Contaminant Closeup: Utility Fights Disinfection Byproducts

Water pros in Flagstaff, AZ, have spent months trying to figure out why the city’s water system has exceeded federal limits on the potentially cancer-causing contaminant haloacetic acid, and it now appears they have their answer.

“It has to do with vegetation that grew up along the edges of Upper Lake Mary during dry years of low lake levels, then got flooded and started to decompose this spring when several wet storms filled the lake to 70 percent capacity,” the Arizona Daily Sun recently reported.

“That created a large increase in organic carbon in the lake, which, when it interacts with chlorine used in the city’s water treatment plant, can form the haloacetic acid compounds. Good news is that so far, the city’s efforts to remediate the problem appear to be working,” the report said.

Three public schools in Flagstaff were among the affected customers. The Daily Sun explained in a previous piece: “The amounts of the acid compounds measured at one of the city's eight sampling locations on Aug. 13 exceeded EPA maximum contaminant level goals by 3 percent.”

Haloacetic acids are disinfection byproducts, according to the EPA. They occur when “naturally-occurring organic and inorganic materials in the water react with the disinfectants, chlorine and chloramine. Some people who drink water containing haloacetic acids in excess of the [maximum contaminant level] over many years may have an increased risk of getting cancer,” the agency says.

Director of Utilities Brad Hill explained that to begin rectifying the situation, the city opened up “more valves to allow increased water flows through [certain] pipes. The longer that organic carbon and chlorine interact, the more time they have to create disinfection byproducts. Moving a greater volume of water through the pipes decreases that period of potential interaction,” the report said.

“Since it discovered the haloacetic acid problem, the city has been sampling its distribution system weekly for disinfection byproducts to make sure the operational changes it has already implemented are actually working. The samples that matter in terms of the city’s compliance with Clean Water Act standards will be taken in mid-November,” the report said.

For similar stories, visit Water Online’s Drinking Water Contaminant Removal Solutions Center.