Parua Bay Wastewater Scheme

Project typeWastewater system improvements

A photo looking out across Parua Bay on a sunny day.

We are working on three workstreams aimed at improving the Whangārei Heads and Parua Bay wastewater systems following overflows from the wastewater storage tank at Parua Bay.

Keeping things clean

We have been keeping the area as clean and spill-free as possible. This has included transporting waste from the wastewater storage tank at Parua Bay to the wastewater treatment plant on Kioreroa Road, while we have been investigating the causes of the overflows.

Investigating the causes

We know that stormwater is getting into the wastewater network and filling the wastewater storage tank faster than it can empty, causing overflows. We are now investigating where and how the stormwater is getting into the system. Usually it gets in through broken pipes (we call this infiltration), or low-lying gully traps or cross-connections (we call this inflow).

In November 2024, we will be smoke testing one of three catchments. This involves blowing smoke into the wastewater pipes. The places the smoke escapes from are likely to be the same places where stormwater is getting into the pipes during wet weather.

Find out more about smoke testing:

Smoke testing in our wastewater network

Designing the solutions

When we know where the stormwater is getting into the system, we will have a clearer idea of where pipe repairs or replacements are needed and can use this information to design a solution.

Background

We are working to keep the area as clean and spill-free as possible while we determine where stormwater is getting into the wastewater system and working out next steps for increasing the capacity of the wastewater scheme. Here is some background information on the work we are doing.

Wastewater

The wastewater system is designed to take the wastewater that comes from showers or baths, washing machines, toilets and other household or business sources, keeping it separate from stormwater.

In Parua Bay, the wastewater system pipes the wastewater to the storage tank, and it is then pumped through to the main wastewater treatment plant in Whangārei.

Stormwater

The stormwater system is designed to gather the rainwater that flows off the land and rises up through the ground, keep it separate from the wastewater system, and direct it into streams, ponds or the sea.

Stormwater in the storage tank

Wastewater drains into the pump station / storage tank from surrounding household connections. When it reaches the right level, a pump sends the wastewater to the next pump station along the line.

It does not empty the tank fully. It sends a manageable amount of wastewater to the next pump station to deal with.

When more wastewater flows into the storage tank, it is added to the amount already in storage and the level rises again, starting the pump again.

The wastewater system along Whangārei Heads depends on every pump along the line working properly, and pumping out at the right time to a storage tank that is empty enough to take the new load.

This cycle works well when wastewater is coming into and being pumped out of the system steadily, but not when there are big fluctuations and very large quantities of wastewater mixed with stormwater coming into the tank very suddenly. When that happens, the tank can be overloaded and there can be an overflow.

Our aim is to direct as much stormwater into the stormwater system as possible and to keep it away from the wastewater system.

To do this, we need to know where it is getting into the wastewater system, so we will be carrying out catchment studies on groups of properties (about 30 at a time) that are connected to the wastewater system.

Inflow and Infiltration

Inflow is when stormwater flows into the wastewater system from above ground from:

places where downpipes are draining into gully traps
gully traps that are underneath leaking spouting / guttering
damaged gully traps or gully traps that are set low that enable stormwater to drain into them
non-compliant connections, stormwater connections to the wastewater pipelines
places where stormwater forms ponds that are higher than the gully trap, letting water flow in.

Infiltration is when water builds up in the ground. As the level rises the pressure on pipes under the ground increases and water can escape into pipes, including wastewater pipes, through holes or cracks or poor connections.

Testing and investigating

We are investigating the catchments around the Parua Bay storage tank to establish how much stormwater is making its way into the wastewater system, and where it is getting into the system. Investigations have included site visits and questionnaires to residents.

In November 2024, we will begin smoke testing each of these catchments. This involves blowing smoke (vapour) into the wastewater pipes and seeing where it escapes. Where the smoke is getting out could be the locations where the stormwater is getting in.

Mapping

This information will be mapped, so we can see where the 'hotspots' are. From there, if improvements are required, we will be talk with community members about what needs to be done on the properties, while we address problems on public property.

Keeping the system working

Keeping the tanks empty

While we are finding out where the stormwater is getting into the wastewater pipes and working out how to stop that from happening, we will be emptying out the storage tank(s) by sucker truck, so they can contain the maximum amount of wastewater volume.

The sucker trucks

Sucker trucks are removing wastewater from the wastewater storage tank at Parua Bay to free up storage capacity and taking it to the wastewater treatment plant on Kioreroa Road.

The smell

Opening the cover at the pump station when we began emptying it caused an odour problem, so we have modified the lids and will not need to fully open them as often in future.

Long term planning

When we have completed our investigations and undertaken immediate repairs and improvements, we will have a clearer idea of what needs to be done to meet the needs of the community now and into the future. Planning, design and construction work will begin at that point.