"Trust fund" shall mean a form of financial assurance, including: cash deposited in a federally insured account; negotiable bonds "held in escrow" by a political subdivision and endorsed by the operator, and rated "A" or better by a nationally recognized bond rating organization; or negotiable certificates of deposit in a federally insured depository. (§ 1, Ord. 1191, eff. September 5, 1996; as amended by Ord. 1518, eff. February 13, 2020)