SEPTIC MAINTENANCE GUIDE

Septic Gases: What You’re Smelling and What to Do

Keep the septic tank lid closed if you’re investigating an odor. Gas can collect above the wastewater and escape suddenly when the lid is lifted. Anyone standing close or leaning over the opening can be exposed in seconds. The air inside a tank can contain poisonous gas and too little oxygen to breathe. Keep lids secured and keep children and pets away. Never enter a septic tank, even to help someone inside. If someone collapses near or inside a tank, call 911. CDC confined-space safety guidance

What gases form in a septic system?

Microorganisms naturally break down waste in a septic tank. Much of that activity happens where there is little or no oxygen, and it produces a mixture of gases.

Hydrogen sulfide: Can smell like rotten eggs and can be poisonous. Your nose can stop detecting it even while it’s still present.
Methane: Has no odor. It can ignite if it builds up and reaches a spark or flame.
Carbon dioxide: Has no odor. It can build up in an enclosed space and make the air unsafe to breathe.

An odor can alert you to a problem, but it can’t tell you whether the air is safe. CDC guide to hydrogen sulfide · CDC guidance on gases in tanks

If you smell sewage outside

From a safe distance, notice where and when you smell it. Is it near the tank, over the drainfield, or downwind of a roof vent? Does it happen after heavy water use or when an aeration unit runs? Those details can help a technician narrow down the cause.

Near a roof vent. Plumbing vents release gases outside. Wind can carry the smell down toward the yard or windows. A blocked or frozen vent can also cause odors. Have a plumber check a suspected vent problem.
Near the septic tank. The tank may be due for pumping or the outlet filter may need cleaning, especially if several drains are also slowing down. An odor alone doesn’t tell you whether the tank needs pumping. Have a septic professional check the tank, lid, and filter.
Near an aeration unit. The aerator bubbles air through the wastewater and stirs it. You may notice an odor near the unit or its vent while it runs. If the smell is strong, lasts, or is worse than usual, have the unit checked, especially if an alarm sounds.
Over the drainfield. A sewage smell along with wet, spongy ground or standing wastewater can be a sign the field isn’t absorbing wastewater properly. Keep people and pets away, reduce household water use, and call a septic professional promptly.

EPA guidance on septic odors and signs of failure

For a mild odor near an indoor drain or fixture

If the smell is mild and clearly coming from one fixture, note where it’s strongest. That can help a plumber find how sewer gas is getting in.

Basement floor drain, guest shower, or rarely used sink: The water in the drain trap may have evaporated. That water normally keeps sewer gas from coming up through the drain. If the fixture drains normally and there’s no backup, add water to refill the trap.
Around the base of a toilet: A loose toilet or worn seal may let sewer gas escape around the base. Have a plumber check the seal and mounting.
Laundry room or utility area: The odor may come from a floor drain, utility sink, or washer drain. A plumber can check the traps and drain connections.
Several fixtures, especially if they gurgle: A blocked vent or a restriction farther down the drain line could be involved. A plumber can trace the source.

Plumbing trap and vent guidance · Indoor sewer gas guidance

If the mild odor keeps coming back, start with a plumber. If you also notice a septic alarm, sewage backing up from several fixtures, or wet ground near the tank or drainfield, contact a septic professional too. EPA guidance on septic system problems

Concerned about an odor near your tank, aeration unit, or drainfield? Call Moore’s Septic Services at 740-415-7760. Tell us where you smell it, when it started, and whether you’ve noticed an alarm, slow drains, or wet ground.