Graymont’s Role in Watercare’s Central Interceptor Project.
Watercare, together with construction partners Ghella Abergeldie Joint Venture (GAJV), set out to build Auckland’s $1.2-billion Central Interceptor – New Zealand’s largest wastewater project – with sustainability at its core.
A major challenge was managing the 66,000 tonnes of spoil generated over six years. The GAJV had committed to diverting more than 80 per cent from landfill, but the excavated material was too wet and unstable for direct reuse or transport.
Graymont played a vital role by supplying a calcium-based solution to transform wet spoil into stable backfill. Collaborating with GAJV and Watercare, Graymont developed a tailored lime treatment solution. Trials determined the optimal dosing rate, and Graymont ensured a reliable supply from its Otorohanga and Te Kuiti plants using pneumatic tankers, minimising packaging waste.
As spoil surfaced on the tunnel conveyor, it was treated with quicklime. The exothermic reaction dried the soil, improving handling and transport for deposit at Puketutu Island, Māngere, where Watercare is restoring a former quarry.
Quicklime delivers many environmental benefits in the construction sector: it can assist to neutralise acid sulphate soils, mitigate undesirable leachates, treat wastewater and biosolids, and dewater and fortify soils.
This collaboration turned a waste challenge into environmental success, supporting Auckland’s infrastructure while contributing to land regeneration.