Millions of gallons of raw sewage have been illegally bypassing the treatment plant in Elizabeth Township and flowing into the lower Youghiogheny River for more than a year.

The sewage overflows continued yesterday and have occurred every day since Nov. 25. During those seven weeks, more than 95 million gallons have flowed into the river, including one day, Dec. 16, that the overflow was measured at 6.3 million gallons.

Despite the continuing, significant overflows -- each a violation of the federal Clean Water Act -- township officials and state and county regulators have so far been unable to determine why they are happening or how to stop them.

"We're looking to find the source of this problem. Obviously it's unacceptable, both in the frequency and magnitude of the bypasses," said Guillermo Cole, a spokesman for the Allegheny County Health Department. The health department has regulatory authority over the treatment plant.

The Elizabeth Township Sanitary Authority, which owns the Buena Vista treatment plant in the southeastern corner of Allegheny County, met last week with the county health department and the state Department of Environmental Protection. Mr. Cole said the county will soon issue an order directing the authority to submit a plan for correcting the problem.

The authority may also be subject to fines and penalties by the county and state since overflows are illegal from a sanitary sewer system like that in Elizabeth Township.

Mr. Cole said there have been no reports of fish kills or damage to other aquatic life in the Youghiogheny River and no problems reported by the Municipal Authority of Westmoreland County, which draws water from the river in McKeesport, about 10 miles from the Elizabeth Township sewage treatment plant's discharge pipe.

"There's just no question this is a stunning violation," said Helen Humphreys, a DEP spokeswoman. "It really brings into focus the need to focus on proper maintenance and oversight of the region's infrastructure."

The first sewage overflows occurred in the summer of 2006, and may have continued intermittently through the next 12 months. The overflows were reported to the state DEP, as required by law. But the Elizabeth Township Sanitary Authority didn't install a flow meter to measure the overflows until August 2007.

That meter first measured an overflow of 409,000 gallons on Aug. 19, and then a 1.34-million-gallon overflow on Aug. 23. There were no overflows reported in September and the first three weeks of October, but they have occurred almost every day since.

"I'm flabbergasted. Dry weather overflows like that are horrendous," said John Schombert, executive director of 3 Rivers Wet Weather, a nonprofit formed to work on a cooperative approach to the region's sewer problems. "We don't have very many areas where there are dry weather overflow problems that are chronic like that. I think they may have a creek coming into their system."

The Buena Vista treatment plant, built in the 1970s, originally had a capacity of 890,000 gallons a day. As the result of a plant upgrade, its capacity was increased to 2.3 million gallons a day, with a daily average of 1.4 million gallons, and the authority contracted to provide sewage service to customers in Sutersville and parts of Sewickley Township in Westmoreland County, and parts of Forward in Allegheny County.

But the plant has been treating an average of less than 1 million gallons a day, indicating that some of the overflowing sewage could be treated but isn't making it to the plant, said Lou Ann Baker, a spokeswoman for Veolia Water North America Operating Services, a French-owned firm hired by the authority to operate the plant a year ago.

"There's clearly an overflow happening outside the plant that is designed to function when the plant reaches capacity," Ms. Baker said. "This is a system issue rather than a plant issue."

Bill McKeever, vice president of Senate Engineering, the township's engineering firm for 25 years, said Drnach Environmental Inc. has been hired by the authority to monitor flows and locate the problem. He said because the system is old, storm water may be getting into the sanitary sewers through broken pipes, causing the high flow rates.

"I'm hoping it's something that came about quickly," Mr. McKeever said, "and we can eliminate it the same way."