What are the signs of a failing septic system?

The short version

A failing septic system usually tells you in one of three places: inside the house, in the yard over the tank and drainfield, or in nearby water. One sign on its own can have an innocent cause. Several at once, or any sewage you can see or smell outside, means it is time to call a licensed septic professional.

Signs inside the house

These are the signs EPA lists first, and the ones most owners notice first:

• Backups. Sewage or dirty water coming back up through toilets, drains and sinks^[1] is the clearest signal. Look for backups first in the plumbing fixtures at the lowest elevations in the house, such as a basement bathtub or first-floor toilet.^[4]
• Slow drains. Tubs, showers and sinks that drain very slowly^[1] matter most when it is happening across the house. Virginia Cooperative Extension notes that sluggish drains may point to a problem in the absorption field, although they could just be clogged pipes.^[2]
• Gurgling. Gurgling in the plumbing^[1] often comes along with slow drains.
• An alarm. Pumped and alternative systems have a high-water alarm, often a small box with a warning light and horn. VDH's instruction is plain: "If the AOSS is equipped with an alarm and the alarm goes off, immediately contact your service provider."^[5]

Signs in the yard

• Wet ground. Standing water or damp patches over or near the tank or drainfield^[1] are a classic sign. EPA adds: "Soft, wet, or spongy soil (especially when there have been no significant rainfall events) around your drainfield is a good indication of a system failure."^[1] Standing water above the drainfield is a stronger warning when it is discoloured and smells unpleasant.^[2]
• Smells. Sewage smells around the tank or drainfield^[1] deserve a look. Not every smell is a failure: a smell can come from a roof vent or other vent pipe, which is a normal part of the system, and a vent clogged with leaves or frozen in a cold spell can push odors inside or outside.^[1]
• Too-green grass. EPA lists bright green, spongy grass over the tank or drainfield that stays lush even in dry weather.^[1] Extension cautions that drought and low fertility can produce a similar effect, so a professional should look before you assume the worst.^[2]

Signs in nearby water

A failing system can show up away from the house. EPA's list includes high nitrate or coliform bacteria levels in nearby surface water or drinking-water wells,^[1] and algae blooms in nearby lakes and other water bodies.^[1] When checking a property, Extension also looks for eutrophic water in nearby ditches.^[3] If you drink from a private well, this matters directly: VDH warns that contaminated groundwater can quickly find its way into a drinking water source.^[7]

What Virginia counts as a failure

VDH's assistance program describes sewage backing up into the house or basement, or erupting outside on the ground surface, as a possible sign of a failing system.^[6] Under the state's rules as Extension summarises them, a failure is known to exist when sewage backs up into the dwelling, sewage is seen on the ground surface, or sewage pollutes ground water.^[2] When the health department documents one, a Notice of Alleged Violation is issued to the owner, setting out the steps to fix it and a time frame for the design and repair.^[2]

Why systems fail

Knowing the likely cause helps you describe the problem when you call:

• Skipped pumping. One of the most common reasons septic systems fail is that the tank is not pumped often enough,^[2] so solids escape into the drainfield and clog the soil.
• Worn parts. Baffles that keep solids out of the drainfield can degrade, which is more common in concrete tanks.^[2]
• Too much water. A system undersized for the number of people in the house can overload the drainfield.^[2]
• The drainfield itself. Building or planting on the drainfield, tree and shrub roots, and long spells of very heavy rain with water standing over the field all cause failures.^[2]

Sometimes the problem is temporary. Flooding may also make a system sluggish simply because the soil in the dispersal area is saturated,^[4] and it may recover as the ground drains. Until then, VDH advises that you minimise water use in the house to keep raw sewage from discharging to the ground surface.^[4]

Stay safe while you wait

If sewage backs up into your home, avoid contact with it, because it may contain harmful pathogens, and contact your local health department for guidance.^[1] Keep children and pets off wet areas in the yard, and leave the tank lids closed: septic tanks can contain dangerous gases such as methane and hydrogen sulfide.^[8] Cut back on laundry, long showers and dishwasher loads until the system has been checked.

When to call a licensed pro

Call a licensed septic professional as soon as you see sewage inside or outside, when several drains are slow at once, when an alarm sounds, or when wet, smelly ground over the field does not dry out with the rest of the yard. An inspection and pump-out will often show whether the problem is in the tank, a pipe or the drainfield. Our page on why a septic system backs up into the house covers backups in more detail.

The fix depends on the cause. In Extension's words, "These failures can require relatively simple and easy fixes or costly system relocations."^[2] A failed drainfield usually needs a new design and a permit. If a system has failed, the owner is responsible for repairing it, a repair permit is required, and the local health department must issue it before the repair.^[2] In the meantime, licensed professionals can sometimes pump the effluent out and haul it away on a schedule, but only for a limited time until the system is repaired or replaced.^[2] Read what a drain field repair involves and whether you need a permit for a septic repair.

Hire only licensed people. In Virginia, no individual may operate or maintain a conventional or alternative onsite sewage system without a valid operator licence,^[9] and no individual may install one without a valid installer licence.^[10] Browse more excavation and septic answers or septic system services.

When something looks wrong, describe the problem once and get quotes from licensed septic businesses.