InspectAPedia ^®

This page describes how to diagnose, find, and cure odors in buildings including septic or sewage or sewer gas smells or "gas odors" in buildings with a focus on homes with a private onsite septic tank but including tips for owners whose home is connected to a sewer system as well. What makes the smell in sewer gas? Sewer gases are more than an obnoxious odor.

Because sewer gas contains methane gas (CH₄) there is a risk of an explosion hazard or even fatal asphyxiation. Sewer gases also probably contain hydrogen sulfide gas (H₂S) In addition some writers opine that there are possible health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation). Depending on the sewer gas source and other factors such as humidity and building and weather conditions, mold spores may also be present in sewer gases. Also see Wet Weather or Cold Weather Septic Odors or Sewage Odor Diagnosis & Repair Guide for additional odor tracing and cure advice for odors occurring during wet or cold weather.

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author.

Technical review by industry experts has been performed and is ongoing - reviewers welcomed and are listed at "References." © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Septic System or Sewer Piping Blockage or Failure Can Produce Sewer or Septic Gases Outdoors OR Indoors

• Check for a sewer line vent through the building foundation wall: I often find that a vent has been placed at a house foundation wall just above where the sewer line leaves the building. I suspect the plumber thought that this would aid drainage into the septic tank. Millions of homes have been built without this vent so I doubt it's needed. See if that's an odor source, and review the installation with your plumber.
• Install a gas diverter in the septic tank: the sludge in the bottom of a septic tank is being digested by anaerobic bacteria and perhaps also other microbes which form methane gas as a product of the decomposition of sewage. In some septic tanks the sludge layer may produce an occasional "burp" of gas that forms a large methane/hydrogen sulfide bubble. In a single compartment septic tank such bubbles can force unwanted solids up the tank outlet tee and into the absorption system. If this is suspected, special gas deflection devices (much like an upside down chimney cap) can be installed on the tank outlet tee.
• Sudden and unusually large septic system system usage that causes a large volume of water to enter the system, such as many loads of laundry or many visitors to a property which served by a small septic system might temporarily dilute the bacteria in the septic tank. It would be odd for this problem to persist. Normally bacteria would recover, probably in a day or so. If a septic system drain, tank, or drainfield are partly blocked, usage surges can produce this condition more often and at an increasing rate as the system deteriorates.
• Prolonged cessation of usage of the septic system, such as a home being left vacant for years. It would be odd to have to do anything special about this condition as when the system is returned to use it should recover quickly. However if the home has been vacant for a long time and/or if you simply don't know the condition of the septic system, it would be smart to have a septic contractor locate the tank, open it, pump it, and report on its condition both for operating confidence and more, for safety. (Is the septic tank cover safe?
• Acidic septic tanks: An Australian website suggested that (for the Australian climate) the septic tank contents may become too acidic. They recommend the following remedy, which I do not recommend in other areas without first consulting with local septic experts. And certainly do not attempt this process nor any process using any other septic additive or product before you know in fact where the odor is coming from. If, for example the odor is from improper plumbing vent installation, flushing lime down a toilet is not a fix it's simply silly.
  • Reduce the septic tank acidity by preparing a mix 0.5kg of lime with 10 liters of water.
  • Flush the lime mixture down the toilet 2 or 3 times a day for 3 to 4 days, until a total of about 5kg is used.
  • Alternatively the 5kg of lime to 10 liters of water can be inserted into the septic tank in one dose, however this can be more difficult to flush through the system, especially with new dual flush cisterns.
  • If the odours persist, repeat this process after 7 days.

This Australian septic system advice was paraphrased/near-quoted from advice given by Adelaide Hills Council, Australia. In some areas such as South Australia, aerobic wastewater treatment is used to treat effluent to a sufficient level of sanitation that it can be used for irrigation within the property - in other words it is dispersed on the soil for the purpose of both disposal and for irrigation.

Share this Article      

...

Technical Reviewers & References

Search InspectAPedia

• Daniel Friedman - principal author/editor of the InspectAPedia^® Website
• InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
• Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
• Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

MVOCs & MOLDY MUSTY ODORS
ODORS & SMELLS DIAGNOSIS & CURE
PLUMBING TOPICS
GAS MEASUREMENT TOOLS
SEPTIC SYSTEMS HOME
SEPTIC SYSTEMS ONLINE BOOK
SEPTIC SYSTEM DESIGN BASICS
SEPTIC DESIGN ALTERNATIVES
SEPTIC INSPECTIONS
SEPTIC & CESSPOOL SAFETY
SEWER GAS ODORS
  First Steps for Sewer Gas Odors
  Dangerous Conditions
  Building Drain & Sewer Line Odors
  Cure Odors in Septic Systems
  Other Causes of Odors from a Septic System
  Plumbing Fixtures or Traps
  Plumbing Vent Definitions, Types
  Plumbing Vent Defects
  Septic System or Sewer Piping
  Site, Weather, or Failing Neighbors
  Tests for Indoor Sewer Gas
  Tracking Odors to Source
SEWER GAS ODORS in COLD WEATHER
Toxic Gas Test Procedures

• Thanks to Slade Franklin for the reminder that a leaky wax ring at a toilet can lead to septic odors in bathrooms. 11/2007
• Thanks to J.V. (privacy protected) for the reminder to make a detailed inspection of the plumbing vent system when sewer gas odors are present. 07/2008
• Thanks to Roger Hankey & Cheryll Brown, www.hankeyandbrown.com, ASHI home inspectors in Minnesota, for the deteriorated transite pipe gas flue vent photograph and comments. Mr. Hankey is a past chairman of the ASHI Technical Committee, serves as co-chairman of ASHI legislative committee, and has served in other ASHI professional and leadership roles. 7/2007.

More Information on Building Diagnostic Inspections and Repairs

• Cold Weather Septic Odors or Sewage Odor Diagnosis for additional odor tracing and cure advice focused on sewer gas odor tracking in cold or wet weather.
• Drain Noises: may indicate defective or clogged plumbing: how to diagnose and cure drain sounds


• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.
• 
  What is a Septic System An Engineer's View - Types of treatment tanks, adsorption systems, pumps, and other special equipment are discussed in some further detail in this text
  Components of a Septic System- the Basic Parts of a Conventional Septic Tank and Leachfield, a chapter in the Home Buyers Guide to Septic Systems
  A Toxic Gas Testing Sampling Plan for Residential Indoor Air Investigations

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.)

InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Building Inspection, Problem Diagnosis, Forensic Investigation & Testing, Repair Consulting

Contact Daniel Friedman for website content suggestions or for fee-paid consulting