Antidegradation review

Antidegradation review. (1) Purpose. The purpose of this section is to establish the implementation procedures for the application of the antidegradation policy under s. NR 102.045 to storm water discharges regulated under ch. 283 , Stats. (2) Applicability. (a) This section establishes antidegradation requirements applicable to any person proposing to increase an existing storm water discharge or create a new storm water discharge to the surface waters of the state, at the time of any of the following after July 1, 2026: 1. Submittal of an application for an individual WPDES permit issuance, reissuance, or modification. 2. Departmental notice of intent under sub. (6) to issue, reissue, or modify a WPDES general permit. (b) An antidegradation demonstration under this section is not required for a temporary discharge or for a water quality trade that results in an overall net reduction to the receiving water of the pollutant being traded. (3) Definitions. In this section: (a) “Designated use” has the meaning established under s. NR 102.03 (1L) . (b) “Existing use” has the meaning established under s. NR 102.03 (1p) . (c) “Great Lakes system” has the meaning established under s. NR 102.03 (1pr) . (d) 1. “Increased discharge” means an actual or proposed change in the area or site conditions that results in or will result in an increase in the concentration, level, or load of a pollutant associated with a currently permitted storm water discharge. 2. “Increased discharge” does not include any of the following if the applicant or permittee is not proposing an increase in the concentration, level, or loading of a pollutant in the discharge: a. Reissuance of a WPDES individual or general permit, including reissuance of an administratively continued permit. b. Issuance of a WPDES individual or general permit for a category of existing discharges that did not previously require a permit under state or federal regulations. c. A permitted MS4 that incorporates under its jurisdiction a previously unincorporated area. (e) 1. “New discharge” means a storm water discharge that would first occur after the permittee’s start date of coverage under a permit issued under s. 283.33 , Stats., to a surface water to which the facility did not previously discharge storm water. 2. “New discharge” does not include an increase in a storm water discharge to a surface water to which the facility discharged on or before coverage under the permit. (f) “Practicable” means technologically possible, able to be put into practice, and economically viable. (g) “Parameter” means a chemical, physical, or biological property that can be tested or monitored as a measure of water quality. (h) “Receiving water" has the meaning established under s. NR 216.002 (25m) . (i) “Surface waters" means all waters of the state, as designated under s. 283.01 (20) , Stats., except groundwater, as defined under s. 299.01 (5) , Stats., or navigable waters used for post-construction storm water treatment meeting the criteria under s. NR 151.003 (2) . (j) “SWPPP” means storm water pollution prevention plan. (k) “Temporary discharge” means a proposed new or increased discharge that may lower water quality for less than 90 days if the discharge will not lower water quality in the receiving water after the discharge ceases and best management practices applicable to the type of discharge are implemented. “Temporary discharge” does not include seasonal discharges that reoccur in subsequent years, or new or increased discharges of bioaccumulative chemicals of concern. (4) Antidegradation implementation. (a) General implementation. Consistent with the antidegradation policy under s. NR 102.045 , the department shall conduct a review of any new or increased discharge and determine whether it will lower water quality in a surface water of the state. (b) Performance standards. The requirements established under this chapter and the performance standards and prohibitions under ch. NR 151 shall be utilized to prevent degradation of all receiving waters. Upon issuance, reissuance, or modification of general and individual permits, the department shall impose additional permit conditions to address instances when the specific categories of a receiving water or specific characteristics of a regulated discharge require a permittee to incorporate additional practices to meet antidegradation requirements. (c) Pollutants of concern in an impaired water. Where a discharge consists of a pollutant of concern as defined under s. NR 216.002 (23m) , any increase in discharge is addressed through ss. NR 216.007 , 216.07 (10) (b) , 216.27 (3) (j) 6. , and 216.49 (3) unless there is an approved TMDL for the pollutant of concern. (d) General permits. For general permit issuance, reissuance, or modification, the department shall use the procedures under sub. (6) . (e) Individual permit coverage and screening. If an applicant or permittee proposing a new or increased discharge is not eligible for coverage under a general permit, the applicant or permittee shall follow the screening procedures for individual permits under sub. (7) . (5) Water quality data and additional information. The department may require an applicant or permittee to submit additional information for the purposes of conducting the antidegradation screening or review under subs. (7) to (9) , and to determine whether coverage under a general permit is applicable or coverage under an individual permit is required under ch. 283 , Stats. The permittee or applicant shall follow applicable instructions and use department-approved forms to submit any of the following information, as applicable: (a) Surface water identification. Identification of all surface waters located, at a minimum, within one-quarter mile from the proposed new or increased discharge. For each identified surface water, the permittee or applicant shall identify the respective antidegradation category under s. NR 102.045 and whether the surface waters are listed as impaired on the section 303 (d) list or whether they are subject to a TMDL. (b) Proposed or expected parameters. A list of the parameters that are proposed or expected to change in concentration, level, or loading in the new or increased discharge. (c) Background water quality data. The department shall determine existing concentrations or levels of the parameters listed under par. (b) for the receiving water using data that are sufficient, representative, and credible. Determinations shall be made using the most recent representative data available, not to exceed 10 years old unless the department determines that those levels are still representative. If the department determines that existing data are no longer representative of current conditions based on changes at the local or watershed scale, more recent data may be required. In this case, a permittee may request that the department determine background water concentrations or levels as specified under subd. 1. , or shall indicate to the department that they wish to collect the data under subd. 2. Water quality data collected shall be representative of locations upstream of the proposed discharge location, but outside the direct influence of the discharge. One of the following shall be used to determine background water quality concentrations or levels where the department determines representative data does not exist: 1. The department may determine background water concentrations or levels by collecting water quality data during the next sampling season or using other scientifically defensible methods such as data from representative sites in watersheds with similar characteristics based on the parameters listed under par. (b) . The department shall consider all relevant factors listed under subd. 3. 2. If a permittee or applicant wishes to collect the background water quality data where data is not already available, sampling and reporting of the background water quality data shall be provided for the receiving waters, shall include the parameters listed under par. (b) , and shall consider the factors listed under subd. 3. If the applicant wishes to obtain and submit sufficient data for the department’s determination, it shall collect data in the receiving water in accordance with the department’s monitoring and quality assurance protocols for each parameter. The department shall determine existing concentrations or levels of parameters of concern. 3. The following factors will be used when determining where data is sufficient, representative, and credible: a. The sensitivity of the receiving water to degradation of existing or designated uses. b. The parameters of concern in the proposed discharge. c. The representativeness of any surrogate water information proposed for baseline water quality relative to the receiving water under review, including geographic, hydrologic, geologic, water use, and water quality characteristics. d. The validity of any baseline concentrations assumed to be below detection levels. e. The quantity, date of analysis, analytical method, detection level, and spatial and temporal scope of any submitted data. f. Applicable seasonal or natural variability. (d) Best management practices. Practices and procedures the permittee or applicant will implement to limit impacts to specific classes of surface waters. (e) Modeling or other data. Modeling or other information related to pars. (a) to (d) . (f) Social or economic analysis and alternatives analysis. If the department notifies an applicant under sub. (7) that information under subs. (8) and (9) are required, a social importance analysis or economic importance analysis under sub. (8) (c) 1. , an alternatives analysis under sub. (8) (c) 2. , and a demonstration that resulting water quality will be adequate to fully protect existing uses. (6) Antidegradation procedures for general permits. The department shall apply the antidegradation policy under s. NR 102.045 to general storm water WPDES permits issued under this chapter and ch. 283 , Stats. For each new, reissued, and modified general permit, the following antidegradation implementation procedures under this subsection shall apply, as applicable: