The health officer shall set a time for an informal hearing, at which the parties may be heard before him or her or his or her representatives. A notice in writing shall be served upon the interested parties at least 15 days prior to the hearing. The informal hearing shall be private and limited to questions of fact. Appearances may be made in person or by attorney. Testimony may be taken and evidence introduced as to the correctness of the findings made by the person making the examination or performing the analysis.