DANVILLE — Over the past three years, nitrate levels that exceed drinking-water standards have been recorded in Lake Vermilion, Aqua Illinois officials told Vermilion County landowners Thursday.
David Cronk, production manager for the company that provides water from the lake to Danville and other area towns, said nitrate levels seemed to be on the decline prior to 2012, a drought year, but shot up in 2013, remained up in 2014 and increased in 2015 before dropping a bit this year.
But not enough to appease Aqua and the Lake Vermilion Water Quality Coalition.
Although low levels of nitrates can occur naturally in water, higher levels can be dangerous, especially for infants and pregnant women. The U.S. Environmental Protection Agency's drinking water standard for nitrates is 10 parts per million, equal to 10 milligrams per liter.
In Lake Vermilion, they've reached as high as 16 parts per million in June 2015, according to data presented by Cronk at a water-quality coalition meeting Thursday at the Vermilion County Farm Bureau.
The concern is as much a financial one as a water-quality one.
Cronk said a $4 million system built in 2000 treats the water flowing into Lake Vermilion, removing nitrates. But the higher the levels and the longer those higher levels exist, the more treatment Aqua must perform, which is costly, Cronk said Thursday.
The Lake Vermilion watershed spreads over more than 295 square miles to the northeast of Danville and drains into the North Fork River. About a third of the northeastern portion is in Indiana, and 86 percent of the Illinois portion is in row crops.
Nearly a decade ago, the Vermilion County Soil and Water Conservation District took the lead in creating a planning committee, which devised a plan to protect and enhance the water quality in the North Fork watershed.
In April 2015, Michael Killough, a conservation district resource conservationist, began weekly testing at 10 sites throughout the watershed — some along the North Fork, some in branches that drain into the North Fork.
In May 2015, he said, all 10 sites had nitrate levels above the EPA standard.
With grant funding for the testing exhausted by the end of 2015, Killough said the district opted to continue testing on its own because the summer nitrate levels were high and the Aqua removal system was operating at full capacity.
"We wanted to see how those numbers played out in the fall and winter months once the crops were out," Killough said.
Additional sampling in 2016 showed a drop in nitrate levels through winter, but they shot back up in the spring, beyond the EPA standard.
The good news, Killough said, is that the time frame in which levels were above the standard was shorter than in the past, meaning Aqua didn't have to use its removal system as much. The hope, he said, is that a downward trend will emerge, minimizing the need for the additional treatment.
"And it obviously provides safer drinking water for the public," Killough said.