AGRU Protective Liner to Support the Auckland Central Interceptor | AGRU America

AGRU Protective Liner to Support the Auckland Central Interceptor

The Auckland Central Interceptor is the largest wastewater project in New Zealand. This super-sized wastewater tunnel will transport sewage from the city’s west to the Māngere Wastewater Treatment Plant in the east. AGRU supplies concrete protective liners made from polyethylene to protect the wastewater tunnel against concrete corrosion in the long term.

[Georgetown, South Carolina, June 7, 2022—] AGRU, a market leader in high-performing plastic solutions, is supplying more than 200,000 m2 of AGRU-ULTRA GRIP® concrete protective liner (CPL) for the Central Interceptor project in Auckland, New Zealand.

Commissioned by Watercare Services Ltd, the new wastewater tunnel will cost around NZD 1.2 billion and is scheduled for completion by 2026. The Central Interceptor Tunnel is 4.5 meters in diameter and will run for 14.7 km from Grey Lynn under central Auckland and Manukau Harbour to Māngere. The tunnel is situated between 15 and 110 m below the surface. With two smaller connecting tunnels, the main tunnel will collect wastewater from the existing network and convey it to the Māngere Wastewater Treatment Plant. Watercare Services Ltd. has chosen AGRU concrete protective liners for maximum durability of the multi-billion infrastructure project.

Protecting against concrete corrosion

The high-quality lining of high-density polyethylene (HDPE) effectively prevents concrete corrosion and abrasion. Thanks to their 13 mm long anchor studs, AGRU Ultra Grip CPL has an enormously high pull-out force. The thermoplastic lining protects the concrete against corrosive gases generated by the wastewater in the tunnel, maximizing the service life of the tunnel structure. The tunnel is divided into four colored sections for easier sewer inspection and damage detection. AGRU supplies the Ultra Grip concrete protective liners in 3 mm thickness. While the access shafts are lined in green, the sewer tunnel is lined in yellow, pink, blue, and grey and sealed by extrusion welding.

The finished wastewater tunnel will have a gradient of 1:1000 to allow wastewater to drain to Māngere. A total of sixteen access shafts with a depth of up to 65 meters will be built for maintenance and operation. Control and overflow structures and air treatment facilities will also be made for future operation.

Future-proofing an expanding city

The Central Interceptor project is intended to accommodate the growing population in this major city of 1.7 million inhabitants, projected to reach 2 million by 2030. In older parts of downtown Auckland, wastewater and stormwater flow into a combined pipe network. During heavy rains, stormwater can flood these pipes. Currently, stormwater contaminated by fecal matter is discharged into Waitematā Harbour during heavy rains. The new wastewater tunnel is expected to reduce these overflows significantly.

“We are pleased to support the Central Interceptor project as it aligns with AGRU’s commitment to building a better future through innovative plastic solutions,” says Alois Gruber jr., president of AGRU. “Ultra Grip will help ensure the longevity of the Central Interceptor for generations to come.”

Before the project’s construction, AGRU and its subsidiaries provided technical support for installing the lining for the shafts and tunnel. AGRU provided on-site extrusion welding support and training to the site crew. AGRU will supply approximately 210,000 m² of lining for the project.

About AGRU America, Inc.

Since 1988, Georgetown, SC–based AGRU America, Inc. has been on a mission to build a better future by developing innovative plastics solutions and fostering relationships built upon the highest quality, service, and dependability standards. AGRU America is a subsidiary of AGRU GmbH, an Austrian family-owned business since 1948 with production facilities in Austria, the United States, Germany, and China. AGRU solutions, which include state-of-the-art products such as AGRU geosynthetics, concrete protective liners, pipes and fittings, and semi-finished products, are distributed in over 80 countries worldwide. Learn more about AGRU America at and AGRU at

About Watercare Services Ltd

Watercare is an infrastructure asset management council-controlled organization (CCO) that manages the drinking water and wastewater services of the Auckland Region of New Zealand. Watercare is registered with the New Zealand Companies Office as Watercare Services Limited and is 100% owned by Auckland Council. Learn more about Watercare at