An East Side Madison well plagued by high levels of an industrial carcinogen probably will be permanently shut down, according to officials with the Madison Water Utility.

Well No. 3, which serves the East Isthmus, has in the last six years produced drinking water that tested high for carbon tetrachloride, an industrial solvent that has been shown to cause cancer. The well was shut down earlier this month after a test taken in September showed levels of the chemical at 6.2 parts per billion. The health standard set by the Environmental Protection Agency for the contaminant is 5 parts per billion.

Because the well, built in 1928, is the oldest of the city's 24 wells, it makes more sense to build a new well than invest in expensive equipment that would remove the carbon tetrachloride, said Al Larson, the utility's principal engineer.

"We're talking about millions of dollars to fix this well," Larson told the Board of Water Commissioners on Tuesday at its monthly meeting. "Our preferred option is to start the process of looking for another well site."

The well is one of several giving the utility fits. Also Tuesday, the board approved a plan to study replacing Well No. 29, a new well on the Far East Side that has had high levels of the mineral manganese. Previously, the board approved adding a $2.4 million filter to rid the well of manganese. Money for the filter was included in the proposed city budget.

But Tuesday, on Larson's recommendation, the board voted unanimously to recommend the budget proposal be amended so that the money could also be used to replace the well. Larson said he is working with an engineering firm that will advise the utility on whether a new well untainted by manganese can be built.

Ultimately, Larson said, building a new well and using the existing reservoir and pump station would be less expensive than adding the manganese filter to Well No. 29.

In both instances, finding a supply of clean water is a challenge, according to Larson. Replacing Well No. 3 will be especially difficult because of the history of industry and manufacturing on the Isthmus. One legacy of that past is the presence of contaminants such as carbon tetrachloride.

"It's going to be a challenge," Larson said, estimating the process of siting and building a well will take about five years.

In the meantime, residents on the East Side of the Isthmus will be served by other nearby wells, including wells No. 24, 8 and 11. The only problem might come during a hot, dry summer. If one of the other wells were to break down, Larson said, the utility would probably have to issue water use restrictions.

"But if people had to choose between carbon tetrachloride in their water and not watering their lawn, I think they'd probably choose not watering their lawns," Larson said.