A 10-inch sewer line ruptured early Thursday south of Alexandria in Fairfax County, forcing the dumping of about eight million gallons of untreated sewage a day into the Potomac River.

Crews have been working around the clock on the ruptured pipe that runs from the Belle Haven pumping station to the Westgate sewage treatment plant, but officials said it will be sometime this weekend before it can be repaired.

Fairfax County spokesman Edmund L. Castillo said most of the sewage is being released through a pipe that empties into the middle of the river. About 500,000 gallons of sewage a day, however, are being drumped into a drainage ditch that empties into the river.

"A bypass of this amount (of sewage) for 48 hours or so is no great problem for the river," Castillo said. He said that in the early 1970s greater amounts of sewage were pumped into the Potomac every day.

Castillo said the county treats about 33 million gallons of sewage a day. He could not recall a similar incident where a main sewage line broke.

The drainage ditch used to run sewage into the Potomac will be flushed after pipe repairs are made, Castillo said. He said workman are slowed in their repairs because of the marshy ground where the pipe broke.