Environment & heritage

The Tagus estuary is one of Europe’s most important wetlands for waterbirds. It has had a Natural Reserve since 1,97615, is a Ramsar site of 14,563 ha16 and a Natura 2000 Special Protection Area17.

The crossing lies downstream of the reserve, but in the same estuary. That is why we chose to bore beneath the bed rather than dredge a trench: no works on the water, no stirred-up sediment, no barriers to fish movement.

• No dredging and no structures on the water; works are limited to the two station boxes on land.
• Monitoring of turbidity, underwater noise and riverbed vibration while the TBMs pass.
• Bentonite slurry in a closed loop with a separation plant at Cacilhas; contingency plan for slurry escaping to the riverbed (frac-out).
• Electric operation, with an estimated shift of ≈ 20–30% Estimate of car trips in the Cacilhas–Lisbon corridor.

Digging two tunnels and two stations produces about 400,000 m³ Estimate of material. Instead of crossing Lisbon by truck, it leaves by barge from the Margueira worksite next to Cacilhas, avoiding about 40,000 truck trips Estimate.

Destination: chemical testing of every batch; reuse of clean sands and soils in licensed fills and port works; controlled disposal of the rest. Most tunnel spoil is estuary sediment, which may carry contamination from decades of industrial and port activity; no batch leaves untested.

Most of the work is underground. Noise is concentrated at the station worksites, with limited hours and acoustic barriers. When the TBMs pass beneath buildings at Cais do Sodré, vibration is monitored in real time. In service, the track sits on resilient supports so trains are not felt at the surface.

• Construction noise per the Portuguese General Noise Regulation; night-work permits limited to rail interfaces.
• Vibration: limits by building type per NP 2074, tighter for listed heritage.
• Floating slab track under buildings (ch 0+000 to 0+250).

Lisbon’s waterfront grew over the river through successive landfills since the 16th century. Beneath Cais do Sodré square there may be old quays, port structures and remains of vessels. Station excavation will be watched by archaeologists from day one, and the programme sets time aside for it.

• Geophysical survey and archaeological trial pits in 2033–2034, before the diaphragm walls.
• Protocol with the heritage authority for recording, removal and possible display of finds in the station concourse.
• Cacilhas: waterfront with industrial and naval heritage, to be integrated into the square’s design.

Before any works, the project goes through an Environmental Impact Assessment with public consultation, planned for 2029–2031. That is where residents, passengers, associations and councils can comment and propose changes.

1. Scoping and alternatives (including immersed tube and enhanced ferry service).
2. Environmental Impact Study with a full year of fieldwork (bird and tidal cycles).
3. Public consultation under the Portuguese EIA legal regime.
4. Environmental Impact Statement and post-assessment during construction.