The Louisville Water Co. (LWC), which serves about 850,000 residents with water in the Kentucky region, found the source of its hexavalent chromium issues: its own equipment.
The LWC concentrations were already extremely low at less than one part per billion, but when a controversial environmental group identified Louisville as having one of 31 high levels of hexavalent chromium in its drinking water, community leaders became concerned.
LWC began studying its hex chrome levels even more in January 2011 after the EPA recommended water utilities monitor quarterly for hex chrome at the source, in the finished water and in the distribution system. Currently, the EPA is conducting research to determine if it will create a regulatory standard for hex chrome.
So when LWC decided to take the research a step further and examine each step of the treatment process at its two treatment plants, they learned that ground water at its B.E. Payne Plant—which is naturally filtered in its riverbank filtration tunnel—had no hex chrome levels. But as the water moved through the treatment process, the hex chrome level increased to 0.28 ppb in the finished water, four times the level found in the finished water of the Crescent Hill Plant.
After further studying the issue, LWC scientists discovered a link between the chemical softening process in water treatment and the increased hex chrome. It appears LWC used lime as a softening agent, and by moving the lime feed to the beginning of the treatment process the formation of hex chrome was significantly reduced.
“The absence of dissolved oxygen, the presence of ferrous ion and other reducing agents in the riverbank filtered water such as iron sulfate also lowered the formation of hex chrome,” says a spokesperson for LWC, which claims it cut the hex chrome levels by 80 percent through the change.
LWC has shared its data with other regional water utilities to show that the hex chrome issue may not be caused by finishing companies as originally thought. They are also is working with other utilities on a national study that will look to reduce hex chrome levels in drinking water.
“What Louisville has done is really original,” says Rob Renner, executive director of the Water Research Foundation. “The utility went beyond what was required. While each utility’s' treatment process is unique, the research in Louisville can help others understand how hex chrome is formed and how it can be managed in the treatment process.”
But Renner cautions that the questionable data from the environmental group may be causing water utilities to spend money they don’t need to spend in the first place.
“It’s really a tough issue for the water utilities,” he says. “The public health issues haven’t been totally proven.”