Chennai Metro Rail Limited suspends tunneling near Kutchery Road due to gas leak

The tunneling work between Light House and Thirumayilai is being carried out as part of corridor 4 of the Rs 63,246 crore Phase II Project between Light House and Poonamallee. Photo: File | Photo Credit: M. SRINATH

Chennai Metro Rail Limited (CMRL) stopped tunnel work near Kutchery Road last week due to gas leak. He had operated two tunnel boring machines (TBMs) from Light House to construct twin tunnels via Kutchery Road to Thirumayilai. After reaching Kutchery Road, these machines will proceed towards Thirumayilai without making any headway at Kutchery Road station.

Sources said that about a week ago, during tunneling works, personnel on the site detected a gas leak and the machines were stopped immediately. “Gas detectors in the tunnel found small amounts of methane and carbon monoxide. Levels were measured at 10 ppm (parts per million) which is not too worrying. But we are pumping clean air into the tunnel and are still looking for the source of the leak to plug it. A source said workers were safe and work was done.” He said they had not reported any discomfort since the immediate stop.

According to CMRL officials, the machine entered Kutchery Road, passing the church in Santhome. “We think it may come from the soil. The work is being carried out at a depth of about 18 m. This is a minor problem as the levels of gases are low, but we are still investigating. If necessary, we will appoint an environmental expert,” said an official.

The tunneling work between Light House and Thirumayilai is being carried out as part of corridor 4 of the Rs 63,246 crore Phase II Project between Light House and Poonamallee.

Possible sources

Methane can be formed in anaerobic conditions where there is little or no oxygen, said an official of the Tamil Nadu Pollution Control Board. If organic matter had been present in the area long ago, soil bacteria could have broken it down, leading to the release of methane. But he wasn’t sure about the presence of carbon monoxide because it contains oxygen and doesn’t form in the same way as methane in such areas.

An environmental expert, who did not want to be named, said methane is a flammable gas and carbon monoxide is poisonous. “The methane may be coming from old waste or landfills in the area. Carbon monoxide is not generally found in soil, which suggests some type of gas-related activity may have occurred there historically,” he said. The expert added that once the gas is identified, it must be removed and the area must be ventilated to clear the gases.

(Contributed by Geetha Srimathi)