Trains were up and running on the TTC's Line 1 Wednesday but the agency is still trying to figure out how a construction crew managed to punch a hole in the tunnel.
The incident shut down service on Line 1 between St. Clair and Lawrence for four hours during Tuesday's afternoon rush.
"Our crews had to go in overnight, put a plate on the inside of the wall and then fill it with concrete," TTC spokesperson Stuart Green told Moore in the Morning.
He says the agency is investigating and, "there are remedies available in terms or recovering some costs for any work that we had to do."
He says the contractor had the correct permits. The agency will be looking into where they were drilling and whether they were in the correct location.