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Wisconsin Administrative Code
Agency - Department of Natural ResourcesEnvironmental Protection - Wisconsin Pollutant Discharge Elimination SystemChapter NR 210 - Sewage Treatment Works
Subchapter II - Monitoring Requirements and Effluent Limitations
Section NR 210.07 - Effluent limitation variance categories

Wis. Admin. Code Department of Natural Resources NR 210.07

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Current through November 25, 2024
Section NR 210.07 - Effluent limitation variance categories

Modifications to limitations specified in s. NR 210.05(1) to (3) may be approved as follows:

(1) INDUSTRIAL WASTES. For publicly owned treatment facilities receiving effluent from certain categories of industries, the applicable effluent limitations for BOD5 and SS as set forth in s. NR 210.05(1) may be modified. The limitations for BOD 5 and SS in s. NR 210.05(1) may be adjusted upwards provided that:
(a) The discharge of such pollutants attributable to the industrial category will not be greater than that allowed by applicable effluent limitations if such industrial category were to discharge directly into the waters of the state; and
(b) The flow or loading of such pollutants introduced by the industrial category exceeds 10% of the design flow or loading of the publicly owned treatment works. When such an adjustment is made, the limitations for BOD5 or SS in s. NR 210.05(1) shall be adjusted proportionally.
(2) AERATED LAGOONS AND STABILIZATION PONDS. A variance for SS may be made in cases where aerated lagoons or waste stabilization ponds are the principal treatment processes. The SS limitation may be raised to a maximum of 60 mg/l for a 30-day average. This variance is not applicable to polishing or holding ponds which are preceded by other biological or physical/chemical treatment processes.

Note: See s. NR 110.24 for design requirements of aerated lagoons and stabilization ponds.

(3) pH. The effluent pH limitations may be adjusted on a case-by-case basis if the permittee or the owner can demonstrate that the limits need to be adjusted based on the following:
(a) Inorganic chemicals are not added as part of the treatment process; and
(b) In the case of a publicly owned treatment works, contributions from industrial sources do not cause the pH of the effluent to be less than 6.0 or greater than 9.0.
(4) CBOD5. Upon request by the permittee, the parameter CBOD5 may be substituted for the parameter BOD5, provided the following conditions are met:
(a) For treatment facilities with BOD5 limitations specified in s. NR 210.05(1) (a), (2) (a), or (3) (a), the permittee shall provide paired sampling of the effluent for BOD5 and CBOD 5 for the months of January and July. The sample frequency shall be at the same frequency as required by the permit for BOD5 sampling. Additional sampling for nitrogen compounds (NH3-N, NO3-N) or other sampling may also be required on a case-by-case basis.
(b) For treatment facilities with BOD5 limitations established in accordance with those specified in s. NR 210.05(1) (e), (2) (g), or (3) (f), the permittee shall provide paired sampling of the effluent for BOD5, CBOD5, NH3-N and NO3-N. At the end of the BOD5 test, an analysis of that BOD5 sample for NO3-N shall also be conducted.
1. This sampling shall be provided for the months of January, February, July, and August at a frequency of 3 times weekly for facilities with a design flowover 0.5 MGD and for those facilities which discharge to trout waters or may impact trout waters.
2. This sampling shall be provided for the months of January and July at a sample frequency as required by the permit for BOD5 sampling, with a maximum of 3 times weekly for facilities with a design flow less than 0.5 MGD.
(5) TREATMENT EQUIVALENT TO SECONDARY TREATMENT.
(a) Facilities eligible for treatment equivalent to secondary treatment as defined in s. NR 210.03(6) shall provide the following minimum level of effluent quality in terms of the parameters BOD5, SS, and pH. All requirements for the specified parameters in subd. 1., 2. or 3. shall be achieved except where provided for in sub. (2) or par. (b), (c), or (d).
1. The following effluent limits for BOD5 apply:
a. The 30-day average may not exceed 45 mg/l.
b. The 7-day average may not exceed 65 mg/l.
c. The 30-day average percent removal may not be less than 65%.
2. The following effluent limits for SS apply: except where SS values have been adjusted in accordance with s. NR 210.07(2):
a. The 30-day average may not exceed 45 mg/l.
b. The 7-day average may not exceed 65 mg/l.
c. The 30-day average percent removal may not be less than 65%.
3. The requirements of s. NR 210.05(1) (c) shall be met.
(b) Except as limited by par. (d) and subject to EPA approval, the department may after notice and opportunity for public comment, adjust the minimum levels of effluent quality set forth in par. (a) 1. a., b., 2. a. and b. for trickling filter facilities and in par. (a) 1. a. and b. for waste stabilization pond facilities to conform to the BOD5 and SS effluent concentrations consistently achievable through proper operation and maintenance by the median (50th percentile) facility in a representative sample of facilities within a state or appropriate contiguous geographical area that meet the definition of facilities eligible for treatment equivalent to secondary treatment.
(c) Where data are available to establish CBOD5 limitations for a treatment works subject to this subsection, the department may substitute the parameter CBOD5 for the parameter BOD5 in pars. (a) and (b), on a case-by-case basis.
1. The levels of CBOD5 effluent may not be less stringent than the following:
a. The 30-day average may not exceed 40 mg/l.
b. The 7-day average may not exceed 60 mg/l.
c. The 30-day average percent removal may not be less than 65%.
2. To apply for the CBOD5 variance, the permittee shall provide the data outlined in sub. (4).
(d) Any permit adjustment made pursuant to this section may not be any less stringent than the limitation required pursuant to sub. (5) (a). The department shall require more stringent limitations when adjusting permits if:
1. For existing facilities the permitting authority determines that the 30-day average and 7-day average BOD5 and SS effluent values that could be achievable through proper operation and maintenance of the treatment works, based on an analysis of the past performance of the treatment works, would enable the treatment works to achieve more stringent limitations, or
2. For new facilities, the department determines that the 30-day average and 7-day average BOD5 and SS effluent values that could be achievable through proper operation and maintenance of the treatment works, considering the design capability of the treatment process and geographical and climatic conditions, would enable the treatment works to achieve more stringent limitations.
(6) COMBINED SEWERS. Treatment works which have a combined sewer system may not be capable of meeting the percentage removal requirements established in sub. (5) (a) 1. c. and 2. c. or in s. NR 210.05(1) (a) 3. and (b) 3. during wet weather where the treatment works receive flows from combined sewers. For each treatment works, the decision shall be made on a case-by-case basis as to whether any attainable percentage removal level can be defined, and if so, what the level should be.

Wis. Admin. Code Department of Natural Resources NR 210.07

Cr. Register, October, 1986, No. 370, eff. 11-1-86.