Common Drain Field Problems and What Causes Them
Short answer: A failing drainfield usually shows up as slow drains, sewage smells, or soggy, unusually green grass over the field. Once a drainfield's soil is clogged, it generally can't be repaired, only replaced or, where the lot allows, relocated.
What causes a drainfield to fail
The drainfield's job is to let effluent filter through soil, doing the final stage of treatment. It typically fails because too many solids reached it, often from a tank that wasn't pumped on schedule, because tree or shrub roots grew into the pipes, because heavy vehicles or construction compacted the soil above it, or because the system was undersized for the household in the first place.
Once the soil in a drainfield clogs with a layer of solids, sometimes called a biomat, in excess, water can no longer filter through fast enough, and it backs up or surfaces.
Warning signs
Standing water or soggy ground over the drainfield, sewage odor in that area, and grass that's noticeably greener there than elsewhere, even in dry weather, are the classic signs. See our full list of septic warning signs for what else to check.
Prevention
Pump the tank on schedule so solids don't reach the drainfield, don't park or build over it, keep tree roots away, and don't send more water through the system than it's sized for, for example by spreading laundry loads out over the week rather than running several in one day.
Sources
Checked July 2026.