Condition assessment and rehabilitation/renewal of wastewater rising mains

This paper discusses techniques for the condition assessment and rehabilitation/replacement of wastewater rising mains.

Rising mains are an essential component of the wastewater network. However, they often have no redundancy, with each pumping station being served by only one rising main. Problems with rising mains have the potential to cause pollution, damage property and adjacent services, resulting in significant costs.

Rising mains are very difficult to inspect, as they are under pressure and frequently cannot be taken out of service. Faults that cause problems may be very small and are often not identified from the inspections that are carried out.

Techniques for rehabilitation of pressure pipes are available, but are not as well established and not as proven as those used for the rehabilitation of gravity pipes.

This paper contains a review of available condition assessment and rehabilitation/replacement techniques. A risk based approach to the management of rising mains is recommended, where the likelihood and consequence of failure is determined. Inspections and rehabilitation/replacement is concentrated on those areas that result in the greatest reduction in risk. Contingency planning for rising main failure is also considered.

The paper considers the findings from the WERF reports “Inspection Guidelines for Ferrous Force Mains” and “Inspection Guidelines for Wastewater Force Mains”, which were based on surveys of practices and techniques used in the United States of America. The paper uses rising mains on the North Shore City Council’s wastewater network as a case study to compare the relevance of WERF’s findings to the New Zealand context. The paper also makes comparison between practices used for the management of wastewater rising mains with those used for gravity wastewater pipes and potable watermains.