Sewer Lines and Trees

The City of Bismarck Public Works Department often receives calls from residents dealing with sewer backups. Many times the resident will find that tree roots have clogged their sewer service line and then make the request for the tree to be removed. There are several misconceptions with this approach.

The first misconception is that the tree caused the damage to the sewer line in the first place. In most cases the sewer line has a defect in it to begin with allowing the tree roots to enter the line. Many older, clay sewer lines will be cracked or broken or the joints will have shifted due to soil settlement. Tree roots enter these defects and then clog the sewer line. Trees need water, oxygen, and nutrients to thrive and be healthy, these defects in the sewers release oxygen and some moisture signaling to the tree that there is a good growing medium within the line. Fine root hairs will grow through these defects entering into the line which then leads to the sewer line blockage.

The second misconception is that removing the tree will take care of the blockage of tree roots in the sewer line. Tree roots can spread out 3 to 5 times the height of the tree. So the closest tree to the sewer line may or may not be the only tree causing the problem. If multiple trees are causing the problem removing one tree will not address this issue. Also if the tree is removed, the root system will continue to grow for a few years depending on the species of tree.

The third misconception is that by using mechanical or chemical control the problem will be eliminated for a few years. The fact is that if the line is damaged and the defect is not corrected the tree will continue to send new roots into the line, or another adjacent tree will start to grow into the line. Mechanical or chemical root control is a temporary solution that must be repeated on a regular basis.

The best solution is to repair or replace the defective sewer line. Repeated blockage indicates that the line is collapsed or badly damaged. Many plumbers or sewer cleaning services have cameras that can inspect the line to determine the nature and extent of the problem. This can be a great assistance in planning the most cost effective repairs to the service line.