COLUMBIA — The levels of a cancer-causing compound in Columbia's drinking water dropped significantly after the city began adding chloramine to its treatment process in August. But whether that change is the direct cause of the decline and whether it will be enough to ensure levels of the contaminant don't rise again remains in question.
In 2007, the level of trihalomethanes, or THMs, in Columbia's drinking water violated Environmental Protection Agency standards for the contaminant, which forms when water and organic matter mix with the chlorine used in water treatment.
The permissible level for THMs in a water supply is 80 parts per billion; the THM levels in the city water supply in 2007 rose to 82.3 parts per billion.
Connie Kacprowicz, spokeswoman for Columbia Water and Light, said THM levels continued to hover around that amount until the city added chloramine to the treatment process in early August. Samples taken in late August showed THM levels had dropped to 37 parts per billion, less than half the permissible amount.
“Chlorine is still used in the disinfection process and kills the water-borne pathogens and any kind of bacteria,” Kacprowicz said. “Then a tiny amount of ammonium sulfate* is added — equivalent to six grains of salt in a gallon of water — which is enough to stop the reaction of chlorine and organic material.”
The ammonium sulfate when mixed with water and chlorine creates chloramines.
Other factors, however, might have had an influence on the decline in THMs.
“There are a lot of different things that can affect the chemical reaction, such as time. For instance, if people are watering their lawns more it won't take three days for water to leave the system because people are using it more,” she said. “Another thing is the temperature of the ground.”
There also are seasonal variables. Kacprowicz said the EPA’s process of averaging quarterly compliance tests will help determine how much of those affect THM levels.
A report done by MU's department of civil and environmental engineering and Missouri Water Resources Research Center between July 2008 and June 2009 analyzed the potential of disinfectant byproducts, such as THMs, to form in the city’s water supply.
A portion of the report said that tests suggest the use of chloramine will “stall disinfection byproduct formation at approximately one-half of the current compliance sample concentrations.”
Enos Inniss, an assistant professor in the department of civil and environmental engineering, was involved with the study. He said chloramines were used as a quick way to fix the THM problem. He said that future testing will determine whether longer-term solutions suggested in the report, such as enhanced water softening, are in the best interest of the city. Other options mentioned in the report were preoxidation and magnetic ion exchange.
"These are things I know work in other places and have been tried in other places," Inniss said. "The question is if they will work in the city of Columbia. They have to test and in future planning may decide that using chloramines is the best way to go."
The report and the status of the city’s drinking water supply will be the subject of a public hearing during the Columbia City Council’s regular meeting at 7 p.m. Monday.
Kacprowicz said an important point Columbia Water and Light took from the report was that there was minimal difference in the formation potential of THMs in samples taken from the 15 wells that draw the city’s drinking water from the aquifer beneath the McBaine Bottoms near the Missouri River. The well field is near Eagle Bluffs Conservation Area, where wastewater goes after it's treated.
Inniss said during a briefing Tuesday that data from his study doesn't answer the question of whether the well field’s proximity to Eagle Bluffs contributes to the potential formation of THMs.
“From the university's report, we found there was no variation, so we cannot find a direct link between the wetlands and the THM problem,” Kacprowicz said.