(1) Alternative discharge standards for trickling filters which were constructed and/or expanded prior to November 1984 are:

(a) Up to a thirty-day average of 45 mg/L BOD, 45 mg/L TSS. Seven-day averages shall not exceed 65 mg/L BOD, 65 mg/L TSS. In addition, the thirty-day average percent removals of BOD and TSS shall not be less than sixty-five percent of influent concentrations;

(b) Notwithstanding (a) of this subsection, not any less stringent than "effluent concentrations consistently achievable through proper operation and maintenance" of the wastewater facility based on an analysis of the past performance, the design, and the design capacity of the wastewater facility;

(c) Fecal coliform and pH discharge standards are as established in WAC 173-221-040.

(2) Alternative discharge standards for waste stabilization ponds which are the principal treatment process and which either have less than a two million gallon per day design capacity or have received, prior to the effective date of this regulation, the department's approval under chapter 173-240 WAC, for a greater design capacity, are:

(a) Up to a thirty-day average of 45 mg/L BOD, 45 mg/L TSS. Seven-day averages shall not exceed 65 mg/L BOD, 65 mg/L TSS. Additionally, the thirty-day average percent BOD removal shall not be less than sixty-five percent of influent concentrations.

(b) The discharge standards for TSS in (a) of this subsection may be adjusted by the department to conform to the "TSS concentrations achievable with waste stabilization ponds," provided that operation and maintenance data indicate that the TSS values specified in (a) of this subsection cannot be achieved.

(c) Notwithstanding (a) and (b) of this subsection, not any less stringent than "effluent concentrations consistently achievable through proper operation and maintenance" of the wastewater facility based upon an analysis of the past performance.

(d) Fecal coliform and pH discharge standards shall be as established in WAC 173-221-040.

(3) For domestic wastewater facilities which receive flows from combined sewers, the department shall decide on a case-by-case basis whether any attainable percent removal can be defined during wet weather. If it can be defined, the department will set an alternative percent removal effluent limitation for the wet weather period. A permittee who requests such alternative limits shall submit supporting documentation to the department.

(4)(a) For domestic wastewater facilities which receive less concentrated influent wastewater, permittees can request and submit supporting documentation for:

(i) A lower percent removal effluent limitation than the discharge standards set forth in WAC 173-221-040, or subsections (1) and (2) of this section; or

(ii) A mass loading limit based upon the lower percent removal.

(b) To qualify for alternative effluent limitations because of less concentrated influent wastewater, the permittee must demonstrate:

(i) The wastewater facility is consistently achieving, and/or will consistently achieve, the effluent concentration limits and mass limits based upon the effluent concentrations in its permit; and

(ii) That to meet the percentage removal requirements set forth in WAC 173-221-040 or subsections (1) and (2) of this section, the wastewater facility would have to achieve an effluent concentration at least 5 mg/L below the effluent concentration which is otherwise required; and

(iii) The less concentrated influent is not the result of excessive infiltration and/or inflow. The department will use federal regulations and guidance in defining excessive infiltration and inflow; and

(iv) The development and implementation of a program, subject to the department's approval, for ongoing wastewater facility maintenance, repair, and replacement, including infiltration and inflow control. A goal of the program shall be eventual achievement of the percent removal requirements specified in WAC 173-221-040 and subsection (1) or (2) of this section, whichever is applicable. The department shall incorporate the approved infiltration and inflow control program into the permit for the wastewater facility.

(5) Subject to the department's approval, a request for alternative effluent limitations pursuant to subsections (1) through (4) of this section must meet all of the following conditions:

(a) The effluent shall not cause water quality violations; and

(b) The permittee shall identify effluent concentrations consistently achievable through proper operation and maintenance; and

(c) The permittee shall demonstrate that industrial wastewater does not interfere with the domestic wastewater facility; and

(d) The wastewater facility must be within department approved hydraulic and organic design capacity; and

(e) The permittee must complete an analysis of whether seasonal alternative effluent limits are more appropriate than year-round; and

(f) The wastewater facility must be able to meet all other permit requirements and conditions.

(6)(a) At the option of the department, in lieu of the parameter BOD and the levels of the BOD effluent quality specified in WAC 173-221-040, the parameter CBOD may be substituted as an effluent limitation with the following levels of the CBOD effluent quality provided: The thirty-day average shall not exceed 25 mg/L. The seven-day average shall not exceed 40 mg/L. Additionally, the thirty-day average percent removal shall not be less than eighty-five percent of the influent concentration.

(b) At the option of the department, in lieu of the parameter BOD and the levels of the BOD effluent quality specified in subsections (1) and (2) of this section, the parameter CBOD may be substituted as an effluent limitation on a case-by-case basis where data are available. The levels of CBOD effluent quality shall not be less stringent than the following: The thirty-day average shall not exceed 40 mg/L. The seven-day average shall not exceed 60 mg/L. The thirty-day average percent removal shall not be less than sixty-five percent of the influent concentration.

(c) Permittee applications for substitution of CBOD for BOD under (b) of this subsection shall include parallel CBOD and BOD data.