The systems are binary karsts developed in the chalk under the cover of surface formations. The intensity of karstification varies spatially within the Paris Basin.
These sites may correspond to natural karst springs (Norville, Radicatel), to borehole captures (Norville, Yport), or to the unsaturated zone of the chalk: the boundary of the saturated/unsaturated zone (the Saint Martin le Nud underground quarry) or the recharge zone with flow to the perched aquifer in cover formations (Bouville). These sites together thus make it possible to characterize almost completely the various hydrologic processes at work in the karstified chalk aquifer of the Paris Basin.
The Radicatel and Yport sites provide almost all of the potable water to the agglomeration of Le Havre (CODAH), which ensures the maintenance and monitoring of the sites. An agreement has been set up between the M2C laboratory and CODAH. The study of other sites is done with the support of the Normandy region and Ile de France region and the federations FR CNRS 3730 SCALE and IPSL, among others. Chalk karst observation activities also benefit from the support of the piezometric network in regions maintained by BRGM.