Patterns of groundwater chemistry: implications of groundwater flow and the relation with groundwater fluoride contamination in the phreatic aquifer of Odisha, India

Abstract

The work analyzes the patterns of quality parameters and hydrochemical facies of 1105 nos (n = 685 in hard rock; n = 420 in alluvium) of groundwater samples drawn from the phreatic aquifer in Odisha, India. The study explores the possible relations of the groundwater chemistry including the fluoride (Fˉ) contaminations with the flow mechanisms. The hydrochemical facies types of Na-Mg-Ca-Cl-HCO3 characterize the groundwater discharge corridors lying close to the river valleys, and in parts of coastal alluvium, particularly in the Mahanadi deltaic region. In contrast, the facies types of Ca-Mg-HCO3-Cl dominate the groundwater recharge areas, located at relatively higher elevations. The recharge areas in the state are largely free from groundwater Fˉ contamination. The study delineates the ratio of Ca2+/Na+ and its distribution patterns to interpret the source of Fˉ (> 1.0 mg/L) in groundwater. The Ca2+/Na+ ratios of 1.0 are characterized by water types like Ca-Mg-HCO3 (Cl) of recent meteoritic origin. These are distributed in the groundwater recharge-midline areas where significant infiltration to groundwater occurs. The largest such cluster is observed in the Hirakud Canal Command area in the western parts of the state, indicating the role of anthropogenic sources of groundwater Fˉ contamination through irrigation return flows.