BREWER, Maine — City leaders thought that they had completed the last of the federally mandated sewer separation projects back in 2011, but a consulting engineering firm recently discovered that 10 streets — mostly near the Penobscot River — still need work.

“We updated our master plan and we found some additional [storm] water we needed to remove,” Ken Locke, Brewer’s environmental services director, said Friday.

The city and other communities that line the Penobscot River, including sister city

Bangor, received orders in the late 1980s and early 1990s to separate stormwater and sewer lines that years ago would dump sewage into the state’s largest waterway whenever the system flooded.

City councilors hired Olver Associates of Winterport at their last meeting to design and inspect the $1.9 million project, which is being funded through a USDA Rural Development grant valued at $400,000 and a $1.5 million low-interest loan.

“The $1.9 million also includes some electrical projects at the plant and replacing a sewer flushing truck,” Locke said. “The actual sewer separation cost is $805,000.”

The high-priority sewer separation projects are located on Longmeadow Drive, North, South, East and West streets, Kings Court, Davis Court, Elm Street, Church Street and South Main Street. Work will begin this year after Olver designs the projects.

Between April 1989 and April 1991, Brewer Treatment Plant reported 264 discharge violations. The violations, logged with the state’s Department of Environmental Protection, led to Brewer entering into an administrative consent agreement with the U.S. Environmental Protection Agency in 1992 to correct the problems.

The city has since eliminated 99.9 percent of the problem, Locke said.

The first step city officials took was to upgrade the Wastewater Treatment Plant, now called the Water Pollution Control Facility, at a cost of $7 million, and each year since the city has tackled a project or two on the corrective list, mostly involving separating combined stormwater and sewer lines. At the beginning, 75 percent of the city’s 46 miles of collection lines, built between 1900 and 1960, had combined sewer and stormwater lines.

The sewer separation project has cost more than $25 million over the years, with customer rates doubling in the same time period to pick up the local tab. The USDA has provided funding more than once and the city also got federal stimulus funding to help with the separation projects needed to protect the river.

“We’re going to complete these projects, then review the system to see if [additional projects are required],” Locke said.

The city has done such an effective job solving the problem that the EPA in January recognized the city’s cleanup efforts by awarding it the 2015 EPA Regional Wastewater Treatment Plant Excellence Award at a ceremony in Boston.

“We haven’t had a violation in almost 22 years,” Locke said of the plant’s long-term compliance record.

The Brewer Water Pollution Control facility has not reported a violation of its treatment discharge permit since 1994.

“The Brewer facility was nominated by the Maine Department of Environmental Protection to acknowledge the outstanding work that has been performed over the years by Ken Locke, superintendent, and his staff,” Justin Pimpare, EPA regional pretreatment coordinator, said in the letter notifying the city of the award.