Will the tunnel have an impact on the environment? Could the tunnel impact the springs of the town hall park?

The tunnel section of the T7 tram is about 900 metres long; It includes a covered part (tunnel and cut-and-cover) of 510 metres and a 240-metre part of access hoppers.

The tunnel will run deep enough under the City Hall Park to have no impact on the built heritage. Plant compensation will be implemented with at least one tree replanted for one tree removed during the tunnel creation phase.

The first surveys were carried out in 2010, then completed in 2014, and 2018 to 2020, in order to know the constitution of the subsoil at the level of the City Hall park. These surveys confirmed the feasibility of the tunnel and defined the construction methods adapted to the environment. In addition, the resulting surveys and tunnel design studies have made it possible to protect the area's aquifers and springs, which will therefore be very little impacted by this underground structure.

Hydrogeological studies (i.e. groundwater in relation to soil types) were carried out in order to adapt the design and methodologies of the works to the characteristics of the soils and the aquifers and springs.