What is meant by a high-risk supply chain under ISCC EU RFNBOs, and when is a mandatory surveillance audit required?

Under ISCC, a high-risk supply chain covers newly certified economic operators that generate, collect, process, store or trade materials which may be eligible for extra incentives in EU Member States, such as waste, residues or waste- and residue-based products. For these operators, a mandatory surveillance audit is required six months after the initial certification and must be conducted on-site. In RFNBO supply chains, this will often concern operators using CO₂ as a carbon source, as ISCC identifies CO₂ as a common input for hydrocarbon RFNBOs production and applies specific audit checks where CO₂ is used.

Related question: What is verified during a mandatory surveillance audit in a high-risk RFNBO supply chain involving CO₂?