Six months after giving it a national award, the U.S. Environmental Protection Agency has sued the Brewer wastewater treatment plant.

The agency contends the plant does not have a proper oil spill response plan in place and it has threatened to fine the facility up to $27,500.

Brewer officials said they were “blindsided” by the lawsuit notice, which came last week.

“We thought everything was OK until they sent us a letter saying they were suing us,” said Kenneth Locke, director of environment and public works for the city.

Last September the EPA awarded Brewer second place in a national wastewater excellence program. The award was physically presented to local officials last month.

“One hand doesn’t know what the other is doing,” Locke said.

A spokesman for the EPA in Boston said the court filing does not mean the Brewer plant is not well run.

“We’re not saying this is not a conscientious, well-run plant, but their plan was outdated,” said Andrew Spejewski.

The Brewer plant was one of nine in New England that was sued. It was the only one in Maine.

Spejewski said his agency was looking at other plants and may file complaints against them as well. The first nine plants were targeted because they are located on major waterways and therefore posed higher risks than others. The Brewer plant is on the Penobscot River.

Despite filing the complaints against the facilities, the EPA acknowledged that all of them had come into compliance with federal oil spill control regulations or would do so by the end of the month.

According to Locke, the EPA changed its rules in 1994 and required that new oil spill plans be drawn up for municipal wastewater treatment plants. He said the agency did not inform facilities of the changes.

The Brewer facility was inspected by EPA officials 11/2 years ago and that is when local officials were told their oil spill plan was out of date. The plan was updated and sent off to the EPA. Brewer heard nothing until being notified of the lawsuit last week, Locke said. He said the plan met all the criteria that the EPA had asked for.

The plant, which treats 5.2 million gallons of water a day, must have an oil spill plan in place because there are above-ground tanks storing heating oil and oil for the plant equipment on site.

There has never been a spill at the facility, Locke said.

He speculated that the whole situation was merely a way for the EPA to raise money. Spejewski, however, said the agency doesn’t keep fine money. It goes into the general federal treasury.

The intent of the lawsuits is not to raise money, but to ensure that waterways such as the Penobscot are protected, Spejewski said.

To rectify the situation, Brewer intends to sign a consent decree with the EPA and pay a $2,000 fine, City Manager Stephen Bost said. The city already has complied with the terms of the agreement, which include having a spill plan in place, but paying the small fine seems to be the best way to settle the matter, he said.

“We thought we were in full compliance,” Bost said. “We’re extremely proud of the facility.”

The award from the EPA hangs on a wall at the treatment plant. Bost said he doesn’t expect to hang up the notice of the lawsuit next to it.

But, he said ruefully: “There is a touch of irony there.”