Major Ion Chemistry of Groundwater in Delhi Area: Chemical Weathering Processes and Groundwater Flow Regime

Groundwater is moderately to highly saline in all parts of Delhi area. No definite explanation has emerged so far about the source of salinity. Study of major ion chemistry of groundwater has been conducted to identify the source of major ions in terms of chemical weathering processes. The chemistry of groundwater is dominated by carbonate weathering. The excess of sodium ion over chloride ion can be attributed to silicate weathering to a certain extent. The groundwater in northern and western parts of the area is primarily alkaline and secondarily saline and in the southern and southwestern parts it is primarily saline and secondarily alkaline. Highly correlated positive linear trend between sodium and chloride indicates mixing of two groundwater bodies with different end member composition (i.e. fresh and saline). Multicomponent mixing may also be taking place within the local flow regimes. The large lateral variation of chloride concentration indicate recharge and discharge zones of local flow regime. Local recharge to the unconfined aquifer is more dominant than recharge from lateral flow. The very high Cl and SO₄ contents in some groundwaters seem to be related to long evaporative and to sulphur oxidising conditions in topographically low area.