnviroGeoChimica Acta Abstract: Hydrogeochemical investigations were carried out in Salem taluk of Tamil Nadu, India to identify the suitability of water quality and the major geochemical processes that regulate groundwater chemistry. A total of 23 groundwater samples were collected from open wells in pre-monsoon (May 2013) and post- monsoon (December 2013) and analyzed for pH, EC, TDS, calcium, magnesium, sodium, potassium, carbonate, bicarbonate, chloride, nitrate, sulfate and fluoride. Geochemical data were interpreted using SAR, Na %, RSC, CAI & Wilcox diagram which revealed that 85 % of the groundwater is fit for domestic and irrigation purpose. In Pre monsoon and Post monsoon seasons, most of the samples are Ca-Mg-Cl type and some samples fall in Ca-HCO3 and Na-Cl type. Venkatesan D • Suresh Gandhi M • Thivya C Department of Geology, University of Madras, Guindy Campus, Chennai-600 025 Corresponding author e mail: msureshgandhi@gmail.com Keywords: Geochemistry, Quality, Weathering, Rock-water interaction. Groundwater. Introduction The assessment of groundwater quality gains its importance due to higher contamination in recent times due to intense urbanisation, industrialization and agricultural activities (Ackah et al. 2011; Sayyed and Wagh 2011; Tiwari 2011). These water pollution threats human health, economic development and social prosperity (Milovanovic 2007). The quality depends on its physical and chemical parameters evolved due to weathering, decomposition and their changes occur with respect to time and space (Bhargava and Killender 1988; Prasad 1984). The chemical composition of groundwater is mainly controlled by the composition of the precipitation, geololgy, lithology, lineaments, influence of effluents from agricultural return flow, industrial and domestic activities. The quality studies in groundwater proved to be an important technique in solving different geochemical problems (Chebotarev 1955; Hem 1959; Back et al. 1966; Gibbs 1970; Srinivasamoorthy et al. 2005). Increasing population growth and limiting natural resources have increased problems associated with the disposal of wastewater. The water bodies have often been treated as a convenient disposal site for various industrial and municipal wastes (Gowd 2005; Scanlon et al. 2010; Scapini et al. 2010; Vojtekova et al. 2010). The study area, Salem distirct, has fluoride contamination in groundwater. Hence, an attempt has been made to study the present status on quality of groundwater in salem taluk of Salem district. Materials and methods Study area The study has been carried out in Salem Taluk (Fig.1) which is situated in Salem district of Tamil Nadu. The district enjoys a tropical climate and covers an area of 672 km 2 . The taluk is situated between the 78° to 78°20'22" E and 11°30' to 11°50' N longitude and latitude. It is surrounded by reserved forest and Thirumanimutharu river is flowing north east to south west direction. Geologically, the area is covered by basic and ultra basic rocks, like, Magnetite, Quartzite, Pyroxene, Granulites, Charnockite, Ultra basic complex, pink Migmatite, Granitoid gneiss, and Fissile 63