Iowa Admin. Code r. 567-62.2 - Secondary treatment information: effluent standards for POTWs and semipublic sewage DSs

(1) General. This subrule describes the minimum level of effluent quality attainable by secondary treatment in terms of CBOD₅; suspended solids (SS), the pollutant parameter total suspended solids; and pH. The pollutant measurement CBOD₅is used in lieu of the pollutant measurement BOD₅, as noted in 40 CFR § 133.102(a)(4). All requirements for each pollutant measurement shall be achieved by POTWs and semipublic sewage DSs except as provided for in 62.2(2) and 62.2(3).

a. CBOD₅, as noted in 40 CFR § 133.102(a)(4). The 30-day average percent removal shall not be less than 85 percent, and the percent removal shall be calculated by adding five units to the effluent CBOD₅monitoring data and comparing that value to the influent BOD₅monitoring data. Site-specific information on the relationship between BOD₅and CBOD₅shall be used in lieu of the five-unit relationship if such information is available.

b. SS, as noted in 40 CFR § 133.102(b).

c. pH, as noted in 40 CFR § 133.102(c).

(2) Special considerations.

a. Combined sewers and percent removal. 40 CFR § 133.103(a) is adopted by reference.

b. Industrial wastes and POTWs; standard secondary adjustment. 40 CFR § 133.103(b) is adopted by reference.

c. Waste stabilization lagoons. Secondary treatment standards for waste stabilization lagoons are the same as those found in 62.2(1) concerning secondary treatment with the exception of the SS standards, which are as follows:

(1) The 30-day average shall not exceed 80 mg/l.

(2) The 7-day average shall not exceed 120 mg/l.

d. Less concentrated influent wastewater for separate and combined sewers; lower percent removal or mass loading limit. 40 CFR § 133.103(d) and (e) are adopted by reference.

e. Upgraded facilities designed to operate in a split flow mode.

(1) The department may substitute either a lower percent removal requirement or a mass loading limit for the percent removal requirements in 62.2(1), provided that the treatment works is designed to split part of the primary treated wastewater flow around the secondary treatment unit(s). The design to accommodate split flow must be approved by the department and consistent with applicable design standards for wastewater treatment facilities. Paragraph 62.2(2)"d" applies to facilities considered under this subrule. This subrule shall not be considered for facilities eligible for treatment equivalent to secondary treatment under 62.2(3).

(2) Any applicant requesting a permit limit adjustment pursuant to this subrule must include as part of the request an analysis of the infiltration and inflow (I/I) sources in the system and a plan for the elimination of all inflow sources such as roof drains, manholes, and storm sewer interconnections. Infiltration sources that can be economically eliminated or minimized shall be corrected.

f. Dilution. Nothing in this subrule or any other department rule shall be construed to encourage dilution of sewage as a means of complying with secondary treatment effluent standards. Reasonable efforts to prevent and abate infiltration of groundwater into sewers, and prevention or removal of any significant source of inflow, are required of all persons responsible for facilities subject to these standards.

(3) Treatment equivalent to secondary treatment. 40 CFR § 133.105 is adopted by reference. Treatment works shall be eligible for consideration of effluent limitations described for treatment equivalent to secondary treatment in accordance with 40 CFR § 133.101(g). The pollutant measurement CBOD₅will be used in lieu of the pollutant measurement BOD₅, as noted in 40 CFR § 133.105(e).

Notes

Iowa Admin. Code r. 567-62.2

Adopted by IAB May 14, 2025/Volume XLVII, Number 23, effective 6/18/2025