Atrazine may be a threat to Clinton Lake’s water. That’s what an Army Corps of Engineers water quality report on Clinton Lake said in 2001.

Atrazine is typically used to control weeds in corn crops. The farmers who use atrazine usually put it on their crops during springtime, said Dan Devlin, professor of agronomy at Kansas State University. The atrazine levels in Clinton reservoir go up during spring rains after farmers have applied the herbicide.

“Most of the runoff occurs on the first rain after you apply it,” Devlin said.

The water report found that atrazine levels in Clinton Lake were typically highest in May and June. That’s when levels can exceed the limit set by the Environmental Protection Agency.

The EPA set a safety standard for atrazine in 1992 after some studies showed that long-term exposure to the herbicide might cause heart damage and cancer. The federal standard stands at 3 parts per billion for the annual average in drinking water and aquatic habitats.

“For human health, it appears that the standard is very conservative, even overprotective,” said Steve Randtke, professor of civil and environmental engineering at Kansas University. He said that the level set by the EPA was 35,000 times safer than anything that’s been shown to have an effect on humans.

Two fishermen spend time on the Wakarusa arm of Clinton Lake, an area managed by the Kansas Department of Wildlife and Parks.

“It’s hard to communicate that to the public because they want 100 percent safety, which isn’t possible,” Randtke said.

Although not all of the atrazine can be removed, the city tries to get the levels in the drinking water as low as possible.

“Most of the time we bring it down to less than half a part per billion in our drinking water,” said Keith Whealy, Lawrence water treatment manager.

To remove atrazine, the water treatment facility uses carbon activated powder, an additional step in the treatment process that also removes taste and odors. When there are high levels of atrazine in the water, the plant uses more carbon. That adds to treatment costs. The total carbon price tag for Clinton this year is $87,000.

“Carbon seems to be the most expensive part of the treatment process at Clinton,” Whealy said.

The level set by the EPA may be safe for most humans, but even low levels of atrazine may have an impact on the aquatic life of the lake and its surrounding streams and rivers.

“It’s a continual stressor on the system of the lake,” said Paul Liechti, assistant director of the Kansas Biological Survey.

Some of the algae and fish that eat the algae will not survive as well with atrazine present, Liechti said. He said he would like to see the safe level for reservoirs set even lower, to 1 part per billion.

“But that’s for somebody else to decide,” he said.