What’s that smell?

Cities often have “signature smells” and Twin Falls is no exception.

Residents are familiar with the occasional burnt-toast smell of sugar beets being processed at Amalgamated Sugar, burn piles from surrounding farms, or the smell of fries from Lamb Weston wafting around Rock Creek.

There are a number of locations in Twin Falls that just plain stink.

With notes of rotten eggs, manure lagoons, or rotting food, a smell emanating from the sewer in a few regular locations is unmistakable.

For the last several years, when people catch a whiff of something wretched, they have the option to drop the city a line using an odor complaint form on their website. The form, which helps the city track down stinky odors, asks people to describe the smell and provide a time and location.

In the past year, the city has received more than 125 odor complaints.

“The sick, cabbage odor is in our office and outside. It is so strong it is making us sick. We will finish the most important work … then we will send everyone home.”

“It was very pungent. Had to bring the Sunday lunch from the porch into the house.”

“It not only stinks, it’s an eye-burning sewage smell. I grew up on a dairy. I know what normal odor is, but … this is absolutely unbearable.”

To tackle the sewage smells that have become overbearing in places around town, the city hired Consor Engineering to track down the cause of odors in 2017. The study sought to find exactly what was causing the smell and why it was so strong in some neighborhoods and not others.

This year, new information and a range of new tools and tricks are available in the fight against odors and the city is hopeful that the solution is near.

“As we’re understanding what goes on,” city Environmental Manager Nathan Erickson said, “I think we’re closer to a permanent solution.”

A network that connects everyone

Consor’s study to tackle odors has focused on the Grandview trunkline, a major collector that handles most of the wastewater from the city west of Blue Lakes Boulevard.

The trunkline begins on Washington Street South and runs north to follow Rock Creek. At Addison Avenue, the line is pumped up from Rock Creek to just west of the County West building, where the line continues northwest to Grandview Drive. At Canyon Rim Road, the trunkline turns east and drops sharply into the Snake River Canyon before entering the wastewater treatment plant.

The Grandview trunkline is more than 5 miles of pipe, ranging in diameter from 8 inches to 48 inches, and it’s almost entirely plastic. There are no subterranean caverns, no phantoms of the opera, and no ninja turtles.

Odors have always been present in the line. The Grandview Drive and Canyon Rim Road area has been nicknamed “Poo Corner” long before the neighborhood sprouted up around it. As the city has grown, more users — both industrial and residential — are connected to the line, increasing the volume of sewage. More connections to the line offer more opportunities for gasses to escape, as well.

In 2022, the Times-News spoke with Nathan Bishop, whose home at Canyon Rim Drive and Grandview Road has been filled with sewage odors off and on for 20 years.

Bishop told the Times-News that in the past five years, the smell has gotten much worse. Older houses in the area are on septic systems, but Bishop’s house is connected to the Grandview trunkline near its end, where all the sewage from half of Twin Falls drops off a cliff and into the canyon.

One putrid odor

As Erickson told the council in April, smells that stay in the sewer differ from smells that come out of the sewer and into the community.

“If we were going to go out and pop a manhole and stick our nose down in there, it’s going to smell,” Erickson told the city council in April. “That’s understandable. But what is not acceptable is when that odor comes out into the community.”

Most of the smells are caused by gasses in the sewer system, he said. One gas — hydrogen sulfide — is responsible for a majority of the odors.

According to the National Institute for Occupational Safety and Health, hydrogen sulfide concentrations of 100 parts per million are immediately dangerous to life or health. Concentrations greater than 500 ppm can cause a person to collapse within five minutes and concentrations exceeding 700 ppm can cause immediate death.

But the smell of hydrogen sulfide, usually described as rotten eggs or raw sewage, is detectable by humans at a level far below where it poses a danger. Catch a whiff of even a small amount — 0.00047 ppm — will make a person check to see if they stepped in something.

“We are very very good detectors of this,” Mark Cummings from Consor Engineering told the city council in April.

Hydrogen sulfide can also become sulfuric acid, which is corrosive. The study has shown that concrete and steel have degraded around many of the line’s 103 manholes, making it even more likely the gas will escape into the community.

We know the culprit but where is it coming from?

Hydrogen sulfide gas can be produced within the sewer system by ordinary bacterial processes, or it can be introduced by sewer users. Cummings told the council how Consor determined there wasn’t a lot of hydrogen sulfide inherently being created by natural processes inside the system. Most of the hydrogen sulfide, he said, was being introduced by large industrial users, otherwise known as point sources.

There are several permitted wastewater dischargers in the southern portion of the trunkline: Glanbia Nutritionals, Lamb Weston Inc., Aramark Uniform Services, and West Rock are a few.

Over the summer and fall of 2022, gadgets called odor loggers were lowered into the sewer to “sniff” the gasses and record the concentrations. The results produced a graph with irregular spikes, showing that the hydrogen sulfide level fluctuated irregularly from the summer into the fall.

No single fix

The new air scrubber is one component of the city’s effort to reduce the impact of sewer odors on the community, but it is just one part of reducing the amount of hydrogen sulfide in the system.

“There’s not a silver bullet that’s going to solve all of our problems,” Erickson told the council.

The air scrubber is basically a big filter. About the size of a large refrigerator, the scrubber will connect to a manhole with a large suction fan that pulls gasses out of the sewer. Inside the scrubber, a vat of carbon pellets absorbs the hydrogen sulfide gas and neutralizes it.

“This type of filter is ideal for addressing when there are spikes when it’s a changing amount of hydrogen sulfide” Erickson told the Times-News.

The Grandview trunkline essentially has three segments that could be treated with the odor scrubber, and, Consor recommended using three to five of these scrubbers to treat the entire line. Before diving into a half-million dollar project, the city wanted to make sure it worked as intended and authorized $150,000 to purchase one unit and a trailer, which allows city workers to quickly set up at different locations to respond to changing conditions.

Limiting hydrogen sulfide starts with industrial users

The main effort of ultimately reducing hydrogen sulfide sits with partnering with industrial users to troubleshoot any processes that introduce large amounts of hydrogen sulfide and brainstorm any changes that can be made to decrease the odorous offender.

It’s taken some detective work, but through cooperation between the city and the industrial partners, they have used the data from the study to troubleshoot what is resulting in too much hydrogen sulfide in the system.

“There’s quite a bit of work going on behind the scenes by a lot of the point sources in the community to try to address whatever they can if it’s coming from them,” Erickson said. “We’re learning more, and in partnering with some of these point sources, … we share the data we’re collecting and letting them know what we’re seeing.”

Lamb Weston is one point source that has met regularly with the public works department to review the information on their wastewater discharge. Company spokesperson Shelby Stoolman said those meetings helped the company reduce its hydrogen sulfide levels to almost nothing.

“We used the data that the city collected to better understand the levels, and have implemented several improvements to our wastewater system, investing money and resources which have contributed to the reductions we’ve achieved in H2S levels,” Stoolman said in an email to the Times-News. “Since the city began monitoring last fall, we’ve significantly reduced average measured H2S levels, and have achieved current levels close to zero.”

The ‘R word’: If everything else fails, regulation is a last resort

If these initial efforts and voluntary contributions from industrial users don’t go far enough to curb the hydrogen sulfide levels, Consor said they may recommend the city create limits on what industrial contributors can put into the sewage system. But neither the city nor the industrial users are eager to see regulation come into play.

“As a responsible city we have to have a contingency,” Erickson told the council. “If we were ever to get to a point where we weren’t able to get the results into our system from point sources — then local limits.”

To get an idea of what other cities have done to reduce hydrogen sulfide in their systems, the city has studied how wastewater systems in Los Angeles County, California, and King County, Washington, have used regulations to reduce dangerous and offensive substances from their wastewater.

But this is Idaho, where limited regulation is a cornerstone of a business-friendly environment.

“Ideally we can just get the point sources so they are cleaned up enough where we wouldn’t have to (regulate),” Erickson told the Times-News.

Odor complaints help

Reports from citizens are one of the main tools the city can use to identify when and where gasses become noticeable. The city has a form on its website where people can report information about foul smells, and it is valuable data.

“I think it’s important that the public understand that speaking up if there are odors that are not acceptable,” Erickson told the Times-News. “When it is bad it’s nice to have citizens let me know so we can use that information to try to figure out what to do to fix it.”

Perhaps soon, residents can enjoy Sunday lunch on the back porch.