(a) Generally
The Secretary is authorized and directed in the manner hereinafter provided to classify or to reclassify, from time to time but not more often than at five-year intervals, as to irrigability and productivity those lands which have been, are, or may be included within any project.

(b) Necessity for request
No classification or reclassification pursuant to the authority of this subchapter shall be undertaken unless a request therefor, by an organization or duly authorized representatives of the water users, in the form required by subsection (c) of this section has been made of the Secretary. The Secretary shall plan the classification work, undertaken pursuant to the authority of this section, in such manner as in his judgment will result in the most expeditious completion of the work.

(c) Furnishing data
In any request made to the Secretary for a land classification or reclassification under this section, the organization or representatives of the water users shall furnish a list of those lands which are considered to be of comparatively low productivity or to be nonproductive, and of those lands which are considered to be of greater or lesser productivity than indicated by existing classifications, if any, made pursuant to the Federal reclamation laws, and shall furnish also such data relating thereto as the Secretary by regulation may require.

(d) Primary determination
Upon receipt of any such request the Secretary shall make a preliminary determination whether the requested land classification or reclassification probably is justified by reason of the conditions of the lands involved and other pertinent conditions of the project, including its contractual relations with the United States.

(e) Probable justification
If the Secretary finds probable justification and if the advance to the United States hereinafter required is made, he shall undertake as soon as practicable the classification or reclassification of the lands listed in the request, and of any other lands which have been, are, or may be included within the project involved and which in his judgment should be classified or reclassified.

(f) Expenses
One-half of the expense involved in any classification work undertaken pursuant to this section shall be charged to operation and maintenance administration nonreimbursable; and one-half shall be paid in advance by the organization involved. On determining probable justification for the requested classification or reclassification as provided in this section, the Secretary shall estimate the cost of the work involved and shall submit a statement of the estimated cost to said organization. Said organization, before commencement of the work, shall advance to the United States one-half of the amount set forth in said statement and also shall advance one-half of the amount of supplementary estimates of costs which the Secretary may find it necessary to make from time to time during the progress of the work; and said amounts shall be and remain available for expenditure by the Secretary for the purposes for which they are advanced, until the work is completed or abandoned. After completion or abandonment of the work, the Secretary, shall determine the actual costs thereof; and said organization shall pay any additional amount required to make its total payments hereunder equal to one-half of the actual cost or shall be credited with any amount by which advances made by it exceed one-half of said actual cost, as the case may be.

(g) Classification as prerequisite to contract
If in the judgment of the Secretary a classification or reclassification pursuant to the provisions of this section is a necessary preliminary to entering into a contract under section 485b or 485c ¹ of this title, he may require the same as a condition precedent to entering into such a contract.

(h) Modification of existing obligations
No modification of any existing obligation to pay construction charges on any project shall be made by reason of any classification or reclassification undertaken pursuant to this section without express authority therefor granted by Congress upon recommendations of the Secretary made in a report under subsection (f) of this section.