What is meant by heavy maintenance, since it is mentioned as being ineligible? If "heavy maintenance" could restore vehicles to operable status -- instead of scrapping -- you would call that repair?

Heavy maintenance generally refers to occasional or periodic maintenance on facilities, such as track work, or cleaning a station and making minor repairs to that station after the storm, as opposed to restoring vehicles to operable status. Repairing vehicles seriously damaged in the storm to an operable status is an eligible expense.