Distraught Jean Carberry had put the urn of ashes into a bag for cleaning, but she mistakenly put this into the bin with rubbish bags.
Refuse manager Bill Oakley said: 'Sadly she contacted us too late. We had no chance to retrieve the ashes among the 600 tonnes of rubbish from the 150 lorry movements we have every day.'
Mrs Carberry wanted to visit the council's landfill site at Humberfield quarry. The council had to explain that the urn would first have been crushed and baled at its Wilmington transfer site before reaching Humberfield.
He said it was not unheard of for people to visit landfill sites, but an increase in the baling of rubbish made it almost impossible to find anything.