Chapter NR 106

NR 106.06(2)(br)2. 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:

NR 106.06(2)(br)2.a. a. For the BCC discharged, the permittee is in compliance with and will continue to comply with the WPDES permit requirements and this chapter.

NR 106.06(2)(br)2.b. 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.

NR 106.06(2)(br)3. 3. Approval Requirements. If the department approves a mixing zone for a BCC under this paragraph, the following requirements shall be met:

NR 106.06(2)(br)3.a. a. The approved mixing zone is no larger than necessary to account for the technical constraints and economic effects identified under subd. 2.

NR 106.06(2)(br)3.b. 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).

NR 106.06(2)(br)3.c. 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.

NR 106.06(2)(br)3.d. 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.

NR 106.06(2)(br)3.e. 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.

NR 106.06(2)(br)3.f. 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.

NR 106.06(2)(br)3.g. 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.

NR 106.06(2)(c) (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.

NR 106.06(3) (3) Limitations based on acute toxicity.

NR 106.06(3)(a) (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).

NR 106.06(3)(b) (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:

NR 106.06(3)(b)1. 1. A limitation shall be calculated using the following conservation of mass equation whenever sufficient site-specific data exist:

Limitation = (WQC) (Qs+(1-f)Qe) - (Qs- fQe) (Cs)
Qe

NR 106.06(3)(b)2. 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.

NR 106.06(3)(b)3. 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.

NR 106.06(3)(bm) (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).

NR 106.06(3)(c) (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:

NR 106.06(3)(c)1. 1. The discharge is not at the water surface or at the shoreline.

NR 106.06(3)(c)2. 2. The discharge does not constitute a significant portion of the streamflow or otherwise dominate the receiving water.

NR 106.06(3)(c)3. 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.

NR 106.06(3)(c)4. 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).

NR 106.06(3)(c)5. 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.

NR 106.06(3)(c)6. 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.

NR 106.06(3)(d) (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.

NR 106.06(3)(e) (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.

NR 106.06(4) (4) Limitations based on chronic toxicity or long-term impacts.

NR 106.06(4)(a) (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. (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).

NR 106.06(4)(b) (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).

NR 106.06(4)(b)1. 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:

Limitation = (WQC) (Qs+(1-f)Qe) - (Qs- fQe) (Cs)
Qe

NR 106.06 Note Note: In applying this equation, all units for the flow and concentration parameters respectively, shall be consistent.

NR 106.06(4)(b)2. 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:

Limitation = 11 (WQC) - 10Cs

On a case-by-case basis other dilutional factors may be used, but in no case may the dilution allowed exceed an area greater than the area where discharge induced mixing occurs. The discharge is also subject to the conditions specified in s. NR 102.05 (3). The discharger may be required to determine the size of the mixing zone using acceptable models or dye studies.

NR 106.06(4)(b)3. 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.

NR 106.06(4)(c) (c) Receiving water design flow (Qs). The value of Qs to be used in calculating the effluent limitation for discharges to flowing waters shall be determined as follows:

NR 106.06(4)(c)1. 1. The department shall make reasonable efforts to determine the area of the zone of passage and the dilution characteristics of discharges.

NR 106.06(4)(c)2. 2. The department may require that the discharger provide information on the discharge mixing and dilution characteristics of discharges.

NR 106.06(4)(c)3. 3. The discharger shall be allowed to demonstrate, through appropriate and reasonable methods that an adequate zone of free passage exists in the cross-section of the receiving water or that dilution is accomplished rapidly such that the extent of the mixing zone is minimized. In complex situations, the department may require that the demonstration under this subdivision include water quality modeling or field dispersion studies.

NR 106.06(4)(c)4. 4. Following the determinations under subds. 1. to 3., the value of Qs of the receiving water for calculating effluent limitations based upon the chronic toxicity criteria specified in s. NR 105.06 or secondary chronic values shall be determined on a case-by-case basis. In no case may Qs exceed the larger of the average minimum 7-day flow which occurs once in 10 years (7-day Q10) or, if sufficient information is available to calculate a biologically based receiving water design flow, the flow which prevents an excursion from the criterion or secondary value using a duration of 4 days and a frequency of less than once every 3 years (4-day, 3-year biological flow).

NR 106.06(4)(c)5. 5. If the requirements of subds. 2. and 3. are not satisfied, the department shall notify the permittee and identify the deficiencies and allow additional time, if necessary, to complete the demonstration. If the demonstration cannot be completed satisfactorily, the value of Qs of the receiving water for calculating effluent limitations based upon the chronic toxicity criteria specified in s. NR 105.06 or secondary chronic values shall equal 1/4 of the 7-day Q10 or 1/4 of the 4-day, 3 year biological flow. In no case may the value of Qs, of the receiving water, for calculating effluent limitations based upon the chronic toxicity criteria or secondary chronic values developed according to ch. NR 105, exceed 1/4 of the 7-day Q10 or 1/4 of the 4-day, 3-year biological flow if the department determines that the discharge has a potential to jeopardize the continued existence of any endangered or threatened species listed under ch. NR 27 and conforming to section 7 of the endangered species act, 16 USC 1536.

NR 106.06(4)(c)6. 6. Qs may be reduced from those values calculated in subds. 3. to 5. where natural receiving water flow is significantly altered by flow regulation.

NR 106.06(4)(c)7. 7. Following the determinations under subds. 1. to 3., the value of Qs of the receiving water for calculating effluent limitations based upon the wildlife 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 90-day flow which occurs once in 10 years (90-day Q10) or if the 90-day Q10 flow is not available, the average minimum 30-day flow which occurs once in 5 years (30-day Q5) or 85% of the average minimum 7-day flow which occurs once in 2 years (7-day Q2).

NR 106.06(4)(c)8. 8. If the requirements of subds. 2. and 3. are not satisfied, the department shall notify the permittee and identify the deficiencies and allow additional time, if necessary, to complete the demonstration. Except as provided in subd. 12., if the demonstration cannot be completed satisfactorily, the value of Qs of the receiving water for calculating effluent limitations based upon the wildlife criteria specified in s. NR 105.07 shall equal ¼ of the 90-day Q10 or ¼ of the 30-day Q5 or ¼ of 85% of the 7-day Q2. In no case may the value of Q5 of the receiving water, for calculating effluent limitations based upon the wildlife criteria or secondary values developed according to ch. NR 105, exceed ¼ of the 90-day Q10 or ¼ of the 30-day Q5 or ¼ of 85% of the 7-day Q2 if the department determines that the discharge has a potential to jeopardize the continued existence of any endangered or threatened species listed under ch. NR 27 and conforming to section 7 of the endangered species act, 16 USC 1536.

NR 106.06(4)(c)9. 9. Except as provided in subd. 12., following the determinations under subds. 1. to 3., the value of Qs of the receiving water for calculating effluent limitations based upon the human cancer criteria, human threshold criteria or secondary values developed according to ch. NR 105 shall be determined on a case-by-case basis. In no case may Qs exceed the harmonic mean flow.

NR 106.06(4)(c)10. 10. If the requirements of subds. 2. and 3. are not satisfied, the department shall notify the permittee and identify the deficiencies and allow additional time, if necessary, to complete the demonstration. Subject to subd. 12., if the demonstration cannot be completed satisfactorily, the value of Qs of the receiving water for calculating effluent limitations based upon the human cancer criteria or secondary values or the human threshold criteria or secondary values specified in ch. NR 105 shall equal ¼ of the harmonic mean flow.

NR 106.06(4)(c)11. 11. Except as provided in subd. 12., the value of Qs shall equal the mean annual flow of the receiving water for calculating effluent limitations based upon the taste and odor criteria as specified in ch. NR 102.

NR 106.06(4)(c)12. 12. Qs may be reduced from those values calculated in subds. 9., 10., and 11.,whenever the department determines such discharges may directly affect public drinking water supplies.

NR 106.06(4)(d) (d) Effluent flows (Qe).

NR 106.06(4)(d)1. 1. For dischargers subject to ch. NR 210 and which discharge for 24 hours per day on a year-round basis, Qe shall equal the maximum effluent flow, expressed as a daily average, that is anticipated to occur for 12 continuous months during the design life of the treatment facility unless it is demonstrated to the department that such a design flow rate is not representative of projected flows at the facility.

NR 106.06(4)(d)2. 2. For all other dischargers not subject to ch. NR 210, Qe shall equal either subd. 2. a. or b. for effluent limitations based on aquatic life chronic criteria or chronic secondary values, and shall equal either subd. 2. a. or c. for effluent limitations based on wildlife, human threshold, human cancer or taste and odor criteria or secondary values. Whenever calculating Qe, the department may consider a projected increase in effluent flow that will occur when production is increased or modified, or another wastewater source, including stormwater, is added to an existing wastewater treatment facility. This subdivision does not waive the requirements of ch. NR 207.

NR 106.06(4)(d)2.a. a. The maximum effluent flow, expressed as a daily average, that has occurred for 12 continuous months and represents normal operations; or

NR 106.06(4)(d)2.b. b. The maximum effluent flow, expressed as a daily average, that has occurred for 7 continuous days and represents normal operations; or

NR 106.06(4)(d)2.c. c. The maximum effluent flow, expressed as a daily average, that has occurred for 30 continuous days and represents normal operations.

NR 106.06(4)(d)3. 3. For seasonal discharges, discharges proportional to stream flow, or other unusual discharge situations, Qe shall be determined on a case by case basis.

NR 106.06(4)(e) (e) Background concentrations of toxic or organoleptic substances (Cs). The representative background concentration of a toxic or organoleptic substance shall be used in deriving chemical specific water quality based effluent limitations. Except as provided elsewhere in this paragraph, the representative background concentration shall equal the geometric mean of the acceptable available data for a substance. Background concentrations may not be measured at a location within the direct influence of a point source discharge.

NR 106.06(4)(e)1. 1. The department shall determine representative background concentrations of toxic substances on a case-by-case basis using available data on the receiving water or similar waterbodies in the state, including acceptable and available caged or resident fish tissue data, available or projected pollutant loading data, and best professional judgment.

NR 106.06(4)(e)2. 2. The department may utilize representative seasonal concentrations and may consider other information on background concentrations submitted to the department.

NR 106.06(4)(e)3. 3. When evaluating background concentration data, commonly accepted statistical techniques shall be used to evaluate data sets consisting of values both above and below the level of detection. When all of the acceptable available data in a data set category, such as water column, caged or resident fish tissue, are below the level of detection for a pollutant, then all the data for that pollutant in that data set shall be assumed to be zero.

NR 106.06(4)(f) (f) The department shall use the methodology in s. NR 106.07 (3) to (5) to express water quality-based effluent limitations derived in this section as permit effluent limitations.

NR 106.06(5) (5) Values for parameters which affect the limit. For toxic substances with water quality criteria related to one or more other water quality parameters, the department may calculate effluent limitations in consideration of those other water quality parameters. Water quality parameters include but are not limited to pH, temperature and hardness. The department shall determine the value of the water quality parameters on a case-by-case basis as follows:

NR 106.06(5)(a) (a) Receiving water.

NR 106.06(5)(a)1. 1. The geometric mean of available data for the receiving water shall be used, except the arithmetic mean for pH shall be used.

NR 106.06(5)(a)2. 2. Representative seasonal values may be used.

NR 106.06(5)(a)3. 3. If information on the water quality parameters is not available, then information on the quality of similar water bodies in the area and best professional judgment may be used.

NR 106.06(5)(a)4. 4. The receiving water value of the water quality parameter shall be used to determine the effluent limitation. The receiving water value may be modified to account for the mixture of the receiving and effluent flows when any of the following conditions occur:

NR 106.06(5)(a)4.a. a. When the value of the water quality parameter in the effluent is significantly greater than or less than the value in the receiving water;

NR 106.06(5)(a)4.b. b. When the effluent flow is relatively large in comparison to the receiving water flow used in the calculation of the effluent; or

NR 106.06(5)(a)4.c. c. When, as a result of demonstrated or measured physical, chemical or biological reactions, the value of the water quality parameter, after mixing of the receiving water and the effluent, is significantly different than the background value of the water quality parameter in the receiving water.

NR 106.06(5)(b) (b) Effluent.

NR 106.06(5)(b)1. 1. The geometric mean of available data for the effluent shall be used, except the arithmetic mean for pH shall be used.

NR 106.06(5)(b)2. 2. If information on the water quality parameters is not available, then values representative of similar effluents may be used.

NR 106.06(6) (6) Effluent limitations based upon elevated background concentrations. Whenever the representative background concentration for a toxic or organoleptic substance in the receiving water is determined to be greater than any applicable water quality criterion or secondary value for that substance, the calculation of an effluent limitation and the determination of the need for the limitation in a permit shall be performed subject to all of the following:

NR 106.06(6)(a) (a) If the department has developed an EPA approved TMDL for the toxic or organoleptic substance in the receiving water, an effluent limitation for that substance shall be consistent with the TMDL.

NR 106.06(6)(b) (b) If no EPA approved TMDL has been developed and if the intake source of the wastewater is all from the same waterbody as the receiving water of the discharge, the department may determine that the discharge does not have a reasonable potential to cause or contribute to an excursion above the applicable water quality criterion or secondary value for the substance, and may determine that a numeric limitation is not necessary, provided the permittee has demonstrated that all of the following conditions are met:

NR 106.06(6)(b)1. 1. The permittee withdraws 100 percent of the intake water containing the substance from the same waterbody into which the discharge is made.

NR 106.06(6)(b)2. 2. The permittee does not contribute any additional mass of the identified intake substance to its wastewater.

NR 106.06(6)(b)3. 3. The permittee does not alter the identified intake substance chemically or physically in a manner that would cause adverse water quality impacts to occur that would not occur if the substance were left in-stream.

NR 106.06(6)(b)4. 4. The permittee does not contribute to a statically significant increase in the identified intake substance concentration, as determined by the department, at the edge of the mixing zone or at the point of discharge if a mixing zone is not allowed, as compared to the concentration of the substance in the intake water, unless the increased concentration does not cause or contribute to an excursion of water quality standard for that substance.

NR 106.06(6)(b)5. 5. The timing and location of the discharge would not cause adverse water quality impacts to occur that would not occur if the identified intake substance were left in the receiving waterbody.

NR 106.06(6)(c) (c) If no TMDL has been developed and the conditions in par. (b) are not met, an effluent limitation shall be included in the permit if the department determines that the discharge has a reasonable potential to cause or contribute to an excursion above the applicable water quality criterion or secondary value for the substance. The limitation shall be applied as follows:

NR 106.06(6)(c)1. 1. For discharges within the Great Lakes system, the effluent limitation for that substance shall be equal to the most stringent applicable water quality criterion or secondary value.

NR 106.06(6)(c)2. 2. For discharges outside of the Great Lakes system:

NR 106.06(6)(c)2.a. a. When all of the intake source of the wastewater is from the same waterbody as the receiving water of the discharge and the permittee has demonstrated that the conditions in par. (b) 3. to 5. are met the effluent limitation for that substance shall equal the representative background concentration of that substance in the receiving water. If the conditions in par. (b) 3. to 5. are not met, the effluent limitation for that substance shall be equal to the most stringent applicable water quality criterion or secondary value for that substance.

NR 106.06(6)(c)2.b. b. When all of the intake source of the wastewater is from a waterbody that is different than the receiving water of the discharge, the effluent limitation for that substance shall be equal to the lowest applicable water quality criterion or secondary value.