PORTLAND — As it prepares to break ground on a pair of massive underground conduits designed to reduce sewage overflow into Back Cove, the city is negotiating with the U.S. Environmental Protection Agency over fines for past overflows.

The city and EPA are trying to reach agreement on penalties for illegal discharges of sewer and storm water between 2007 and 2009, City Manager Mark Rees said last week in a prepared statement.

A settlement is expected next month. Fines could total more than $170,000, according to City Hall spokeswoman Nicole Clegg.

The violations of the federal Clean Water Act occurred when untreated sewage from the city’s sanitary sewer system overflowed into waterways as a result of mechanical failures, blockages and collapses in the sewer lines, according to Rees.

“These overflows pose significant environmental as well as expensive challenges for the city,” he said.

Many of Portland’s sewer lines were built of brick around the time of the Civil War, and most pumping stations date back to the early 1960s. When machinery fails or a line is clogged or collapses, raw sewage can back up into other parts of the system and eventually into Casco Bay, Back Cove, the Fore River and other bodies of water.

The Sept. 9 collapse of a line under Clark Street was a recent example of such overflows.

While the current negotiations concern overflows from the sanitary sewer system, which carries raw sewage, the city also is working to respond to other requirements of the Clean Water Act and of a consent agreement with the state Department of Environmental Protection. They include provisions for handling storm water as well mixes of sewage and storm water.

The end goal is to create a comprehensive strategy for dealing with all forms of waste water.

“An integrated approach would allow the city to develop a long-range plan with agreed-upon priorities addressing the various aspects of sewer and storm water that is both manageable operationally and financially for the city’s rate payers,” Rees said.

The city has been working for two decades to address sewage overflows. A recent example is the two, 1-million-gallon conduits that the Department of Public Services will soon begin constructing under Baxter Boulevard and Payson Park.

The conduits will store a combination of storm water and sewage and prevent it from being discharged into Back Cove.

Construction was to begin this month, but because of permitting delays is now expected to start in January, Clegg said Tuesday. During construction, the boulevard will be closed between Vannah and Bates streets for up to eight months. The boulevard’s pedestrian trail will remain open.

In 2014, the city will begin a $170 million, 15-year program to better separate storm water and sewage. The initiative is expected to reduce overflow volumes to 87 million gallons annually, down from a 2010 level of 420 million gallons.

William Hall can be reached at 781-3661 ext. 106 or whall@theforecaster.net. Follow him on Twitter: @hallwilliam4.