Irked residents complain to the city about every two days, records show, and municipal inspectors focus on familiar industrial emitters, including a 91-year-old pet food factory, marijuana producers, asphalt factories, an oil refinery, and processors of grocery and slaughterhouse waste.
"It's horrible, to wake up in the morning to that smell," Dawn Diaz, 38, said in front of her house in hard-hit Globeville, where her extended family and five children with respiratory ailments have lived all their lives. "Definitely somewhere I wouldn't choose to live," said Diaz, who finds her eyes water frequently and relies on nasal spray and allergy meds for relief. "You get sick more."
Adams County Commissioner Steve O'Dorisio, recalling marathoners' disgust during a race along the South Platte River in 2015, called the air quality "embarrassing." The installation of these electronic noses expands Denver's approach of requiring more than 330 industrial facilities inside city boundaries to submit odor control plans that identify sources and mitigation measures such as filters.
Starting this spring as part of a $50,000 pilot project, city environmental health inspectors have been monitoring readings from the e-nose sensors that measure concentrations of ammonia, hydrogen sulfide and volatile organic chemicals. These are combined to calculate odor intensity. Inspectors then look at wind speed and directional data and try to pinpoint sources of the most heinous stenches.
Four gray cubes containing e-noses were placed near where children play in odor-prone north Denver at Swansea Elementary, an existing air quality monitoring station in Globeville along Interstate 25, Garden Place Elementary, and the Bruce Randolph Middle and High School.
Denver leaders' efforts to control odor reflect widening public concerns about urban environmental health in an increasingly crowded city. They're anticipating more complaints in the future as gentrification of north Denver neighborhoods, historically home to factories interspersed with workers' homes, displaces the workers who gradually were desensitized after decades of exposure. Newcomers complain more. And a greenspace cap over the reconfigured Interstate 70 between the South Platte River and Colorado Boulevard is expected to accelerate a shift toward a cleaner environment.
"We're trying to get a better handle on it," said Gregg Thomas, environmental quality division director for the Denver Department of Public Health and the Environment.
"We don't own these units. We don't know if they're going to work for us," Thomas said, referring to the e-noses. The measurements "will just give us a sense, help us at least triangulate. Then we can go to a suspected source and ask, 'Were there any issues you knew about? Was the plant running? Was the odor control technology operational?' "
"Odor is a nuisance," he said. "It doesn't cause a physical health impact. But if you are exposed to odors all the time, there's a mental health impact."
Frequent Emitters of Foul Odors
The 1,038 complaints that residents have submitted since 2016 help city inspectors hunt for sources of smells.City analyses of patterns identified frequent emitters that include marijuana facilities (more than 320 around the city), Owens Corning roofing and asphalt plants, the Nestle Purina PetCare factory, the DAR PRO animal rendering plant and the Suncor oil refinery just north of Denver in Commerce City.
Annual complaints in Denver increased from 146 in 2016 to 260 in 2019, but decreased to 202 last year, city records show.
One possible explanation for that decline may be the decommissioning in June 2020 of a Koppers Inc. creosote wood treatment facility, which produced telephone poles and emitted fumes that smelled similar to mothballs. Another possibility: City health officials say particulate-heavy smoke from raging western wildfires from August through October, normally a peak period for odor complaints because temperatures are still warm and people are outside, may have diminished residents' ability to detect industrial odors.
While city enforcers rarely issue tickets to odor offenders tickets — they ticketed 15 over the past five years — they make house calls to inspect odor-control equipment and conduct delicate conversations. During the pandemic, these visits stopped, but officials said they'll resume later this year.
Polluters who emit significant smells often own up.
"The aromas from our factory are a result of cooking food for pets. We're similar to other food manufacturers and do not adversely impact the environment or public health," said Wendy Vlieks for the Nestle Purina plant, one of Denver's longest-running factories, a main supplier for the Rocky Mountain West by a corporation that, nationwide, supplies food for 51 million dogs and 65 million cats.
Over the past decade, Purina has invested more than $5 million on odor control, including a plasma injection system that removes odor particles before funneling fumes out a stack, reducing the aromas, Vlieks said.
"We comply with all environmental guidelines and levels as regulated by the U.S. EPA, the state, and the city and county of Denver," she said.
Trying to Triangulate Source of Stenches
But residents flummoxed by odor have reason to pay close attention. A bad smell can signal potential risks to human health, according to the federal Agency for Toxic Substances and Disease Registry at the Centers for Disease Control and Prevention. Sometimes people can smell chemicals in the air before concentrations reach harmful levels, federal officials have found.A 2014 American Association for the Advancement of Science-backed study published in the journal Science concluded that the human nose can detect roughly 1 trillion different smells, far more discriminating than previously understood.
No machine can come close to that. And adding technological heft to try to quantify odor detection has proved difficult.
For years, Denver officials dispatched health inspectors when they received more than five complaints in 12 hours about a smell. The inspectors would lug bullhorn-like tubular devices to the spots where residents reported bad smells. They'd hoist these Nasal Ranger devices up to their nose level and inhale the allegedly tainted air through the tubes. They'd turn a dial controlling dilution of the air with pure air. If the inspector could still detect odor after a seven-fold dilution of the air the city would document a possible problem.
This seldom happened.
Spurred by rising complaints in 2016, Denver leaders tightened the city's nuisance law and lowered the threshold number of complaints triggering an inspection to five within a month.
Shifting winds, industrial operational adjustments, and moving people complicate odor detection. University of Colorado researchers several years ago concluded that resident complaints grounded in detail about likely sources of stench generally proved correct.
Some of the bad smells afflicting Denver come from outside the city. Factories to the north in Commerce City churn out odors that, when the wind blows, sweep for miles through city streets.
Elected officials north of Denver were aware of this problem. Adams County Commissioner O'Dorisio said he's considering a tougher odor nuisance ordinance. For years, O'Dorisio said, he's been trying to address constituents' concerns by talking with industrial polluters.
"They blame each other. And it is ridiculous," he said. "I'm fed up."
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