Okara Park Pump Station Upgrade
Whangarei City’s aging sewer reticulation network, like that of many other cities in New Zealand, suffers from extensive infiltration during rain storms. The wastewater pipe and treatment systems are prone to overloading during such events, resulting in spillage of untreated sewage into the upper reaches of the Whangarei Harbour.
As part of a multi-faceted approach to resolving this issue, the Whangarei District Council in 2010 let a contract to United Civil Construction for the upgrade of the Okara Park Sewer Pump Station. The pumping capacity of the station, which was originally constructed in 1967, was approximately 60% of that of the incoming pipelines and substantial and frequent overflows following heavy rain from this facility into the immediately adjacent Hatea River (Whangarei Harbour) had become a focus of ongoing community concern and media interest.
The scope of the upgrade work which had to be undertaken, all whilst maintaining the capacity and functionality of the existing facility, included:
Given the importance of the pumping station - it is from here that the majority of the city’s wastewater is pumped to the nearby treatment plant - extensive pre-planning, risk analysis and the development of comprehensive contingency measures were an essential prerequisite to the actual construction, so as to ensure the facility remained operational at all times. These pre-planning measures extended to the fabrication of scale models of key pipe components, so as to confirm that the geometry of these were compatible with the existing pipework in what was a very confined space that left no room for error.
Construction operations were typically undertaken during periods of minimum flow; namely 2 o’clock in the morning. It was essential that critical tasks were completed within a 4 hour window, after which time the limited upstream storage capacity of the system would be exceeded resulting in overflow.
There was an ongoing need for redesign due to numerous challenges that presented themselves during construction, and the specified methodology was subject to frequent modification. A significant change to the design of the pump suction pipework arose as a result of a United Civil initiative, eliminating the need for staff to enter the wet well (i.e. sewage tank). The primary driver for this change was to eliminate the HSE hazards associated with working in a live sewer.
That the upgrade of the Okara Pump Station was completed within tight and inflexible deadlines, on budget and without incident, serves as a testament to the technical expertise, project management and risk management of United Civil Construction staff. This project received the New Zealand Contractor’s Federation Construction Award for 2011 (for projects with a value between $1 million and $10 million).
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