40 CFR §62.14810

If you plan to permanently close your incinerator rather than comply with this subpart, you must submit a closure notification, including the date of closure, to the Administrator by March 31, 2004. In addition, while still in operation, your air curtain incinerator is subject to the same requirement to apply for and obtain a title V operating permit that applies to an air curtain incinerator that will not be permanently closing.