Hydrogeochemistry of Purna alluvial basin, Central India

Hydrogeochemical status of the Purna alluvial basin, Maharashtra has been interpreted on the basis of 158 groundwater samples collected from dug wells (60) i.e., shallow aquifer and bore wells (98) i.e., deep aquifer each during pre- and post-monsoon periods of the year 2009. The samples were analyzed for their physicochemical parameters i.e., pH, EC, TDS, Ca, Mg, Na, K, TH, Al, Cl, SO4, NO3 and HCO3. The mean values of cation concentration show a trend of Na>Ca>Mg>K, while anions are in order of HCO3>Cl>SO4>NO3 from both deep and shallow aquifers. The plot of chemical data on Piper's trilinear diagram reveals that majority of the groundwater samples fall in the fields of alkalis exceeding alkaline earths, weak acids exceeding strong acids, carbonate hardness exceeding 50%, and no cation and anion pairs exceeding 50%. The cationic and anionic triangular fields of the diagram show that sodium-potassium type (Na+K) of water is dominant in the cationic, and bicarbonate type (HCO3) in the anionic category. The analytical data also reveal the existence of six groundwater facies in the area, i.e., (i) Ca-Mg-HCO3, (ii) Na-Cl, (iii) Na-HCO3, (iv) Ca-Cl, (v) Na-Ca-HCO3 (mixed type) and, (vi) Ca-Mg-Cl (mixed type). Ca-Mg-HCO3 facies is predominant in the northern, northeastern, eastern, southeastern and northwestern peripheries of the alluvial basin. Na-Cl and Na-HCO3, facies are confined to certain parts of the eastern and central regions, as well as in a few small patches along the Purna river channel. These areas are represented by moderate to high salinity. Na-Cl-SO4 facies is limited to a small patch situated in the central part of the basin representing excess concentrations of sodium and chloride.Water of Na-Ca-HCO3 (mixed type) is the most dominant covering most of the area on both sides of the Purna main channel in the eastern, central and western regions. Two small patches having Ca-Mg-Cl type of water has also been identified in the basin area.