In the July 30, 2018 issue of Onsite Installer, there was an article discussing how an installer can troubleshoot the drainfield and yard, but the homeowner can also use this information if they notice some issues in the plumbing of their home. The article mainly discusses the distribution box, but it also discusses roots and root entering and clogging the lines. The article can be found by clicking here.  

The article is also copied here (Onsite Installer, July 30, 2018 issue, written by Jim Anderson, Ph.D.):

Previously I discussed looking at troubleshooting indicators in the residence and in the sewer pipe from the house to the septic tanks. Now we turn to the next likely possibility in any troubleshooting effort. The drainfield and surroundings need to be looked at if the system is having problems.

Distribution, dropboxes or valve boxes should be located and opened. It has always amazed me how many times while troubleshooting that, even though the plans from the local permitting authority show the presence of a distribution box, when the area is excavated there is no box at all and distribution is through a series of pipes and elbows. The first task is determining that all of the parts of the drainfield distribution system are present and operating.

The boxes themselves should be checked for structural soundness and whether there is any indication of root penetration or sludge accumulation. Bottoms and sides of the boxes should be checked to determine that there are solid walls and bottoms. Any cracks or crevices can lead to root penetration or water infiltration.

The presence of roots indicates the potential for pipe blockage as a part of the problem. They may also indicate that surface water has entered the system, potentially flooding out the drainfield. Sludge accumulation could indicate that the septic tank has lacked maintenance and solids have been delivered to the drainfield; there may be plugging in the soil dispersal and treatment area.

Piping into and out of the boxes should be evaluated. Does the piping come in and out of the box at the angle it should or is it skewed or cocked at the wrong angle? This could have taken place during installation or happened as the soil around the box has settled over time. If the piping is bowed or at the wrong angle, it could be preventing effluent from properly moving out of the box into the drainfield trench. The result could be that only part of the system is being used — leading to effluent surfacing from the trench or trenches that are receiving effluent.

The presence and depth of water in the boxes should be evaluated. Is the box full to the level of the outlets to the trenches? In a distribution box, are speedy levelers or some other method used to direct effluent in sequence to the trenches? If the water in the house is shut off, there should be no water running into or out of the box. Does it appear that water is moving out of all outlets in the distribution box? If not, it may indicate only part of the system is being used, which could lead to surfacing.

Similarly, with dropbox distribution, the lowest line in the sequence is where surfacing should occur. All dropboxes should be checked to make sure they are all full. If not, there is an interruption or problem with the distribution to the higher lines and this needs to be determined and corrected so the entire series of trenches is used.

As I have written many times, I feel dropbox distribution is superior to using distribution boxes; the presence of several boxes allows for more management of the trenches and easier troubleshooting if there is a distribution problem.

About the author
Jim Anderson is connected with the University of Minnesota onsite wastewater treatment program and is an emeritus professor in the university’s Department of Soil, Water and Climate. Send him questions about septic system maintenance and operation by sending an email to