Is the RMP submission date the postmark date or EPA's receipt?

Initial RMPs must be "submitted" by a certain date, and RMPs must be updated at least every five years from the date of its submission. What constitutes "submission" for purposes of meeting and determining these deadlines - postmarking the RMP or EPA's receipt of the RMP by the due date?

EPA generally uses the postmark date to determine both compliance with the deadline for submitting initial RMPs and the 5-year anniversary for updating RMPs. The RMP Reporting Center records both the postmark date and the date your RMP was received. If the postmark date is illegible, then the postmark date is left blank in the RMP and the date received is used for tracking compliance.