As a result of the earthquake in 1987 and subsidence in the intervening years, the wastewater system in Edgecumbe has been significantly damaged.
Due to the damage and faults, there is a higher inflow and infiltration of water into the system through cracks and seepage.
There is up to three times more water entering the system than would be expected for a town of this size. This puts an extremely high amount of pressure on the lines and oxidation ponds to hold capacities that they are not designed for, and in turn leads to overflows. Overflows are a public health risk and also cause significant inconvenience.
The whole network was badly damaged in the earthquake, although the worst affected infrastructure was the 16 kilometres of pipes and manholes. The impact on the 10 pump stations and oxidation ponds was significantly less.
The Council is responsible for the main lines, manholes, pump stations and oxidation ponds.
A number of repairs and limited investigations were undertaken immediately after the earthquake, to get the system operational. There was no comprehensive study at the time.
Following repetitive issues and rising maintenance costs in the intervening years, the Council initiated a full investigation of the system earlier this year using smoke testing and CCTV.
Smoke testing involves pumping white smoke through the lines so that cracks and faults can be seen above ground. Smoke testing also identifies unauthorised down pipe connections in the wastewater lines. CCTV involves sending remote control video cameras through the pipes to allow a visual assessment.
These investigations and studies identified defects and faults in the system. The Council has prepared a plan to undertake all required repairs to provide a long-term solution.
The project is included in the draft Long Term Council Community Plan (LTCCP) 2009-19 and is programmed to be implemented from 2010/2011 to 2015/16 on a priority basis. All faults and defects that have been identified as priority works will be repaired during the first two to three years including necessary pump station upgrades. The majority of the priority works are located west of the Rangitaiki River as shown on the Priority Zones Map (PDF, 1.2 MB), although works will be undertaken throughout Edgecumbe in the first two to three years.
At this stage, Council has not programmed the specific timing of the repairs. Property owners will be advised of the specific work programme and the effects closer to the time.
Work on the identified faults and defects mostly involves repairing displaced joints and replacing dipping pipes. Where possible, the Council will use trench-less technology to minimise the inconvenience and impact on the public, although it will be necessary to dig or trench in some of the worst affected areas. The majority of the works will take place on council owned land.
The network also incorporates approximately 640 service connections (to houses and businesses) that were also badly damaged. The maintenance of these connections is the responsibility of the landowner and most connections have been repaired since 1987, which is a credit to the community. Smoke tests are a way of monitoring stormwater connections and are regularly undertaken to ensure compliance.
To ensure the success of the remedial works, it is important that landowners ensure their gutters and drainpipes (stormwater) are not connected to the wastewater system and the lateral connection lines are in good working order. Also, make sure your sewer gully trap (the grate and drain where the internal sinks connect together externally) is at least 100mm above ground level to reduce the likelihood of infiltration.
The goal of the Edgecumbe Sewer Mitigation Project is to address all faults and defects to provide a long-term solution.
The maintenance cost of the wastewater system has been increasing rapidly over the past few years and will continue to increase without these works. A large component of the maintenance costs is due to call outs required when manholes and pump stations overflow.
The preliminary cost estimate is $3.3 million for all the remedial works required. The Council will make applications for external funding from central government and other sources to assist with minimising the cost to the community.