In the case of a grant to a recipient for a construction project under section
3141 or
3149 of this title, if the Secretary determines, before closeout of the project, that the cost of the project, based on the designs and specifications that were the basis of the grant, has decreased because of decreases in costs, the Secretary may approve, without further appropriation, the use of the excess funds (or a portion of the excess funds) by the recipient—