News Release, Kansas Geological Survey, Sept. 24, 2008
LAWRENCE--Uranium is in everything from rocks to soil and plants to water. It occurs mostly in low levels and is not considered a public health risk.
But too much of the radioactive element is a concern even when it's from a natural source, as it is in several water supplies in Kansas, said Don Whittemore, Kansas Geological Survey geochemist.
In 2003 the U.S. Environmental Protection Agency (EPA) set a drinking-water standard for uranium at a maximum contamination level (MCL) of 30 parts per billion and gave public water providers until December 2007 to complete monitoring. Not all Kansas communities were able to meet the standard.
Because long-term exposure to high levels of uranium may cause kidney damage and increase the risk of cancer, the MCL for uranium is a primary standard, meaning it was enacted to protect public health and is legally enforceable. Natural uranium's capacity to be toxic, or poisonous, not its weak radioactivity, is what raises health concerns.
"Like mercury and arsenic, uranium can be toxic in high doses over a long period," Whittemore said.
"The Arkansas River corridor in southwestern Kansas is especially susceptible to levels of uranium above EPA standards due to water-consuming agricultural practices in eastern Colorado," said Whittemore, who has studied water quality along the Arkansas in western Kansas. "Low levels of naturally occurring uranium picked up by the river from Cretaceous shales in Colorado are increased as water is lost to evaporation and transpiration."
Water from the river and shallow aquifers in Colorado is diverted into irrigation canals, farm fields, and reservoirs, giving it greater exposure to evaporation and transpiration. As a result, flows decline and concentrations of almost all chemical constituents, including uranium, increase before the river enters Kansas.
"When these enriched levels are added to natural uranium already present in groundwater in portions of the Ogallala aquifer in Kansas, it doesn't take much to get above the standard," Whittemore said.
The expansive High Plains aquifer, which includes the Ogallala, is the major source of drinking water in western Kansas.
Some cities along the Arkansas River, including Garden City and Dodge City, have approaches in place to reduce contaminants and were able to meet EPA standards. In Lakin, uranium levels in the city's main well were above the standard over the four-year monitoring period.
"When out of compliance, communities such as Lakin are responsible for fixing the problem," Whittemore said.
A water supply that does not meet EPA standards has to be monitored quarterly while the community works to reduce the contaminants. Possible solutions include relocating wells, buying water from other suppliers, or installing a treatment system, such as reverse osmosis.
Lakin and other Kansas communities are currently investigating their options.
Unacceptable levels of uranium also were found in several water systems outside the Arkansas River valley. The nine Kansas communities and water districts whose water consistently registered above federal standards were Atwood, Clay Center, Gaylord, Morganville, Norton, Oberlin, Lakin, Rooks County Rural Water District 1, and a Garden City subdivision. Private wells are not monitored.
As in the Arkansas River valley, high levels of uranium in other parts of the state are derived from Cretaceous-age shales deposited between 65 and 142 million years ago. The uranium leaches into the groundwater when the subsurface shales are weathered by rainfall recharge.
"Cretaceous shales tend to contain higher concentrations of naturally occurring uranium than other rocks in the Great Plains," Whittemore said.
In Kansas, the Kansas Department of Health and Environment's Bureau of Water is responsible for regulating all public water supply systems and has adopted the EPA's drinking water standards.
The EPA also recommends secondary, nonbinding, standards for dissolved solids, such as sulfate and chloride. High levels of these nontoxic salts and minerals, common in the Arkansas River system, negatively affect the aesthetic qualities of water, including taste, smell, and color, but are not generally health hazards.