A divided South Portland City Council last week denied a power plant’s request to add two 20,000-gallon oil tanks near the Knightville waterfront so the plant could provide more electricity in the case of a widespread blackout.

The vote was 4-3 against granting FPL Energy Cape a waiver from a city tank ordinance, and the council will be asked Tuesday to approve a formal statement on the reasons for its denial so the company can appeal the decision if they choose.

A 1995 city ordinance does not allow the addition of above-ground oil tanks in South Portland that would, either individually or together, store more than 25,000 gallons of fuel. The City Council, however, can waive that restriction for “special circumstances” and if the extra oil storage is “in the interest of public health, safety and general welfare.”

The Energy Cape facility at 2 Ocean St. has two 12,000-gallon oil tanks. The company said it needs to add 40,000 more gallons to its capacity to meet Independent System Operator New England’s standards of being a “black-start resource.”

“Black-start resources are critical to the resilience of the power grid because they can generate electricity that can be used to reenergize the grid after a blackout event,” said Sarah King, project manager at Woodard and Curran speaking on behalf of Energy Cape at the Feb. 6 council meeting.

A blackout event is different from a power outage. It is “when the power grid goes partially or completely dark,” she said.

To meet ISO New England’s regulations, Energy Cape needs to have enough oil to supply the grid independently for at least 12 hours. With its current 24,000 gallons, King said, the facility can only do so for about five hours.

Councilors and residents at the meeting opposed to the waiver said they were concerned about the location of the proposed new tanks near the waterfront because of rising sea levels and climate change.

Despite being on the coast, the proposed new tanks would not be built in a FEMA flood zone, Energy Cape representatives said. The facility was not flooded or impacted by last month’s storms and record-breaking high tides, they said, and is also designated by the Maine DEP as an “insignificant” producer of carbon emissions.

Councilors Linda Cohen, Richard Matthews and Steven Riley were in favor of granting a waiver.

Riley and Matthews said the tank project would be subject to Planning Board review to ensure it would meet the city’s environmental standards.

Cohen said allowing Energy Cape to provide the blackout service serves the interest of public health, safety and general welfare and meets the requirements for a waiver.

“To sit here tonight and to say ‘I don’t think there will ever be a complete blackout,’ with the way the world is? I can’t say that,” Cohen said. “I’m not thinking I can deny the waiver request, and I do believe the Planning Board is going to look at all the various issues.”

Multiple councilors noted that blackouts occurred in New England and along the Atlantic coast in the 1960s and in 2003.

Councilors asked if there were other black-start facilities in the region, but Energy Cape’s representatives said they didn’t have that information because ISO New England’s list is confidential due to safety concerns, such as an attack on the power grid.

In her argument for denying the waiver, Councilor Natalie West referred to the 1995 ordinance and efforts to limit the number of oil tanks in the city.

“I’ve thought about my children and my grandchildren and the world I’m leaving to them,” West said. “I’m not going to vote for expanding the use of hydrocarbons in our society.”

Other councilors who voted to deny the waiver argued that ISO New England hasn’t said it needs the Energy Cape facility to be a black-start site. If ISO New England requires more black-start facilities, they can likely find them elsewhere, they said.

They encouraged the company to explore other ways to meet the 12-hour criteria, such as environmentally friendly energy sources or finding a different property, farther from the coast, to install oil tanks.

The Energy Cape facility on Ocean Street was built in the 1920s, King said. By the 1980s it had two 1.23 million-gallon tanks. One of those tanks was removed in 1985 and the other in 2007, when the two 12,000-gallon tanks were installed.