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Why a six-mile sewer line is under construction along Antelope Island’s causeway

As summer approaches, add toxic algal blooms to the long list of Great Salt Lake problems attributed to climate change, growth and uncontrolled water consumption of the Wasatch Front.

The Great Salt Lake is, after all, the result of what humans are letting flow downstream, and it’s poised to hit a record low for the second year in a row. As the lake shrinks and the population swells, many more nutrients flow downhill. And with less water to dilute these pollutants, combined with warming temperatures fueled by climate change, dangerous algae and cyanobacteria have proliferated.

But a sewage treatment plant, which is at least in part the source of algal blooms in the Great Salt Lake, offers a creative solution. The North Davis Sewer District is building a six-mile pipeline to divert its sewage west of Antelope Island into Gilbert Bay, rather than into the shallower, algae-plagued Farmington Bay, where it will operate.

“Gilbert Bay is a lot saltier than Farmington Bay,” said Kevin Cowan, district manager of North Davis Sewer. “It’s so salty that the harmful algae don’t grow.”

The project could also ensure a steady – and improved – flow of water to the lake.

A call to arms’

(Christopher Cherrington | The Salt Lake Tribune)

Nutrient pollution is not a problem unique to the Great Salt Lake, the largest body of water in the West. Blossoms have angered bodies of water across Utah, from Mantua Reservoir to Utah Lake to Zion National Park. They are so prevalent that the state recently updated its limits on phosphorus discharges into treated wastewater.

“There was a call to arms,” ​​said John Mackey, interim director of the Utah Division of Water Quality, “to start controlling nutrients before it became a bigger problem.” It is one of the biggest and most expensive problems we face in wastewater treatment today.”

Wastewater treatment plants must meet the stricter regulations by 2025. Some operators have made large, costly upgrades in response, including Salt Lake City Public Utilities, which is building a new $700 million wastewater treatment plant.

(Trent Nelson | The Salt Lake Tribune) Treated water from the North Davis Sewer District enters Farmington Bay on Tuesday, May 31, 2022. A new pipeline will channel this water into the Great Salt Lake west of Antelope Island.

But Utah’s new phosphorus limit allows an exception for “innovative alternative approaches,” and water quality regulators found the North Davis pipeline proposal met those conditions.

“It took a lot of thought and deliberation,” Mackey said. “But really, Gilbert Bay … doesn’t have the kind of environmental issues that we deal with.”

The pipeline is approximately half completed and runs alongside the Antelope Island Causeway. The final price will be around $43 million, Cowan said, saving his taxpayers hundreds of millions by avoiding the need for a new facility.

“All in all, it’s a win-win-win situation,” said Cowan. “It’s a win for the nutrient problem, a win for the county because it’s the least expensive alternative, and a win for the environment.”

Balancing the growing demand with a shrinking lake

North Davis serves a population of approximately 225,000 people in a rapidly expanding area spanning Weber and Davis counties.

As the Wasatch Front adds more people and Utah’s drought worsens, there is growing demand for water,” said Jeff DenBleyker, a water resources engineer, during a presentation on the pipeline at the Great Salt Lake Issues Forum earlier this month.

Municipalities are turning to recycled wastewater as a possible solution – especially now that it’s being treated to a higher standard.

“If you have a source of clean water and there is a need for that water, the water usually goes where that need is,” DenBleyker said, especially when communities are spending millions to purify it. “That means their discharge into the Great Salt Lake would be eliminated.”

(Trent Nelson | The Salt Lake Tribune) Construction of the North Davis Sewer District’s new pipeline along the Antelope Island Causeway on Tuesday, May 31, 2022. The pipeline will divert treated water into the Great Salt Lake west of Antelope Island rather than at Farmington Bay.

Treating North Davis’s wastewater to the same standard and sending it to the nutrient-poor Gilbert Bay eliminates that pressure, district managers noted.

Aside from keeping the water flowing downstream, the project also creates side effects for the Great Salt Lake.

Dense stands of invasive phragmites have developed along the current district outflow channel. The thirsty plants gobble up about a fifth of the 20 million gallons that North Davis releases each day before pouring into the lake, according to Cowan’s calculations.

“This [pipeline] will avoid this situation,” Cowan said. “It will go out where there are no phragmites.”

(Trent Nelson | The Salt Lake Tribune) Treated water from the North Davis Sewer District enters Farmington Bay on Tuesday, May 31, 2022. A new pipeline will channel this water into the Great Salt Lake west of Antelope Island.

The salinity varies throughout the lake, creating different ecosystems. Sections that are close to freshwater sources, such as Bear River Bay, have low salt concentrations. Farmington Bay, which is currently more of a channel due to the lake’s low elevation, contains about 5% salt at normal levels. Gunnison Bay, in the northern arm of the lake, contains at least 28% salt because it is virtually cut off from all freshwater sources by a rock-filled railroad levee.

Brine shrimp in Gilbert Bay rely on nutrient flows from fresher bays and graze on the resulting phytoplankton so heavily that the water becomes visibly clearer between spring and fall. The pipeline project will ensure that these nutrients get to the shrimp even as the lake continues to shrink.

“We have ravenous brine shrimp out there,” DenBleyker said, “that would love as much phytoplankton and algae as we can give them.”

By granting the phosphorus limit variance, the state authorities are requiring North Davis Sewer to mitigate phragmites in Farmington Bay. The district will also conduct ongoing studies into the impact of sewage on Gilbert Bay and whether coping with storm surges or occasional runoff into Farmington Bay will benefit the ecosystem and its migratory birds.

(Trent Nelson | The Salt Lake Tribune) Treated water from the North Davis Sewer District enters Farmington Bay on Tuesday, May 31, 2022. A new pipeline will channel this water into the Great Salt Lake west of Antelope Island.

“You’re going to be able to balance that and move water to one place or both places as the environment requires,” Mackey said. “We will continue to be able to be helpful and control nutrients at Farmington Bay.”

John Luft, director of the Great Salt Lake Ecosystem Program, has long monitored salinity, brine shrimp and bird populations for the Utah Division of Wildlife Resources. He expressed cautious optimism about the North Davis pipeline project.

“Any water in the lake at that point — we need to get more water there,” Luft said. “It was to their advantage and to our advantage, at least for now. If that affects the water, we will of course come back.”

This article is published by the Great Salt Lake Collaborative, a solutions journalism initiative that brings together news, education and media organizations to educate people about the plight of the Great Salt Lake — and what can be done to help make a difference before it’s too late. Read all of our stories below greatsaltlakenews.org.

https://www.sltrib.com/news/environment/2022/06/04/solution-great-salt-lakes/ Why a six-mile sewer line is under construction along Antelope Island’s causeway

Joel McCord

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