(a) Upon the completion of the construction of an Indian irrigation project, or unit thereof, subsequent to the determination of the partial per acre construction assessment rate which was fixed prior to July 1, 1957, pursuant to § 134.4 the Secretary of the Interior or his authorized representative shall determine such additional construction cost and distribute that cost on a per acre basis against all of the irrigable lands of the project, or unit thereof, and 1/40th of such per acre additional construction cost thus determined shall be assessed and collected annually from the non-Indian landowner of the project, or unit, thereof. The first installment shall be due and payable on November 15 of the year following the completion of such additional construction work or, if such additional construction work on the project, or unit thereof, has been completed prior to July 1, 1957, and the per acre annual rate determined, the first installment of the additional construction cost to be repaid by such non-Indian landowners shall be due and payable on November 15, 1958. This annual per acre rate shall be in addition to, and run concurrently with, the per acre construction rate assessed annually under § 134.4.

(b) Project lands in Indian ownership are not subject to assessment for their proportionate share of the per acre construction cost of the project, or unit thereof, until after the Indian title to the land has been extinguished. At that time the total annual per acre assessment rate against non-Indian lands of the project, or unit thereof, shall be assessed against the former Indian lands for each and every acre of irrigable land to which water can be delivered through the project works, beginning on November 15 of the year following the extinguishment of the Indian title to the land and on November 15 of each year thereafter over a forty year period. In cases where the Indian title to project land was extinguished prior to July 1, 1957, the assessment rate shall be due and payable on November 15, 1958.