Hi D, can't share but suggest that your site is unique and anybody else's checklist would be useless. Each line will have its own features and potential leak points thus a generic approach is unlikely to be up to the job. Sorry, but this looks like a bespoke checklist is needed.

When did you last have an inspection PIG through the pipeline? That report should be quite detailed, showing wall thicknesses, obstructions, flange / valve locations. Use that to map your pipeline and then draw up a visual inspection checklist - e.g. condition of bolts, signs of external corrosion, impact damage, seepage etc. Ask the EPA for further advice on what they want covered and seek assistance from your PIGging contractor.