Preference right leases shall be issued for a term of 20 years and for so long thereafter as coal is produced in commercial quantities as defined in § 3483.1 of this title. Each lease shall be subject to readjustment at the end of the first 20-year period and at the end of each period of 10 years thereafter in accordance with subpart 3451 of this title.
43 C.F.R. §3430.6-3