Neb. Rev. Stat. § 23-316

As soon as the contract or contracts are let for the construction of the work as provided in section 23-315 , the supervisors or board of county commissioners shall levy a special assessment on all the lands specially benefited in accordance with the benefits received as confirmed and adjudged in a sum as may be necessary to pay for the work and all costs and expenses accrued or to accrue, not exceeding the whole benefit upon any one tract.