"We're putting a 2km extension on to the 300m outfall we have now. The fundamental advantage of that is that it takes it into deeper water, so the dispersion is enhanced, and incorporates a 400m diffuser."
The project would extend the existing pipe, which led 300m into the sea, by a further 2km.
The pipeline option was chosen after nine months of consultation, and was seen as the most effective option.
"This has been a significant project, in more ways than one because its about retaining a clean environmental footprint. It's also involved a lot of consultation with neighbours and iwi, and has been seen as the ideal compromise for what has been a complicated issue."
The outfall pipeline, built by the same people who constructed Hastings District Council's pipeline from the same spot last year, should be working by next month.
The pipeline was constructed at Clive, where it was launched into the sea.
NZ Diving and Salvage team principal Dougal Fergus said it had taken almost three months to build the pipeline.
"We launch it off the beach here at Clive and then it gets towed."
The piece had been towed to the plant and would be sunk and joined onto the pipe this morning.
Mr Fergus said the project had also benefited the local economy.
"We welded all the pipes up here and all the concrete blocks have been made locally as well."
Hawke's Bay Regional Council (HBRC) chairman Rex Graham said Pan Pac had done their best to mitigate the discolouration issue with this extension.
Council scientists had studied the water and found no issue with it, he said.
When big companies are involved in communities there often would have to be compromises but Pan Pac had gone the extra mile in this case, Mr Graham said.
"To their credit they're doing their best for the environment."
The treated pulp mill effluent coming from the outfall pipe would include sawmill effluent, water treatment plant effluent and landfill leachate.