If the department determines that the application for or compliance with any license required under s. 291.23 or 291.25 would cause undue or unreasonable hardship to any person, the department may issue a variance from the requirements of s. 291.23, 291.25, 291.29 or 291.87 but the variance may not result in undue harm to public health or the environment and the duration of the variance may not exceed 5 years. The department may renew or extend a variance only after opportunity for a public hearing.