A wave splashes against the shore of Lake Auburn at the Route 4 turnout in May. Sun Journal file photo

AUBURN — Water officials at Lake Auburn have temporarily halted a lake-wide treatment of aluminum sulfate to analyze the project’s impact so far on phosphorus levels.

Sid Hazelton, superintendent of the Auburn Water District, said the stoppage is a precautionary measure after testing showed trace amounts of aluminum in the lake and treatment system.

Levels of algae-producing phosphorus have increased at Lake Auburn in recent years, and aluminum sulfate is used to bind with phosphorus in the water column, sinking it to the bottom of the lake.

When announcing the $730,000 program in early July, officials said the project is expected to give the Water District several years of improved water clarity that will buy more time to “implement additional watershed protection efforts that will limit the amount of phosphorus that is entering the lake.”

An announcement from the Auburn Water District this week said the treatment is 50% complete, with about 550 acres treated so far.

Hazelton said Tuesday the treatment was halted Aug. 2 to analyze data so far, and could restart in September, with completion in the fall or early spring.

“We’re continuously examining lake data every day to see how effective the treatment was,” he said.

The project has been monitored by the Maine Department of Environmental Protection; Lake Stewards of Maine; Tighe & Bond, an engineering consultant; the USDA; and Lewiston and Auburn Water District staff.

Hazelton said given the large treatment zone, which encompasses 75 percent of the lake, “it was not unexpected that we have detected low aluminum levels in the lake and treatment system.”

“In accordance with guidelines set by the Environmental Protection Agency for aesthetic considerations, such as taste, color and odor, we have continually provided product to Lewiston and Auburn customers below these guidelines,” according to an announcement from the Auburn Water District.

“These guidelines are not regulatory in nature and EPA does not consider these levels to present a risk to human health.”

Hazelton said this time of year the upper 30 feet of the water is “quite warm, which is causing some of the aluminum in suspension not to sink as quickly as we thought it might initially.”

He stressed, however, the water quality continues to meet both the EPA’s primary and secondary tier of drinking water standards.

Water treatment at Lake Auburn has become a political issue over the past year. Auburn Mayor Jason Levesque and others have renewed calls for building a water filtration plant at the lake, which would replace the district’s treatment methods that give the district a filtration waiver.

Because of historically clean water, the Auburn Water District receives a waiver allowing it to treat the water with ultraviolet light and other means, without having to pay to filter it.

Hazelton and Bates College professor Holly Ewing have said as more nutrients are entering the lake from storm runoff and other means, further watershed protection will be needed to stave off irreparable damage.

As of now, the district plans to complete the treatment, with Hazelton saying there is still consensus it will be the “most effective for the lake.” He said alum treatments have proven effective and are used widely as a coagulant and in lakes to improve water quality.

“We’re still anticipating all the benefits that were discussed when we decided to do this project,” Hazelton said. “We are committed to finishing this project.”

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