16 U.S.C. § 459j-2
Except for property deemed necessary by the Secretary for visitor facilities, or for access to or administration of the seashore, any owner or owners of improved property on the date of its acquisition by the Secretary may, as a condition of such acquisition, retain for themselves and their successors or assigns a right of use and occupancy of the improved property for noncommercial residential purposes for a definite term not to exceed twenty-five years, or in lieu thereof, for a term ending at the death of the owner, or the death of his spouse, whichever is the later. The owner shall elect the term to be reserved. Unless the property is wholly or partially donated to the United States, the Secretary shall pay to the owner the fair market value of the property on the date of such acquisition less the fair market value on such date of the right retained by the owner.
The Secretary may terminate a right of use and occupancy retained pursuant to this section upon his determination that such use and occupancy is being exercised in a manner not consistent with the purposes of sections 459j to 459j-8 of this title, and upon tender to the holder of the right of an amount equal to the fair market value of that portion of the right which remains unexpired on the date of termination.
The term "improved property", as used in this section shall mean a detached, noncommercial residential dwelling, the construction of which was begun before January 1, 1971 (hereafter referred to as "dwelling"), together with so much of the land on which the dwelling is situated, the said land being in the same ownership as the dwelling, as the Secretary shall designate to be reasonably necessary for the enjoyment of the dwelling for the sole purpose of noncommercial residential use, together with any structures, necessary to the dwelling which are situated on the land so designated.
Except as otherwise provided, the Secretary shall have the authority to use condemnation as a means of acquiring a clear and marketable title, free of any and all encumbrances.
16 U.S.C. § 459j-2