Effect of artificial recharge by treated wastewater on the quality and quantity of the Korba-Mida coastal aquifer (Cap Bon, Tunisia)
Résumé
The Korba-Mida aquifer on the eastern coast of Cap- Bon (Tunisia) has underwent overexploitation since the 60's (270 wells) to 2011 (9500 wells), leading to reversal of hydraulic gradient and saline intrusion. Water quality of groundwater is often degraded by different processes : salt water intrusion, diffuse pollution. The coastal aquifer of the Plio-Quaternary is one of the first studied examples of groundwater depletion, seawater and salinization. Since the sixties, large quantities of water have been collected by the agricultural and the industrial sectors resulting in a spatiotemporal evolution of piezometric depletion and degradation of groundwater quality due to sea water intrusion. Artificial recharge of groundwater has been introduced as an alternative method to cope with the scarcity of water resources and with an accentuated variability of climate in space and time. Crucial for local agriculture, aquifer management led to the implementation of artificial recharge with treated wastewaters at the end of 2008. At vicinity of the recharge site, groundwater quality was monitored to trace the progression of artificial recharge in groundwater. Before recharge, the salinity of groundwater in wells and piezometers varied from 1 to 12 g/l. All the piezometric levels are below the sea level, over the entire study area and varies between zero from the Korba wastewater treatment plant to -7m at the left site of the Ennajar Wadi. After three years of recharge (1 Million m(3)) of wastewater treated in the three basins, there has been an increase in processes of salinity 1 g/l. The piezometric surface appears with positive values (1 to 2 m) near the recharge site. Boron isotopes which are a good tracer of groundwater salinization and domestic sewage were analyzed to determine the different system components. Also recognized as a pertinent tracer for wastewater contamination, carbamazepine, which is an anti-epileptic known to pass through the wastewaters treatments, was also measured. Samples were taken from recharge control piezometers and in surrounding farmers' wells.