Article courtesy of Emery Cowan | October 28, 2015 | AZ Daily Star | Shared as educational material
Flagstaff’s utilities department thinks it has figured out why the amount of haloacetic acid, a water contaminant, exceeded federal limits in one part of the city’s water system.
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.
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.
Also good news is that so far, the city’s efforts to remediate the problem appear to be working.
Turning off Lake Mary
In September, the city alerted 91 customers along an area of east Butler that their water contained haloacetic acids at concentrations that exceeded EPA maximum contaminant level goals by 3 percent. Among the customers were three public schools and Little America.
According to the EPA, some people who drink water containing haloacetic acid concentrations in excess of the maximum contaminant levels over many years may have an increased risk of getting cancer.
After receiving the testing data back, the city’s utility department officials immediately set their eyes on Lake Mary as the potential source of organic carbon contributing to the violation.
They turned off Lake Mary as a source of water for the city on Oct. 2 and have kept it off since then as they reevaluate treatment processes and search for ways to reduce disinfection byproducts, an umbrella category that includes haloacetic acids.
The city hired two engineering firms to help with that task, said Brad Hill, director of the city’s utilities department.
Already, the city has modified operations in its distribution system in the affected area, opening up more valves to allow increased water flows through those 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, Hill said.
The city has flushed those pipes three times over a recent two-week period as well, he said.
With help from one of the engineering firms, the city also is considering using chlorine dioxide, also a disinfectant, at locations within the city’s treatment plant where chlorine is currently used. Chlorine dioxide minimizes the formation of disinfection byproducts because it oxidizes or reduces the organic compounds in surface water, city treatment plant officials said.
The city’s goal is to begin taking water from Lake Mary again as soon as possible, but no later than the spring, Hill said. The absence of Lake Mary water hasn’t posed supply issues because demand is much lower due to the onset of fall and winter and because the city has received so much moisture with the recent storms, Hill said.
The other sources of the city’s water are springs in the Inner Basin and deep groundwater wells in and around the city.
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, Hill said.
“But (the recent samples) clearly indicate we’re moving in the right direction,” he said.