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Septic or Sewer Gas Odor Smell Source Table:
This article provides a table listing known sources of sewer odors, septic odors, methane gas odors, sulphur smells, hydrogen sulfide smells or similar odors found inside or outside and around buildings. In an alphabeticl list by odor source we describe each smell location, it's occurrence indoors or outdoors, and we link to diagnostic and repair articles.
Air conditioning and heating systems using air ducts and blower fans can pick up odors from one source and move them to another destination. In some cases local negative air pressure may also overcome normal drain pipe venting, especially if plumbing traps are omitted or defective or if there are loose toilets leaking odors into a room.
Air conditioning / heat pump condensate drain connections: an improper connection of the condensate drain from an A/C or heat pump system directly to a sewer line or drain / waste / vent piping system can permit back-drafting of sewer gases through the drain system and into the HVAC system air handler where in turn it may pass through the HVAC ducts into other building areas.
Indoors at air conditioner or heat pump air handler
Drain trap odors: Found sewer gas odors at plumbing fixture traps whose water trap was lost due to trap siphonage due in turn to missing, improperly installed (too distant), or blocked plumbing vent piping.
Where dry plumbing traps pass sewer gases back into a building the problem may be worse in cold weather or when building vent fans are decreasing the in-building air pressure, drawing gases out of drain piping
Septic system drainfield failure, no visible effluent
Private Septic System Failures: Found sewer gas leaks outside due to a failing septic drainfield and/or blocked sewer piping causing backups that leaked outdoors. In a case where odors were traced to leaks at a septic tank, odors from the septic tank were strongest at the front entry door to the home, perhaps in part because the system was in failure and backing up.
Sewer/Septic Piping Leaks: Found DWV (drain-waste-vent piping) plumbing piping leaks: had a plumber pressure test the drain waste vent piping to find sewer gas leaks due to mechanical damage, rust, corrosion in piping, improper sewer vent locations, or inadequate/missing waste pipe venting. Also
Sewer Piping Joint Leaks: Found sewer gas leaks where plastic pipes had never been properly glued in a wall, ceiling or floor, from original construction. Found by pressure testing.
Sewer Piping Punctures: Found sewer gas leaks where drain waste vent pipes had been perforated by a nail from flooring or in one case from hanging a picture on the wall
Swamp gas or marsh gas: Traced sewer/septic gas odors to swamp gases or marsh gas, also potentially dangerous, especially if swamp gas leaks into and accumulates inside a building, as reported in the NY Times, appears to have occurred in Cancun, Mexico in November 2010. Swamp gases include methane produced by the decomposition of organic materials in subsoils.
Toilet seal leaks: Found sewer gas leaks at a toilet with a bad seal - a toilet can be leaking sewage water or just gases around its base if the toilet is not properly mounted, even if the toilet is not obviously loose on the floor=
Also see SULPHUR & SEWER GAS SMELL SOURCES for our master list of sources of sulphur like odors in buildings. This list includes sources of sewer or sulphur like smells beyond those originating at a septic system or sewer piping.
CONTACT us to add other sewer gas odor sources you've found - it will help others
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 Amoore, J.E. and Hautala, E., 1983. Odor as an aid to chemical safety: odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. Journal of Applied Toxicology 3, 272-290.
 Bates, M.N., Garrett, N. and Shoemack, P., 2002. Investigation of health effects of hydrogen sulfide from a geothermal source. Archives of Environmental Health, 57(5): 405-411.
ASTM E2600 - 08 Standard Practice for Assessment of Vapor Intrusion into Structures on Property Involved in Real Estate Transactions is available from the ASTM at astm.org/Standards/E2600.htm
"This practice is intended for use on a voluntary basis by parties who wish to conduct a VIA on a parcel of real estate, or more specifically conduct a screening evaluation to determine whether or not there is potential for a VIC, and if so, identify alternatives for further investigation."
The standard goes on to emphasize the uncertainty in testing any site for gases and vapor intrusion.
Amoore, J.E. and Hautala, E., 1983. Odor as an aid to chemical safety: odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. Journal of Applied Toxicology 3, 272-290.
Bates, M.N., Garrett, N. and Shoemack, P., 2002. Investigation of health effects of hydrogen sulfide from a geothermal source. Archives of Environmental Health, 57(5): 405-411.
Gangolli, S. (Ed.), 1999. The Dictionary of Substances and their Effects, 2nd edn. The Royal Society of Chemistry. Cambridge.
Sax, N.I. and Lewis, R.J., Sr., 1989. Dangerous Properties of Industrial Materials, 7th edn. Van Nostrand Reinhold. New York.
Snyder, J.W., Safir, E.F., Summerville, G.P. and Middleberg, R.A., 1995. Occupational fatality and persistent neurological sequelae after mass exposure to hydrogen sulfide. American Journal of Emergency Medicine, 13(2): 199-203.
EMS Testing Laboratories (a nationwide chain in the U.S.) - see http://www.emsl.com
"Draft Report on Preliminary Microbiological Assessment of Chinese Drywall", U.S. CPSC, draft report 26 March 2010, - Web Search 08/03/2010, original Source: http://www.cpsc.gov/info/drywall/microbio.pdf
Lori Saltzman, M.S., Director, Division of Health Sciences, U.S. Consumer Product Safety Commission, 4330 East West Highway,
Bethesda, MD 20814, Prepared By: Environmental Health & Engineering, Inc., 117 Fourth Avenue, Needham, MA 02494, EH&E Report #16512,
March 26, 2010
"Drywall Flaws: Owners Gain Limited Relief, Chinese Product Forces Many From Homes", Andrew Martin, The New York Times, p. 1, 18 September 2010
Chinese Drywall information hosted by the US Consumer Product Safety Commission, and supported by the US CDC (Centers for Disease Control), the U.S. EPA (Environmental Protection Agency), and HUD, the U.S. Department of Housing and Urban Development - http://www.cpsc.gov/info/drywall/index.html
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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