Napier Sewer Rehabilitation and Pressure Testing

Protecting the purity of Napier

To ensure Napier City Council’s drinking water, drawn from in-ground bores, gained secure water supply status, it was essential that there was no possibility of contamination from the nearby sewers.

Interflow was engaged to provide water tight liners in two sewer pipelines, one reinforced concrete and one asbestos cement. While these pipelines showed obvious evidence of leakage, the biggest defects were found in the private sewers connecting from the houses along the route. Clearly water-tight liners were required in these too.

Following Expanda Pipe lining of the main sewers, Interflow’s cured-inplace Interflex® liner was installed in the private sewers, which came in a variety of materials.

Preparation for private sewer work was done Council and their sub-contractors. Each householder was contacted, and access conditions agreed. All private sewers were CCTV inspected and access points identified. Where required, access points were hydroexcavated just before the crew arrived, shortening the time the excavations were open. The access points were replaced with rodding eyes after liner installation.



Two sewer pipelines


Interflow’s proprietary Interfit® junction seal was installed at each lateral connection from within the lined sewer, overlapping the Interflex liner and connecting it to the Expanda Pipe liner.

After work completion, pressure testing of the entire system confirmed water tightness. Testing needed the ends or all private and main sewers to be temporarily sealed. Successful testing was carried out to the same Specification as for new sewer construction. Final reinstatement of driveways and landscaped areas was completed after pressure test signoffs.

The challenge

Interflow was commissioned to protect the purity of Napier City Council’s water supply by ensuring the water tightness of the sewers mains, private sewers and connections adjacent to Council’s bore water sources.

The work needed to be successful if Napier was to gain secure supply status, which had implications for on-going compliance and treatment requirements.

The solution

Interflow installed Expanda Pipe spiral wound liners in the two reticulation sewers that ran near the bores and their associated pipework. Private sewers were renewed using Interflow’s Interflex cured-in-place liner.

Sealing was completed by installing Interflow’s proprietary Interfit® to seal the connection between the house service lines and the main sewers. Pressure testing confirmed successful sealing.


All work, including documentation, was completed to a tight time-frame to allow the Consultant and Drinking Water Assessor time to make an assessment before the end of the financial year.

The success of these works helped Napier City Council comply with the required drinking water Standards.

Napier City Council


Napier, NZ


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