Odors from wastewater treatment plants are primarily caused by gases like hydrogen sulfide, a heavier-than-air substance which can accumulate in poorly ventilated spaces or low-lying areas during low wind, leading to noxious smells.

These odors can intensify due to operational failures such as the accumulation of floating scum, fats, oils, and grease in settling tanks or malfunctions in the anaerobic digesters used to process sewage sludge. To control these emissions, facilities rely on properly functioning ventilation systems and specialized sensors to monitor gas concentrations.

Use the tool below to view recent air monitoring data. Each parameter tells a story about the atmosphere.  For odors related to the plant, there are four parameters most helpful. Here are the most relevant indicators for the public are listed below along with the specific variable name codes you will see on the display:

H2S GCC: Hydrogen Sulfide (ppb) can capture the smell from wastewater treatment.  H2S odor threshold occurs between 5 and 120+ ppb, depending on the sensitivity of the individual. 100 ppb is the same as 0.1 ppm.​ 

CH4_C GCc: Methane (ppm) is the primary component of natural gas.  Smaller amounts can naturally occur in water. About 2 ppm exists as a natural background.

CO GCc: Carbon Monoxide (ppb) is a good tracer for car exhaust or other inefficient burning/combustion processes.  Clean air has less than 150 ppb of CO.

PM2.5: Fine particulate matter (2.5 microns or smaller) has an abundant number of sources.  High concentrations may be evidence of nearby burning.  Clean air has less than 9 ug/m3.

The H2S sensor can be sensitive to mercaptan, a natural gas odorant that mimics the rotten egg smell typically associated with wastewater treatment. Because of this, some readings may actually reflect the presence of natural gas rather than hydrogen sulfide from the plant. The presence of methane is a key indicator of this phenomenon.