Columbia police, fire and EMS responded shortly after 7 p.m. Tuesday to a natural gas leak at a construction site in the 700 block of South Main Street.

Main Street was closed in both directions for nearly nine hours as firefighters, police, EMS and Ameren worked to repair the leak and monitor the area.

Workers using a backhoe during construction of a new office building accidentally cut a 2-inch gas line that was incorrectly marked, according to information provided by Columbia Fire Department Assistant Chief Jim Broshears.

“The markings on the concrete and grass (for the gas line) were not where it actually was,” Broshears said.

Residents of Reflections at Garden Place, a senior care facility located near the source of the leak, were evacuated after firefighters discovered elevated levels of gas in the building as well as an unrelated gas leak from a stove, per Ameren’s recommendation. They were able to return by about 1 a.m.

The residents were transported on two small Columbia School District buses to another nearby Garden Place facility, on DD Road in the Columbia bottoms. Two residents of Reflections were transported to area hospitals for treatment of symptoms consistent with exposure to high levels of gas.

Dupo EMS provided assistance to Columbia EMS in monitoring Reflections residents as they were evacuated and checking their conditions as they arrived at their temporary lodgings.

Nearby businesses and residential neighborhoods were monitored throughout the incident but none were found to have unsafe levels of gas.

Main Street was reopened at about 4 a.m., Wednesday.