# Wis. Admin. Code NR § 106.06: Calculation of water quality based effluent limitations for toxic and organoleptic substances

> Wisconsin · Regulations · In force

URL: https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_06

## Section

- **Citation:** Wis. Admin. Code NR § 106.06
- **Heading:** Calculation of water quality based effluent limitations for toxic and organoleptic substances
- **Jurisdiction:** Wisconsin
- **Kind:** Regulations
- **Status:** In force
- **Text as of:** August 14, 2026
- **Source:** Compiled text
- **Location:** Wisconsin Administrative Code / NR / Chapter NR 106 / § NR 106.06

## Text

Calculation of water quality based effluent limitations for toxic and organoleptic substances.
(1) Basis for limitations.
(a) The department shall establish water quality based effluent limitations for point source dischargers whenever such limitations are necessary, as determined by any method in this section, to meet the applicable water quality standards, criteria and secondary values as determined in chs. NR 102 to 105 .
(b)
1. Water quality based effluent limitations for toxic and organoleptic substances shall be determined to attain and maintain water quality standards and criteria or secondary values, specified in or determined according to procedures in ch. NR 105 , at the point of discharge. Effluent limitations shall be established to protect downstream waters whenever the department has information to make the determinations.
2. For discharges to Green Bay that are north of 44 ° 32’ 30” north latitude, the cold water community criteria shall apply in effluent limit calculations. For discharges to Green Bay that are south of 44 ° 32’ 30” north latitude, effluent limitations shall be established in accordance with subd. 1.
(2) Limitations for bioaccumulative chemicals of concern (bccs).
(am) In this subsection, the following definitions apply:
1. “New discharge” means any discharge from a point source that first received WPDES permit coverage from the department after November 6, 2000. “New discharge” does not include a discharge from a publicly owned treatment works if the discharge from the treatment works is caused by a project that is correcting or preventing a public health problem.
2. “Existing discharge” means any discharge from a point source that currently has a WPDES permit and that has continually had WPDES permit coverage since November 6, 2000 or earlier
er 6, 2000. “New discharge” does not include a discharge from a publicly owned treatment works if the discharge from the treatment works is caused by a project that is correcting or preventing a public health problem.
2. “Existing discharge” means any discharge from a point source that currently has a WPDES permit and that has continually had WPDES permit coverage since November 6, 2000 or earlier. “Existing discharge” includes a discharge from a publicly owned treatment works that becomes permitted after November 6, 2000 if the discharge from the treatment works is caused by a project that is correcting or preventing a public health problem.
3. “Expanded portion of an existing discharge” means any increase in concentration, level, or loading of a BCC, which would exceed a limitation specified in a current WPDES permit, or which according to the procedures in s. NR 106.05 , would result in the establishment of a new limitation in a reissued or modified WPDES permit. “Expanded portion of an existing discharge” does not include an expanded discharge from a publicly owned treatment works if the expanded discharge from the treatment works is caused by a project that is correcting or preventing a public health problem.
(bg) Notwithstanding any other provisions in chs. NR 102 and 106 , mixing zones may not be used for effluent limitations for new discharges of BCCs or for the expanded portion of an existing discharge of BCCs into the Great Lakes system. Effluent limitations for new discharges of BCCs and for expanded portions of existing discharges shall equal the most stringent applicable water quality criterion or secondary value for the BCC. Effluent limitations for an expanded portion of an existing discharge of BCCs shall be determined by means of a mass balance where the limitation for the existing portion of a permitted discharge that meets the provisions of par. (br) 1. or 2. shall be determined using the requirements of sub
scharges shall equal the most stringent applicable water quality criterion or secondary value for the BCC. Effluent limitations for an expanded portion of an existing discharge of BCCs shall be determined by means of a mass balance where the limitation for the existing portion of a permitted discharge that meets the provisions of par. (br) 1. or 2. shall be determined using the requirements of sub. (4) and the limitation for any expanded portion of the discharge may not exceed the most stringent criterion or value for that BCC.
(br) Effluent limitations for existing discharges of BCCs into the Great Lakes system may not include a mixing zone or exceed the most stringent applicable water quality criteria or secondary values for BCCs, except as provided under subd. 1. or 2.
1. Water conservation. A mixing zone may be granted and an effluent limitation may exceed the most stringent water quality criterion or secondary value for a discharged BCC if the permittee demonstrates in the permit application that failure to grant a mixing zone for the BCC would preclude water conservation measures that would lead to an overall load reduction of the BCC, even though a higher concentration of the BCC occurs in the effluent.
2. Technical and economic considerations. A mixing zone may be granted and an effluent limitation may exceed the most stringent water quality criterion or secondary value for the discharged BCC, if the permittee demonstrates and the department concurs that all the following conditions are met:
a. For the BCC discharged, the permittee is in compliance with and will continue to comply with the WPDES permit requirements and this chapter.
b
. A mixing zone may be granted and an effluent limitation may exceed the most stringent water quality criterion or secondary value for the discharged BCC, if the permittee demonstrates and the department concurs that all the following conditions are met:
a. For the BCC discharged, the permittee is in compliance with and will continue to comply with the WPDES permit requirements and this chapter.
b. The permittee has reduced and will continue to reduce loadings of the BCC for which a mixing zone is requested to the maximum extent possible, such that any additional controls or pollution prevention measures to reduce or ultimately eliminate the BCC discharged would result in unreasonable economic effects on the discharger or the affected community because the controls or measures are not feasible or cost-effective.
3. Approval Requirements. If the department approves a mixing zone for a BCC under this paragraph, the following requirements shall be met:
a. The approved mixing zone is no larger than necessary to account for the technical constraints and economic effects identified under subd. 2.
b. All water quality criteria or secondary values for the BCC shall be met at the edge of an approved mixing zone or be consistent with the applicable U.S. environmental protection agency (EPA) approved total maximum daily load (TMDL).
c. The permit shall contain a numeric effluent limitation for the BCC, determined using the requirements of sub. (4) and the limit shall not be less stringent than the limit that was effective on November 6, 2000.
d. The permit shall include requirements for an ambient water quality monitoring plan if the department determines these requirements are appropriate to ensure compliance with water quality criteria and consistency with any applicable TMDL.
e
n for the BCC, determined using the requirements of sub. (4) and the limit shall not be less stringent than the limit that was effective on November 6, 2000.
d. The permit shall include requirements for an ambient water quality monitoring plan if the department determines these requirements are appropriate to ensure compliance with water quality criteria and consistency with any applicable TMDL.
e. The permit shall include requirements for an evaluation of alternative means for reducing the BCC from other sources in the watershed if the department determines these requirements are appropriate to ensure compliance with water quality criteria and consistency with any applicable TMDL.
f. Any mixing zone for a BCC approved by the department pursuant to this paragraph shall be limited to one permit term unless the permittee applies for a mixing zone approval at the next reissuance and the department approves the mixing zone in the subsequent permit applications in accordance with the requirements of this paragraph.
g. The corresponding permit fact sheet for an approved mixing zone shall specify the mixing provisions used in calculating the permit limits and shall identify each BCC for which a mixing zone is approved.
(c) Effluent limitations for discharges of BCCs into waters of the Great Lakes system as defined in s. NR 102.12 that are based on human health criteria or secondary values calculated according to procedures in ch. NR 105 , shall be also based on the most protective designated use: cold water, public water supply.
(3) Limitations based on acute toxicity.
(a) The department shall establish water quality based effluent limitations to ensure that substances are not present in amounts which are acutely harmful to animals, plants or aquatic life in all surface waters including those portions of the mixing zone normally habitable by aquatic life and effluent channels as required by s. NR 102.04 (1) .
ater supply.
(3) Limitations based on acute toxicity.
(a) The department shall establish water quality based effluent limitations to ensure that substances are not present in amounts which are acutely harmful to animals, plants or aquatic life in all surface waters including those portions of the mixing zone normally habitable by aquatic life and effluent channels as required by s. NR 102.04 (1) .
(b) To assure compliance with par. (a) , the department shall calculate the water quality-based effluent limitation for a substance using the following procedures whenever the background concentration of the substance in the receiving water is less than the acute water quality criterion or secondary value:
1. A limitation shall be calculated using the following conservation of mass equation whenever sufficient site-specific data exist:
2. A limitation shall be calculated equal to the final acute value or secondary value as determined in s. NR 105.05 for the respective fish and aquatic life subcategory for which the receiving water is classified.
3. The department shall use the more restrictive calculated effluent limitation derived in subds. 1. and 2. as the water quality-based effluent limitation. If the background concentration of the substance in the receiving water is greater than the acute water quality criterion or secondary value for the substance, then the procedure in sub. (6) shall be used to calculate the limitation.
(bm) The value of Qs of the receiving water for calculating effluent limitations in par. (a) based upon the acute fish and aquatic life criteria or secondary values developed according to ch. NR 105 shall be determined on a case-by-case basis. In no case may the Qs exceed the average minimum 1-day flow which occurs once in 10 years (1-day Q10) or if the 1-day Q10 flow data is not available, 80% of the average minimum 7-day flow that occurs once in 10 years (7-day Q10).
tations in par. (a) based upon the acute fish and aquatic life criteria or secondary values developed according to ch. NR 105 shall be determined on a case-by-case basis. In no case may the Qs exceed the average minimum 1-day flow which occurs once in 10 years (1-day Q10) or if the 1-day Q10 flow data is not available, 80% of the average minimum 7-day flow that occurs once in 10 years (7-day Q10).
(c) Except as provided in sub. (2) , water quality-based effluent limitations as derived in par. (b) may exceed the final acute value or the secondary acute value within a zone of initial dilution provided that the acute toxicity criteria or secondary acute values are met within a short distance from the point of discharge. A zone of initial dilution shall only be approved if the discharger demonstrates to the department that mixing of the effluent with the receiving water in the zone of initial dilution is rapid and all the following conditions are met:
1. The discharge is not at the water surface or at the shoreline.
2. The discharge does not constitute a significant portion of the streamflow or otherwise dominate the receiving water.
3. The discharge velocity is not less than 3 meters per second (10 feet per second) unless an alternative discharge velocity, which similarly minimizes organism exposure time, is determined appropriate for the specific site.
4. The acute toxicity criteria or secondary acute values shall be met within 10% of the distance from the edge of the outfall structure to the edge of a mixing zone which may be determined in accordance with s. NR 102.05 (3) .
5. The acute toxicity criteria or secondary acute values shall be met within a distance of 50 times the discharge length scale in any direction. The discharge length scale is defined as the square root of the cross-sectional area of any discharge outlet. If a multiport diffuser is used, the requirement in this subdivision shall be met for each port using the appropriate discharge length scale for that port.
6
toxicity criteria or secondary acute values shall be met within a distance of 50 times the discharge length scale in any direction. The discharge length scale is defined as the square root of the cross-sectional area of any discharge outlet. If a multiport diffuser is used, the requirement in this subdivision shall be met for each port using the appropriate discharge length scale for that port.
6. The acute toxicity criteria or secondary acute values shall be met within a distance of 5 times the local water depth in any horizontal direction from any discharge outlet. The local water depth is defined as the natural water depth (existing prior to the installation of the discharge outlet) prevailing under the mixing zone design conditions for the site.
(d) For toxic substances with water quality criteria related to one or more other water quality parameters, effluent limitations shall be calculated using the effluent value for the water quality parameter. Water quality parameters include, but are not limited to, pH, temperature and hardness.
(e) The department shall use the methodology in s. NR 106.07 (3) to (5) to express water quality-based effluent limitations derived in this subsection as permit effluent limitations.
(4) Limitations based on chronic toxicity or long-term impacts.
(a) Water quality criteria and secondary values. The department shall calculate water quality based effluent limitations to ensure that the chronic toxicity criteria (CTC), the wildlife criteria (WC), the taste and odor criteria (TOC), the human threshold criteria (HTC), and human cancer criteria (HCC) appropriate for the receiving water as specified in chs. NR 102 to 105 and the secondary chronic values determined according to ch. NR 105 will be met after dilution with an appropriate allowable quantity of receiving water flow as specified in this subsection, subs. (5) to (11) and s. NR 106.11 . The available dilution shall be determined according to par. (c) unless the conditions specified in s. NR 102.05 (3) or sub
ceiving water as specified in chs. NR 102 to 105 and the secondary chronic values determined according to ch. NR 105 will be met after dilution with an appropriate allowable quantity of receiving water flow as specified in this subsection, subs. (5) to (11) and s. NR 106.11 . The available dilution shall be determined according to par. (c) unless the conditions specified in s. NR 102.05 (3) or sub. (2) require less dilution or no dilution be allowed. Effluent limitations for substances for which criteria may be expressed as dissolved concentrations may be established according to sub. (7) .
(b) Calculation of limits. Water quality based effluent limitations to meet the requirements of this subsection shall be calculated using the procedure specified in subd. 1. or 2. , except as provided in sub. (2) or (6) .
1. For discharges of toxic or organoleptic substances to flowing receiving waters, the water quality based effluent limitation for a substance shall be calculated using the following conservation of mass equation whenever the background concentration is less than the water quality criterion or secondary value:
2. For discharges of toxic or organoleptic substances to receiving waters which do not exhibit a unidirectional flow at the point of discharge, such as lakes or impoundments, the department may calculate, in the absence of specific data, water quality based effluent limitations using the following equation whenever the background concentration is less than the water quality criterion or secondary value:
3. The limitation calculated in subd. 1. or 2. may be converted to a maximum load limitation by multiplying the calculated concentration limitation by the rate of effluent flow as determined in par. (d) and appropriate conversion factors.
uality based effluent limitations using the following equation whenever the background concentration is less than the water quality criterion or secondary value:
3. The limitation calculated in subd. 1. or 2. may be converted to a maximum load limitation by multiplying the calculated concentration limitation by the rate of effluent flow as determined in par. (d) and appropriate conversion factors.
(c) Receiving water design flow (Qs). The value of Q s to be used in calculating the effluent limitation for discharges to flowing waters shall be determined as follows:
1. The department shall make reasonable efforts to determine the area of the zone of passage and the dilution characteristics of discharges.
2. The department may require that the discharger provide information on the discharge mixing and dilution characteristics of discharges.

## Nearby sections

- [Wis. Admin. Code NR § 106.01 Purpose](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_01.md)
- [Wis. Admin. Code NR § 106.02 Applicability](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_02.md)
- [Wis. Admin. Code NR § 106.03 Definitions](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_03.md)
- [Wis. Admin. Code NR § 106.04 General](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_04.md)
- [Wis. Admin. Code NR § 106.05 Determination of the necessity for water quality based effluent limitations for toxic and organoleptic substances](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_05.md)
- [Wis. Admin. Code NR § 106.06 Calculation of water quality based effluent limitations for toxic and organoleptic substances](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_06.md)
- [Wis. Admin. Code NR § 106.07 Application of and compliance with water quality based effluent limitations in permits](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_07.md)
- [Wis. Admin. Code NR § 106.08 Determination of the necessity for whole effluent toxicity testing requirements and limitations](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_08.md)
- [Wis. Admin. Code NR § 106.09 Whole effluent toxicity data evaluation and limitations](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_09.md)
- [Wis. Admin. Code NR § 106.10 Noncontact cooling water additives](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_10.md)
- [Wis. Admin. Code NR § 106.11 Multiple discharges](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_11.md)
- [Wis. Admin. Code NR § 106.14 Analytical methods and laboratory requirements](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_14.md)
- [Wis. Admin. Code NR § 106.15 Limitations for mercury](https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_15.md)
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Source: Frix Law Library, https://www.frixlaw.com/law-library/statutes/STATE_WI_ADC_NR_106_06. Check the current official text before relying on it. Not legal advice.