43 U.S.C. § 396

On and after December 25, 1924 , the Secretary of the Interior is authorized to receive moneys from any State, municipality, irrigation district, individual, or other interest, public or private, expend the same in connection with moneys appropriated by the United States for any cooperative investigation of the feasibility of reclamation projects, and return to the contributor any moneys so contributed in excess of the actual cost of that portion of the work properly chargeable to the contribution.