Work targets Akaroa’s old wastewater pipes

Akaroa’s ageing wastewater infrastructure is about to be overhauled in preparation for work to replace the town’s wastewater treatment and disposal systems.

Christchurch City Council Senior Project Manager Kylie Hills says the work will be disruptive but is essential, with parts of the town’s wastewater pipes nearing the end of their expected service life.

The red line on this map indicates where the wastewater main is being replaced.

“To minimise the impact of the disruption, we have waited until the cruise ship season is over and until after Easter,” Mr Hills says.

The Council is still working on options for disposing of the town’s treated wastewater, but Mr Hills says the work being done now will be needed regardless.

There are several aspects to the work, which centres on reducing the amount of extra water getting into the wastewater system through ingress and infiltration from groundwater, from roof gutters and downpipes illegally connected to the network (down pipes are supposed to be connected to the stormwater system or roadside kerbs) and from private gully traps that receive surface water runoff.

Last year Council completed a survey of the Akaroa wastewater network using a system called distributed temperature sensing. This identifies where colder groundwater and rainwater have been entering the network and where pipe repairs or replacements may be needed.

“The survey showed that ingress and infiltration makes up about 40 per cent of the annual volume of wastewater reaching the Beach Road treatment plant,” Mr Hills says.

“That’s much higher than we would like, and this work aims to reduce the volume of wastewater from Akaroa and improve the quality of treated wastewater being discharged into the harbour. It will also reduce the size and cost of the new disposal system, whichever option is chosen.”

Throughout 2019 Council will undertake detailed inspections so that repairs can be priced and will complete the first wave of renewal and repair work, initially focusing on work north of the fire station.

The work includes:

• Wastewater main replacement (from the domain to the fire station): the new main will be bigger and able to support future changes planned for the network.
• Private property and lateral inspections: 138 properties are suspected to be discharging stormwater or groundwater to the wastewater network. The contractor will visit each property to do a CCTV camera inspection of the wastewater pipe to check for damage. Where gutters or downpipes are connected to the wastewater network property owners will be advised how to direct the flow to the stormwater network. Property owners are responsible for repairing wastewater laterals inside property boundaries.
• Manhole inspections: 73 manholes are suspected to be allowing rain water or ground water to enter the wastewater network. Each of these will be inspected to scope repair or replacement work. Many of these manholes are more than 75 years old and near the end of their service life.
• Additional pipe repairs: 86 sections of wastewater pipelines in the council’s part of the network are suspected to be a source of groundwater ingress and infiltration. These pipes will be cleaned and inspected with CCTV so that repair or replacement work can be planned.