### 546 40 CFR Ch. I (7–1–06 Edition) § 133.102

(d) BOD. The five day measure of thepollutant parameter biochemical oxygen demand (BOD).

(e) CBOD5 . The five day measure of the pollutant parameter carbonaceous biochemical oxygen demand (CBOD5 ).

(f) Effluent concentrations consistently achievable through proper operation and
maintenance. (1) For a given pollutant parameter, the 95th percentile value for the 30-day average effluent qualityachieved by a treatment works in a period of at least two years, excluding values attributable to upsets, bypasses, operational errors, or other unusual conditions, and (2) a 7-day averagevalue equal to 1.5 times the value derived under paragraph (f)(1) of this section.

(g) Facilities eligible for treatment equivalent to secondary treatment. Treatment works shall be eligible for consideration for effluent limitations described for treatment equivalent to secondary treatment (§133.105), if:

(1) The BOD 5 and SS effluent concentrations consistently achievablethrough proper operation and maintenance (§133.101(f)) of the treatment
works exceed the minimum level of the effluent quality set forth in §§133.102(a) and 133.102(b),

(2) A trickling filter or waste stabilization pond is used as the principal process, and

(3) The treatment works provide significant biological treatment of municipal wastewater.

(h) mg/l. Milligrams per liter. (i) NPDES. National Pollutant Discharge Elimination System.

(j) Percent removal. A percentage expression of the removal efficiency across a treatment plant for a given pollutant parameter, as determined from the 30-day average values of theraw wastewater influent pollutant concentrations to the facility and the 30-day average values of the effluent pollutant concentrations for a given time period.

(k) Significant biological treatment.
The use of an aerobic or anaerobic biological treatment process in a treatment works to consistently achieve a30-day average of a least 65 percent removal of BOD 5

.

(l) SS. The pollutant parameter total suspended solids. (m) Significantly more stringent limitation means BOD 5 and SS limitations necessary to meet the percent removal requirements of at least 5 mg/l more stringent than the otherwise applicable concentration-based limitations (e.g.,less than 25 mg/l in the case of the secondary treatment limits for BOD 5 and SS), or the percent removal limitations in §§133.102 and 133.105, if such limits would, by themselves, force significantconstruction or other significant capital expenditure.

(n) State Director means the chief administrative officer of any State orinterstate agency operating an ‘‘approved program,’’ or the delegated representative of the State Director.

[49 FR 37006, Sept. 20, 1984; 49 FR 40405, Oct. 16, 1984, as amended at 50 FR 23387, June 3, 1985]

§ 133.102 Secondary treatment.

The following paragraphs describe the minimum level of effluent quality attainable by secondary treatment in terms of the parameters—BOD 5 , SS andpH. All requirements for each parameter shall be achieved except as provided for in §§133.103 and 133.105.

(a) BOD5

.(1) The 30-day average shall not exceed 30 mg/l.

(2) The 7-day average shall not exceed 45 mg/l.

(3) The 30-day average percent removal shall not be less than 85 percent.

(4) At the option of the NPDES permitting authority, in lieu of the parameter BOD 5 and the levels of the effluent quality specified in paragraphs (a)(1), (a)(2) and (a)(3), the parameter
CBOD 5 may be substituted with the following levels of the CBOD 5 effluent quality provided:

(i) The 30-day average shall not exceed 25 mg/l.

(ii) The 7-day average shall not exceed 40 mg/l.

(iii) The 30-day average percent removal shall not be less than 85 percent.

(b) SS. (1) The 30-day average shall not exceed 30 mg/l.

(2) The 7-day average shall not exceed 45 mg/l.

(3) The 30-day average percent removal shall not be less than 85 percent.

(c) pH. The effluent values for pH
shall be maintained within the limits


### 547 Environmental Protection Agency § 133.103

of 6.0 to 9.0 unless the publicly owned treatment works demonstrates that: (1) Inorganic chemicals are not added tothe waste stream as part of the treatment process; and (2) contributions
from industrial sources do not cause the pH of the effluent to be less than 6.0 or greater than 9.0.

[49 FR 37006, Sept. 20, 1984; 49 FR 40405, Oct. 16, 1984]

§ 133.103 Special considerations.

(a) Combined sewers. Treatment works subject to this part may not becapable of meeting the percentage removal requirements established under §§133.102(a)(3) and 133.102(b)(3), or §§133.105(a)(3) and 133.105(b)(3) during
wet weather where the treatment
works receive flows from combined sewers (i.e., sewers which are designedto transport both storm water and sanitary sewage). For such treatment works, the decision must 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.

(b) Industrial wastes. For certain industrial categories, the discharge to navigable waters of BOD5 and SS permitted under sections 301(b)(1)(A)(i), (b)(2)(E) or 306 of the Act may be less stringent than the values given in §§133.102(a)(1), 133.102(a)(4)(i), 133.102(b)(1), 133.105(a)(1), 133.105(b)(1) and 133.105(e)(1)(i). In cases when wastes
would be introduced from such an industrial category into a publicly owned treatment works, the values for BOD 5 and SS in §§133.102(a)(1), 133.102(a)(4)(i), 133.102(b)(1), 133.105(a)(1), 133.105(b)(1),and 133.105(e)(1)(i) may be adjusted upwards provided that: (1) The permitteddischarge of such pollutants, attributable to the industrial category, would not be greater than that which would be permitted under sections 301(b)(1)(A)(i), 301(b)(2)(E) or 306 of the Act if such industrial category were to discharge directly into the navigable waters, and (2) the flow or loading ofsuch pollutants introduced by the industrial category exceeds 10 percent ofthe design flow or loading of the publicly owned treatment works. When such an adjustment is made, the values
for BOD 5 or SS in §§133.102(a)(2), 133.102(a)(4)(ii), §133.102(b)(2), 133.105(a)(2), 133.105(b)(2), and133.105(e)(1)(ii) should be adjusted proportionately.

(c) Waste stabilization ponds. The Regional Administrator, or, if appropriate, State Director subject to EPA approval, is authorized to adjust the minimum levels of effluent quality set forth in §133.105 (b)(1), (b)(2), and (b)(3) for treatment works subject to thispart, to conform to the SS concentrations achievable with waste stabilization ponds, provided that: (1) Waste stablization ponds are the principal process used for secondary treatment; and (2) operation and maintenance data indicate that the SS values specified in §133.105 (b)(1), (b)(2), and (b)(3) cannot
be achieved. The term ‘‘SS concentrations achievable with waste stabilization ponds’’ means a SS value, determined by the Regional Administrator,or, if appropriate, State Director subject to EPA approval, which is equal to
the effluent concentration achieved 90 percent of the time within a State or appropriate contiguous geographical area by waste stabilization ponds that are achieving the levels of effluent quality for BOD 5 specified in §133.105(a)(1). [cf. 43 FR 55279].

(d) Less concentrated influent wastewater for separate sewers. The Regional Administrator or, if appropriate, State
Director is authorized to substitute either a lower percent removal requirement or a mass loading limit for the percent removal requirements set forth in §§133.102(a)(3), 133.102(a)(4)(iii), 133.102(b)(3), 102.105(a)(3), 133.105(b)(3) and 133.105(e)(1)(iii) provided that the permittee satisfactorily demonstratesthat: (1) The treatment works is consistently meeting, or will consistently meet, its permit effluent concentrationlimits but its percent removal requirements cannot be met due to less concentrated influent wastewater, (2) tomeet the percent removal requirements, the treatment works would have to achieve significantly morestringent limitations than would otherwise be required by the concentration-based standards, and (3) the less
concentrated influent wastewater is
not the result of excessive I/I. The determination of whether the less concentrated wastewater is the result of