43 U.S.C. § 2623
Additional sum from surplus for meeting payments due from insufficient annual receipts; maximum aggregate of decennial payments; covering of excess receipts into general fund of Treasury
If, during any one year, 75 per centum of the receipts are insufficient fully to meet the payments due the counties hereunder, the Secretary of the Treasury, upon certification by the Secretary of the Interior, may pay an additional sum from any surplus of 75 per centum of prior year receipts: Provided, however, That in no event shall the aggregate of payments during any ten-year period commencing with the period beginning