Local Government Magazine
3 Waters

Timaru's 15-year wastewater strategy

The Timaru District Council’s Wastewater Strategy has been named as one of Australia and New Zealand’s most outstanding public works engineering projects. The council was recently presented with the Institute of Public Works Engineering Australasia (IPWEA) Excellence in Water Project 2017 award for the Timaru Districtwide Wastewater Strategy at an awards dinner in Perth.

Back in 1997, Timaru District Council embarked on a strategy to upgrade its sewer system and wastewater treatment plants in the north-eastern part of the district. The strategy recognised the need to cease discharges to inland waterways and the Opihi River and its tributaries, rising standards for ocean discharges, and the need to upgrade or replace existing ageing and under-capacity pump stations and trunk sewer pipelines.
Timaru District Council adopted an approach involving wide community and stakeholder engagement and consultation through a working party structure. This involved an independent facilitator, a wide range of stakeholder and community representatives, iwi and staff, and had support from specialist advisors.
The manager of the DB Brewery in Timaru, Kim Haack, was involved in the development of the strategy.
“As an industrial discharger to the Timaru District Council sewer network, we have been heavily involved in the development of the Timaru Wastewater Treatment and Disposal Strategy,” he said.
“The Wastewater Working Party concept, which included representatives of industrial dischargers such as ourselves, ensured that the strategy was fit for purpose.
“The implementation had been staged so that it was affordable and it allowed industries sufficient time to plan, fund and construct their own on-site wastewater treatment facilities.
“This inclusive concept and the outcomes achieved over an extended timeframe have been really positive for the industrial sector and the Timaru District as a whole.”
Timaru District Council engaged consultants Beca to carry out all the necessary technical work to implement the adopted strategy over approximately 15 years. This included preparing an Assessment of Environmental Effects for separate sets of resource consents for diversion of inland town effluent to the ocean outfall, continued use of the ocean outfall itself, and construction of the Waste Water Treatment Plant (WWTP) upgrades.
Ashley Harper, group manager infrastructure at Timaru District Council, said that while the overall strategy had been implemented using well-known engineering practices and design techniques, there were a number of challenges to be met on the way.
“Elimination of ongoing energy and maintenance costs associated with pump stations was the key driver in deciding to pursue a gravity trunk main system from the Timaru CBD to the Aorangi Road Treatment Plant eight kilometres away,” he said.
“The available fall between both points resulted in the two gravity mains (one domestic and the other industrial) being laid at a gradient of 1:1800, which is extremely flat.
“This required very careful computer modelling of pipe flow under a wide range of flow conditions and very precise construction. Six metre lengths of large diameter HDPE pipe had to be consistently placed with little more than 
3.33mm fall.
“The decision to implement a gravity system over this length also required construction of three tunnels through low-lying ridges between the Timaru CBD and Aorangi Road WWTP.
“The task of connecting up the inland towns was also a major challenge. When it was constructed in 2003, the 35 kilometre-long inland town pipeline was the longest wastewater pipeline in New Zealand. The use of HDPE piping was still novel in the wastewater field in the South Island, and specialist advice was engaged to ensure that correct welding and installation was used.”
The benefits of this project were:

  • Meeting compliance with the Opihi River Regional Plan by eliminating discharge from inland towns to water courses;
  • Replacement of an ageing trunk sewer network with new sewers constructed in modern materials with enhanced 
service life;
  • Elimination of pump stations and their associated energy and maintenance costs, as well as eliminating safety and welfare hazards associated with maintenance;
  • Separation of domestic and industrial effluent streams, resulting in very substantial capital cost savings on the Aorangi WWTP upgrade;
  • Retention of existing assets as part of overall strategy (utilising inland town ponds for buffering flows, Aorangi Road milli-screen plant treating industrial waste, existing ocean outfall);
  • Ease of operation of the overall scheme;
  • A community which is happy with the very affordable scheme for which the Uniform Annual Charge per property peaks at $374 (including GST) per annum, which is low by national standards; and
  • Trade waste charges to industrial dischargers of $0.66/cubic metre fixed charge and $0.11/cubic metre variable charge (including GST), which, again, is low and affordable by national standards.

The overall Wastewater Strategy from 1997 to 2014 involved an expenditure of $60.7 million. The last phase of the strategy, the Aorangi Road Domestic WWTP 
($19.1 million), was completed in January 2015.
Timaru District mayor Damon Odey said it was awesome news that the project was getting the recognition it deserved.
“Sometimes these long-term, large infrastructure projects can fly under the radar, so it’s great that a panel of engineering peers has recognised this project,” he said.
“The award is testament to the vision, work and long-term commitment of this council, from past and present elected members, through to the excellent team within our organisation, and it shows that we are a forward thinking and leading council, producing some world-class work in Timaru.
“The project has caused improvements for ratepayers, local businesses and the local environment, so it’s something that should be celebrated by the whole community.”
What the judges said
Judged by a panel of industry experts, the IPWEA awards finalists represented the industry’s best of the best, having already won their category from each Australian state and 
New Zealand between 2015 and 2017.
The judges noted: “This project involved wide community and stakeholder engagement and consultation to arrive at a scheme that eliminates discharges to the river from the inland towns, by piping treated wastewater to the existing ocean outfall, replacing a network of pump stations and trunk sewers with gravity sewers, separating domestic and industrial flows, and upgrading the existing waste water treatment plant (WWTP) for treatment of the domestic wastewater stream.
“It’s fantastic that Timaru District Council has remained on programme and completed the implementation plan that was set in place 15 years ago,” they concluded.

This article was first published in the October 2017 issue of NZ Local Government Magazine.

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