Terms used in this part are defined as follows:

(a) 7-day average. The arithmetic mean of pollutant parameter values for samples collected in a period of 7 consecutive days.

(b) 30-day average. The arithmetic mean of pollutant parameter values of samples collected in a period of 30 consecutive days.

(c) Act. The Clean Water Act (33 U.S.C. 1251 et seq., as amended).

(d) BOD. The five day measure of the pollutant 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 quality achieved 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 average value 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 BOD5 and SS effluent concentrations consistently achievable through 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 the raw 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 a 30-day average of a least 65 percent removal of BOD5.

(l) SS. The pollutant parameter total suspended solids.

(m) Significantly more stringent limitation means BOD5 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 BOD5 and SS), or the percent removal limitations in §§133.102 and 133.105, if such limits would, by themselves, force significant construction or other significant capital expenditure.

(n) State Director means the chief administrative officer of any State or interstate 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]