Sec. NR 205.067 - Reasonable potential for water quality based effluent limitations

ยง NR 205.067. Reasonable potential for water quality based effluent limitations

(1) GENERAL.

(a) The department shall include an effluent limitation for a pollutant in a WPDES permit when the department determines that the discharge of the pollutant causes, has the reasonable potential to cause, or contributes to an excursion above the allowable ambient concentration of a numeric water quality criterion in chs. NR 102 to 104 in the receiving water or a downstream water.

Note: Downstream water includes downstream waterbodies in other states or tribal waters that have EPA approved standards under 40 CFR 130.

(b) Limitations shall control all pollutants or pollutant parameters, including conventional, nonconventional, and toxic pollutants, that the department determines are or may be discharged at a level that will cause, have the reasonable potential to cause, or contribute to an excursion above any water quality standard in chs. NR 102 to 104, including narrative criteria for water quality.

(2) FACTORS TO CONSIDER. When determining under sub. (1) or (4) whether a pollutant discharged causes, has the reasonable potential to cause, or contributes to an exceedance of a numeric or narrative water quality standard, the department shall consider all of the following factors:

(a) Existing controls on the discharge.

(b) Controls on the pollutant discharged by nonpoint source pollution in the watershed.

(c) The variability of the pollutant or parameter in the effluent discharged.

(d) Sensitivity of species to toxicity testing when evaluating whole effluent toxicity as defined in s. NR 106.03(14).

(e) Dilution of the effluent in the receiving water.

(3) WATER QUALITY BASED EFFLUENT LIMITATIONS. If the department determines a limitation is necessary under this section, the limitation shall:

(a) Be consistent with a total maximum daily load as defined in s. NR 217.11(7) if a total maximum daily load has been approved by the EPA for the receiving waterbody.

(b) Ensure achievement of a level of water quality derived from, and in compliance with, the applicable water quality standard.

(4) IN ABSENCE OF NUMERIC WATER QUALITY CRITERIA.

(a) When a chemical pollutant, for which a numeric water quality criterion does not exist, is present in an effluent at a concentration that causes, has the reasonable potential to cause, or contributes to an excursion above a narrative criterion within an applicable water quality standard, effluent limits shall be established using one or more of the following options:

1. Establish effluent limits using a calculated numeric water quality criterion for the pollutant that the department demonstrates will attain and maintain applicable narrative water quality criteria and will fully protect the designated use. Such a criterion may be derived using data for a proposed criterion or other relevant information such as EPA's Water Quality Standards Handbook, risk assessment data, exposure data, information about the pollutant from the Food and Drug Administration, and current EPA criteria documents.

Note: EPA's Water Quality Standards Handbook is available at the following link: https://www.epa.gov/wqs-tech/water-quality-standards-handbook.

2. Establish effluent limits on a case-by-case basis, using EPA's water quality criteria, published under 33 USC 1314(a), supplemented when necessary by other relevant information.

3. Establish effluent limits on an indicator parameter for the pollutant of concern, provided that all of the following are true:

a. The permit identifies which pollutants are intended to be controlled by the use of the effluent limitation.

b. The fact sheet sets forth the basis for the limit, including a finding that compliance with the effluent limit of the indicator parameter will result in controls on the pollutant of concern that are sufficient to attain and maintain applicable water quality standards.

c. The permit requires all effluent and ambient monitoring necessary to show that, during the term of the permit, the limit on the indicator parameter continues to attain and maintain applicable water quality standards.

d. The permit contains a reopener clause allowing the department to modify or revoke and reissue the permit if the limits on the indicator parameter no longer attain and maintain applicable water quality standards.

(b) If there is reasonable potential under par. (a) to exceed a narrative criterion and if required under s. NR 106.08, a limitation for whole effluent toxicity shall be included in the permit.

Note: Limitations and procedures for whole effluent toxicity are established in subch. II of ch. NR 106.

(5) LIMIT CONTINUATION.

(a) Subject to par. (b), if a permit includes a water quality based effluent limitation for a pollutant because the limitation is required under this section or is required under the procedures in another chapter, the water quality based effluent limitation for the pollutant shall be included in a subsequently reissued permit if all of the following apply:

1. Treatment or pollutant control measures were added to comply with the water quality based effluent limitation for the pollutant and the water quality based effluent limitation took effect in a prior permit.

2. The facility has the ability to alter or suspend the treatment or pollutant control measures for the pollutant to the degree that there is continued reasonable potential to exceed the applicable standard.

(b) If the department determines a more stringent limitation is necessary to comply with water quality standards, a more stringent water quality based effluent limitation shall be included in the permit for the pollutant. Also, the department may include a less stringent limitation provided water quality standards, including antidegradation, as well as antibacksliding requirements in ch. NR 207 are met.

(6) EXCEPTION. Subsections (1) to (4) do not apply to pollutants or limitations that are subject to the procedures in ch. NR 106 or 217.

(Adopted by, CR 17-002: cr. Register April 2018 No. 748, eff. 5-1-18; correction in (5) (a) (intro.), (6) made under s. 35.17, Stats., Register April 2018 No. 748, eff. 5/1/2018)

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