By Shishir Prashant 
PrashantNews
Tunnelling work at NTPC’s controversial 520-MW Tapovan-Vishnugad hydel project in Chamoli district of Uttarakhand was suspended following water seepage from a cavity inside the main tunnel, officials said on Monday.
All workers in the affected area were immediately evacuated as a precautionary measure and excavation work was stopped following the incident on August 15.
“Work in the concerned area was stopped immediately and all workers were evacuated as a safety precaution,” an official said. A specialised team of workers and technical experts is currently carrying out treatment and stabilisation work. Tunnelling will resume only after the cavity has been safely treated and the area is declared suitable for further excavation.
The latest incident has once again highlighted the complex geological conditions encountered during construction of major hydropower projects in the Himalayan region.
The Tapovan-Vishnugad project, located near the land-subsidence affected Joshimath, has a particularly troubled construction history. In February 2021, the devastating flash flood in the Rishiganga valley caused extensive destruction to the project and claimed around 200 lives. The disaster severely damaged infrastructure associated with the project.
Construction has also faced geological and engineering challenges in the past, including water ingress inside tunnels. A tunnel boring machine (TBM) worth several crores of rupees remained trapped for a prolonged period after water entered the main tunnel leading towards the powerhouse near Salang village.
The latest cavity and water seepage have renewed concerns on the geological risks involved in tunnelling through the young and fragile Himalayan mountain system.
However, NTPC has sought to allay safety concerns, maintaining that the affected section is being treated strictly in accordance with prescribed safety standards. The corporation said the necessary technical measures are being undertaken and tunnelling will resume only after the area has been adequately stabilised. In the past, NTPC has also made it clear that the Topovan Vishnugad project was not responsible for the land subsidence in Joshimath area.