A failing septic system in Missouri

The clearest sign is water that should be underground appearing above it: effluent surfacing over the lateral field, a patch of ground that stays wet and green through dry weather, or a smell outdoors that does not clear. Indoors, the tell is timing rather than severity. Backups that return within days of a pump-out are a field problem. Backups that go away for a year after a pump-out were a full tank.

Repeat pumping at short intervals is the most commonly missed warning. It feels like maintenance because it is a plumbing bill, but a system that needs emptying every few months is telling you the ground is no longer accepting the water.

When it is a major modification or major repair. At that point the same requirement applies that applies to a new build: notify the city, county or department, apply on the department's form, pay the fee that body sets, and obtain a construction permit before the work happens. Replacing a tank or building a new absorption field sits on that side of the line.

The rule also reaches backwards. Any construction, operation, major modification or major repair has to be in accordance with the rules regardless of when the system was originally constructed, so an old system does not carry an exemption on the strength of its age.

Source: Section 701.046, Revised Statutes of Missouri, read 2026-08-26.

Often, yes, and this is the part that surprises people who assume a like-for-like swap. The new field has to meet the current rule, which means it is sized on a soil evaluation and it has to hold the required vertical separation: at least one foot between the trench bottom and the limiting layer or seasonal high water table, and four feet to groundwater or bedrock in highly permeable soils and in cherty clay soils in areas of severe geological limitations.

A field installed decades ago may not have been built to that, and the ground it sits in has not improved. That is why a failed field sometimes comes back as a mound, a drip field or an engineered design rather than as new trenches in the same place.

Source: 19 CSR 20-3.060(5)(A)2., Missouri Code of State Regulations, read 2026-08-26.

Get a diagnosis before you buy a solution. The useful question is which part has failed: the tank, the line between the house and the tank, or the absorption field. They have very different prices, and a tank replacement in front of a failed field is money spent twice.

A real inspection that opens the tank and assesses the field is worth more than three quotes based on a description over the phone.