Monitoring of the infiltration of a planted discharge area by a continuous water quality observation system, a case study in Coutières (79)

Abstract

This article presents a project that seeks to better characterize the relevance of vegetated discharge areas with regard to the treatment capacity of the subsoil of the area. It aims at better understanding the respective shares of the soil and subsoil to purify wastewater and distinguish the contribution to decompose the zero discharge into evaporated, evapotranspirated and infiltrated parts. These objectives are achieved by implementing an innovative metrology, with a particular focus on monitoring the quality of the subsoil through electrical conductivity as a guide to quality of groundwater. The data record highlight the infiltration dynamics of treated wastewater, the role of vertical and horizontal circulation of groundwater in the natural treatment of the environment, and the role of the underlying groundwater depending on its low or high position. The data show the predominance of infiltration (90%), the efficiency of the purification system in the reduction of nitrate and its buffering role in case of heavy precipitation. Permeability and geological nature of the subsoil play an essential role in the dynamics of infiltration. The project site is certainly representative of a majority of cases of shallow clay subsoil.