Demolition of old sewer pipeline begins

A digger at work yesterday on the old sewer pipeline. The rubble will be used for roads. Photo / Dean Purcell

A digger's hydraulic jaws bit into the concrete crust of the old Hobson Bay sewer yesterday at the start of a four-month project to remove it from the mudflats where it perched on stilts for nearly 100 years.

Last month, the 3km pipeline and its 40-year-old pump station were replaced by a high-capacity tunnel and pump which cannot be seen from the harbour-facing slopes of Parnell or Remuera.

The $120 million structures have already shown they can hold their own, according to Auckland Transition Agency chairman Mark Ford, who headed Watercare Services when the project started.

Last week's torrential rain entering the sewer system brought none of the usual overflows at Orakei into the eastern bays of Waitemata Harbour.

Two crews will break up the pipeline into lumps and diggers will pick them off the mud and load the debris on to trucks using a temporary road built alongside.

A surprise finding was the prime condition of the reinforced steel concrete structure in many places.

"It was remarkably well built and even after 100 years in the marine environment some of it is in good shape," said project manager Mike Sheffield.

However, the structure was strapped together and did not meet today's design or earthquake standards.

The 4000cu m of rubble will be carted 25km to the Mangere Wastewater Treatment Plant to form roads needed in rehabilitating the No 2 oxidation pond in Manukau Harbour.

Piles bearing the pipeline will be cut off below the seabed but a 20m stub of pipe will be retained on the edge of the bay, near Ngapipi Rd, as a heritage object.

The pipeline was built between 1908 and 1914 to serve up to 300,000 people and carried untreated wastewater to Okahu Pt, where it was released on the ebb tide. Later, the load was diverted to Mangere for treatment via a pump station in Orakei.