Hydrogeology, the science of groundwater: what is it used for?
To control the quality and monitor the behaviour of groundwater around its facilities in the Aube (Aube disposal facility, CSA; Industrial facility for grouping, storage and disposal, Cires), Andra relies on the expertise of hydrogeologists. The aim is to understand the geological environment in order to assess the radiological impact of the facilities and detect any potential abnormalities.
UNDERSTANDING THE GEOLOGICAL ENVIRONMENT...
The Aube facilities were designed to contain the radioactivity inside the waste packages as much as possible and delay its transfer into the environment for as long as possible. The geological ‘layer cake’ that makes up the subsoil constitutes a natural barrier to this transfer.
This schematic cross-section has been simplified to illustrate the hydrogeological environment of Andra’s Aube disposal facilities. It is in no way intended to provide a precise interpretation of local geology.
Expertise in hydrogeology
Types of subsoil, position and behaviour of water tables, groundwater circulation and outlets: the sites where the disposal facilities are located have been and continue to be studied in minute detail by hydrogeologists. They are tasking with identifying the different types of geological layers and the interactions between them in order to determine the most suitable sites and ensure that monitoring is appropriate, proportioned and effective.
...AND HOW WATER CIRCULATES ON THE SURFACE AND UNDERGROUND
When rain falls, rainwater evaporates, runs off or infiltrates the ground before joining a waterway. Its run-off depends on the drainage divide, which is different at the surface and underground. This is why it is so important to understand and monitor the behaviour of groundwater.
This schematic cross-section has been simplified to illustrate the hydrogeological environment of Andra’s Aube disposal facilities. It is in no way intended to provide a precise interpretation of local geology.
TO MONITOR WASTE DISPOSAL FACILITIES EFFECTIVELY
The monitoring system implemented by Andra at its Aube facilities aims in particular to monitor both the quality and behaviour of water below the ground (flow direction, levels, etc.) thanks to piezometers.
140 piezometers are used to monitor the behaviour of the Aptian water table (recharge, levels and flow directions).
23 piezometers are used to take groundwater samples to control the radiological quality (every month) and physico-chemical quality (every 6 months) of the water.
Samples are also taken in the Upper Barremian sandstone, below the clay layer (Lower Aptian), although less frequently, given the time that it takes groundwater to flow through these layers.
What is a Piezometer?
It is a borehole used to measure the groundwater level at a given point in the water table and to take samples.