In our workshops, one of the installation keys we discuss at great length is making sure sewage tanks, piping between system components and distribution or dropboxes are watertight. The reason for having watertight system components is twofold. First, you don’t want them leaking raw sewage or septic tank effluent into the surroundings or to create a pathway for runoff or groundwater to infiltrate into the system. Second, if the components are watertight, they will be resistant to root penetration.

Across the country, different types of vegetation are problematic to septic systems in terms of their roots aggressively searching for water and nutrients. They will take advantage of even the slightest openings to penetrate and obtain the water. A couple of examples of trees often identified as being problems with roots: In humid areas, willows and white pine; in arid or tropical regions palm trees; also, in arid regions mesquite and palo verde.

No matter where you live and work, you can’t escape the threat of root intrusion. This is why it is important to inform the homeowner not to plant this type of vegetation around their septic system. We spend time in our classes discussing establishment of vegetative cover with fibrous root systems, not deep-penetrating roots. Elimination or avoidance of problem vegetation is the first line of defense to protect from root problems.

Resourceful roots

Avoidance only goes so far because even less aggressive types of vegetation will seek out water to survive during dry periods or droughts. It is why if you dig alongside an operating sewage treatment trench, you will often find an accumulation of roots along with the developed biomat. The plants are tapping into the water and the nutrients in that area.

One important note is that roots do not typically plug the entire drainfield because they do not grow where there is a lack of oxygen, for example when there is sewage ponded in the trench. If the trench is empty — as it may be in sequential distribution with dropboxes — it may be because the necessary water is not there.

In sewage tanks something similar operates. Where sewage is contained at depth, the roots do not grow into the anaerobic environment. Rather, they will be found in areas with intermittent flow or just on the outside of the sewage. Therefore, when roots penetrate the tank, a root mass may often be found on the lid and then growing into the baffles and piping to other components.

At any point where pipes penetrate the tank — for example lids, risers, manholes — it is critical for tanks to be sealed and watertight. An important note: Do not seal the manhole in a way that makes it difficult or impossible to gain access to the tank for inspection and pumping.

Any piping in or out of the tank should have gaskets at the penetration; either cast into the tank when manufactured or added by the installer. Follow the manufacturers specification to attach and seal the tank lid and any access to the tank or baffles.

It’s also important to make sure the piping between parts of the system remain watertight. For typical installations, pipe sections are connected using solvent welds with slip joints. These connections are effective with PVC pipe as long as the PVC primer and cement are used properly. When we discuss this in class, it usually causes a couple of snickers, because of course we know how to glue pipe! Nevertheless, we have been on multiple sites troubleshooting systems where there are root problems only to find one or more (usually more) connections was not properly made.

Joining pipe

There are a couple important items to keep in mind when “gluing” pipe. It is critical both the exterior and interior surfaces to be joined are clean and dry. If not, the connection will not be solid. Before applying the primer and then the cement, test the connection to see if it fits properly, this will avoid having to start over when the connection is glued and it is obvious the connection is not proper.

An improper connection like this is not watertight and is a location where roots can enter the piping and expand. Remember to use the cleaner first to remove any final dirt from the pipe and fittings and then use the primer to soften the pipe and finally apply the cement (glue). The last gluing step needs to be done quickly before the glue dries, so everything needs to be ready.

Some other common ways piping connections or pipe itself loses watertightness and is subject to root penetration is when the system is backfilled. It is entirely the responsibility of the installer to properly backfill around tanks and piping so the piping into the tank doesn’t end up at an angle due to settling around the tank. It is important to be careful that piping is not damaged or joints are separated when the supply trench is backfilled. Any opening like this is subject to root penetration.

It takes some time for root problems to show up. In the extreme, roots can totally block and fill up the piping to the point it allows little to no water to pass through. This is when you get the call sewage is backing up into the house or surfacing and you find roots are the problem. Locating and fixing problem areas is time-consuming and expensive; with the homeowner hovering over you expecting you to fix it. Better to do it right from the start.