Q: We live in a single level one-bathroom home with a crawl space and septic system. We have noticed a sewer/natural gas odor outside periodically. And occasionally we can smell it inside in the bathroom only. When the odor is in the bathroom, we can't detect if it is coming from the sink, shower or toilet. When we smell it outside we can't detect where it's coming from. Sometimes it's in the front and others it's in the back. Our utility company has been out twice and determined that it was not a natural gas leak. We have had the septic tank inspected and cleaned. This odor is not always present inside or outside, but when you can smell it ... it's very noticeable. It never seems to be inside and outside at the same time either. We plan on selling the house this summer and would like to have this problem solved. Do you have any ideas or solutions?
A: Tracing an odor is difficult because, as you said, it's not always there and not always in the same place. With a septic system you not only have a tank for the collection of waste, but you have a field bed system to distribute the wastewater to the soils.
After the waste enters the first half of the septic tank, it is turned from a solid to a liquid by anaerobic bacteria. As the level of the liquid increases, it enters the second chamber of the tank where it flows to a distribution box. From there, the liquid flows downhill to a series of buried pipes known as the field bed system where the wastewater seeps into the soils. At this point aerobic bacteria takes over eliminating any remaining odorous bacteria.
If the field bed pipes become clogged with solids or the field is saturated with rain or snowmelt, the wastewater can surface and bring with it the unpleasant odors you mentioned. To check the field bed, an inspector pours a liquid tracer dye into a toilet and then allows the dye to work through the septic system for several days. A visual inspection of the field bed and all the lower areas of the property including ditches, lakes and waterways is then performed to see if the dye has surfaced. If the dye is discovered, you will know there is a problem with the field bed and repairs or total replacement will be necessary. The reason the odors appear one day and not the next depends on the weather and the direction of the winds. If the dye does not surface, the odors could be coming from a neighbor's septic system and the wastewater from their system could be on your property or the odors from their system could be carried by the winds.
C. Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 268, Evansville, Ind. 47702 or e-mail him at d.Barnett@insightbb.com.