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A dramatic increase in Mapleton's cancer rate the past 15 years can't be attributed to contaminated drinking water, but the possibility can't be ruled out either, according to a Utah Department of Health study.

Elevated nitrate levels in the groundwater beneath Mapleton the past few years alarmed many residents, most noticeably former legislator David Nemelka. Some people believe nitrates and explosives in the drinking water might be responsible for the higher cancer rate.The state Bureau of Epidemiology found 123 cases of cancer reported in Mapleton between 1978 and 1993. Ten types of cancer occurred more than three times during that 15-year period with prostate and female breast cancer comprising nearly 44 percent of all cases. Six cancers - prostate, female breast, colorectal, lung and bronchial, soft tissue and chronic lymphocytic leukemia - were found to be occurring at a higher rate in Mapleton than in Salt Lake County, the area used for com-par-i-son.

Dr. Joseph Miner, director of the City/County Health Department of Utah County, said none of those six cancers are known to be associated with nitrates. "RDX (an explosive detected in some wells) is a question mark," he said.

Cancer cluster studies rarely provide insight into the causes of cancer.

"This investigation provided little evidence that cancer in Mapleton was associated with nitrate exposure," Kim M. Blindauer, acting manager of the state's environmental epidemiology program, concluded in the study.

Blindauer said the study provides evidence that cancer rates were increasing but "it was not possible to establish the cause of these cancers with certainty."

The scope of the study made drawing conclusions problematic. Potential sources of error include migration of people in and out of Mapleton before 1978 and lack of data on individual nitrate exposure and cancer risk factors.

Because of those limitations, "we cannot rule out the possibility that there may have been adverse health effects in Mapleton with nitrate exposure" that could not be detected, Blindauer concluded.

The cancers increasing in the city of about 4,000 residents are not considered uncommon or unusual. "While dealing with small populations can show dramatic increases, it might not be statistically significant," Miner said.

Blindauer suggests the cancer increases might have been related to a large influx of residents over age 40 between 1980 and 1990, diet, smoking or genetics.

Nevertheless, Nemelka called the study's results a "major unexplained outbreak" of cancer. Nemelka said University of Utah epidemiologist Lynn Lyon, who worked with Downwinders, told him that. But Lyon said Wednesday morning that Nemelka is stretching a "private conversation" the two had.

"It's well beyond what I said to him," Lyon said. Lyon said the U. was considering studying the Mapleton case in depth, but now might not because of a press release Nemelka sent out Tuesday quoting Lyon. He referred all calls about the study to the state Health Department.

Nemelka believes there's only one thing in the city making people, including his wife, sick, and it's not air, sunlight or food.

"What is left that could have possibly affected the entire population of Mapleton at one time? Drinking water," he said.

The state Division of Water Quality determined that the contamination came from Trojan Corp., an explosives manufacturer south of Mapleton. Nine years ago, the synthetic lining of a nitric acid holding pond ruptured, draining 750,000 gallons in two days. The nitric acid bonded with a layer of limestone under the pond to form nitrate. A tainted plume of groundwater began moving through local aquifers.

Water officials also recently discovered the explosive RDX in one city well.

Until recently, Trojan has denied it was the source of the contamination. But Larry Mize, state groundwater protection manager, said the company is developing a remediation plan for explosives in the water.

"Wrapping it in a nutshell, they're confessing," he said.

Miner, the county health director, said Mapleton's culinary water is not harmful. It meets the U.S. Environmental Protection Agency's safe drinking water standards. He said Mapleton should prepare a plan for another water system should nitrate or explosives exceed accepted standards.

"I hate to think of ever drinking any RDX because it's such an unknown quantity," he said.

Private well owners in south Mapleton, including Nemelka, should continue using bottled water, which they have done since September.

After an hourlong speech about his personal investigation into Mapleton's drinking water, Nemelka told Mayor Richard Maxfield the onus is now on government to take immediate action.

"I want to shift this burden off my back and give it to you and to the state and to the county," he said. "Why do we have to wait until we kill more people?"

Maxfield told Nemelka to quit needlessly scaring people. "I'm not going to take theory from a man like you. I'm going to get the facts and tell the people the facts," he said.