Characterization and evaluation of processes governing the groundwater quality in parts of the Sabarmati basin, Gujarat using hydrochemistry integrated with GIS Kumari Rina, 1 P. S. Datta, 2 Chander Kumar Singh 1 and Saumitra Mukherjee 1 * 1 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi-110067, India 2 Indian Agricultural Research Institute, New Delhi-110012, India Abstract: Intense agricultural and industrial activities in any area are likely to make groundwater vulnerable with respect to its quality. In one such area which is a part of Sabarmati river basin of Gujarat, factors influencing the groundwater hydrochemistry in pre- and post-monsoon season were evaluated. Groundwater samples were collected from 5 km  5 km grids on the basis of spectral signature of vegetation and soil, observed on satellite image. Integration of Conventional graphical plots, Piper plot, saturation index values (estimated using PHREEQC) and GIS was helpful not only to create the database for analysis of spatial variation in respective water quality parameters but also to decipher the hydrogeochemical process occurring in such a large area. USSL diagram and % sodium were used to characterise the suitability of groundwater for irrigation. It was observed that leaching of wastes disposed from anthropogenic activities and agrichemicals is the major factor influencing the groundwater quality, in addition to the natural processes such as weathering, dissolution and ion exchange. Sea water relics are also impacting the groundwater quality. Control of indiscriminate and unplanned exploitation of groundwater, application of fertilizers and disposal of industrial wastes in the affected areas can possibly ensure groundwater protection from further pollution and depletion. Copyright © 2011 John Wiley & Sons, Ltd. KEY WORDS evaluation; processes; groundwater; hydrochemistry; Sabarmati basin; Saturation index; GIS Received 4 December 2010; Accepted 19 August 2011 INTRODUCTION Gujarat is one of the most economically fast growing states, situated in the west coast of India, dominated by intense growth of agricultural and industrial activities, accounting for 11% of the country’s share in industrial output (Mukherjee, 2007). Change in cropping pattern and intensive agriculture led to different types of fertilizer use and water abstraction especially for cash crops. In 1960–1961, total N, P, K fertilizer consumption was 11,071 tonnes which increased to 1,716,983 tonnes in 2008–2009 (Fertiliser Association of India, 2009). The number of tube wells has trebled since the 1970s. The new tube wells tap water from strata as deep as 350–400 m (Gupta and Deshpande, 2004). Rapid increase of industrialization, agriculture and population has induced unplanned abstraction of groundwater for more than 3 decades causing decline in water table/piezometric surface at a rate of ~ 3 m/year making the area water deficit. Groundwater salinity and contamination have also increased in many parts. During the last 3–4 decades, high concentra- tions of fluoride in groundwater have been noticed in North Gujarat (Gupta and Deshpande, 1998, 2005; Vasavada, 1998, Salve et al., 2008) which has adversely affected the health of the people from dental and skeletal fluorosis in many areas of this region (Gupta and Deshpande, 1998). Although efforts in the past have been made to describe the general quality of groundwater, little effort has been made so far to understand the processes governing the water quality. In this brief background, the present study attempts to identify the factors controlling the groundwater quality in the study area for both pre-monsoon and post-monsoon period, using hydrochem- istry in integration with Geographical Information System (GIS) to suggest groundwater management strategies. PHYSIOGRAPHY AND CLIMATE OF THE STUDY AREA The study area (~7221 sq.km; Figure 1) is a part of the Sabarmati River basin (total drainage area ~22,000 sq.km; longitudes 72  15 and 73  49E and latitudes 22  15 and 24  53N) which is located in western India. The river originates at an altitude of 782m in the Aravalli Hills in the Rajasthan, and it traverses a distance of 416 km up to the Gulf of Cambay in Gujarat state (Jain & Tandon, 2003). The drainage area of the Sabarmati basin in Gujarat state is ~17,550 sq.km (Irrigation Commission Report, 1972). The basin is bound in the north and northeast by the Aravalli hills; in the east, by a ridge separating it from the Mahi Basin; in the south, by the Gulf of Cambay; and in the west, by a ridge separating it from the basins of minor streams draining into the Rann of Kutch. Geologically, the basin comprises crystalline rocks of Archean age in the northern and northeastern parts, while *Correspondence to: Saumitra Mukherjee, School of Environmental Sciences, Jawaharlal Nehru University, New Delhi-110067 India. E-mail: saumitramukherjee3@gmail.com HYDROLOGICAL PROCESSES Hydrol. Process. (2011) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/hyp.8284 Copyright © 2011 John Wiley & Sons, Ltd.