Tricks Of The Trade: Tackling Sewage Odors

By B. Kevin Folsom, CEP
Published in the October 2013 issue of Today’s Facility Manager (and also feature as the Question of the Week on September 30, 2013)

QI am having ongoing battles with sewer odors in several buildings. We have attacked this issue from several angles without a cost-effective total solution. I have treated drains, traps, and grease traps, and I have replaced grease traps. I have checked for air balance to ensure no negative air pressures. I have installed air emittance devices on vents. In cool weather, the odors still seem to invade two of our buildings. What am I missing? I know there may not be a silver bullet, but any suggestions are welcome.

Lenny Allen
Director of Maintenance
Ruidoso Municipal Schools
Ruidoso, NM

AThanks for writing, Lenny! It sounds as if you understand the basic engineering of sewer systems so I’ll avoid discussing that further. I have encountered this type of issue and it is a dreaded one! There are three more issues that you did not mention and that I have personally encountered in my career.

  1. If vent stacks are too short and/or too close to rooftop HVAC units (RTU) this can be a problem. Newer RTUs have adjustable fresh air vents to provide a proper fresh air mixture; these can suck in methane emissions from the vent stack if it’s too close and/or not high enough to get proper draft to take it away from the building.
  2. Cracked pipes in the wall are another possibility. The most cost-effective way to begin testing for this is with a plumbers smoke. The pipes are filled with a special smoke so you can visually see where the methane gas is going, or not going.
  3. Bad seals in the water closets and urinals. There are no P-traps behind or below water closets or urinals. If the seal is old, dried out, or shifted, you have a straight shot into the methane gas supply.


  1. A grease recovery device or GRD is a quality replacement to the old grease trap technology. A GRD does not store the rotting grease and food solids like a passive grease trap or interceptor. A GRD is emptied daily of fats, oils, and grease (FOG) and food solids. Grease trap pumping is not required. Recovered grease is recycled with the waste vegetable oil from the deep-fryers.

Comments are closed.