Groundwater dynamics of a saline impacted coastal aquifer of western Maharashtra,India: insights from a radiotracer study

This paper presents application of a radiotracer technique in coastal groundwater for assessing the aquifer dynamics, which is very crucial for understanding flow conditions of an aquifer and its vulnerability to salinity and other contamination. Groundwater dynamics in shallow and deep zones of Palghar Taluk located in west coast of Thane district were studied using point dilution method. ⁸²Br in the form of NH₄Br solution was used as the radiotracer and loggings were carried out by NaI (Tl) scintillation detector. From the analysis of the radiotracer activity loggings, it is found that shallow groundwater is relatively dynamic as compared to deeper groundwater at the two studied sites. The groundwater velocity is about 40–50 cm/day in the shallow zone while it is in the range of 4–40 cm/day in the deep zone. High salinity in deeper parts could be due to seawater intrusion through fractured basalt, which is diluted/flushed in the shallow zone by rain and river water. These findings are helpful in assessing groundwater dynamics in shallow and deep zones of this region and also on the impact of pumping activity on groundwater dynamics.