Post decommissioning monitoring is key to ensure any residual safety and environmental risks are managed through perpetuity for other users of the sea. This can include monitoring of derogated structures, jacket footings, monitoring of drill cuttings piles and further environmental sampling that may be required. Dependent on the outcomes of the comparative assessment, monitoring of remaining subsea infrastructure may also be required. Marine signals may also be required for positioning reference of infrastructure and could also include Well monitoring if subsea abandonment has not yet been completed.