COLUMBIA — When people in Columbia turn on their taps, every bit of water comes from the sandy, gravel-filled Missouri River bottoms.
In McBaine, about 10 miles south of Columbia, brick well houses sit atop this aquifer that holds about 44 billion gallons of water.
Just two decades ago, the river bottoms were the focus of a controversy about whether to pipe treated city sewage directly to the Missouri River or use natural wetlands to provide a higher level of treatment.
Voters overwhelmingly approved a bond issue to construct clay treatment cells lined with cattails near McBaine — a strategy that attracted state and national attention. The city then agreed to let the Missouri Department of Conservation use the treated wastewater effluent to flood wetlands at its Eagle Bluffs Conservation Area.
Twenty-two years later, evidence continues to indicate that treated city wastewater coursing through Eagle Bluffs has infiltrated the underground water that supplies the city's well field for drinking water.
A task force working on ways to protect the city's drinking water has not found any evidence suggesting this mixing of water supplies poses an immediate health risk, but the task force is recommending possible changes to how city wastewater is used in the state conservation wetlands.
Chloride levels on the rise
Despite the overwhelming voter support for building the treatment wetlands, the plan drew criticism from a few in the water industry.
John Betz, the retired superintendent of the water treatment plant, volunteers on the water protection task force. Although Betz does not see the wastewater effluent in Eagle Bluffs as a threat to water safety, he does think it makes its way into the city's well field.
Betz was among those who initially questioned constructing the treatment wetlands near the city's water supply.
"Back in the early '90s we were upfront about 'no, we don’t want wetlands near the city wells,'" Betz said. "You have 45 billion gallons of this pristine groundwater, a supply that many communities would do anything to have...In my world, I don’t want anybody building anything down there."
In a 2008 US Geological Survey report detailing changes in the water supply between 1992 and 2007, one thing stands out: Since the city introduced treated wastewater into the McBaine bottoms, levels of chloride in the groundwater have risen dramatically.
More recent testing has continued to show elevated chloride levels in several city wells, particularly the two nearest Eagle Bluffs wetlands.
Chloride itself is innocuous and doesn't pose a threat to the quality of the city's drinking water but is an indicator of wastewater.
Tom O'Connor, a water engineer on the water protection task force and the Water and Light Advisory Board, said Missouri River water usually has chloride levels at about 20 milligrams per liter; chloride levels in wastewater are usually closer to 250 milligrams per liter.
Increasing levels of chloride in the aquifer means wastewater made its way into the city's well field, O'Connor said.
"I don't think there's a lot of political will to do much about it," O'Connor said. "I don't even think there's political will to discuss it very openly. It's supposed to remain one of our little indiscretions."
In 2012, the levels of chloride in the four city supply wells being tested ranged from about 10 milligrams per liter to about 80 milligrams per liter in one of the two wells closest to the Eagle Bluffs wetlands.
“When we started seeing chloride levels over 45, the most probable source was the (wastewater) effluent," said Missouri Water Science Center hydrologist Mike Kleeschulte of the U.S. Geological Survey.
The treatment of wetlands themselves have been implicated in previous elevated chloride levels near city wells. As noted in the survey, the Missouri River flooded in 1995 and damaged one of the treatment cells, causing a significant leak.
Floyd Turner, manager of water operations for the city, said the chloride levels could be affected by interplay between the Missouri River and groundwater in the McBaine bottoms.
City suspends, then resumes, chloride testing
After the 2008 report came out, O'Connor and his father, former MU professor of civil engineering John O'Connor, published a study through their private firm, H20'C, on the effect of the wetlands on the city's water supply. The study said the safety of the city's water had not been compromised, but it urged the city to keep testing all of its wells for chloride and bacteria that indicate fecal matter in the water.
Even so, the city stopped regularly testing all but four of its 14 supply wells for chloride in 2010. The city earlier this year resumed regular chloride testing on all of its wells based on discussions with the Source Water Plan Protection Task Force.
Betz said he hasn't seen anything that has made him concerned about the safety of the city's drinking water, but disagreed with the decision to stop testing all the wells for chloride.
"The reason it is important is to see if there is any interaction between the wetlands and the water supply," he said. "You want to be on top of things."
What comes next?
Given the evidence that points to treated city wastewater migrating from Eagle Bluffs to the city's well field, there have been hints at changing the way wastewater is handled at Eagle Bluffs. The task force addressed the wetlands in a draft plan that outlines steps the city could take to protect its drinking water.
In the plan, the task force recommended "changing protocols" at the Eagle Bluffs wetlands. This proposed change was deliberately vague so the people running the wetlands would be able to decide how best to protect the water quality, Tom O'Connor said.
Changes could include using river water to flood the conservation wetlands closest to city wells and using the treated wastewater to flood conservation pools farther south, O'Connor said. “If you could take that wastewater farther south away from the wells, it couldn’t hurt,” he said.
It is expensive for the Missouri Department of Conservation to pump water from the Missouri River into its wetlands rather than using treated city wastewater, and there have not been serious conversations about ending the practice of using treated wastewater in the Eagle Bluffs wetlands, said Eagle Bluffs wildlife biologist Vic Bogosian III.
Bogosian also serves on the task force and said he didn't want to speculate about what the changing protocols might mean until the city had issued more formal recommendations.
The task force's recommendations are not binding, but will be presented to the City Council, Columbia Water and Light and the Missouri Department of Natural Resources.
Turner said the idea of putting wastewater directly into the river after it moves through the city treatment lagoons has been discussed since the city started sending its treated sewer water into Eagle Bluffs.
"It's a topic that's been taken seriously," he said.
Turner also said he doesn't think the city will change its relationship with Eagle Bluffs anytime soon.
"We just need to be prepared to treat the water to make it safe and meet all standards, despite what the influences are on the source water, but it’s very expensive to do that," he said.
The city, meanwhile, is looking at expanding its water treatment plant at McBaine to meet growing demand. In the early stages of planning the expansion, the city commissioned an engineering report that looked at different ways the city could treat water to a higher standard. The options that treated for more contaminants cost significantly more money.
Even the cheapest option for expansion is projected to cost the city $65 million. The more expensive options in the plan treat for more contaminants like pharmaceutical drugs, that are often found in wastewater.
Turner said it is unlikely that the city will change how it treats water with this next expansion of the treatment plant, but might down the line.
"The next expansion is probably going to be dealing more with capacity, maybe some modifications in our treatment process, but not major changes," he said.