Why there's a horrible smell wafting through Paso Robles

New ponds at Firestone Walker Brewing Co. are designed to treat the water the brewery uses to rinse its tanks.
New ponds at Firestone Walker Brewing Co. are designed to treat the water the brewery uses to rinse its tanks. dmiddlecamp@thetribunenews.com

The stench of rotten egg has returned to Paso Robles, but this time, the city’s well-known, underground sulfur springs aren’t to blame.

The smell is coming from Firestone Walker Brewing Co.’s new tank-rinse ponds at the back of its campus on the south end of town. The ponds are designed to treat the water that rinses tanks used for making beer.

Fixes have been implemented, but brewery co-founder Adam Firestone said it will “take a few days” for the smell to weaken and 10 to 15 days before it dissipates entirely.

The smell began when unseasonably warm temperatures hit the North County in the past two weeks, affecting the condition of the ponds installed this year — filled with water that included pure organic matter such as yeast and grain.

The stench worsened Thursday as the brewery added bacteria-filled sludge to the ponds to help break down the organic matter more quickly in order to get rid of the smell.

“The engineers warned that all ponds take time to find their chemistry, and it was hoped that a wet, cold winter would mask any impacts,” Firestone said. “That just didn't happen, as we acutely realize.”

“The smell is horrible,” he added. “It’s like rotting fruit or if you’ve ever left your trash can for a week in the sun with no wind.”

Frustrated with the smell, Firestone said he has apologized to his neighbors in letters and personal visits.

“It’s crushing to us to upset our neighbors and our hard-earned customers and friends,” he said.

The city has received several complaints about the smell, which has reportedly wafted north from the brewery’s site off Ramada Drive into various neighborhoods — including in and around Centennial Park on the city’s east side as well as the hilltop neighborhood on 15th Street on the city’s west side.

City officials say the lack of springtime winds is causing the stench to collect over the town and drift into northern Templeton, too.

Firestone created the two ponds — one containing 4 million gallons and the other 6 million gallons — after state and federal regulators told the city that the brewery’s tank rinse water needed to be treated separately from the city’s wastewater system.

The brewery had typically been using 10 percent of the capacity of the city’s wastewater treatment plant, city wastewater manager Matt Thompson said.

Regulators required Firestone to create its own private system “to protect the infrastructure and to maintain the long-term capacity of the city’s wastewater treatment plant,” Thompson said.

The concept for the ponds had been in the works for the past four years, Firestone said, and came online this year.

As of Friday, the San Luis Obispo County Air Pollution Control District had received six complaints about the smell, district planning manager Aeron Arlin-Genet said.

Since the brewery’s ponds are considered a small wastewater treatment operation, Arlin-Genet said Firestone wasn’t originally required to apply for a permit from the air control district, but the complaints triggered the requirement. The brewery was told March 20 that it must apply for a permit for the ponds and submit an odor-management plan by April 3. The permit helps the agency regulate the ponds.

Firestone has been very responsive in working with the air district, Arlin-Genet said. The brewery’s human sewage is still connected to the city’s sewer and is not part of the ponds.

The city also issued two permits to Firestone to build and operate the ponds, under the expectation that they would not emit smells, Thompson said. Since the stink violates the conditions of the permit, the city could take enforcement action but is not at this time because “Firestone brewery is doing everything in its power to fix the problem,” he added.

Some residents have called the city in recent days to see whether the smell was related to the city’s new wastewater treatment plant under construction on the north end of town, Thompson said, but noted that there is no “extraordinary odor coming from the city’s wastewater plant at this time.”

The city smelled of rotten eggs for several years after the 2003 San Simeon Earthquake caused an underground sulfur spring to erupt in the City Hall parking lot.