9. Fly ash and incineration residue that contains fly ash must be landfilled in separate disposal areas reserved exclusively for that type of residual material and sited as provided by the applicable provisions of sections 20 to 24.
That requirement does not apply to ash or residue that has been decontaminated by means of a contaminant extraction process and that presents a risk to the environment no greater than that for other residual materials that may be accepted at the landfill.