Conquering Extreme Turbidity

The Kerepehi Water Treatment Plant is subject to extreme turbidity (1700 NTU +) caused by King Tides in the Hauraki Gulf and low river flows. This paper looks at the technology selected to deal with this extreme turbidity as well as methods for reducing the impact, and recounts the first two King Tide events to hit the plant after commissioning.

This paper will look at the technology selection process, the options considered and will build upon last year’s paper “King Tides – A Royal Problem” by Nicola Brown, Harrison Grierson(2012). It will examine how the existing plant and originally proposed upgrade was unsuitable for the raw water conditions. It will also provide an in-depth and detailed assessment of two different technologies and explain how a saving of over $3 million dollars was achieved on the initial estimates.

The paper will focus on the close collaboration between Hauraki District Council and the design engineers at Harrison Grierson and how investment and the beginning of the project led to savings being achieved in the final designed delivered to the client.

The project has produced a plant that has exceeded the expectations of the designers and Hauraki District Council. During the one-in-70-year drought over the summer 2012/13, water supply did not restrict milk production as it may have done many summers past.