Abstract
The main objective of this study is to evaluate the wastewater contamination of the water resource in a Mediterranean watershed, the Hérault River basin (South of France). Two surveys of surface and ground waters (wells supplying drinking water) and of wastewater treatment plant (WWTP) effluents were achieved in February and July 2003. The chemistry of WWTP effluents allowed to select some potentials tracers (PT) of wastewater contamination (Gd anomaly, boron, chloride...). However, these PT are ubiquitous in the Hérault watershed waters where they can be supplied by the lithology (in particular by evaporites present in the western area), sea spray (proximity of the Mediterranean Sea) or agriculture (mainly vineyards). Taking into account the different contributions, the presence of wastewater was identified in two tributaries of the Hérault River and in few wells. The seasonnal variability observed between February and July 2003 shows that the wastewater impact is less significant in summer, in spite of a strong decrease of river flow. This can be explained by a particular discharge strategy, which aims to dispose wastewater not directly in the river, but at proximity, in small creeks or ditches. A monthly monitoring was achieved from January 2004 to February 2005 on sites exhibiting clues of wastewater contaminations. We have shown that the groundwaters are vulnerable to wastewater contamination during recharge periods, i.e. period characterised by high precipitations. Moreover, the wastewater contribution was estimated to about 20-40% in two wells. Finally, pharmaceuticals were detected in these sites, confirming wastewater contaminations and reflecting the recycling impact as regards pharmaceuticals contamination.