C.R.S. § 32-9-142

Any unexpended balance of such security proceeds remaining after the completion of the purposes for which such securities were issued shall be credited immediately to the fund or account created for the payment of the principal of said securities and shall be used therefor, subject to the provisions as to the times and methods for their payment as stated in the securities and the proceedings authorizing or otherwise appertaining to their issuance, or so paid into a reserve therefor.