Assessment of groundwater geochemistry and health risks in rural areas of Lucknow district of Indo-Gangetic basin through an entropy-weighted approach

The groundwater geochemistry in rural parts of the Indo-Gangetic basin (IGB) is greatly influenced by geogenic and various anthropogenic activities. This study deals with the assessment of groundwater geochemistry and associated health risk in rural parts of Lucknow district which comes under IGB. The entropy-weighted approach is used here along with various water quality indexing and multivariate statistical techniques to determine the suitability of groundwater for drinking and irrigation use. The concentration of major ions (Ca2+, Mg2+, Na+, K+, HCO3-, SO42-, Cl- and F-), showed that most of the samples (n=56) are appropriate for drinking usage. However, two sites show the elevated pH (>8.5), which may be due to dissolution and leaching of hydroxide-containing materials. TDS concentration shows the occurrence of fresh quality water, about 71% of the samples below the <500 mg L-1 range, and about 29% of in the permissible (500-1000 mg L-1) range for drinking. Also, the elevated NO3- concentration is found a concern in the region at few specific locations, where it was found above the no-relaxation limit of 45 mg L-1 set by the Bureau of Indian Standards (BIS). Based on the entropy-weighted water quality index (EWQI) scale, about 37% of the samples show good water quality, while 57% of the samples show medium and about 6% of the samples show poor quality water. The bivariate and Gibbs plots indicate that ionic elemental chemistry is primarily controlled by rock-water reactions, especially silicate weathering, in the study area due to the forward ion exchange. The Piper plot specifies that Ca2+-HCO3- was the key hydrochemical facies, along with the prevailing existence of Na+-HCO3- resulting in mixed Ca2+-Na+-HCO3- category water. The quality of groundwater assessed for irrigation using various indices and ratios shows that most of the groundwater of the area is suitable for irrigation by ignoring the magnesium hazard ratio (MHR), which suggests that 87% of the samples are inappropriate for irrigation use. The total hazard index (THI) value was higher in children (max. 4.20, mean 0.69) in comparison to adults (max. 3.11, mean 0.51) which shows children are more vulnerable than adults in the area. Keywords: Groundwater; Indo-Gangetic basin; Lucknow district; Entropy-weighted water quality index; Total hazard index