Failed Septic System Drainfields as a Source of Septic Odors or Smells InspectAPedia® -
How to diagnose sewer odors in wet or cold weather
Causes and cures for sewer gas odors related to wet or cold weather
How to find and cure bad smells in buildings
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This article discusses the diagnosis and correction of sewer gas or septic odors (and other building smells and odors with focus on diagnosing odor sources and causes in cold weather.
Some of the diagnostic steps pertain to all seasons.
The photograph at page top shows green septic dye appearing in a septic system drainfield during a septic loading and dye test. Even before we performed this test to confirm that the liquid found on the surface of the drainfield area was indeed septic effluent (coming from the septic tank), sewage odors in the drainfield area outdoors told us that the septic field was in trouble. Readers who need a complete guide to inspecting the septic drainfield should see SEPTIC FIELD INSPECTION. Also see ODORS & SMELLS DIAGNOSIS & CURE for procedures to diagnose and cure all kinds of odors in and around buildings.
Also see our broad-scope article on diagnosis and cure of sewer gas and septic odors: Sewer Gas Odors diagnosing, finding, and curing septic tank and sewer line smells.
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This is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems an online book on septic systems.
How to Investigate & Repair Failed Drainfields and Septic Odors
Notice sewage odors present outdoors, strongest in and traced to the known or most-likely area for the septic drainfield or leach field, also called the soakaway bed or soil absorption system.
Look for wet areas in or near the septic drainfield. Consider performing a septic loading and dye test to confirm that the wet areas found are septic effluent from the septic tank.
Even if wet areas around a septic leach field are local ground water or runoff, the added water load that those conditions place on the septic drainfield may themselves constitute a septic failure or may require site work to redirect those water sources away from the drainfield.
If the septic system drainfield is blocked or failed it may be possible to reroute effluent to an un-used or under-used section of the drainfield (if effluent was not being distributed uniformly in the first place) - check the distribution box (if any).
There will be additional evidence of septic field condition in the D-box; if the box is flooded either these lines are blocked (such as by poor, uneven installation, tree roots, or a collapse, something not too likely unless you drove a truck over the fields), or the field has stopped percolating and needs replacement.
If on opening the D-box or excavating a drainfield line you see standing water in the leachfield line, either the field is saturated - lost perc - or the line has collapsed nearby and is not flowing.
You can test this by running a hose into the leach line from the D-box or from your point where you've cut it open.
Sometimes you'll see that only one field line is saturated and failed - you can close it off in the D-box and just use the others to give the saturated one a rest, but at the end of the day, you probably need a new drainfield.
See SEPTIC D-BOX INSPECTION for help in finding and inspecting the septic system drainfield distribution box.
Septic Repair Shortcuts and Septic Treatment Products and "Magic bullet" septic repair products and procedures like chemicals, additives, root killers, or soil restorers are mostly ineffective, waste money, and in some cases are illegal as they contaminate the environment. If the septic system drainfield is blocked or failed, most often the property needs a new drain field.
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Herb Reed County Extension Director, Agricultural and Natural Resources Educator, Calvert County Maryland - private email to DF 9/5/2006 adding comments about odors and partial blockages.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include
Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and
Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by
Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)
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