Auditors have told a council it should ensure it reviews the "actual costs" of bringing its waste collection services in-house.
The local authority in Dumfries and Galloway is spending more than £20m on new vehicles and infrastructure.
It comes after it ended a Private Finance Initiative contract early in 2018 at a cost of more than £6m.
Auditors have warned that it must check the new system delivers the "financial and operating benefits planned".
A draft audit report said the council had identified the move back to an in-house service as "the most efficient and effective model of delivering waste management in the region".
However, it said that came with a significant price tag of more than £8m for new vehicles and bins plus more than £13m on a Zero Waste Park in Dumfries.
The new service is due to be rolled out across the region later this year and into 2021.
Auditors said the council would need to "objectively review" the "actual costs" to ensure it was realising the planned benefits and demonstrating value for money.
The council has promised to provide reviews of costs throughout the implementation process.
It said that would be ongoing for a number of years.