S.D. Codified Laws § 46A-9-64
The proceeds of the sale of the bonds and other evidences of indebtedness of each series issued under the provisions of this chapter shall be placed to the credit of the appropriate construction fund, which fund shall at all times be kept segregated and set apart from all other funds. There shall also be credited to the appropriate construction fund the interest received upon the deposits of moneys in such fund and moneys received by way of gift or grant from the United States or from any other source for the construction of the works. The moneys in each construction fund shall be paid out or disbursed in such manner as may be determined by the board of directors, subject to the provisions of this chapter, to pay the cost of the works as defined in § 46A-9-2. Any surplus which may remain in any construction fund after providing for the payment of the cost of the works shall be added to and become a part of the appropriate debt service fund provided for in § 46A-9-66.
SDCL 46A-9-64