Report on Sewage Spills Released

07 June 2016

A report on three sewage incidents involving the Waitara Pump Station and the Waitara to New Plymouth sewage pipeline has been released by New Plymouth District Council. 

The Council’s inspections and review of data have shown the three incidents earlier this year were unrelated events that involved mechanical, electrical and process issues.

As a result, the Council is undertaking a series of improvements to its control programmes, the operation of the Waitara Pump Station and notification of unauthorised discharges. The Council is also investigating possible improvements to the operation of the sewage reticulation near the Waitara Pump Station and improvements to protect the joints of sewage pipes beneath bridges.

“Whenever we have an incident on the sewerage network, we learn from it and improve our management practices,” says Manager Infrastructure David Langford.

“We can reassure residents that our sewerage system performs well against national benchmarks, both for the number of sewage overflows and our response times to incidents.

“What we had here were three high-profile but unrelated incidents that just happened to occur within weeks of each other.”

The three incidents were:

  • 13 February: Faults to both milliscreens at the Waitara Pump Station resulted in an overflow through the Waitara Marine Outfall. Issues with the Programmable Logic Controller (PLC), which controls the automatic operation of the pump station and raises alarms, are identified and fixed.
  • 26 March: Sewage leaks from a joint in the Waitara to New Plymouth pipeline where it crosses the Waiongana River. A blown gasket, likely due to heat expansion causing the gasket to tear against the bolts holding it in place, was identified as the cause. The pipe was cut so that the damaged gasket could be removed and a new gasket was installed. A special gibault was required to reconnect the pipe where it was cut.
  • 30 March: A circuit breaker at the Waitara Pump Station trips, resulting in loss of power to the PLC which caused the back-up battery power supply to take over. While operating on back-up power the pump station appeared to be operating normally until the batteries ran out of power and the PLC shut down, causing the pump station to also shut down. This resulted in an overflow through the Waitara Marine Outfall.

The report shows that New Plymouth District’s wastewater system treats more than 27 billion litres of wastewater every year – the same volume as 10,800 Olympic swimming pools.

Most overflows are caused by high rainfall flooding the system. In the 12 months from April 2015 to April 2016, 48 overflows (56 per cent) were caused by high rainfall, 13 (27 per cent) by pipe blockages or breaks, and seven (14 per cent) by mechanical or technical breakdowns.

In Water New Zealand’s annual national performance review, New Plymouth District ranks 28th (out of 41 participating districts) for the total number of overflows – a rank that improves to 21st when excluding high rainfall events.

Also, NPDC has the fourth-fastest average time for responding to and resolving sewage overflows.

“There were also questions about how the Waitara sewage system compares to Oakura’s, regarding their comparative costs and operation,” says Mr Langford.

“This report shows there is no quality gap and no tangible difference between the two systems.”

The report will be considered by the Council’s Monitoring Committee at its meeting on Tuesday next week (14 June).

Help keep our sewerage system healthy

More than a quarter of sewage pipe problems are blockages caused by what we flush down the toilet.

What not to flush:

  • Food or fat.
  • Sanitary items.
  • Wet-wipes, cleaning wipes and facial tissues.
  • Bandages.
  • Anything else that doesn’t dissolve in water.

What to flush:

  • Faeces and urine.
  • Toilet paper.