Intrusion of tree roots in sewers is one of the most destructive and disruptive problems encountered by sewer system managers. The need to remove existing roots and control future growth is a balancing act between available finances and delivering a safe, functional system that services both domestic and industrial customers. Therefore, spending available funds in the most cost effective manner is paramount in good sewer management.

Organisations involved with the maintenance of sewer systems would be familiar with the typical problems encountered from root intrusion, including reduction in hydraulic capacity and self-scouring flow velocities, which can result in blockages and overflows or septic pools behind root masses. Another significant problem is structural damage, which can lead to sewage loss to the surrounding environment and infiltration in areas where pipes are seasonally below water tables levels.

Blockages and overflows are readily identified by customers due to the resulting odours and spillage. Unfortunately, structural damage is normally only identified after CCTV inspection is undertaken; the lag time between the structural damage occurring and being identified can result in large volumes of clean water infiltrating the system and large quantities of raw sewage impacting on the receiving environment.

The ultimate goal for sewer management is a blockage and breech free sewer system. Reactive measures including pipe relining or complete pipe replacement are extremely expensive. Based on economic studies and anecdotal evidence, the cheapest course of action to achieve blockage and breech free sewer systems is a proactive root control program.

Root control programs have historically incorporated a variety of root control methods, including:

Pipe lining

Increasingly viewed as a relatively permanent solution to root intrusion in sewer systems, but the costs are often prohibitive and limited by budget constraints.

Mechanical root removal

Continues to be a popular method for controlling roots in sewer lines, however the downside to this technique is the encouragement of root regrowth, which results in prolific and invasive regrowth. All gardeners know that pruning is a critical part of gardening to encourage healthy, strong growth and plant development – this works for tree roots as well! Furthermore, the use of rotary cutting tools raises concerns regarding structural damage to sewer lines.

Mechanical root removal supplemented with chemical root regrowth inhibitors

This helps retard root regrowth and involves the use of herbicides containing dichlobenil (Rootfoam WP and Turbofoam WP).

Chemical root control

As a stand alone technique has been employed in Australia for many years. Metham sodium based products (Sanafoam Vaporooter® and Roo-Pru®) have been around for over 10 years; and more recently (2004), a diquat based product (RootOut) was introduced to the Australian market.

Based on overseas and local experience, chemical root control as a standalone technique is significantly more effective and cheaper than mechanical root removal on its own, or when supplemented with root growth inhibitors.

All pesticides and herbicides used in Australia must be registered with the Australia Pesticide and Veterinary Medicines Authority (APVMA). The following herbicides are currently registered for the control of roots in non-domestic sewer systems. (note: copper based are excluded here, as they are for the domestic market (4” lines); not commercial mains): RootOut, Sanafoam Vaporooter, Roo-Pru, RootFoam WP®, Turbofoam WP®.

These products are applied to sewer lines as foam. The foam removes grease that has built up on root surfaces and floats the chemical above the sewage so that it may contact the tree roots.

RootOut

RootOut has been specifically designed for controlling tree roots in sewers.

RootOut has the following attributes: a high efficacy in root kill; more effective controlling of root regrowth; and it does not pose a significant occupational health and safety hazard during mixture preparation and application. A further benefit is that dead roots do not petrify in sewer lines.

The active ingredient in RootOut, diquat, is a herbicide that has been used extensively in the agricultural sector for many years; it is a non-selective contact herbicide that is not translocated through the tree. This means that when RootOut is introduced to root-infested sewer pipes, it will kill the roots but not travel further up the plant causing damage to an otherwise healthy tree.

A particular advantage of RootOut is that the herbicide does not have any other pesticide activity, and will not have a deleterious impact on bacteria in sewage processing plants.

In Australia, all the organisations that have used RootOut have been impressed with the product’s exemplary results and ease of use. In the USA, where the product has now been used for over 10 years, significant benefits have been observed (note: in the USA the product is branded Razorooter II®).

These benefits include that lines only need to be retreated every three years, rather than every year. Also, cost reductions of greater than 60 per cent are consistently being reported. This is because lines are treated less frequently with RootOut than with other chemical options, but also because, with RootOut, cutting is only required if lines are grossly infested by roots which prevent the entry of a foaming hose.

Greater efficiency in sewer maintenance programs is a further benefit of using RootOut. As the system is simple and time efficient in its application, water authorities have been able to make better use of man hours and can treat greater lengths of sewer lines.

There have also been drastic reductions in choke rates, a 70 per cent reduction observed over a three year period and 95 per cent reduction observed over a period of ten years.

Benefits of RootOut

There are many benefits of using RootOut. Application of the system is simple and safe, and root growth is retarded, enabling a progressive and significant reduction in choke rates.

With the reduction in choke frequency in sewer mains and laterals, the number of emergency call-outs are drastically reduced. RootOut kills the roots in sewers but does not affect the tree itself, does not harm surrounding plants and does not harm important microbes in sewage treatment plants.

Unlike the physical damage caused by rotary cutting equipment, the use of RootOut does not generally require the roots to be cut first, hence reducing the potential for structural pipe damage, and re-entry into the sewer system can occur as soon as the RootOut foam has dried.

RootOut is not volatile, nor does it generate a highly toxic gas. Furthermore, it is not an eye and skin irritant or potent skin sensitiser, and it is not readily absorbed through the skin.

The logical option

In an environment where Water Authorities are charged with the responsibility of implementing safe, efficient and cost effective root control programs, RootOut offers the perfect solution.

This system helps reduce the overall costs of root maintenance programs, whilst being effective in the short and long term. It is supported by scientific studies, but more importantly, has delivered in the field where it counts.

Municipalities that have introduced RootOut to their sewer maintenance program have continued to use it knowing that it is safe, effective and meeting their environmental charter whilst delivering extensive and reliable control within their commercial constraints.