N.J. Stat. Ann. § 27:14-25

The engineer or supervisor may be dismissed at any time by the board of chosen freeholders after a proper hearing upon proof sustaining, to its satisfaction, charges preferred by it or the commissioner, for incompetency, neglect, disability or other cause. In the event of such dismissal, the board shall immediately appoint a new engineer or supervisor to hold for the full term of five years from the date of appointment.