Council goes for 3km pipe, no UV

Christchurch City Council has given the go ahead for the construction of a 3km Ocean Outfall pipeline to take the city’s treated wastewater out to sea.

It has also decided not to proceed with the building of an artificial ultra-violet (UV) disinfection plant. However, work will be done to ensure a plant can easily be added later if water quality outcomes change in the future.

The report to the City Council at its meeting on 29 July considered the results of public consultation earlier this year, studies of ocean-current modelling and ecology, as well as results from the recently completed upgrades to the oxidation ponds and cost considerations.

Mike Stockwell, the Council’s water and waste manager, says the staff recommendation — for a 3km pipeline and no artificial UV disinfection plant — balanced the technical evidence and the wishes of the community.

“Technically, a 2km pipeline without artificial UV easily meets safe swimming and shellfish-gathering standards at the beach. However, community opinion, based on a representative survey of 600 people, favoured a 3km pipeline without UV.

“Par ticipants in the representative survey … represented a cross-section of the city’s residents,” Mr Stockwell says.

Recent results from the treatment plant and oxidation pond upgrades, combined with the ocean current modelling, are also very encouraging.

“The ponds provide natural UV disinfection and their upgrade is proving to be very effective in reducing bug numbers without additional ongoing costs to ratepayers,” Mr Stockwell says.

“It’s important that people understand that work either completed or under way at the Christchurch Wastewater Treatment Plant and throughout the city’s sewerage system is already producing a very high standard of treated wastewater.”

Construction of the pipeline is expected to begin in 2007 and be completed in 2009. In general terms the pipeline would run from the oxidation ponds at the treatment plant, under the estuary, beneath Jellicoe Street and 3km out to sea. It would be buried 3m-4m deep through the surf zone and a minimum of 1m below the lowest known seabed level.

The cost to build the 3km pipeline would be about $50 million. Adding an artificial UV disinfection plant would have cost an extra $7m and a further $1 million a year to operate.

Background

In 2001, the City Council applied for a 15- year extension to continue discharging the city’s treated wastewater into the Avon-Heathcote Estuary. That application was based on upgrades to the Christchurch Wastewater Treatment Plant.

Following appeals, however, Environment Canterbury said the estuary discharge could only continue until 2009. The Council needed to find an alternative and, in October 2002, resolved to prepare an Assessment of Environmental Effects for an Ocean Outfall through a pipeline of no less than 2km.

Pipe route

After considerable consultation with the South Brighton community and advice from independent experts, the City Council on 11 December 2003 approved Jellicoe Street as the pipe route for the Ocean Outfall.