A sewer odor coming from your basement drain can indicate a problem with your plumbing. Sewer odor is produced by sewer gas, which is a mixture of toxic and nontoxic gases created by decaying household waste. This gas typically includes hydrogen sulfide and ammonia, which are extremely toxic, requiring you to address sewage odors immediately.
In addition to hydrogen sulfide and ammonia, sewer gas contains methane, carbon dioxide, sulfur dioxide and nitrous oxides. Exposure to hydrogen sulfide at low levels can cause eye and respiratory irritation. High concentrations can affect your sense of smell and, at even higher levels, exposure to hydrogen sulfide can cause loss of consciousness. With long-term exposure, death may result. High concentrations of methane can cause suffocation because in confined spaces, methane reduces the oxygen in the air. When there is methane in the air, symptoms can occur rapidly and unconsciousness can result with little warning. Methane and hydrogen sulfide are also flammable and explosive.
One of the most common causes for sewer odors in your basement is a dried-out drain trap, which must be filled with water to prevent sewage gas from coming up through the drain and entering the home. Every time water flows into the drain, the trap is filled. If you've gone away for an extended period, typically longer than a week, or the drain isn't often used, there is no water available to keep the drain trap continually full. Flush basement toilets every three weeks and faucets above sinks, tubs and showers, including your laundry tub should be turned on regularly to keep the traps filled.
Poorly Capped Drains
Occasionally during remodeling a drain might be capped with tape rather than a proper drain cap. The tape eventually dries out, which allows sewer gas to escape. If the drain is no longer in use, cap it with a proper cap to stop the odor.
Splits or cracks in the drain piping and loose or damaged connections in a drainpipe that are located below the drain trap may cause the sewer gas to escape, causing the odor to fill your basement. Call a plumber if this is suspected to have the problem properly fixed. If this isn't the cause, a plumber can use a smoke generator to pinpoint the problem. Smoke generators connect to your drain system, which is blocked temporarily, and fill it with smoke. The smoke escapes through the problem pipe or joint.
Recurring or Persistant Odors
If the odor persists, despite taking measures to correct it, contact a qualified professional to inspect your plumbing and drain traps. The issue may not be something that you can fix on your own, and the longer that the sewer gas is allowed to seep into your basement, the more at risk you and your family are of having ill effects from the toxins. If symptoms such as headache, nausea, dizziness, or fatigue occur, seek medical attention and evacuate the home. Contact your local fire department to inspect as methane gas can ignite quickly from a match, lighter or an electrical spark.