(a) The amount of the grant award shall remain available for obligation by the grantee during the period specified in the grant award or until otherwise terminated. Such period may be extended by revision of the grant with or without additional funds pursuant to paragraph (b) of this section where otherwise permitted by law.

(b) When it is determined that special or unusual circumstances will delay the completion of the project beyond the period for obligation, the grantee must in writing request the Assistant Secretary to extend such period and must indicate the reasons therefor.