Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

P. S. Datta ¹, S. K. Bhattacharya ², P. Mookerjee ¹, S. K. Tyagi ¹

Affiliations
1 Nuclear Research Laboratory, IARI, New Delhi-110012, IN
2 Physical Research Laboratory, Navarangpura, Ahmedabad-380009, IN

Abstract

Stable isotopic composition of groundwaters and their hydrochemistry have been used for investigating possible existence of both palaeo-water and replenishable groundwater in Pushkar (Ajmer) Valley, Rajasthan. Causes of salinity increase in some of the groundwaters and intermixing of saline and fresh groundwaters have also been studied. The δ¹⁸O values of water samples show a wide range varying from -6.3‰ to +4.0‰, indicating different sources of origin of these waters. There is a depletion of δ¹⁸O with increasing depth of water table which may be due to stratification in groundwater with shallower zones being recharged from relatively modern rainfall. The chemical composition of groundwatlbrs shows a wide variation with electrical conductivity ranging from 150μmhos/cm to 8400μmhos/cm. Linear relationship between δ¹⁸O and Cl^- is a clear indication that the groundwaters are freshwater intermixed with different amounts of a saline endmember. Highly depleted, low salinity groundwaters seem to be of palaeo-origin. The most probable genesis of the ¹⁸O enriched, high salinity groundwater is from an originally evaporitic environment.

Keywords

Groundwater, Stable Isotope, Hydrogeology, Pushkar, Rajasthan.

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P. S. Datta ¹, S. K. Tyagi ¹

Affiliations
1 Nuclear Research Laboratory, Indian Agricultural Research Institute, New Delhi - 110 012, IN

Abstract

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.

Keywords

Groundwater, Hydrochemistry, Chemical Weathering, Delhi.

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