oil (non-petroleum) storage. Is the owner/operator required to prepare a PE- certified SPCC Plan, even though the APSA regulated petroleum storage amount is less than 5,000 gallons?

More discussion on this topic is found in Chapter 2, Section 2.10.6 of the SPCC Guidance for Regional Inspectors.

4.12 A facility has 4,000 gallons of petroleum storage and 7,000 gallons of edible oil (non-petroleum) storage. Is the owner/operator required to prepare a PEcertified SPCC Plan, even though the APSA regulated petroleum storage amount is less than 5,000 gallons?

Yes. Since the APSA statute (HSC Section 25270.4.5) requires facilities to prepare and implement an SPCC Plan that complies with 40 CFR Part 112, the non-petroleum oil is required to be included in the total storage capacity of the facility and in preparing an SPCC Plan for the facility.