BETHEL — The Board of Selectmen will hold a special meeting Wednesday to deal with a sewer line draining from the Bethel Post Office into the sewer system and eventually into a brook.

The special meeting starts at 5:30 p.m. in the Town Office meeting room.

Town Manager Christine Landes said Monday the mistaken hookup was discovered last week when wastewater treatment plant employees inspected the basement during a sewer customer inventory. They suspected something wasn’t right with the internal piping, she said. The employees put dye into the toilet water of the building’s two bathrooms and discovered it was coming out in Sanding Brook, which empties into the Androscoggin River.

Landes said the brook flows largely underground to the river.

She said the Maine Department of Environmental Protection was notified and a staff member from the Division of Water Quality Management is working with the town on the problem. Landes said DEP officials want the problem fixed within a couple of weeks.

She said the overall impact of the sewage flow is likely relatively minimal, because the bathrooms are not public and there are only a few employees. And unlike a house, there are no large discharges of water, such as for showers or washing machines.

Fixing the problem will involve digging up the ground under a sidewalk that runs alongside the Post Office, next to a parking lot. The storm drain runs under High Street behind the building, Landes said.

Code Enforcement Officer Toby Walker wrote building owner Carl Glidden a letter dated Jan. 26 noting the problem, but also stating that the communication was not a letter of violation but rather one of finding “and a means to open the lines of communication between the town and you regarding this matter.”

As for responsibility for the error and the fix, Landes said the mistake was likely made when an addition to Post Office was built about 20 years ago. She said it is unclear which private contractor did the work, but the town would have inspected and approved it.

She said technically the property owner is financially responsible for fixing the problem but selectmen, who are the trustees for the wastewater department, could discuss whether the town might also participate.