With approval all but certain, Randy Leonard’s proposal to fluoridate drinking water will head to the Portland City Council for a public hearing Sept. 6 and a vote Sept. 12.

Already, Mayor Sam Adams has joined Commissioners Leonard and Nick Fish in announcing support. Leonard’s controversial proposal has prompted mounting opposition, however, with an electronic petition flooding inboxes at City Hall.

Leonard said Monday that he has received about 1,300 emails, a majority against his plan. But Leonard said he is comfortable acting on a public health issue without a public vote. Historically, Portlanders have voted against fluoridation three times.

“This is our decision to make and we shouldn’t duck it,” he said of the City Council.

The Sept. 6 hearing will be at 2 p.m., Leonard said, with a vote Sept. 12. The ordinance would take effect 30 days later.

Although fluoride opponents haven’t announced plans, options could include a referendum of the council vote or an initiative effort. They’ve scheduled a press conference for noon on Wednesday in front of Portland City Hall.

A referendum would require gathering 19,868 valid signatures from city voters within 30 days of council action.

An initiative effort, however, would give opponents about two years to collect signatures but would require about 10,000 more signatures.

Building a fluoride facility would cost an estimated $5 million and take five years, although it could potentially be built in three years, according to the Portland Water Bureau.