Identification and evaluation of hydrogeochemical processes in the groundwater environment of Delhi, India

A study of the hydrogeochemical processes in the national capital territory of India was carried out with the objective of identifying the geochemical processes and their relation with groundwater quality as well as to get an insight into the hydrochemical evalution of groundwater. Salinity and nitrate contamination are the two major problems in the area, which is alarming considering the use of this water for drinking. Various graphical plots and statistical analyses have been carried out using chemical data to deduce a hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies and factors controlling groundwater quality. The prevailing hydrochemical processes operating here are simple dissolution, mixing, weathering of carbonate minerals, locally known as 'kankar', and of silicate, ion exchange, and surface water interaction. Limited reverse ion exchange has been noticed in a few parts of the study area especially in post-monsoon periods. Periodic seasonal switch-over has been clearly noticed in these hydrogeochemical processes that control groundwater quality of the area. The number of factors that control the overall mineralization and water quality of Delhi vary from season to season. In pre-monsoon, there are four factors while in post-monsoon it increases to five. The study highlights the descriptive capabilities of conventional and multivariate techniques as effective tools in groundwater evaluation.