43 U.S.C. § 423a

The construction charges prior to May 25, 1926 , paid on permanently unproductive lands excluded from the project shall be applied as a credit on charges due or to become due on any remaining irrigable land covered by the same water-right contract or land taken in exchange as provided in section 423c of this title . If the charges so paid exceed the amount of all water-right charges due and unpaid, plus the construction charges not yet due, the balance shall be paid in cash to the holder of the water-right contract covering the land so excluded or to the irrigation district affected; which in turn shall be charged with the responsibility of making suitable adjustment with the landowners involved. Should all the irrigable lands of a water-right applicant be excluded from the project as permanently unproductive, and no exchange be made as provided in said section, the total construction charges paid before May 25, 1926 , less any accrued charges on account of operation and maintenance, shall be refunded in cash, the water-right contract shall be canceled, and all liens on account of water-right charges shall be released.