Water experts baffled by increase in Lake Mead radiation levels

Tuesday, Nov. 10, 1998 | 11:02 a.m.

Radiation levels in Lake Mead, the source of Southern Nevada's drinking water, have been creeping above federal standards for the past several years, and officials have no idea what is causing the rise in contamination.

What is most puzzling is why radiation levels are higher in treated water than either the surface of Lake Mead or the intake pipe 150 feet below the surface.

In samples taken since 1992, levels of radiation in treated water have been about 2 picocuries above levels of untreated water -- and above federal standards for safe drinking water. A picocurie is a trillionth of a unit of radiation called a curie, which measures radioactivity in the environment. In addition, the levels of radiation in untreated water have hovered around and above the federal levels of 5 picocuries per liter at which more testing is required.

The radiation levels have not violated the Safe Drinking Water Act to the point where state officials need to take enforcement action. To be considered unhealthful, and trigger enforcement, the alpha radiation levels would have to reach 15 picocuries per liter in treated water.

But Douglas Zimmerman, in charge of the state's Bureau of Water Quality, said the elevated radiation "bears more study."

The Southern Nevada readings are not the only ones showing rising radiation levels. Records kept by the Metropolitan Water District of Southern California, which has sampled Lake Mead's surface water for 18 years, also showed increasing levels of alpha radiation.

At Metropolitan's own intake, radiation levels stay between 4.0 and 5.3 picocuries per liter, which is considered safe, Marshall Davis, deputy manager at the water agency, said.

A new sample for alpha in Lake Powell, above Lake Mead, indicated levels ranging from 3.2 to 5.4 picocuries per liter, Davis said. "The levels are quite comparable" to what the agency finds in lakes Mead and Havasu, he said.

Experts within the Southern Nevada Water Authority say the higher readings may be little more than a change in testing methods. They and state health officials maintain that the health risks of drinking water from Lake Mead are minimal.

Officials of the Metropolitan Water District of Southern California, downstream from Lake Mead, have been keeping a nervous eye on the rising radiation levels in Southern Nevada, Davis said.

"Of course, any rise in radiation is a concern to us," Davis said.

Radiation comes in three types of particles: alpha, beta and gamma. Alpha radiation found in the Lake Mead samples exceeded the federal levels of 5 picocuries per liter in 1993, 1994 and 1997. Beta has been well within federal standards, and since atomic testing ended in the state, gamma is no longer measured.

However, alpha radiation is most worrisome in water, because it poses dangers to human health if it is ingested, breathed or absorbed through a cut in the skin -- all very likely scenarios with water.

Once in the body, it can enter lungs, bones or other organs and cause cancer.

In fact, state health officials base their confidence in the water's safety on their tracking of cancer rates. There has been no rise in bone cancer rates -- the most likely type of cancer to be caused by contaminated water -- in Clark County to coincide with the rise in radiation levels, state Health Officer Dr. Randall Todd said.

In addition, the alpha radiation levels detected in the water are so small that they can be blocked by a sheet of newspaper.

The Southern Nevada Water Authority has responded to the elevated radiation levels by expanding its tests of water quality to check for traces of radium, microbiologist Peggy Roefer said.

Once alpha radiation is detected, radium is considered the most likely source in water and the Safe Drinking Water Act requires further tests. Those tests showed traces of radium of less than 3 picocuries, which is considered minimal. No further testing is required.

The higher levels of alpha radiation in the drinking water might be due to sensitive testing methods, Roefer said. Two monitors can be the same brand and work the same way and give slightly different readings. Experts consider differences of up to 5 picocuries acceptable for alpha radiation, since unhealthful levels are not reached until 15 picocuries.

Southern California water district readings showed similar changes. The highest reading the agency recorded in Lake Mead was in January 1994, when gross alpha measured 16 picocuries per liter, Davis said, adding "I'm very suspicious of that reading." A month later the levels dropped to 4.4 picocuries per liter, and the agency switched laboratories doing the analysis.

The state division has been keeping an eye on possible sources of radioactivity that could be running into the Las Vegas Wash and the drinking water supply.

There are three likely sources of radioactivity in the soils and ground water draining into the lake: carsonite, a mineral found in the area; old industrial ponds in the area; or mining tailings in Utah that may be feeding radiation into the Colorado River, Robert Kelso of the Nevada Division of Environmental Protection said.

Evaporation ponds held contaminated runoff from plants at the Basic Industrial Management complex. Titanium Metals Corp. used a radioactive ore from Australia in its process, which could contribute to the contamination.

A 10-foot high pile of uranium mill tailings perched on the shoreline of the Colorado River near Moab, Utah, is under study by the Nuclear Regulatory Commission for either capping or removal. Environmentalists and Utah residents want to remove the radioactive tailings from the river.