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Treating Sewage on the Ballot
Tuesday, November 1, 2022


The 13-building campus sits largely out of sight and out of mind, nestled behind tall pines bordering the bike path just northwest of Elkhorn Road and River Ranch Drive.

But the City of Ketchum is trying to put the Ketchum sewage plant front and center as the Nov. 8 election nears.

The city is asking voters to approve a revenue bond of up to $14 million to help fund upgrades to the 42,000-square foot plant, which was built in 1968.

The bond would:

  • Upgrade the treatment plant’s processes so it can continue to meet current—and future—State of Idaho regulations concerning ammonia concentrations discharged into the Big Wood River.
  • Replace old equipment with highly efficient hybrid blowers to reduce the current power consumption. All new equipment will have high-efficiency motors with variable speed drives to reduce energy consumption.
  • Upgrade two 54-year-old aeration basins, a 38-year-old aerobic digester tank and a 38-year-old clarifier.
  • Add additional aerobic digestion facilities to accommodate flow increases as the population increases. Most days it has 50 percent capacity, but that capacity goes down to 30 percent as it processes 1.35 million gallons a day during the Christmas holidays.

Currently, the treatment facility exceeds State of Idaho standards, creating clean high-quality water. Between 60 percent and 70 percent of the water is used in to water lawns in the Weyyakin subdivision at Ketchum’s south end and the Elkhorn golf course. Water that is not reused is discharged to the Big Wood River.

“I have not drunk it, but I would drink it if I had to,” said Mick Mummert, Ketchum’s wastewater division supervisor. “By the time we’re done with it, it’s fully sanitized—there’s nothing in there that would harm you.”

Right now, solids are taken to the Ohio Gulch dump where they’re dried into powder in lagoons. But the plant is working with Winn’s Compost on a pilot project to mix biosolids with green waste to create an Exceptional Quality Compost.

Mummert has been taking small groups on tours of the facility, offering a behind-the-scenes look at what happens to wastewater that arrives from Ketchum and Sun Valley.

He showed how it comes up on a conveyor belt and runs through an odor scrubber. When things are working correctly, no one should notice the smell, he said.

This summer a part broke and the plant emitted an overpowering odor that assaulted residents in the area and those using the bike path. Supply chain issues delayed getting parts.

After larger solids are removed, the wastewater is allowed to settle so more solids can be removed. It then goes to large basins where microorganisms are added to create a bug stew. The microorganisms, which include protozoa, eat away at the sewage oxidizing ammonia into nitrate.

“They’re like a sourdough starter, always reproducing,” Mummert said, adding that he recycles them to the beginning of the process once they’re done with the sludge they’ve been working on.

Once the bugs have had their way with the sewage, the liquid goes through a clarifier that removes tiny solids. Ultraviolet light kills remaining pathogens before the water is released.

Ketchum City administrator Jade Riley noted that the treatment facility is meeting and even exceeding standards right now, but that the city is looking ahead to the next decade when the state will likely impose even more stringent requirements.

Several Idaho cities, including Boise, McCall and Driggs, have failed to meet requirements and it’s difficult to catch up once that happens. McCall, for instance, was ordered to stop discharging its wastewater into Payette River and had to put in holding facility to allow the sewage to evaporate.

The federal government sued Driggs this week for dumping toxic wastewater full of e. Coli and ammonia  into a healthy stream.

“Our facility is getting old and some parts are 15 years beyond their useful life. And we want to make adjustments to provide more capacity for future population growth,” Riley said.

The 20-year project will cost a little over $37 million. The City of Ketchum hopes to fund it with up to $14 million of the proposed revenue bond and 7 percent higher sewer rates in 2023, followed by 5 percent increases the following years, subject to annual review.

the monthly sewage rate for a single-family home is $41.85.

If the bond doesn’t pass, rates could increase as much as 60 percent in 2023 with additional increases of 25 percent from 2024 to 2026, Riley said. 

The Sun Valley Water 7 Sewer District will pay $18 million for its share of the project.

Ketchum’s bond needs 50 percent approval from voters to pass.

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