WHEELING, W.VA., JAN. 11 -- City officials heaved a sigh of relief and declared Wheeling's water emergency over today, four days after a massive diesel fuel slick cut off the city's water supplies from the Ohio River.

"We are pumping at 60 percent of capacity and our reserves are at 70 percent," said assistant city manager Nancy Vapner, her face wreathed in smiles. "We should be at 100 percent by late evening."

Wheeling has struggled since Friday to keep taps running in this city of 60,000, the latest victim of a million-gallon spill that has had Ohio Valley communities scrambling since it entered the river 11 days ago from an Ashland Oil Company facility east of Pittsburgh.

Down river, residents of Sistersville, W.Va., population 2,200, frantically stockpiled water in anticipation of the oil slick's arrival and worried about the condition of the town's 19th-century water treatment plant.

"We have a lot less options than Wheeling does because of the age of it," Tyler County emergency services Director Mitch Wilcox said.

The slick, actually more of a churned-up pool of pollution, is now more than 120 miles long and advancing about 12 miles a day.

Ongoing sampling of raw water at the intake pipes of eight utilities between Pittsburgh and Wheeling has turned up tiny amounts of such cancer-causing chemicals as methylene chloride, benzene and chloroform and such neurotoxins as xylene and toluene, according to spokesmen for the Environmental Protection Agency and a Pennsylvania utility. Since there are no federal drinking water standards for the pollutants, it is impossible to determine how dangerous they are at detected levels,

EPA spokesman Ray Germann said that the chemical concentrations diminish as the slick moves downstream and that the treatment process of utilities that have resumed service purifies the water. He said water quality of the Monongahela and Ohio rivers is steadily improving.

"So far there's no indication of a health hazard," said Germann.

But the Ashland spill already has entered local lore as one of the worst environmental accidents in the Ohio Valley, and its slow journey downstream underscores the fragility of the water systems that supply these river towns.

Cities and towns cluster along the Ohio River, sharing its water with an endless stream of barge traffic and factories that rise from its banks like industrial cathedrals. Water engineers here are accustomed to dealing with low levels of industrial contaminants, but few are equipped to handle a spill the size of this one.

John Potter, chief scientist at the Wheeling water plant, said the city was nearly brought to its knees several years ago by a crude oil spill less than one-fifth the size of the Ashland slick. "We made it through by the skin of our teeth," he said. "This one is worse, much worse."

Steubenville, Ohio, confident that the four-step filtration system required by state law would see it through the crisis, was virtually shut down for a day last week when the greasy water overwhelmed its treatment plant.

By then it was too late. More than a day after the slick had passed, water coming through Steubenville pipes still smelled of diesel. The city said the water was safe but mobile water tanks were made available for residents who did not feel comfortable drinking it.

Wheeling, with nearly a week's advance notice, was able to string temporary water lines to nearby unpolluted streams and arrange for barges to haul clean water to its treatment plant.

Even the elaborate plan wasn't enough to forestall business interruptions as the city's normal 9 million-gallon water reserve dropped to 500,000 gallons within 24 hours of the spill's arrival. Businesses closed, community events were canceled, laundry piled up, and Saturday-night entertainment in Wheeling came down to family vigils around the water faucet.

Assistant city manager Vapner said the temporary pipelines would be disconnected tonight, but the main line to Martin's Ferry, Ohio, would not be dismantled immediately.

"I'm sure we'll have a critique of this crisis," she said.

The command post in the city hall basement, where officials huddled in around-the-clock strategy sessions for more than a week, was deserted by midday. Only a National Guardsman remained, seeking advice on where next to dispatch a fleet of mobile water tanks.

Their emergency ended, Wheeling officials are free now to turn their attention to the next water dilemma: last week, the West Virginia Public Service Commission suspended a rate increase sought by city officials to improve the water storage system.Staff writer Michael Weisskopf contributed to this report in Washington.