Significance of silica in identifying the processes affecting groundwater chemistry in parts of Kali watershed, Central Ganga Plain, India

Chemical geothermometry using silica was employed in the present study to estimate the sub-surface groundwater temperature and the corresponding depth of the groundwater in parts of Kali watershed in Bulandshahr and Aligarh district. 42 groundwater samples each were collected from borewells during pre-monsoon and postmonsoon season 2012 and analysed for all major ions and silica. Silica values in the area range from 18.72 to 50.64 mg/l in May 2012 and from 18.89 to 52.23 mg/l in November 2012. Chalcedony temperature >60 degrees C was deduced for five different locations in each season, which corresponds to a depth of more than 1,000 metres. Spatial variation of silica shows high values along a considerable stretch of River Kali, during pre-monsoon season. Relationship of silica with Total Dissolved Solids and Chloride was established to infer the role of geogenic and anthropogenic processes in solute acquisition. It was found that both water-rock interaction and anthropogenic influences are responsible for the observed water chemistry.