WEST ELIZABETH, PA., JAN. 3 -- The collapse of a new storage tank poured an estimated one million gallons of diesel fuel into the Monongahela River, threatening drinking water for 750,000 residents of suburban Pittsburgh.

"The problem is that this is so massive. It's bank-to-bank from here to Elizabeth, {Pa.}" Pittsburgh Public Safety Director Glen Cannon said in downtown Pittsburgh, more than 20 miles downriver from the broken oil tank.

One water intake on the river was closed to keep the oil out, and the reduced supply meant some customers could eventually run out.

A pair of fire department pumper trucks was dispatched to connect Pittsburgh water lines to those of Western Pennsylvania Water Co., which serves Allegheny and Washingotn counties.

"The people may still be on low pressure, but . . . they should have water coming through," said city water department spokeswoman Donna Sagmeister.

Pittsburgh draws its water from the unaffected Allegheny River.

Some oil leaked past floating booms and floated into the Ohio River, formed at the confluence of the Monongahela and Allegheny rivers at downtown Pittsburgh.

The smell of diesel oil wafted through communities along 20 miles or more of the river.

The Ashland Oil Co. tank was being filled, apparently for the first time, when it collapsed late Saturday afternoon for unknown reasons, said Ashland Oil spokesman Dan Lacy in Ashland, Ky. A dike around the tank failed to contain the oil.

The tank contained an estimated 3.5 million gallons of oil when it collapsed, said Environmental Protection Agency spokeswoman Ann Cardinal.

"A million gallons at least" entered the river, Cannon said.

"This is a massive cleanup effort. There are going to be people working on this for a month," said John Best, a member of Allegheny County's hazardous materials team. "How long before the river is clean and usable, I don't know," said Cardinal.

Allegheny County's hazardous materials team, private contractors, the Coast Guard and others helped stretch booms across the Monongahela, but downstream, greasy brown ribbons of oil meandered on a four-knot current into the Ohio.

About 1,200 residents of Jefferson Borough were told around midnight Saturday to leave their riverside homes. Authorities said they feared an explosion due to a gasoline leak at the Ashland terminal.

The evacuation order was lifted around noon today after workers used a golf tee, rubber and tape to seal the leak in a pipe elbow .