Section 327IAC5-18-7. Combined wastestreams

   The combined wastestream formula is derived as follows:

(1) Where process effluent is mixed prior to treatment with wastewaters other than those generated by the regulated process, alternative discharge limits may be derived by the control authority or by the industrial user with the written concurrence of the control authority and applied to the mixed effluent. When deriving alternative categorical limits, the control authority or industrial user shall calculate both an alternative daily maximum value using the daily maximum value specified in the appropriate categorical pretreatment standard and an alternative consecutive sampling day average value using the long term average value specified in the appropriate categorical pretreatment standard. 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 must immediately report any such material or significant change to the control authority. Where appropriate, new alternative categorical limits shall be calculated within thirty (30) days.

(2) As used in this section, "average daily flow" means a reasonable measure of the average daily flow for a thirty (30) day period. For new sources, flows shall be estimated using projected values. The alternative discharge limit for a specific pollutant shall be calculated by either of the following formulas:

(A) Alternative concentration limits:

Where:	CT	=	The alternative concentration limit for the combined wastestreams.
	Ci	=	The categorical pretreatment standard concentration limit for a pollutant in the regulated stream i.
	Fi	=	The average daily flow (at least a thirty (30) day average) of stream i to the extent that it is regulated for such pollutant.
	FD	=	The average daily flow (at least a thirty (30) day average) from any of the following:

(i) Boiler blowdown streams, noncontact cooling streams, storm water streams, and demineralizer backwash streams; provided, however, that where such streams contain a significant amount of a pollutant, and the combination of such streams, prior to treatment, with an industrial user’s regulated process wastestream will result in a substantial reduction of that pollutant, the control authority, upon application of the industrial user, may exercise its discretion to determine whether such stream should be classified as diluted or unregulated. In its application to the control authority, the industrial user must provide engineering, production, sampling and analysis, and such other information so that the control authority can make its determination.

(ii) Sanitary wastestreams where such streams are not regulated by a categorical pretreatment standard.

(iii) Any process wastestreams that were or could have been entirely exempted from categorical pretreatment standards pursuant to paragraph 8 of the NRDC v. Costle Consent Decree (12 ERC 1833) for one (1) or more of the following reasons:

(AA) The pollutants of concern are not detectable in the effluent from the industrial user.

(BB) The pollutants of concern are present only in trace amounts and are neither causing or likely to cause toxic effects.

(CC) The pollutants of concern are present in amounts too small to be effectively reduced by technologies known to the administrator.

(DD) The wastestream contains only pollutants that are compatible with the POTW.

F_T = The average daily flow (at least a thirty (30) day average) through the combined treatment facility (includes F_i, F_D, and unregulated streams).

N = The total number of regulated streams.

(B) Alternative mass limits:

Where:	MT	=	The alternative mass limit for a pollutant in the combined wastestream.
	Mi	=	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, F_D, F_T, and N are defined in clause (A).

(3) An alternative pretreatment limit may not be used if the alternative limit is below the analytical detection limit for any of the regulated pollutants.

(4) Self-monitoring required to assure compliance with the alternative categorical limit shall be as follows:

(A) The type and frequency of sampling, analysis, and flow measurement must be determined by reference to the self-monitoring requirements of the appropriate categorical pretreatment standard or 40 CFR 403.12(e) and 40 CFR 403.12(h).

(B) Where the self-monitoring schedules as determined by the control authority for the appropriate standards differ, monitoring must be done according to the most frequent schedule.

(C) Where flow determines the frequency of self-monitoring in a categorical pretreatment standard, the sum of all regulated flows (F_i) is the flow that shall be used by the control authority to determine self-monitoring frequency.

(Water Pollution Control Division; 327 IAC 5-18-7; filed Oct 10, 2000, 3:02 p.m.: 24 IR 301)