By Kelly Werthmann

DENVER (CBS4) – If you live in Denver, you are likely well aware of the scents of the city. From the odor of the nearby refineries to the stench of dog food-in-the-making, and, of course, marijuana.

However, there is a different smell wafting into neighborhoods on the city’s north side, and it’s causing a big stink.

“It’s a weird, rotting smell,”

described to CBS4’s Kelly Werthmann.

Frank has lived in the Swansea neighborhood all his life and knows it can be quite odiferous.

“You come outside and you usually smell the Purina dog factory,” he said. “Even the refinery from Commerce City. Sometimes it’s not very pleasant. Usually you just get used to it.”

Yet, what Frank got a whiff of recently was something his nose could not ignore.

“I came out here and walked with my girlfriend to her car,” he said. “And all you smell is like really bad, moldy. It’s really a horrifying smell.”

Apparently, Frank’s sniffer is not alone. The Colorado Department of Public Health and Environment (CDPHE) has received a number of complaints about the death-like stench.

“Death? Yeah. Could be it,” Frank said.

Death isn’t too far off. Jeremy Neustifter, an Air Quality Planner at CDPHE, told CBS4 by phone that the rancid scent is coming from a rendering facility near 58th Avenue and York Street. It is where DarPro Solutions and Pepcol, owned by Darling Ingredients Inc., process millions of pounds of animal by-products every year.

Neustifter also told CBS4 the facility’s air filtration system malfunctioned in July and August.

“I got a weak stomach,” Frank explained. “You come outside, you come from central air to outside and it’s ‘ugh.’”

Neustifter explained the pungent air is not toxic, and there is no threat to the public, but it is understandable if people with sensitive stomachs become ill because of the stench.

“Not toxic, that’s good,” Frank said. “But still, not healthy. People shouldn’t have to breathe that in.”

Darling Ingredients Inc. released a statement to CBS4 saying it is aware of the recent complaints, and is reviewing its operations for what may be contributing to the awful smell. Neustifter said the rendering facility is currently in compliance with their Air Permit issued by the CDPHE.

“Most of my life I’ve lived with it,” Frank said of the scents in his neighborhood. ”But I kind of hoped it wouldn’t always be there.”

Full Statement from Darling Ingredients Inc.:

Darling Ingredients Inc. (DBA DarPro and Pepcol) operates a food processing byproduct conversion facility in Denver. The ingredients produced are primarily fats and proteins for use in the production of food, feed, fuel, and fertilizer. We operate under and comply with an Air Permit issued by the Colorado Department of Public Health & Environment (CDPHE). Darling has been in contact with the CDPHE over these recent complaints and we are reviewing our operations for any issues that may have contributed to an odor profile from our facility. The facility was not in operation from approximately 8:00 pm Saturday until approximately 1:00 pm today. Darling makes significant investments in odor abatement and we are committed to being a good neighbor in the community.

Kelly Werthmann joined the CBS4 team as the morning reporter in 2012. After serving as weekend morning anchor, Kelly is now Covering Colorado First for CBS4 News at 10. Connect with Kelly on Facebook or follow her on Twitter @KellyCBS4.