Manager of the Ploemeur site : Laurent Longuevergne

The Ploemeur site (Morbihan) is located on an aquifer in fractured crystalline bedrock; since 1991 it has supplied one million m3 of drinking water annually to a town of 20,000 inhabitants. The chemical quality of the water extracted is very good: in particular it has a low content of nitrates in a region that has been strongly affected by widespread pollution. Although the local rocks consist of granites and mica schists, rocks traditionally considered to be impermeable, very rapid flows are observed, confined to a small number of fracture zones. The main problems concern the aquifer’s vulnerability to transfers of anthropogenic pollutants; the potential risk of salinization in this coastal aquifer; and the identification of recharge areas, together with the establishment of a zone of protection. The site has a very dense piezometric coverage, with some fifty boreholes from 30 to 150 m deep. This network allows for long-term monitoring - hydrological, hydrochemical, and geophysical - and the possibility of innovative experiments on the hydrologic parameters of heterogeneous environments. In collaboration with the municipal “Water and Sewage” utility for the Town of Ploemeur, the site is monitored by a team from OSUR and UMR Géosciences Rennes to:

  • Study the environment’s chemical reactivity, and especially the changes in the chemical quality of the waters as extraction proceeds
  • Investigate the vulnerability of the aquifer to climatic variations and to changes in land use
  • Develop methods for imaging underground flows and measuring flow velocities in highly heterogeneous environments
  • Test new methods for characterizing the environment (in boreholes or on surface)
  • Develop techniques for monitoring the ground deformations related to variations in water-table levels
  • Measure the distribution of residence times and estimate the distribution of travel times
  • Acquire the data necessary for testing and validating hydrogeologic modeling methods designed for fractured environments.