Hydrochemical characteristics of groundwater and their changes through geogenic and anthropogenic activities were assessed in the North-western part of Unnao District, Uttar Pradesh, India, to understand the groundwater evolution, to identify the predominant geochemical processes occurring within the groundwater system and to exemplify the anthropogenic processes affecting the groundwater environment. For this purpose, 74 groundwater samples were collected from dug wells during pre-monsoon and post-monsoon 2010 period, respectively, covering an area of about 950 km². The major ion concentration and total dissolved solids (TDS) in the groundwater showed a great variation, with 49% during pre and 89% samples during post-monsoon being brackish. The relationships among the dissolved species allowed identification of the origin of solutes and the processes that generated the present groundwater compositions. Chemical obliteration in groundwater has occurred to a great extent and this alteration was assessed through silica v/s TDS approach. Human activities, in particular, the agricultural and leather tanning activities has led to tremendous change in the groundwater regime which is reflected by fluctuating ion concentrations in the groundwater of the study area.

Key words: Groundwater. Silica geothermometry. Chemical alteration. Unnao district.