摘要
The work investigates the major solute chemistry of groundwater and fluoride enrichment(F^(-))in the shallow phreatic aquifer of Odisha.The study also interprets the hydrogeochemical processes of solute acquisition and the genetic behavior of groundwater F^(-)contamination.A total of 1105 groundwater samples collected from across the state from different hydro-geomorphic settings have been analyzed for the major solutes and F^(-) content.Groundwater is alkaline in nature(range of pH:6.6-8.7;ave.:7.9)predominated by moderately hard to very hard types.Average cation and anion chemistry stand in the orders of Ca^(2+)>Na^(+)>Mg^(2+)>K^(+) and HCO_(3)^(-)>Cl^(-)>SO_(4)^(2-)>CO_(3)^(2-) respectively.The average mineralization is low(319 mg/L).The primary water types are Ca-Mg-HCO_(3) and Ca-Mg-Cl^(-)HCO_(3),followed by Na-Cl,Ca-Mg-Cl,and Na-Ca-Mg-HCO_(3)^(-)Cl.Silicate-halite dissolution and reverse ion exchange are the significant processes of solute acquisition.Both the geogenic as well as the anthropogenic sources contribute to the groundwater fluoride contamination,etc.The ratio of Na^(+)/Ca^(2+)>1.0 comprises Na-HCO_(3)(Cl)water types with F^(-)>1.0 mg/L(range 1.0-3.5 mg/L)where the F^(-)bears geogenic source.Positive relations exist between F^(-)and pH,Na^(+),TDS,and HCO_(3)^(-).It also reflects a perfect Na-TDS correlation(0.85).The ratio of Na^(+)/Ca^(2+)<1.0 segregates the sample population(F^(-)range:1.0-4.0 mg/L)with the F derived from anthropogenic sources.Such water types include Ca-Mg-HCO_(3)(Cl)varieties which are recently recharged meteoritic water types.The F^(-) levels exhibit poor and negative correlations with the solutes in groundwater.The Na-TDS relation remains poor(0.12).In contrast,the TDS levels show strong correlations with Ca^(2+)(0.91),Mg^(2+)(0.80)and even Cl^(-)(0.91).The majority of the monitoring points with the anthropogenic sources of groundwater F^(-) are clustered in the Hirakud Canal Command area in the western parts of the state,indicating the role of irrigation return flow in the F^(-) contamination.
