Fresh-saline water interface response to pumping saline groundwater for desalination; evidence from desalination plant in Almeria (Spain)

Over the past few decades, the global water shortage has increased significantly due to population growth and climate change, especially in arid and semi-arid regions. The region of southern Spain is also experiencing a water crisis due to over exploited aquifers as a result of growing agricultural demand and tourism. In order to cope with the water problem in this region, a desalination plant has been operating for the last twelve years next to the city of Almeria (SE Spain). The desalination plant feeds from saline groundwater beneath the fresh-saline water interface (FSI) of the Andarax coastal aquifer. Despite the water shortage solution that the desalination plant provides, the local impact of the intensive pumping of the saline groundwater on the aquifer was unknown. Therefore, electrical conductivity profiles were conducted in three observation wells during the pumping period in order to monitor the FSI. The long term monitoring shows that the FSI was deepened in the three observation wells as pumping continued. In addition, a 3D numerical model of the Andarax aquifer was established and calibrated with the field data in order to resolve different hydrological scenarios that could explain the observations and predict further behavior (e.g. pumping continue/stop). Moreover, the model shows that the aquifer experienced freshening and the salinity content in the aquifer was reduced by ~15% in the vicinity of the pumping wells, rehabilitating the aquifer. In addition, short term monitoring of the interface in the observation wells were conducted when the pumps stop working for three days and aquifer salinization (recovery) was recorded consequently. This study presents the complex dynamics of the FSI due to pumping saline groundwater for desalination in a real scenario at different time scales and predictions for different real potential scenarios.