Improving Harbour Health Through Underground Storage and Smart Design

As part of Auckland Council’s $40M St Marys Bay & Masefield Beach Water Quality Improvement Project, PDP provided specialist groundwater advice to help reduce wet weather overflows into the Waitematā Harbour.

The project included a 1 km long, 1.8 m diameter storage tunnel beneath St Marys Bay, Herne Bay, and Pt Erin, designed to capture overflows and either return them to the sewer network or discharge them via a new marine outfall during major storm events.

Our role spanned from early investigations in 2017 through to project completion in 2022. We carried out hydrogeological assessments to inform design and consenting, including 2D and 3D groundwater modelling to assess inflows, settlement risk, saline intrusion, and contaminant migration. PDP presented evidence at the council hearing and developed the Groundwater Settlement Monitoring and Contingency Plan (GSMCP) and associated consent conditions.

We also managed the drilling programme, installed telemetry-enabled monitoring systems, and oversaw construction-phase compliance. Acting as SQEP, our team provided ongoing technical advice and regulatory support to ensure groundwater effects were understood and managed throughout.