40 CFR § 27.26 - Form, filing and service of papers.
(1) Documents filed with the hearing clerk shall include an original and two copies.
(2) The first page of every pleading and paper filed in the proceeding shall contain a caption setting forth the title of the action, the case number assigned by the hearing clerk, and a designation of the paper (e.g., motion to quash subpoena).
(4) Papers are considered filed when they are mailed. Date of mailing may be established by a certificate from the party or its representative or by proof that the document was sent by certified or registered mail.
(b) Service. A party filing a document with the hearing clerk shall, at the time of filing, serve a copy of such document on every other party. Service upon any party of any document, other than those required to be served as prescribed in § 27.8, shall be made by delivering a copy or by placing a copy of the document in the United States mail, postage prepaid and addressed, to the party's last known address. When a party is represented by a representative, service shall be made upon such representative in lieu of the actual party.
(c) Proof of service. A certificate of the individual serving the document by personal delivery or by mail, setting forth the manner of service, shall be proof of service.