The council has applied to extend the consents for its Green Island landfill for up to seven years before a new landfill at Smooth Hill opens in 2028-29.
The current consents for the Green Island landfill expire in October.
The economic assessment included in the application for the Green Island extension, by consultants GHD, outlined a "clear case" for further use of the Green Island landfill.
"Additional landfill capacity is needed," the GHD assessment said.
"The most cost-effective solution that minimises emissions, road wear-and-tear, congestion, job losses and site-specific environmental impacts in Dunedin is that resource consent be granted to extend operation beyond October 2023 for the Green Island site and that the void there be expanded.
"This will ensure enough capacity is provided to accommodate delays in commissioning the Smooth Hill site."
Trucking waste out of Dunedin had already been explored by the council, the assessment said.
The nearest regional landfill, the AB Lime site at Winton, would require an about 400km trip from Green Island.
Out-of-district waste disposal could cost more than $150 per tonne, but would need to be about $100 per tonne for it to be financially competitive with the long-term solution of establishing a landfill at Smooth Hill.
The Green Island landfill site would "unequivocally compare favourably" as far as costs went to the Smooth Hill site, because of the significantly lower cost of extending Green Island landfill’s consents compared with construction costs at Smooth Hill.
"By extension then, because the Green Island site is more cost-effective than the Smooth Hill site, it is likely to be at least 33% more cost-effective than the out-of-district option," it said.
Further, there were other costs associated with out-of-district disposal compared with local disposal.
There would be higher carbon emissions, it said.
One truck transporting waste to AB Lime 100 times a year would generate about 75tonnes a year in carbon emissions.
With an estimated 35,000tonnes of council-managed waste needing to be disposed of each year, this would likely mean 1000 trucks carrying 35tonnes each would make the trip annually, creating about 750tonnes of carbon emissions a year.
Further, the trucks would create much higher costs for the roading network in terms of wear and tear, the assessment said.
The 1000 trucks would also add to congestion along the route.
Additionally, closing the landfill in Dunedin in favour of using a Southland landfill would result in the loss of seven or eight jobs in the city, the assessment said.
The complementary assessment of environmental effects, by consultants Boffa Miskell, said the council had also previously considered a waste-to-energy facility for the city.
"However, this was not preferred due to high capital establishment cost, the need to secure large sources of combustible waste, burning waste being unacceptable to mana whenua and the continued need for ash disposal (20%) of incoming waste to landfill."
The application for a Green Island landfill extension has been accepted by the Otago Regional Council but remains on hold awaiting further information from the city council.
