Neb. Rev. Stat. § 81-15,136

The director may revoke, suspend, or refuse to grant the certificate of an operator, following opportunity for hearing, upon any reasonable ground including, but not limited to, the following: (1) The operator has practiced fraud or deception; (2) reasonable care was not used in the performance of duties; (3) the operator is unable to perform duties properly; or (4) for failure to maintain the minimal continuing education requirements of the Wastewater Treatment Operator Certification Act.