The intrusion of tree roots in sewer pipes is probably the most destructive single element that faces those maintaining a sewer collection system today.
Sewers are ageing expensive assets that only attract public attention when they fail. There are more than 35,000 kms of water and sewer pipes in Sydney and 60% of all collection systems are made up of pipes with a diameter of 9 inches (225 mm) or smaller. The potential for tree root intrusion to inhibit flows, produce blocked drains and damage valuable pipes, is enormous.
Tree roots normally do not grow underwater and seldom cause problems where ground water covers the pipe. But in most areas, this is not the case.
Tree Roots Grow One Cell at a Time
When a seed germinates, it adds one cell at a time toward the best environment from which it might extract nutrients and moisture. The growing point of a tree moves best through loosely cultivated soil.
The most common practice used to lay sewer pipes is in an open trench. The back-filled soil offers a good growing medium for tree roots. Because the flow in sewer pipes is a higher temperature than the soil, this causes a condensation to appear on the crown of the pipe.
As the warm moisture from the sewer pipe evaporates up through the soil, the vapours offer an excellent trail for the tree roots to follow. If a vapour leak exists in the pipe, the roots concentrate its efforts at that point. Since some pipe joint compounds are of nutrient based material themselves (like rubber rings or sand cement mix), the root may entirely girdle before entering the pipe.
Roots Allow Accumulation of Debris
Once inside the sewer pipe, the root takes on the appearance of a “veil” or “horse tail” type structure. If flows in the pipes are fairly constant, the root mass hangs down like a veil to the normal flow level where they accumulate deposits of grease, slime and other debris.
Conventional methods of removing tree roots by cutting with an electric eel or a “Rattlesnake” high pressure water drain cleaner tend to increase regrowth; similar to pruning a tree. Removing tree roots inside the pipe solves the immediate problem of clearing the blocked drain, but does nothing to retard the tree root regrowth or destroy the tree roots outside the pipe.
This removal, regrowth and removal cycle of cutting and tearing roots can destroy the structural integrity of the pipe.
Herbicide Fumigants
Herbicide fumigants present the most effective method to destroy tree roots and inhibit their regrowth without affecting the above ground plant life. Vaporooter is a root control herbicide that enters the sewer as a foam. Only tree roots within the pipe and a short distance outside the pipe are affected. Trees and shrubs immediately above ground are not harmed in any way.