Not later than 60 days after the completion of the established post-closure care period for each hazardous waste disposal unit, the owner or operator shall submit to the Secretary, by registered mail, a certification that the post-closure care period for the hazardous waste disposal unit was performed in accordance with the specifications in the approved post-closure plan. The certification required in §A of this regulation shall be signed by the owner or operator and an independent registered professional engineer. Documentation supporting the independent registered professional engineer's certification shall be furnished to the Secretary upon request until the Secretary releases the owner or operator from the financial assurance requirements for post-closure care under 40 CFR §265.145(h), which is incorporated by reference in Regulation .16 of this chapter.