Fly ash, or Air Pollution Control (APC) Residue, is collected on the 2,400 filters at the end of the multi-stage flue gas treatment. It consists of small particles from the waste itself as well as the by-products of the chemical reactions that remove harmful substances. It is transported off-site in special sealed containers and disposed of in the north of England under contract with a specialist contractor. Fly ash is classified as hazardous because it is alkaline (like cement) and contains heavy metals and other particles that we do not want to send up the chimney.