43 U.S.C. § 451b
If an entryman making an exchange under the provisions of this subchapter becomes the direct obligor for payment to the United States of irrigation construction charges for his lieu farm unit or undertakes a contract under which the equivalent, in whole or in part, of such charges is returned to the United States, the Secretary, to the extent to which such charges upon the original farm unit or the equivalent thereof have actually been paid to the United States or to an irrigation district or other form of organization under contract with the United States, may give him credit for such charges upon the lieu unit.
If an irrigation district or other form of organization within the boundaries of which is located the lieu farm unit of an entryman making an exchange under the provisions of this subchapter is or becomes the direct obligor for payment to the United States of irrigation construction charges or undertakes or has undertaken a contract under which the equivalent, in whole or in part, of such charges is returned to the United States, the Secretary may, to the extent to which it gives credit to the entryman for such charges or the equivalent thereof actually paid upon the original farm unit, give the district or other form of organization credit for payment of such charges. Upon the making of an exchange pursuant to the provisions of this subchapter, the Secretary may reduce (i) the reimbursable construction costs of the project or division thereof upon which the original farm unit was located by the amount of such costs which were properly assignable to the original farm unit and which were not then due and payable, and (ii) the reimbursable construction costs of the project or division thereof upon which the lieu farm unit is located by the amount of credit which might be given under the provisions of this section.
In any case in which the benefits of this subchapter are extended to an assignee of an unpatented farm unit or to a resident owner of private lands, as provided in subsection (b) of section 451a of this title, an appropriate extension of benefits may also be made to an irrigation district or other form of organization under subsection (b) of this section.
43 U.S.C. § 451b