At a glance


Western Australia, Australia

Type of project



WA Water Corporation

Contract type




A successful Alliance project

The Alkimos Wastewater Treatment plant was constructed to service the growing population in Perth’s north-western suburbs and take the pressure off existing wastewater facilities.

The $366 million wastewater scheme included a major treatment plant, an ocean disposal outlet and the extension of a main sewer to bring millions of litres of wastewater to the new facilities.

The Alkimos Water Alliance (AWA) was a Water Corporation joint venture between Multiplex, MacMahon Contractors and German-based Zublin. The Alliance was responsible for the delivery of the Alkimos Wastewater Treatment Scheme by bringing together experts in the fields of engineering, procurement, construction and project management.

In October 2007 construction activities commenced for Stage One of the scheme, which included tunnelling works, bulk earthworks and marine works.

The complex tunnelling works for the project required a high level of expertise and procurement capability from Multiplex. It included the installation of 14 x 8.8 metre diameter shafts ranging from 10 metres to 20 metres in depth and the procurement of 220 x 9 metre arc length caisson segments, manufactured in Thailand.

A two-metre diameter dual cutting mode Tunnel Boring Machine (TBM) from Germany was utilised to install almost seven kilometres of two metre diameter sewer pipe. A kilometre-long open trench was excavated for installation of a High Density Polyethylene (HDPE) lined sewer pipe sourced from Perth.

The bulk earthworks also proved to be a large scale task, with some 3,000,000 cubic metres of excavation.

Approximately eight kilometres of temporary access roads and haul roads were constructed and 29 hectares of clearing with approximately 10 hectares revegetated upon completion.

The marine works package entailed about 25,000 cubic metres of marine dredging, approximately 18,000 cubic metres of offshore drill and blast excavation and the installation of a 3.7 kilometre, 1.2 metre diameter outfall pipeline, including diffusers via marine pipe pull. The pipe pull was successfully completed over an intense seven day, 24-hour operation using a 400 tonne winch fixed to a 60 metre long off-shore barge.

The Alkimos Water Alliance Project won the prestigious WA Earth Award in ‘Category Five – more than $75 million’, for the WA Civil Contractors Federation.

MacMahon Contractors and German-based Zublin.