Main Outfall Sewer Inspection
14 May 2004
Main Outfall Sewer Inspection
Hutt City Council (and operations contractor, Hutt Valley Water Services Ltd) plan to inspect the inside of the Main Outfall Sewer pipeline which runs from the new Seaview Wastewater Treatment Plant, along the Eastern Bays Road, to Pencarrow Head. The pipeline is a vital component of the Hutt Valley and Wainuiomata wastewater system. All wastewater from Upper and Lower Hutt is pumped through this pipe and discharged at Pencarrow Head.
The pipeline will not operate during the inspection. Instead the fully treated and UV disinfected sewage (containing no visible solids) will discharge to the Waiwhetu Stream through the overflow outlet near the Hutt River mouth. Short-term discharges to Wellington Harbour will also be required to drain the pipeline through scours located between Seaview and Pencarrow. These discharges, also of fully treated wastewater, will occur for several days, until the pipeline is empty. It will also be necessary to enter and pump out some of the manholes on the Eastern Bays and Pencarrow roads. All discharge locations will be clearly sign posted.
The discharge to Waiwhetu Stream is expected to start on 24th May and finish on 15th June. The discharges to the harbour between Seaview and Pencarrow are expected to start on 24th May and finish on 29th May (if it takes any longer the public will be informed).
The potential effects of the discharges on the receiving environment of Waiwhetu Stream, and Wellington Harbour, were assessed and are considered to be minor due to the high standard of the treatment and the short time of occurrence.
Regional Public Health and Hutt
City Council advise that shellfish should not be taken from
the Petone foreshore or Eastern Bays and that people should
not swim or play near the identified discharge points or in
Waiwhetu stream while this inspection is being carried out.
Regional Public Health further advises that shellfish from
the harbour (or other waters adjacent to urban areas) should
not be eaten at any time as they may be contaminated.
The inspection has been programmed to occur during May and June, at a time when the recreational use of the harbour waters is at a minimum.
This will be the first inspection since the new treatment plant has been operating. The last inspection was made in 1990. We need to have a better idea of the remaining life of the pipeline and whether more work is required to extend its life. This information will also provide information that might help avoid sudden failures of the pipeline in the future. Proposals are also being sought from specialist contractors to offer renovation methods for the pipeline.
The inspection will involve a specialist team entering the pipe to undertake testing and video of the pipe interior to provide an accurate record of condition. During the pipe shutdown assorted maintenance work will also be done on the main pumps and valves. Council's contractor Hutt Valley Water Services is coordinating the work.
The Council consulted widely with community groups and other affected parties late 2002. Resource consent applications were made in December 2002. They were publicly notified by Greater Wellington in January 2003, resulting in some submissions. A 'pre-hearing' meeting was held in March 2003. Consents were later granted by Greater Wellington (and the Minister of Conservation), without the need for a formal hearing.
During the four week period of this important asset inspection work, crews will be working in carriageways in the Eastern Bays (Eastbourne to Point Howard) and Seaview Road areas. Residents and visitors to these areas are requested to respect the speed restrictions in place at various inspection points during this work. The Pencarrow Road (it is a private road) will be closed to the public while the inspection is in progress. This is for Health & Safety reasons for the public and also to ensure the Contractor's various activities which need to be by undertaken are not impeded in any way.
The patience and cooperation of the travelling public is requested during this period.