ASSESSMENT OF IONIC STRENGTH AND VARIATION IN GROUNDWATER LEVEL FLUCTUATIONS IN WEST BENGAL

Abstract

The present study is aimed at understanding variations in the hydrogeochemical parameters by assessment of ionic strength and also to decipher fluctuations in groundwater levels in West Bengal, India, based on data obtained from Central Groundwater Board (CGWB). The physicochemical analysis of groundwater samples showed major anions in the order of Carbonate, Bicarbonate, Chloride, and Nitrate, and the major cations are Calcium, Magnesium, Sodium, and Potassium. The ionic strength of the water varies from 0.07×10-3-2.35×10-3 mol/l. From the ionic concentration of the samples that CGWB collected and analysed, the ionic strength of each sample was calculated. The results showed that chloride concentration is 63.012 mg/l(ionic strength 1.781 mol/l) which is more than its general range(less than 10mg/l), which should be present in natural waters, although it is not harmful to public health. Excessive concentration of Chloride ions indicate that the groundwater of West Bengal may have a saline/marine origin and is also caused by anthropogenic reasons. As for water table fluctuations are concerned, the cartograms showed that for the last ten years, the mean lowest depth was 10m, and the highest mean depth variation was below 0m from the surface. However, in recent times in 2021-22, the lowest depth was ~35m, and the lowest depth was between 0 5m below the surface for 2021-22, indicating a rapid decrease in groundwater levels, due to excessive use and less recharge of aquifers.