Examination of chemical and isotopic data of underground waters of the Naizin watershed

This report proposes the interpretation of data acquired since the beginning of a project concerning the aquifer of the Coet Dan watershed (Morbihan district) where denitrification processes have been highlighted to partly explain the decrease of NO₂ contents with depth. After a recall of the basin hydrogeology, the report comments and discusses tritium contents and a model of water circulation, the denitrification process by oxidation of pyrite and isotopes of dissolved sulfates, and the precipitation of secondary minerals related to pollution.