Tenn. Code Ann. § 69-5-705

The successful bidder shall be required to execute a bond, with sufficient corporate surety or personal sureties, payable to the county, for the use and benefit of the district, in an amount equal to twenty-five percent (25%) of the estimated cost of the work so let, or may deposit such amount in cash with the treasurer of the board of directors as security for the performance of the contract, and upon the execution of such bond or the making of such deposit, the deposit originally made with the bid shall be returned to the bidder.