S.D. Codified Laws § 6-8B-48
Moneys deposited in any escrow, established under § 6-8B-46, may be invested in federal securities and such investments, together with any interest or other yield to be derived from any such investments and any moneys not invested, shall be in an amount at all times sufficient as to principal, interest, any prior redemption premium due, and any charges of the escrow agent payable therefrom, to pay the principal of, premium, if any, and interest on the bonds being refunded as such become due at their respective maturities or due at any designated prior redemption date or dates, if called for redemption. The moneys and investments in such escrow account shall be irrevocably appropriated to the payment of the principal of, premium, if any, and interest on the refunded bonds. The computations made in determining the sufficiency of the escrow shall be verified by a certified public accountant licensed or authorized to practice in this state.
SDCL 6-8B-48