"This is the first such project in the country. Building a tunnel under the river had never taken place elsewhere in India. Further being built under Ganga, it has an emotional value as well," Mr Supriyo, who went inside the tunnel between slab numbers 820 and 840, said.
He has been asked by Prime Minister Narendra Modi to personally supervise the work, said Mr Supriyo while interacting with the officials of Afcons-Transtonnelstroy of South Africa, the agency to build the tunnel between Howrah Maidan and the proposed Mahakaran metro station near Writers Buildings in Kolkata.
Mr Supriyo also collected soil from the place and kept it in two utensils - one for gifting to the prime minister and another for himself as a memento.
The entire stretch of tunnel from Howrah Maidan to the Ganga bank in the city will be 1.7 km, of which a significant part will be on the surface.
"Basically, we reached almost the bottom of the Ganga and spent a considerable time (there). It was an exhilarating experience. I salute the engineers and the workers for the heroic work," Supriyo, the Union Minister of State for Heavy Industries and Public Enterprises said.
Asked about the safety of the project, he said "Let me allay any apprehension about the safety. We did not feel uncomfortable inside though we were 32 m below the river water - that is the sea level."
He said the tunnel went under buildings like Howrah Station but there were no threat to them as the latest technology had been used.
The tunnel boring machine (TBM), used in the excavation work, will now go beyond the slab number 840 to dig up earth under the river bed and finally reach the east bank - that is the city.
Expressing hope that the Howrah Maidan-Esplanade part of Phase II of the project, which would connect Howrah Maidan to Sealdah) will not miss the deadline, Supriyo said "We expect to clear the logjam in the wake of the existing rule that infrastructure projects would not come up within 100 m of the heritage buildings."
"There are three heritage constructions - two synagogues and the Currency Building within 30 m of the proposed tunnel. But IIT-Kharagpur in a feasibility study said the tunnel work and metro movement would not cause any damage to the structures."
"We are not setting up a time-frame and the Union cabinet is preparing a note to exempt the Metro work. Let's hope for the best," he said.
The entire second phase of the East West Project, with 100 per cent funding by the Centre, had been facilitated by the West Bengal government with intervention by Chief Minister Mamata Banerjee and her cabinet colleagues to clear settlements.
Phase 1 of the East-West Metro Corridor Project, he said, is expected to be completed on time and thanked Banerjee for removing encroachments along the route.
"During my chance meeting with the West Bengal CM in 2015 which the media had christened as 'Jhalmuri diplomacy,' I had broached the topic of encroachment and with the intervention of TMC leaders it was resolved.
"The encroachers will be relocated in a new building in the area," he said.
The overhead track on Phase 1 connecting Salt Lake to Sealdah is more or less complete. There will be eight stations, two of which are on underground. All the four stations in Phase II (Sealdah-Howrah) will be underground.
The initial project cost for the Phase I - Phase II stretch had shot up substantially due to realignment of the tunnelling, covering an additional 2 km and cost for elevation.
The costs had gone up from Rs 250 crore in 2011-12 under the UPA rule to Rs 328.81 crore in 2015-16 and now Rs 1937 crore, the union minister added.