Processes affecting groundwater quality in the La Digue aquifer, Seychelles

This paper presents the results obtained by the Public Utilities Corporation (PUC), within the framework of an IAEA TC project, which aims to evaluate the potential of the L a Digue aquifer. Several monitoring activities and hydrochemical and isotopic surveys have been conducted. Results indicate the presence of brackish water at shallow depths, and low redox potentials, attesting to the presence of H2S and heavy metals. Groundwater quality is affected by the concomitant presence of different adverse factors, namely aquifer characteristics, hydrogeology, and anthropogenic pressure. In addition, seawater penetrates the river course during high tides and infiltrates through the recharge area of the aquifer that is close to the actual pumping station. The positioning of non return high tide gates, an easy and low cost intervention, could enhance groundwater quality. The understanding of the main processes affecting groundwater quality helped in the identification of areas favourable for new wells, located at higher elevations.