Stores in the Swansea Schnucks Plaza reopened Thursday after being shut down the day before by a methane leak.
Several stores in the plaza off Illinois 159 were closed as a precaution Wednesday afternoon after a drill punctured an abandoned mine shaft and released methane gas.
The Schnucks anchor store, which is open 24 hours, is operating as usual. A manager said Thursday morning that the closures were limited to stores at the south end of the plaza and the supermarket never closed because of the leak.
The contractor on the job was working on phase two of a plan to stabilize shifting mine shafts beneath the entire shopping center, explained Swansea Fire Chief John McGuire. The plan involves drilling into the mines and pumping them full of a "grout" to prevent the ground from shifting.
"The drill broke through the roof of a mine about 140 feet down and it was full of methane, so, we've got a pretty good methane leak out here," McGuire said.
Eleven stores near the construction area were evacuated while the contractor installed a pipe to vent the odorless, colorless, dangerous gas above the building and away from people. The gas can cause asphyxiation if inhaled.
"We're fortunate it's outside," McGuire added. "It's lighter than air and it's dissipating. The breeze is helping that, too."
Above ground level and out of the breathing zone, the gas presents no hazard to people. No gas was detected in any of the stores, only in the parking lot area, McGuire said. The only way to detect pockets of methane is with specialized instruments. The Fire Department called Ameren to help locate the gas.
"The Ameren people have been very helpful," McGuire said. "It's not a broken gas line, but they know gas and they have ways they can detect it."
The entire area where the plaza was built is riddled with abandoned mines and work has been done over the years to stabilize the ground and stabilize the buildings affected by the collapse of mines.
No injuries were reported.