Use of a time-domain electromagnetic method with geochemical tracers to explore the salinity anomalies in a small coastal aquifer in north-eastern Tunisia [Utilisation d’une méthode électromagnétique dans le domaine temporal et de traceurs géochimiques pour explorer les anomalies de salinité dans un petit aquifère côtier du Nord Est de la Tunisie] [Uso de um método eletromagnético no domínio do tempo com traçadores geoquímicos para explorar as anomalias de salinidade num pequeno aquífero costeiro no nordeste da Tunísia] [Uso de un método electromagnético en el dominio del tiempo con trazadores geoquímicos para explorar las anomalías de salinidad en un pequeño acuífero costero en el noreste de Túnez]

The study area is a small coastal plain in north-eastern Tunisia. It is drained by an ephemeral stream network and is subject to several pollutant discharges such as oilfield brine coming from a neighboring oil company and wastewater from Somâa city, located in the upstream of the plain. Furthermore, a hydraulic head near the coastal part of the aquifer is below sea level, suggesting that seawater intrusion may occur. A time-domain electromagnetic (TDEM) survey, based on 28 soundings, was conducted in Wadi Al Ayn and Daroufa plains to delineate the saline groundwater. Based on longitudinal and transversal resistivity two-dimensional pseudosections calibrated with boring data, the extent of saline water was identified. Geochemical tracers were combined with the resistivity dataset to differentiate the origin of groundwater salinization. In the upstream part of the plain, the infiltration of oilfield brine through the sandy bed of Wadi Al Ayn seems to have a considerable effect on groundwater salinization. However, in the coastal part of the aquifer, groundwater salinization is due to seawater intrusion and the saltwater is reaching an inland extent around 1.3 km from the shoreline. The contribution ratios of saline water bodies derived from the inverted chloride data vary for the oilfield brine from 1 to 13 % and for the seawater from 2 to 21 %. © 2014, Springer-Verlag Berlin Heidelberg.