COLUMBIA — Be careful what you drink, because you might be drinking it again.
Chlorides are creeping into Columbia’s water supply wells in the Missouri River bottoms at McBaine, indicating that treated wastewater, once funneled far from the wells, is finding its way back into the city's supply.
The chlorides themselves aren't harmful, said Tom O'Connor, an environmental engineer who sits on the city's Environment and Energy Commission as well as the Water and Light Advisory Board. Columbia's drinking water currently meets all Environmental Protection Agency standards. However, the presence of chlorides does show that other potentially harmful contaminants, such as pharmaceuticals and other household chemicals, could stay circulating in the water supply.
O'Connor told the City Council on Monday that if council members vote to move forward with placing a new well in a site identified by Columbia Water and Light, they risk adding to the problem. The proposed site sits near four other wells that show significantly elevated chloride levels.
"It seemed like that (site) was questionable from a water quality standpoint," he said.
On Monday, the council voted to allow the Environment and Energy Commission and the Water and Light Advisory Board more time to study the placement of the well. The council also directed city staff to look for alternative sites.
O'Connor suggested that a site to the northwest end of the McBaine bottoms, where existing wells haven't shown elevated levels of chlorides, could be a safer alternative. But a U.S. Geological Survey report presented to the City Council suggested those wells, which sit near the Missouri River, showed higher levels of agricultural contaminants and discharge from cities upstream.
"(Those sites) would be better for some things, but it could be worse for others," said Michael Schmitz, interim director of Columbia Water and Light.
Finding a new site would also require buying new land and building new infrastructure to service the wells, which could also add to the cost of the project. By waiting, the city could also lose access to some economic incentives, including a low-interest loan.
Schmitz said the project would cost as much as $350,000 if constructed on the previously identified site.
Finding a new site would also delay the project beyond next summer, which could strain the city's water supply. Schmitz said the last two cool, wet summers and the economic slowdown could have masked an increase in demand.
"From an engineering perspective, we like to be a step ahead from what we think pumping demand is going to be," he said.
The EPA is expected to tighten its regulations and add to its list of regulated contaminants. Mayor Darwin Hindman said he expects the city will eventually need to look at new water treatment options in the future regardless of where this new well is placed.
Columbia has been in violation of EPA water standards before.
In 2007, tests showed the city's drinking water exceeded Environmental Protection Agency standards for trihalomethanes, cancer-causing compounds that form when water and organic matter mix with the chlorine used in water treatment. To reduce the levels of trihalomethanes, the city switched to ammonium sulfate, an alternative disinfectant.
An analysis of the city's water sources, produced by MU researchers, says the measures taken by the city are a temporary solution. The researchers report that Columbia's wells have high potential for formation of trihalomethanes, suggesting levels of the contaminant will remain close to — or could exceed — the EPA limits.
The report says the city should make other modifications to the water treatment process that would allow an eventual switch back to chlorine. A study commissioned by the council at a previous meeting will study the entire water treatment system and make recommendations based on what the consultant firm, Carollo Engineers, believes EPA standards will look like in the future.