Troubleshooting: Is the Water Level Too High in the Septic Tank?

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When the tank is opened, the proper liquid level for the tank is at the invert of the outlet pipe. If the liquid level is higher than this it indicates some type of problem. With the current use of effluent screens, this may be the problem. The screen is full of solids, not allowing the effluent to exit the tank. The solution of course is to clean the tank and filter. The service provider should discuss with the homeowner a plan for future maintenance on a regular schedule to avoid these backups. But what if there is not an effluent screen or the screen itself is not plugged? 

The tank should be cleaned and the service provider should observe whether water flows back into the tank through the outlet pipe. If water does not flow back out of the pipe, it means that there is some type of blockage in the outlet piping. If an effluent screen is present the blockage is likely not due to solids moving through the outlet; if there is not an effluent screen the blockage could be due to some type of solid material moving through the tank and accumulating at the outlet. Some examples of this are feminine hygiene products and condoms, or scum that moved into the outlet baffle when the tank was not properly cleaned during an earlier service visit. 

It is not enough to merely remove the material causing the blockage. The outlet pipe should be inspected to determine if the piping near the tank has settled creating a bow in the pipe where solids can accumulate. If the piping is not replaced and rebedded, blockages will continue to be a problem. Another reason for the blockage is the accumulation of roots. If the roots are in the piping it means there is a break in the pipe, which has allowed roots to penetrate. Again, the break will need to be located and repaired; simply removing the roots is only a temporary solution. Similarly, if there are roots inside the tank at the outlet baffle it means the seal around the outlet pipe at the baffle will need to be replaced, keeping the roots from penetrating. 

If water flows out of the piping back into the tank it indicates that the problem is further downstream. There could be a blockage in the distribution or the first drop box in a sequence. The boxes will need to be located and evaluated for the presence of solids that have carried over from the tank, or soil and other solids that have infiltrated with excess water into the tank. Roots could also be the problem and will need to be removed, the piping redone and the boxes made watertight. 

The entire drainfield area may be full and the liquid level in the trenches or bed raised to a level where it will flow back into the tank. To determine if the soil treatment area is full to capacity and beyond will require either probing the entire area or having access to all parts of the area through inspection ports or the boxes. In any case, before proceeding with excavating d-boxes or parts of the trench, the homeowner should be consulted and a plan of action agreed upon. 

About the Author: Jim Anderson is connected with the University of Minnesota onsite wastewater treatment education program, is an emeritus professor in the university’s Department of Soil Water and Climate, and education coordinator for the National Association of Wastewater Technicians. Send him questions about septic system maintenance and operation by email to


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