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A popular downtown artesian well is mildly contaminated with perchlorate, an additive to rocket and jet fuel whose health impacts are hotly debated.

The well, at the corner of 500 East and 800 South in Salt Lake City, has been cherished as a pure water source for more than a century. How its water might have become contaminated is a mystery, said Florence Reynolds, water quality and treatment manager for the Salt Lake City public utilities office.

"We don't want to cause a panic," she said, noting that the contamination is roughly equal to four drops of perchlorate in an Olympic-sized swimming pool.

The Salt Lake Valley Health Department has ruled out posting any health warnings at the site.

"The Health Department does not feel there is a public health risk," said Pam Davenport, a department spokeswoman.

Regulation of perchlorate has been controversial for years. The U.S. Environmental Protection Agency has set a guideline of 24.5 parts per billion for drinking water, which is considered a virtually safe dose over a lifetime.

The chemical is an endocrine disrupter, which means it alters hormone levels. Perchlorate tampers with the thyroid, which regulates metabolism in adults and may interfere with proper mental development in fetuses and small children, according to the state Division of Solid and Hazardous Waste. It also may cause thyroid tumors.

Two water tests at the Artesian Wells Park showed levels about 4.6 parts per billion, Reynolds said. At levels that low, there is no evidence and no suggestion from the EPA or the U.S. Food and Drug Administration that there is any harm, Davenport added.

Jim Gieber has been drinking water from Artesian Wells Park for more than 10 years. On Tuesday, he was filling several 5-gallon bottles, because, he said, it tastes better than the water in Bountiful where he lives.

"I'll take my chances," Gieber said. "I trust it. I've never gotten sick or anything."

West Jordan resident Angela Roberts said she worries more about the fluoride cities use to spike their water supplies than about perchlorate. She visits the well about twice a month to fill two dozen 1-gallon water bottles. She and her three daughters, ages 2 to 7, use it for drinking and eating.

Christian Heap, who also was filling blue water bottles Tuesday, said, "I think I'm going to trust Mother Earth over [the city's] pipes."

Some states have set the allowed levels for perchlorate at 200 ppb, said Reynolds. On the opposite, conservative end of the spectrum, the state of Massachusetts has a standard of 1 ppb.

The Department of Agriculture recently notified the city of the contamination. The state agency had embarked on an extensive study of perchlorate in Utah's water last year, after finding traces of the chemical in milk that reached 6.22 ppb.

The city has not typically tested for perchlorate at the Artesian Wells Park, Reynolds said. It didn't seem necessary since there are no military operations nearby, no gunpowder, fireworks, highway flares, air bags, leatherworks, rubber, paint manufacturing, enamel production or other common sources of perchlorate.

"It's really weird it would show up in a downtown area," she said.

The city is considering what kind of notices to post at the well to alert people about the contamination.