Abstract
Abstract
This study presents an integrated assessment of natural background levels (NBLs) and nitrate-fluoride pollution indices (NPI and FPI) to evaluate groundwater quality in semi-arid region, Rajasthan, Western India. A total of 274 groundwater samples collected during dry-season were analysed for pH, EC, TDS, major ions, TH, TA, nitrate, and fluoride. The hydrochemical characteristics reveal substantial spatial variability governed by the combined influences of geogenic processes and anthropogenic activities. Total dissolved solids (195–6780 mg/L, mean: 968 mg/L) indicate significant salinity enrichment, with 62% of samples exceeding the permissible drinking water limit. Nitrate and fluoride concentrations exceeded the recommended limits in 27% and 15% of samples, respectively, particularly in agricultural and wastewater-affected areas. The derivation NBLs, and threshold values (TVs) have effectively distinguished natural contributions from human-induced contamination. The first threshold values (TV1) for pH, EC, Na
+
, Cl
−
, HCO
3
−
, TH, TA, NO
3
−
, and F
−
were 8.2, 480 µS/cm, 49, 35, 135, 72, 135, 16, and 0.26 mg/L, respectively. Several TV2 values (8.5, 620 µS/cm, 715, 610, 561, 250, 360, 55, and 1.56 mg/L, respectively) exceeded drinking water standards, indicating significant water quality deterioration. Nitrate (range: 1-187 mg/L) remains mostly within the natural background range, exceeded the BIS limits at several locations, indicating significant anthropogenic inputs from agricultural practices and urban activities. The NPI (-1.0 to 8.4) has revealed that approximately 68.2% of the samples were affected by nitrate pollution, with distinct hotspots associated with intensive cultivation. Fluoride (0.02-10.0 mg/L) exceeded safe limits (> TV2:1.56 mg/L) in 15% of samples, while the FPI (1.5 to 4.0) indicated that approximately 90.5% samples were moderately to highly polluted by fluoride, enhanced by alkaline condition, HCO
3
-, and high Na
+
/Ca
2+
ratios, particularly within the cropland-dominated areas. These findings demonstrate the effectiveness of integrating NBLs, TVs, and pollution indices for identifying contamination sources, assessing groundwater quality, and supporting sustainable groundwater management and risk mitigation strategies in semi-arid regions.