Sewage odor over the field, standing water or unusually soggy or lush ground there, drains that stay slow even after pumping the tank, and sewage backing up into the house are the common signs of drainfield failure. These tend to appear in that rough order, from early and easy to miss to late and impossible to ignore.
Early failure often looks like nothing more than a patch of grass that grows faster and greener than the rest of the yard, because it is getting extra moisture and nutrients from effluent that is surfacing instead of being absorbed. It is easy to write off as a lawn quirk, which is exactly why field failure often isn’t caught until later.
A more advanced sign is drains that stay slow throughout the house even right after the tank has been pumped — if pumping the tank does not fix slow drains, the tank was probably not the actual bottleneck, and the field itself is failing to accept water at the rate it should.
The most advanced and most disruptive sign is sewage backing up into the house, typically into the lowest drains first. By this stage the field has usually lost significant capacity, and the fix is rarely simple maintenance — it is often partial reconstruction, resting the existing field, or, where soils allow, an alternative system.
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Unusually lush or wet grass over the field, caused by effluent surfacing instead of being fully absorbed by the soil, is typically the earliest visible sign.
It suggests the tank wasn't the bottleneck, and the drainfield itself is not accepting water at the rate it should, which points at field failure rather than a full tank.
Sometimes. Options range from resting part of the field to partial reconstruction to an alternative dispersal method, depending on soil conditions and how much capacity has been lost.
Guide last reviewed 2026-08-31.