Relation Between Water Level Fluctuation and Variation in Fluoride Concentration in Groundwater—A Case Study from Hard Rock Aquifer of Telangana, India

In this study, groundwater level and fluoride data of fifteen years (from 2003 to 2017) have been used to identify the influence of water level and its fluctuation on the variation of fluoride (F−) concentration in groundwater. For this purpose, five locations have been chosen along the groundwater flow direction and amongst these locations, two locations are situated at or near the recharge area, having F− concentration below 1.5 mg/l (most of the time), two other locations are situated around the discharge area, having F− concentration above 1.5 mg/l (most of the time). At the transitional location between recharge and discharge, F− concentration went above or below 1.5 mg/l in a proportional way. The time series plot of the water level and F− concentration at each location show that the addition of freshwater during monsoon generally dilutes F concentration in groundwater. The positive relation between water level fluctuation and fluctuation in F− concentration also reflects that fluoride release in groundwater is mostly due to water-rock interaction. The average fluctuation in F− concentration increases along the flow line, which reflects more water-rock interaction in the discharge area than in the recharge area. The points in the discharge area showed the highest water level fluctuation, fluctuation in F− concentration and the highest hydraulic conductivity.