In employing enforcement officers, the department shall use the criteria as required by the Office of Human Resources and the department. The criteria must include, but are not limited to, a written examination, physical examination, and interview. Each applicant is required to perform at minimal levels as required by the Office of Human Resources and the department. The department shall employ the most qualified applicants. An enforcement officer must reside within the county in which he is assigned, provided that the director, in his discretion, may allow an officer to reside outside the county under special hardship circumstances.