Rehabilitating a critical sewer pipe to avoid a wastewater spill on Wellington’s South Coast

Moa Point Interceptor Rehabilitation

Infrastructure, like sewer pipes, typically have a long service life and are replaced in a timely fashion. Occasionally, a piece of infrastructure requires immediate intervention to avert impacts beyond service interruption. When the Moa Point wastewater treatment plant’s interceptor, a critical sewer line, was at risk of immediate collapse, untreated wastewater threatened Wellington’s South Coast.

Under urgency, our client provided straightforward instruction—quickly rehabilitate the interceptor for a minimum 50-year design life, with minimum impact. We reviewed various rehabilitation methods, designed, consented, procured, and oversaw construction. Challenges included a bend in the pipe, high flows, restricted access, and limited rehabilitation options. The high flows couldn’t be diverted in the existing network. For flow management, Wellington Airport’s security fence was realigned to provide access to a flow balancing chamber. With a robust methodology to isolate the interceptor, we coordinated approvals from Wellington Airport, Wellington City Council, and Veolia to enable extraction of up to 1,200 litres per second of flow.

To further complicate matters, the work was done during penguin breeding season—a fence was built around part of the site to prevent the penguins nesting, and a specialist dog handler checked the area was penguin-free before work started. Despite these obstacles, we successfully rehabilitated the interceptor and in doing so have drastically reduced the risk of a major wastewater spill on Wellington’s South Coast.