LEWISTON — Following a rise in algae blooms in Lake Auburn, water officials in the Twin Cities are planning to treat the lake with aluminum sulfate, which is designed to lower the level of algae-producing phosphorus.

One of two large sections of open water near Taber’s Restaurant and Mini Golf on Lake Shore Drive in Auburn. (Sun Journal file photo)

Officials say the dose, planned for June, will give them more time to determine where phosphorus is entering the lake.

During a Lewiston City Council workshop Tuesday, Public Works Director Dale Doughty said the treatment is designed to stunt the growth of algae in the lake, which he said will “give us some time to better protect the resource.”

The district has been under pressure to come up with answers ever since an algae bloom late last summer led to taste and odor issues in the water.

The lake serves as the public drinking water for both cities and due to historically clean water, the Auburn Water District receives a waiver of filtration that allows it to treat the water with ultraviolet light and other means without having to pay to filter it.

Kevin Gagne, deputy director of Public Services for water and sewer, said Tuesday that the proposed partial treatment is designed to lock up phosphorus that is in the water,  which he said was the primary issue this past fall.

That hopefully means five to 10 years of maintaining a lower amount of phosphorus in the lake and reducing the likelihood of algae blooms, but Gagne said storm runoff and continued warmer weather could shorten that window.

He said in the meantime, the district will continue working with its consultant on watershed protection efforts to determine where exactly the phosphorus is coming from. According to a memo from Gagne to the council, the district has “found phosphorus in certain streams and areas where stormwater enters into the lake,” but they are not considered the primary source.

Previously included in Lewiston’s Capital Improvement Plan was roughly $2 million for treatment of the entire lake, but officials have since cut the proposal to about $750,000, which would be a partial treatment. The cost would be split between Lewiston and the Auburn Water District.

A 2012 algae bloom that caused fish kill led to several studies and work with a Massachusetts-based water consultant that has continued.

Last summer, the water district dosed the lake with an algaecide to help combat the algae bloom, but officials say this year’s treatment focus on phosphorus will pre-empt any algae growth.

The recent algae issue has also revived a debate over the use of Lake Auburn, and whether the two cities should build a filtration plant that could allow for more recreation and lakeside development.

Auburn Mayor Jason Levesque has pushed for creating a joint committee to study whether building a filtration plant is feasible. On Wednesday, he said the aluminum sulfate treatment “is a proven method for temporary mitigation,” but it “highlights that we need a long-term permanent plan to ensure high-quality drinking water for the region.”

Water officials have argued that the best way to combat the issue is through continued watershed protection efforts.

Sid Hazelton, superintendent of the Auburn Water District, has said the filtration plant would be costly, but also highly unlikely to lead to swimming or other expanded recreational uses at the lake.

According to Gagne’s memo to the council, aluminum sulfate treatments “are used in many lakes to bind with phosphorous and are used in many conventional drinking water treatment plants to reduce turbidity. It is not intended to kill algae or other aquatic organisms, it is intended to stunt their growth by removing an essential nutrient,” he said.

The district’s waiver of filtration is based on turbidity levels, which means the overall cloudiness of the water.

The memo states that it takes about seven years for Lake Auburn to cycle phosphorus out of the lake. The consultant’s opinion is “that in order to have time to remediate the sources of phosphorus coming into Lake Auburn, the best and most cost effective option is a treatment of (aluminum sulfate) in Lake Auburn to remove phosphorus from the water column.”

Aluminum sulfate is not considered a pesticide or herbicide and is used in conventional water treatment plants. However, the water district still needs the Maine Department of Environmental Protection to sign off on an amendment to its current approval to treat the water.

Gagne said the project is planned for June and would be roughly 16 days of treatment.

To ultimately move forward, funding for the project will have to be included in the Lewiston Capital Improvement Plan, which is approved in May.

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