Groundwater quality assessment in the Lower Ganga Basin using entropy information theory and GIS.

Mapping and managing groundwater resources are essential for socio-economic and sustainable development. Analysis of hydrogeochemical parameters of the groundwater for the Lower Ganga basin is presented to identify the contamination zones and also to understand the groundwater quality in this region. Drainage pattern analysis identifies five sub-basins in the region. Shannon's entropy information theory has been performed to compute the water quality index (WQI) without having any subjective bias in the analysis. The analysis of the WQI shows that sub-basin 2 (WQI = 38.35) has excellent quality of groundwater, whereas sub-basin 1 (WQI = 52.43), 3 (WQI = 63.94), and 5 (WQI = 82.79) are having good groundwater quality. On the other hand, sub-basin 4 (WQI = 102.99), which covers mostly the central part of the main stream, is found to be most contaminated and having a medium quality of the groundwater. Analysis of the groundwater parameters using the PCA indicates that the quality of groundwater in the study area is controlled mainly by three main factors, which are geogenic process (weathering and leaching of rocks), seawater intrusion (natural process), and anthropogenic activities. Furthermore, hydrometeorological analysis shows a gradual drop in precipitation, water level depth, and the percolation index (PI). This indicates an over exploitation of groundwater resources in the study region under the present circumstances of climate variability, population and industrialization. The results obtained in this paper are useful for identifying suitable sites for tube-wells and bore-wells for drinking and agricultural purposes, and also for developing an effective strategy to avoid further contamination of groundwater aquifers in the region. Results are extremely useful for government agencies and policymakers in achieving the United Nations (SDG-6) goals of suitable planning and sustainable development of groundwater resources by 2030. • The Lower Ganga acts as the accumulation zone of contaminants coming from the Upper Ganga Basin in northern India. • Entropy information theory has been used for the assessment of the WQI. • The primary contaminant in this region are TDS, F−, Cl−, and NO 3 −. • Spatio-temporal analysis of the hydrometeorological parameter shows the changing pattern due to climate variability. • Results are useful in achieving the United Nations Goal (SDG-6) for sustainable development of groundwater resources by 2030. [ABSTRACT FROM AUTHOR]