SDCL § 9-41-10: Transfer of surplus to depreciation account.

If any surplus shall be accumulated at any time in the operation and maintenance fund, in excess of a reasonable reserve for current and anticipated expenses of operation and expenses, any such excess may be transferred at any time by the governing body to the depreciation account to be used for any improvements, expansion, or reconstruction of the municipality's telephone lines or facilities, or for the redemption of any bonds which constitute a lien on the earnings of the telephone lines or facilities, as and when the same become redeemable by their terms.