A common myth about an aerobic systems is that it omits a nasty odor. A stinky septic system is a sign of a problem, one that needs to be addressed sooner than later. The most-common cause of abnormal odors from aerobic septic treatment units or ATUs is insufficient oxygen in the aerobic tank.  The aerobic bacteria become extremely unhappy when the system is not aerating. The area around the system should have an "earthy/compost smell.  Odors around the septic tank, if intermittent and mild, may be normal for your septic system.  
That being said, any problem with the aerobic septic system's aerator, pump, distribution tubing, a failed pump, improper aerobic pump timer settings, disconnected, leaky or kinked aerator tubing, plugged diffusers or orifice in aerobic tank, too much water being used, or a clogged air outlet in the septic tank can cause odors.  The use of antibiotics, chemotherapy, over use of bleach, chemicals can also cause odor.

1.  Check the aerator pump tubing for kinks and leaks.      

2.  Determine the time and conditions under which odors appear.  If the system has smelled  since installation there may be an installation or operation-set-up error. 

3.  If the aerobic system smells only in wet weather there may be a flooding or effluent distribution failure

4.  Review the septic system loading in gallons of wastewater per day versus its design. A surge of wastewater caused by multiple guests or multiple loads of laundry in one day may be overloading your aerobic septic treatment unit.  Check for subtle septic overload sources such as a running toilet. If your aerobic septic treatment unit is overloaded by wastewater volume it may be unable to aerate the sewage enough to prevent odors.

5.  Check the location at which septic odors are most-apparent.

Septic odors apparent indoors?  Odors in the bathroom may be due to a plumbing vent defect (dry drain traps) or caused by leaks at a toilet base.

Septic odors most-apparent outdoors?  In addition to the possible causes of odor stated above, site conditions may be the culprit: oders wafting down from a rooftop plumbing vent, roof height, slope, wind direction, nearby trees, etc. Extending the plumbing vent height, adding a rotating top that keeps the vent facing down-wind, or adding a carbon filter may help.  Please be advised; adding an odor filter to a rooftop plumbing vent may cause slow fixture draining and even loss of the water seal in sink, tub, shower traps if the filter blocks adequate air movement in the vent system.    

Watch out:  Don't rely on chlorine treatment to cure septic system odor.

Septic systems do not require septic system treatment or additive chemicals or products and, in fact, some of these products (for example harsh chemicals or yeast) are harmful to the septic system and some are prohibited by your state or provincial codes.


Other cures for septic system odors;  Call Coleman Aerobic!