We’ve been asked a number of questions about wastewater and stormwater. Are they different systems? Do they connect up together? End up in the same place? We hope the following Q & A - and infographic - helps clarify how our water network works.
What goes into the wastewater network?
Anything from a shower, dishwasher, washing machine and toilet. This goes to the BTF (Biological Trickling Filter) wastewater treatment plant at Awatoto.
Water off roofs, paths and driveways. This goes to the Ahuriri estuary or out to sea, depending on where it comes from.
So what happened early on Thursday morning (6 September)?
Water gets into the wastewater network when stormwater downpipes are incorrectly connected into the wastewater network, and gully traps installed in a way that allows rain falling on paths and driveways to flow into them.
Currently, when we have lots of rain over a period of time, we end up with too much water going into the wastewater network.
We’re faced with a choice which really is no choice. Either let the network overflow - and what would normally head out to the wastewater treatment plant (no need to guess what we’re talking about here) ends up spilling into city streets creating a major public health risk - or discharge into Ahuriri Estuary.
So what is NCC doing about this?
To better understand the scale of the issue and identify where stormwater is infiltrating the wastewater network, we're starting a smoke detection programme within the wastewater network next month.
There are particular areas we’re concerned about – a mix of residential and industrial – that we think could be contributing to this problem. We’ll start there.
How does work? The smoke is fed into the wastewater system and if we see it coming from any downpipes or paved areas, it'll be clear that these have been connected to the wrong network. The necessary change can be made, which will reduce the load on the wastewater network during heavy rain.
How can this happen?
Building consent officers do check to see gully traps comply with regulations before signing off on new builds. However, sometimes landscaping is carried out afterwards which can alter the run-off and contribute to this problem.
It’s up to existing property owners to follow the rules, and if we find properties that don’t comply we let the owner(s) know and ask them to fix it.
While some do, others don’t. In the latter instance, a notice is placed on the property file identifying the breach of the bylaw. When the owner comes to sell that property, any prospective buyer thatrequests a LIM will see it. This usually prompts the seller to fix it - but this can take years.
So we’re looking at strengthening our bylaw. If owners choose not to do this work, we're legally allowed to enter the property, fix it, and send the bill to the owner. Prosecution is a last resort.
How long does this wastewater stay in the estuary?
If wastewater ends up in the estuary, which is tidal, it will disperse. But public signs warning people not to swim, or take shellfish from the affected area(s) will be in place.
People should be aware that swimming, or taking shellfish or fish from rivers, streams, estuaries and the coast, is never a good idea for up to three days after heavy rain. A number of contaminants especially from our roads can be washed into the water.
7 September 2018
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