Coastal erosion along Beach Rd, south of Oamaru, has exposed two former unofficial landfill sites until recently unknown to the Waitaki District Council.
The landfills, presumed to be capped in the 1970s, have spilled waste on to the beach below and now work will be undertaken to determine the size and level of contamination at the coast at the intersection of Beach and Awamoa Central Rds.
Waitaki Mayor Gary Kircher said the discovery was "disappointing''.
"It's just the way things used to be done. It was probably known about at the time and just covered over - and now we've inherited it. Not that good kind of inheritance, but we just have to get on and deal to it.''