Castle Cement has won its appeal to dump kiln dust on site at its Flintshire factory.
The cement producer was refused permission by Flintshire council to dump waste at its Padeswood plant near Mold but the decision was reversed after a public inquiry.
A Castle Cement spokesman said the firm was "pleased" with the decision.
But some local residents are still opposed, claiming the waste could pose a threat to the environment.
Penyffordd councillor Colin Bithell, who lives near the plant, said he was furious the council could be forced to meet the cost of the appeal.
He added: "This could leave land next to the cement works contaminated for years.
"The inspector’s decision is totally wrong from an environmental point of view and people here will be very upset when they learn about it.
"It’s time the Welsh Assembly government drew up a proper strategy for handling waste in consultation with all the councils. At the moment there doesn’t seem to be any clear policy."
But Castle Cement has always maintained it is safer and more environmentally-friendly to bury waste on site rather than transporting it elsewhere.
Flintshire Council denied the company permission to dump at its site last year.
That prompted an appeal, followed by a public inquiry by a planning inspector which started in August 2006.
A spokesman for Flintshire Council said they had received the inspector’s report and the details would be reported to the planning committee in January.