GROUNDWATER ARSENIC CONTAMINATION IN LAKHIMPUR KHERI: A HYDROGEOCHEMICAL PERSPECTIVE

The present study aims to understand the severity of Arsenic contamination along with the hydrochemistry of ground water in Lakhimpur Kheri, one of the largest districts in Uttar Pradesh, India. Ground water samples collected from 102 handpumps from 15 blocks were analyzed for physicochemical parameters and Arsenic. The groundwater quality data were analysed statistically. The characteristic features of groundwater indicated the presence of As (0- 0.224 mg/L), Fe (0.011-8.634mg/L), Na+ (2.84-62.12 mg/L), K+ (1.21-51.20 mg/L), Ca2+ (6-102mg/L), Mg2+ (10-126), Cl- (2.19-133.96 mg/L), SO42- (1-269.92 mg/L), NO3- (0.11-2.61 mg/L) and HCO3- (122-549 mg/L). The pH of the groundwater was found to be neutral to slightly alkaline (6.88-8.45) with high EC (471-1569 µS/cm) and TDS (289-1042 mg/L). Of the total samples analysed, 41.18% contained as > 10µg/L, 13.73% contained as < 10µg/L, while in the rest of the samples as was found to be below detectable limit. Severe As contamination was reported mainly in six blocks of the study area- Pallia, Nighasan, Dhawahara, Ramia Beher, Isanagar and Nakaha. The highly contaminated block was Pallia where all the samples contained as above permissible limit. However, maximum as concentration (0.224 mg/L) was reported from a deep well handpump of village Dubha from Nighasan block. Both Shallow and deep bore handpumps were analysed to study the distribution pattern of as with depth. No systematic relationship was found. Arsenic showed insignificant correlation with EC, TDS, TH, Ca2+, Mg2+, Na+, K+, HCO3-, NO3- Cl- and SO42- but poor correlation with Fe (r2 = 0.391) and pH (r2 = 0.018). Factor analysis was applied to reveal the processes controlling the hydrochemistry of groundwater and to understand the factors responsible for the release of as in groundwater of the study area. Extensive study in the affected areas advocates that the leaching of Arsenic in underground water is controlled by the magnitude of oxidizing environmental conditions created in the affected zones where As (III) oxidized to As (V) is introduced in the aquifers and gets adsorbed on iron rich grains.