Follow These Tips to Prevent Nasty Root Intrusions

Your customer’s big holiday weekend can be ruined with backups when a tiny root grows to knock out their septic system.

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Readers often recount stories of some of the problems they encounter while inspecting or troubleshooting systems. Lately I have had several readers contact me with stories of opening part of a system to find that roots have filled or nearly filled the supply or drainfield piping. Obviously if the piping is filled with roots, sewage will not flow between parts of the system as it should. Over time this results in sewage backups or surfacing.

System piping, sewage tanks, distribution and drop boxes should all be watertight. That means water is not allowed to flow into the system from outside or flow out into the soil from system components except in the soil treatment area. If water is infiltrating the system through a non-watertight component, the excess water can hydraulically overload the system and cause failure. It can also be a source of sewage leaving the system before the soil treatment area, presenting a health or environmental hazard.

The presence of roots in any part of the system indicates a problem due to some defect or poor installation or maintenance activity. The first location to evaluate root penetration is the supply line from the house to the septic tank. If roots have entered the supply line it will lead to blockages and backups into the house. 


Roots can be present in the supply line if the piping was not properly bedded and it was cracked or broken during installation. Other potential causes are poor connections, which could include improper gluing of the piping or the use of inappropriate connections such as couplings not designed to be watertight. 

This is something a neighbor of mine experienced last summer. She had some work done on her system a year ago and apparently the contractor had problems matching up the piping and used a flexible coupling. Roots from nearby conifers entered the pipe creating a blockage. Since it takes the roots some time to enter and block the pipe, it would finally occur during the most inopportune time over the July Fourth weekend when it was difficult to get a hold of her service provider and there was a house full of company with nowhere to go.

Roots can enter the system through the septic or other sewage tanks. Here again if they are in the tank, they can eventually block either the inlet or outlet creating backups to the house or potential for sewage at the surface. Any penetrations or joints in the tanks should be checked for watertightness and root penetrations. 

As we all know, roots can get through what seems to be the smallest crack or opening and then once inside the tank expand and grow very large. You’ve seen photos of a tiny, flattened root going through a small opening between the lid and tank wall and then once inside the tank, forming a huge root ball.

During tank installation, self-sealing gaskets should be applied where the tank lid meets the walls, or better yet, the tank constructed with a tongue-and-groove connection along with the gasket. These days many tanks come with cast-in-place gaskets at the inlet, outlet and where the manhole riser will attach to the tank. 

If these gaskets and connections are not already cast in the tank, it is important that seals and gaskets be fitted to these openings during installation. Simply resting smooth wall plastic pipe on the concrete opening and then applying mortar into and around the opening will not create a watertight connection or keep roots out.


Risers added to bring the manhole to the surface for tank maintenance also need to be watertight. Plastic and concrete sealants are available to make connections between riser sections and must be used.

Another place where roots are likely to enter the system is through distribution or drop boxes. Once in these boxes, roots can grow into the piping providing blockages at the inlet, outlet and even in the system distribution piping. Distribution boxes, whether plastic or concrete, usually have flexible gaskets built in during the manufacturing process. If they are not precast, gaskets need to be installed. Lids on the boxes should have a self-sealing gasket where the lid meets the walls. 

The supply pipe from the house, piping between the tank and distri-bution boxes, or from the boxes to sewage treatment trenches are areas where roots can penetrate if the piping is broken during backfill, connections are not done correctly, or soil has settled in around or under the pipe leading to connections breaking. An indicator of settling at the surface would be dips or low areas around the supply line. There is often wetness in this area as well because sewage is leaking out of the piping.

Distribution pipe in the soil treatment area can also have root problems if the piping was damaged during backfill. The other major cause of roots in the soil treatment area is planting vegetation on or near the system that will aggressively grow into the system. This vegetation could be a variety of types depending on where you live. Where I reside, white pines, willows, basswoods and cottonwoods would be problems. In southern areas palm trees and similar vegetation can be problems.  


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