Residual sodium carbonate (RSC)
Carbonate and bicarbonate are an important parameter for assessing the suitability of groundwater for irrigation uses. The RSC value indicates the alkalinity hazards of earth metals. An excessive concentration of the sum of carbonate and bicarbonate in groundwater over the sum of calcium and magnesium also influence the fitness of groundwater (Balamurugan et al., 2020a). In the study region, the RSC value ranges from -23.96 to 3.01, with a mean of -6.31 (Table.4). The negative value of RSC reveals that concentration calcium and magnesium are higher than those of carbonate and bicarbonate in groundwater. The value of RSC less than 1.25 meq/L is suitable, 1.26 to 2.5 meq/L is marginal, and greater than 2.5 meq/L is unsuitable for irrigation (Table.6). The spatial distribution of RSC value in the study region, 664.91 sq.km areas, is suitable, 1.94 sq.km areas is marginal, and 0.57 sq.km area falls under the unsuitable classes of groundwater (Fig.11c). It indicates that one sample location has a distribution of calcite- and dolomite-rich sediments and large amounts of bicarbonate.