48 CFR §2414.408-70

When only one bid is received in response to an invitation for bids, such bid may be considered and accepted if the Contracting Officer makes a written determination that: (a) The specifications were clear and not unduly restrictive; (b) adequate competition was solicited and it could have been reasonably assumed that more than one bid would have been submitted; (c) the price is reasonable; and (d) the bid is otherwise in accordance with the invitation for bids. Such a determination shall be placed in the file.