Wellington Water’s installation of a 1.2km, 1m wide wastewater pipe from Barber Grove to the Seaview Wastewater Treatment Plant is a critical addition to the city’s infrastructure.
The project duplicates a 50 year-old old wastewater main transporting wastewater from 90 percent of Hutt Valley residents. Vulnerable to earthquakes, a failure in the aging concrete pipeline could have risked wastewater entering nearby Te Awa Kairangi, and the Waiwhetu stream.
Difficult ground conditions and high traffic volumes, (the pipe runs down the middle of Randwick Road) made trenchless tunnelling using Micro Tunnel Boring Machine the preferred option for Wellington Water and lead contractor, McConnell Dowell. This approach reduces disruption to the overall roading network, businesses and nearby residents.
Four Swedish designed and manufactured Grindex Minette pumps were selected to keep the water level down in the tunnel and in the four MTBM launch and recovery shafts vital to the project.
Easy to deploy thanks to a small, 240mm, diameter, and at just 29kgs, the drainage pumps are specially designed for tough applications such as civil infrastructure, where space is often tight. The pumps can run dry indefinitely, a huge benefit when working with water levels which can be variable, as they are at Barber Grove. Grindex pumps also use fewer kWs than other submersible pumps to move the same amount of water, an efficiency that is welcome on all projects.
Prime Pump has three generators on the site; two 13 kVAs, and a sound attenuated 15 kVA with 500L tank, which can run for 270 hours eliminating weekend fuel refilling, saving time and labour costs.
To help meet the site’s water management needs, Prime Pump also provided a 3m3 and a 4m3 settlement tank, along with a state of the art EnviroHub HL20 lamella plate water clarifier. The British designed EnviroHub ensures contaminated water is treated with coagulant and meets compliance standards before discharge, using a unique, flow-proportional intelligent dosing system. This system prevents overdosing or under-dosing. The EnviroHub provides the greatest performance per m2 footprint of any settlement tank – a perfect fit for the busy, compact, roadway site.
In addition, Prime Pump provided a full chemical treatment management, including chemical storage recommendations, for the site.
