Following a first decontamination phase of the Stade de France (SDF) site, hydrocarbon compounds were found at a depth greater than 5 m (area not treated). Antea Group (project manager) and Ménard (soil treatment) came into play with the aim to eliminate two risks presented by the presence of hydrocarbons in the subsurface: the emanation of odors (panic) and the risk of subsurface explosions.
Due to the late discovery of this deeper pollution, this second remediation phase had to be carried out in a very short time-frame and presented access difficulties due to the fact that construction works had begun.
The pollution diagnosis included:
- a historical review,
- the setting up of water monitoring wells,
- gas and water analyses,
- test pumping of groundwater and gas for modeling.
The groundwater was pumped and decontaminated by a treatment plant constructed by Antea Group on the site.
The pressure level of the subsurface of the SDF was set below the atmospheric pressure level under a geosynthetic membrane. An underground network of collection ducts was installed in order for the soil gases to be drained, pumped by five venting systems and incinerated before their release into the atmosphere.
Atmospheric gases sampling and analyses nearby the SDF, above the lawn and particularly in the stands and locker rooms underground structures, confirmed that gases in the soil were no longer present in the environment.
Although the objective of the operation was to maintain gases in the subsurface, the treatment of groundwater and the pumping of soil gases worked towards the quasi elimination of all hydrocarbon compounds in the subsurface.
Currently, soil gases are pumped during stadium events as a safety measure.