Challenge: To improve the hydrogeological knowledge of the area near the oldest French disposal facility built for low- and intermediate-level radioactive waste through the drilling of new boreholes. Historical tritium contamination prevented water from being extracted during field site characterization activities.
Solution: The field investigations included detailed hydrogeological descriptions of the drill cores followed by hydraulic characterization of the aquifer of primary interest. In collaboration with another consultant André Voutta Grundwasserhydraulik, INTERA characterized the hydraulic properties using air pressure sinusoidal testing, a testing methodology that has distinct advantages over conventional testing methods. Because it does not involve net water extraction, this type of testing is advantageous in cases where the potential for contaminant migration exists and can result in high water treatment costs. In addition, sinusoidal hydraulic testing generates signals that can be unambiguously differentiated from background noise. An uncertainty analysis of hydraulic parameter estimates was provided based on analysis of single well and cross-borehole tests.
Results: The installation of four new piezometers with hydrogeological monitoring and sinusoidal testing has improved the hydrogeological knowledge of the northern sector of the CSM site, highlighting the importance of a fracture network. The sinusoidal testing and test interpretations revealed a degree of heterogeneity in the fracture network, characterized by transmissivities varying over two orders of magnitude (ranging between 1.3E-4 and 9.9E-3 m²/s).
