Like many other cities in New Zealand, Whangārei's aging sewer reticulation network suffers from extensive infiltration during heavy rainfall.
This often resulted in spillage of untreated sewage into the upper reaches of the Whangārei Harbour.
Growing public pressure saw local authorities adopt a multi-faceted approach to resolve the problem.
As part of the solution, the Whangarei District Council got United Civil to upgrade the Okara Park Sewer Pump Station in 2010.
The station’s pumping capacity was approximately 60% of the incoming pipelines, leading to substantial and frequent overflows following heavy rain from this facility into the immediately adjacent Hatea River (Whangārei Harbour).
This had become a focus of ongoing community concern and media interest.
The majority of the city’s wastewater is pumped to the nearby treatment plant from this station 24/7 – so extensive pre-planning, risk analysis and the development of comprehensive contingency measures were an essential prerequisite to construction.
These pre-planning measures extended to the fabrication of scale models of key pipe components, to confirm the geometry of these were compatible with the existing pipework in what was a very confined space with no room for error.
Key features included:
- extensive and detailed pre-construction planning and risk analysis
- need for redesign due to numerous challenges that presented themselves during construction – the specified methodology was subject to frequent modification
- completing critical tasks within a four-hour window each day, after which time the limited upstream storage capacity of the system was exceeded, including:
- decommission of existing pumps and the installation of four new pumps
- retrofitting and upgrading existing mechanical systems
- fabrication and installation of new pipework valves, flow meters, lifting beams and external rising main
- supply and installation of associated power and instrumentation components, including a new motor control center
- a significant change to the pump suction pipework design, arising from our desire to remove the need for staff to enter the wet well (i.e. sewage tank) – thereby eliminating the HSE hazards associated with working in a live sewer.
This project was completed within tight and inflexible deadlines, on budget and without incident – efforts which were acknowledged with a New Zealand Contractors’ Federation Construction Excellence Award for 2011 (for projects with a value between $1 million and $10 million).