Minnesota Administrative Rules

7049.0350 COMBINED WASTE STREAM FORMULA.

Subpart 1.

General.

A.

The combined waste stream formula described in this part is used to derive fixed alternative discharge limits to be applied to the mixed effluent when waste streams subject to national categorical pretreatment standards are mixed with waste streams subject to other categorical standards or waste streams not subject to categorical standards. Alternative discharge limits may be derived using the combined waste stream formula by the control authority or by the industrial user with the prior written concurrence of the control authority. Alternative limits must be derived for all applicable limits. When deriving alternative categorical limits, the control authority or industrial user shall calculate both an alternative daily maximum value using the daily maximum values specified in the appropriate categorical pretreatment standards and an alternative consecutive sampling day average value using the monthly average values specified in the appropriate categorical pretreatment standards. The industrial user shall comply with the alternative daily maximum and long-term average limits fixed by the control authority until the control authority modifies the limits or approves an industrial user modification request. Modification is authorized whenever there is a material or significant change in the values used in the calculation to fix alternative limits for the regulated pollutant. An industrial user shall immediately report any material or significant change to the control authority. If appropriate, new alternative categorical limits shall be calculated within 30 days. The industrial user may change monitoring points only after receiving prior written approval from the control authority. The control authority shall ensure that any change in an industrial user's monitoring points will not allow the industrial user to substitute dilution for adequate treatment to achieve compliance with applicable standards.

B.

If process effluent is mixed prior to treatment with wastewaters other than those generated by the regulated process, fixed alternative discharge limits shall be derived by the control authority or by the industrial user with the prior written concurrence of the control authority.

C.

If a treated regulated process waste stream is combined prior to treatment with wastewaters other than those generated by the regulated process, the industrial user may, with the approval of the control authority, monitor either the segregated process waste stream or the combined waste stream to determine compliance with applicable pretreatment standards. If the industrial user chooses to monitor the segregated process waste stream, the industrial user shall apply the applicable categorical pretreatment standard. If the industrial user chooses to monitor the combined waste stream, the industrial user shall apply an alternative discharge limit calculated using the combined waste stream formula as provided in this part. The industrial user may change monitoring points only after receiving prior written approval from the control authority. The control authority shall ensure that any change in an industrial user's monitoring points will not allow the industrial user to substitute dilution for adequate treatment to achieve compliance with applicable standards.

D.

If a regulated process waste stream is combined without treatment with wastewaters other than those generated by the regulated process, the industrial user may, with the approval of the control authority, monitor either the segregated process waste stream or the combined waste stream to determine compliance with applicable pretreatment standards. If the industrial user chooses to monitor the segregated process waste stream, the industrial user shall apply the applicable categorical pretreatment standard. If the industrial user chooses to monitor the combined waste stream, the industrial user shall apply an alternative discharge limit calculated using the combined waste stream formula as provided in this part. However, when no treatment is provided, all waste streams other than the regulated process waste stream are considered to be dilute waste streams in deriving alternative discharge limits. If more than one regulated process waste stream is present at the chosen monitoring point, the combined waste stream formula shall be applied to each regulated process waste stream separately, with all other waste streams considered to be dilute waste streams, and the most restrictive limit applied, for each pollutant. The industrial user may change monitoring points only after receiving approval from the control authority. The control authority shall ensure that any change in an industrial user's monitoring points will not allow the industrial user to substitute dilution for adequate treatment to achieve compliance with applicable standards.

Subp. 2.

Alternative limit calculation; definitions.

For purposes of the formulas in subpart 3, the following symbols have the meanings specified.

C_t = the alternative concentration limit for the combined waste stream.

M_t = the alternative mass limit for a pollutant in the combined waste stream.

C_i = the categorical pretreatment standard concentration limit for a pollutant in the regulated stream i.

M_i = the categorical pretreatment standard mass limit for a pollutant in the regulated stream i (the categorical pretreatment mass limit multiplied by the appropriate measure of production).

F_i = the average daily flow (at least a 30-day average) of stream i to the extent that it is regulated for the pollutant.

F_D = the average daily flow (at least a 30-day average) of dilute waste streams.

If waste streams contain a significant amount of a pollutant and the combination of the streams, prior to treatment, with an industrial user's regulated process waste streams will result in a substantial reduction of that pollutant, the control authority shall determine whether the streams should be classified as dilute or unregulated. Dilute waste streams include, but are not limited to:

A.

boiler blowdown streams, noncontact cooling streams, stormwater streams, and demineralizer backwash streams;

B.

sanitary waste streams when the streams are not regulated by a categorical pretreatment standard; and

C.

process waste streams from processes that were or could have been entirely exempted from categorical pretreatment standards because:

(1)

the regulated pollutants are not detectable in the effluent from the industrial user;

(2)

the regulated pollutants are present only in trace amounts and are neither causing nor likely to cause toxic effects;

(3)

the regulated pollutants are present in amounts too small to be effectively reduced; or

(4)

the waste stream contains only pollutants that are compatible with the receiving POTW.

F_T = the total average daily flow through the combined treatment facility (this includes all F_i, F_D, and unregulated streams).

N = the total number of regulated streams.

For purposes of this subpart, "average daily flow" means a reasonable measure of the average daily flow for at least a 30-day period. For new sources, flows shall be estimated using projected values.

Subp. 3.

Alternative limit calculation; formula.

The alternative limit for a specified pollutant is derived by the use of either of the following formulas:

A.

alternative concentration limit under Code of Federal Regulations, title 40, section 403.6(e)(1)(i); or

B.

alternative mass limit under Code of Federal Regulations, title 40, section 403.6(e)(1)(ii).

Subp. 4.

Alternate limits below detection limit.

An alternative pretreatment limit derived by the combined waste stream formula may not be used if the alternative limit is below the analytical detection limit for any of the regulated pollutants.

Statutory Authority:

MS s 115.03

History:

33 SR 696

Published Electronically:

January 30, 2024