Des Moines updates odor-monitoring program; industry pledges controls and more sensors
Summary
City staff reported 11 months of monitoring showing hydrogen sulfide and VOCs correlate with complaint spikes; the city will raise alert thresholds, add community monitors and weather stations, and industry partners Smithfield and Darling described investments to reduce emissions.
Dalton, neighborhood inspections division administrator for the City of Des Moines, briefed the City Council on Oct. 21 on an 11-month review of the city—s odor-monitoring program and steps to reduce false alerts and focus investigations. The presentation followed complaint data traced back to 2016 and a deployment of 10 sensors and a weather station.
The city—s monitoring and complaint analysis show most odor complaints arrive in summer and fall and between about 6 a.m. and 11 a.m., Dalton said. Staff identified 26 —critical days— (days with five or more complaints) in the monitoring period. On those days, hydrogen sulfide concentrations tended to be higher and winds were slower and more often from the southeast, supporting backward-trajectory analysis that can point to source areas.
"We do think that hydrogen sulfide is one of the compounds that is causing odor complaints in the city," Dalton said. He told councilors the city will change alerting logic to the 99.5 and 99.9 percentiles for H2S and VOCs to reduce low-priority alerts so staff can give more attention to each credible event; the previous system generated about 4,000 alerts that were difficult to investigate in depth. The city approved a change order to Envirosuite about a month earlier to expand the monitoring network.
Industry partners described actions taken at their facilities. Naomi Hoffman, director of environmental health and safety at Smithfield Foods, said Smithfield helped pay for the original sensors, monitors EnviroSuite daily at the plant, and is on the alert distribution list. "We invested over $2,000,000 in this project," Hoffman said, describing a regenerative thermal oxidizer (RTO) the company brought online in February 2024 that the company says is focused on capturing high-intensity points from rendering and is intended to reduce VOCs substantially.
Billy Holmes, director of environmental affairs for Darling, described decades-long use of venturi and packed-bed scrubbers, a room-air scrubber that treats building air, a regenerative thermal oxidizer commissioned in 2015, a recent change to oxidation chemistry to better target H2S, NH3 and VOCs, and an ongoing modernization project with roughly $1.1 million in work to add newer scrubber units and telemetry.
Dalton emphasized the complaint-investigation workflow: investigators use time, date, location and odor description from complaints, check monitor readings and run backward trajectories to see whether a plume likely passed over complaint locations, then contact stakeholders. He also noted Polk County air quality staff have logins to the monitoring system and that county staff told the city the facilities are in compliance with their permits; the neighborhood services office is treating the problem as primarily a quality-of-life issue rather than a public-health emergency. "This just stinks. It's not pleasant," Dalton said.
Next steps include the planned installation of 10 additional monitors and three weather stations (five monitors at the WRA and five in community complaint hotspots such as East Village, Dean Avenue, near the Science Center and Riverwoods Elementary), which staff said will improve trajectory precision and help refine thresholds. The city will continue to work with Smithfield, Darling and other partners such as WRA to compare plant telemetry with Envirosuite data and refine investigations.
Staff cautioned that some numerical threshold values were presented in shorthand during the meeting and that the city intends to publish exact threshold settings and the refined alerting rules as part of follow-up materials. Councilors requested continued reporting on the effect of plant controls and the expanded sensor network.
