Wis. Stat. § 145.24

(1) If an existing private sewage system either is not located in soil meeting the siting standards or is not constructed in accordance with design standards promulgated under s. 145.02 or 145.13 , the owner of the private sewage system may petition the department for a variance to the siting or design standards.

(2) The department shall establish procedures for the review and evaluation of existing private sewage systems which do not comply with siting or design standards.

(3) Upon receipt of a petition for a variance, the department shall require the owner of the private sewage system to submit information necessary to evaluate the request for a variance. If the department determines that the existing private sewage system is not a failing private sewage system, and continued use of the existing private sewage system will not pose a threat of contamination of waters of the state, then the department may issue a variance to allow continued use of the existing private sewage system. The department shall rescind the variance if the existing private sewage system becomes a failing private sewage system or contaminates waters of the state.