Toxic gas is percolating under a Salt Lake City neighborhood. A plan to filter it is causing a stink.

Smelly sewer gas is building up in pipes beneath Poplar Grove and the Salt Lake City Department of Public Utilities has a plan to eliminate it.

But some neighbors are raising a stink about the proposed solution: a $2.5 million so-called biofilter. The device would essentially be a sewer exhaust system with bacteria that eat the toxic gas and spit out water vapor and carbon dioxide.

Concerned residents argue that the device would be better suited for an industrial area, and worry that its installation could pose safety risks and depress home values nearby.

“Best-case scenario is they don’t put it there,” Poplar Grove resident Rachel Ward said. “I feel like they’re experimenting with us, with our neighborhood.”

For their part, Public Utilities officials say the device is safe and suitable for the city-owned property at 1020 W. Pierpont Ave — and for the homes around it. The department is trying to deal with a stinky gas known as hydrogen sulfide that builds up in the sewer system underneath the neighborhood. The substance leaks from manholes, sometimes causing a rotten-egg smell, and leads to pipe corrosion.

The project originally called for a 30-foot tower. On Monday, however, officials said they would cut down the height of the device to 15 feet due to some neighbors’ concerns with “the aesthetics of having a tower in their neighborhood.”

It would be the city’s first biofilter in a residential neighborhood. The department has installed three others in west-side industrial zones. As of Monday morning, 333 people had signed a petition calling for officials to evaluate other sites for the device.

Public Utilities hosted a question-and-answer session at the site last week, where officials said they chose the triangular Poplar Grove property because it’s close to one of the city’s three main sewer lines.

The smell stems from a major junction just to the south at 1000 West and 400 South, where excess sewage from one of the other main lines merges into the 1000 West pipe. The confluence’s turbulent waters create ideal conditions for the emergence of hydrogen sulfide.

Inside the pipe, the gas can be deadly. When it vents through manholes, though, it mixes with the air and becomes much less dangerous, but can cause a smell, Public Utilities deputy director Jason Brown said.

At the Jan. 5 meeting, some said they had never smelled the odor and questioned why the project was needed. According to Public Utilities records, the department has received 10 complaints about the stench in the past five years.

Currently, the department limits the hydrogen sulfide by injecting a chemical into the sewage. However, that treatment is expensive and makes the waste harder to clean downstream at the Water Reclamation Facility.

A camera stationed in the line has also captured images of exposed rebar from corrosion, heightening fears of a major failure.

How the system would work

The device would consist of a fan and a two-part filtration system — one plastic filter in which bacteria live and a second carbon filter that captures anything that gets past the organisms, including the hazardous nitrogen gas compounds they create. In the end, three gases come out of its vents: water vapor, carbon dioxide and nitrogen.

The process also creates a liquid acid. That would be diluted in the device and then washed back into the sewer system via a pipe underneath Pierpont Avenue. Brown said the pipe has been lined with a nonreactive material so it won’t erode and that the acid won’t pose a threat to the sewer system overall.

Residents’ concerns stem partially from a feeling that they didn’t get much information about the impending installation before a notice that construction was due to start this week. Public Utilities officials spoke about the project at an April 2025 Poplar Grove Community Council meeting, but then didn’t have any engagement with the community afterward. The construction timeline has since been pushed back.

Ward and her husband, Alex Ward, aren’t opposed to the idea of the city building a device to filter the sewer gas, but they don’t think it belongs close to homes because the substance it treats is unsafe. Planning officials say city code allows the filter to be placed in a neighborhood because it is considered a utility structure and not a “sewage treatment plant” under city definitions.

While Salt Lake City’s other three devices — which use a different filter but a similar process — are located in industrial zones, a representative of Bio Air Solutions, the company set to supply the device, said most of the firm’s 434 similar systems nationwide are installed in neighborhoods.

“For the most part, they’re all in residential areas,” company representative John Sawyer wrote in an email to a Public Utilities staffer last week. “They’re installed to keep odors [out] of neighborhoods. Some systems are closer than others to housing.”

Fears of declining home values, rising danger

Some residents fear the installation of the device could hit property values in the neighborhood.

“They put that in here,” nearby resident Paul Boruff said after last week’s neighborhood meeting, “these houses aren’t worth sh-- from that moment on.”

Rachel Ward said she’s worried that simply the stigma of having an odor control device nearby could cause prospective buyers to look elsewhere.

As far as the department knows, other sewer infrastructure hasn’t caused property values to decrease, Public Utilities Director Laura Briefer said. The motivation for this project, she said, was removing the odor to improve the neighborhood.

“I’m not aware of any issues related to property value,” Briefer said. “We, of course, want to make sure that we maintain the property so that it’s an amenity to the community.”

Some residents also believe the project poses health and safety risks to the people living around it, especially if it fails. The Wards believe the city is overlooking potential safety issues by placing the device next to homes, even if zoning laws allow it.

They worry about the acid byproduct and potential for explosive gases and nuisance smells that could come from the project.

Brown, the Public Utilities deputy director, said the likelihood of an explosion is “very, very small” because there’s such little space in the filter for gases to ignite. Officials also insist no additional odors would be created.

The system would be monitored daily immediately after it’s installed, and if it failed, the gas would dissipate as it does now.

Brown said the department was not creating any additional risk for people living nearby.

Public Utilities plans to have at least two more public meetings about the system before it’s installed. Brown also said the department is considering changes to the property’s landscaping and fencing to make it more of an amenity for neighbors.