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.
The principal scientific objectives of current experiments and monitoring studies are the following:
- To test new methods for characterizing the environment (in boreholes or on surface) that can be used for imaging bedrock in highly heterogeneous environments.
- To develop techniques for monitoring the ground deformations related to variations in water-table levels
- To acquire the data required for testing and validating hydrogeologic modeling methods designed for fractured environments.
- To develop methods for imaging underground flows and measuring flow velocities in highly heterogeneous environments
- To study the environment’s chemical reactivity and especially changes in the chemical quality of the waters as extraction proceeds
- To measure the distribution of residence times and estimate the distribution of travel times.
- To investigate the vulnerability of the aquifer to climatic variations and changes in land use