Intra-annual variability in the heavy metal geochemistry of ground waters from the Deccan basaltic aquifers of India

Geochemical baseline (geogenic+anthropogenic) and background (geogenic) levels of heavy metals in the ground waters from basaltic aquifers of Deccan Volcanic Province of India depicted intra-annual variability on spatial scale. Classified into ‘Group I’ (Fe > Mn > Zn > Pb) and ‘Group II’ (Mo > Ni > Cr > Cu), metals depicted contrasting enrichment and depletion patterns seasonally, attributable to geologic controls and water table fluctuations. While, fortification in Mo–Ni in post-monsoon (high water table) is on account of combined lithogenic+anthropogenic contributions, pre-monsoon augmentation in Fe–Mn (low water table) is entirely lithogenic. Positive values of Normalised Difference Dispersal Index, replicates the dominant role of soil/vadose zone as a chief supplier of metals to the groundwater during post-monsoon, while negative figures recommend host rock as a primary source of accretion of metals in pre-monsoon. Higher Ni/Cr ratios for wells in alluvial aquifer (fertile agriculture plain) than the basaltic and dyke aquifers, further suggest enhanced input of the elements (Mo, Ni > Cu) from soil and agriculture land use in post-monsoon season. Values of Ni/Cr ratio above unity for majority of the wells in post-monsoon and nearly 50 % wells in pre-monsoon suggest privileged weathering of olivine, followed by pyroxene > plagioclase feldspar (Ni/Cr