Section 310.230  Concentration and Mass Limits

a)         Pollutant discharge limits in categorical pretreatment standards will be expressed either as concentration or mass limits.  Limits in categorical pretreatment standards must apply to the discharge from the process regulated by the standard or as otherwise specified by the standard.

b)         When the limits in a categorical pretreatment standard are expressed only in terms of mass of pollutant per unit of production, the Control Authority may convert the limits to equivalent limitations expressed either as mass of pollutant discharged per day or effluent concentration for calculating effluent limitations applicable to individual industrial users.

c)         A Control Authority calculating equivalent mass-per-day limitations under subsection (b) must calculate such limitations by multiplying the limits in the standard by the industrial user's average rate of production. This average rate of production must be based not upon the designed production capacity, but rather upon a reasonable measure of the industrial user's actual long-term daily production during a representative year.  For new sources, actual production must be estimated using projected production.

d)         A Control Authority calculating equivalent concentration limitations under subsection (b) must calculate such limitations by dividing the mass limitations derived under subsection (c) by the average daily flow rate of the industrial user's regulated process wastewater.  This average daily flow rate must be based upon a reasonable measure of the industrial user's actual long-term average flow rate, such as the average daily flow rate during the representative year.

e)         When the limits in a categorical pretreatment standard are expressed only in terms of pollutant concentrations, an industrial user may request that the Control Authority convert the limits to equivalent mass limits.  The determination to convert concentration limits to mass limits is within the discretion of the Control Authority.  The Control Authority may establish equivalent mass limits only if the industrial user meets all the following conditions in subsections (e)(1)(A) through (e)(1)(E).

1)         To be eligible for equivalent mass limits, the industrial user must undertake the following actions:

A)        It must employ or demonstrate that it will employ water conservation methods and technologies that substantially reduce water use during the term of its control mechanism;

B)        It must currently use control and treatment technologies adequate to achieve compliance with the applicable categorical pretreatment standard, and it must not have used dilution as a substitute for treatment;

C)        It must provide sufficient information to establish the facility's actual average daily flow rate for all wastestreams, based on data from a continuous effluent flow monitoring device, as well as the facility's long-term average production rate.  Both the actual average daily flow rate and long-term average production rate must be representative of current operating conditions;

D)        It must not have daily flow rates, production levels, or pollutant levels that vary so significantly that equivalent mass limits are not appropriate to control the discharge; and

E)        It must have consistently complied with all applicable categorical pretreatment standards during the period before the industrial user requested equivalent mass limits.

2)         An industrial user subject to equivalent mass limits must undertake the following actions:

A)        It must maintain and effectively operate control and treatment technologies adequate to achieve compliance with the equivalent mass limits;

B)        It must continue to record the facility's flow rates through the use of a continuous effluent flow monitoring device;

C)        It must continue to record the facility's production rates and notify the Control Authority whenever production rates are expected to vary by more than 20 percent from its baseline production rates determined in subsection (e)(1)(C).  Upon notification of a revised production rate, the Control Authority must reassess the equivalent mass limit and revise the limit as necessary to reflect changed conditions at the facility; and

D)        It must continue to employ the same or comparable water conservation methods and technologies as those implemented pursuant to subsection (e)(1)(A) if it discharges under an equivalent mass limit.

3)         A Control Authority that chooses to establish equivalent mass limits must undertake the following actions:

A)        It must calculate the equivalent mass limit by multiplying the actual average daily flow rate of the regulated processes of the industrial user by the concentration-based daily maximum and monthly average standard for the applicable categorical pretreatment standard and the appropriate unit conversion factor;

B)        Upon notification of a revised production rate, it must reassess the equivalent mass limit and recalculate the limit as necessary to reflect changed conditions at the facility; and

C)        It may retain the same equivalent mass limit in subsequent control mechanism terms if the industrial user's actual average daily flow rate was reduced solely as a result of the implementation of water conservation methods and technologies, and the actual average daily flow rates used in the original calculation of the equivalent mass limit were not based on the use of dilution as a substitute for treatment pursuant to Section 310.232.  The industrial user must also be in compliance with Subpart J of this Part (regarding the prohibition of bypass).

4)         The Control Authority may not express limits in terms of mass for pollutants such as pH, temperature, radiation, or other pollutants that cannot appropriately be expressed as mass.

f)         The Control Authority may convert the mass limits of the categorical pretreatment standards of Subparts O, T, and CD of 35 Ill. Adm. Code 307 to concentration limits for calculating limitations applicable to individual industrial users under the following conditions.  When converting such limits to concentration limits, the Control Authority must use the concentrations listed in the applicable provisions of Subparts O, T, and CD of 35 Ill. Adm. Code 307 and document that dilution is not being substituted for treatment as prohibited by Section 310.232.

g)         Equivalent limitations calculated in accordance with subsections (c) through (f) are deemed pretreatment standards.  The Control Authority must document how the equivalent limits were derived and make this information publicly available.  Once incorporated into its control mechanism, the industrial users must comply with the equivalent limitations instead of the promulgated categorical standards from which the equivalent limitations were derived.

h)         Many categorical pretreatment standards specify one limit for calculating maximum daily discharge limitations and a second limit for calculating maximum monthly average or four-day average limitations.  If such standards are being applied, the same production or flow figure must be used in calculating both the average and the maximum equivalent limitation.

i)          Any industrial user operating under a control mechanism incorporating equivalent mass or concentration limits calculated from a production-based standard must notify the Control Authority within two business days after the user has a reasonable basis to know that the production level will significantly change within the next calendar month. Any user not notifying the Control Authority of such anticipated change will be required to meet the mass or concentration limits in its control mechanism that were based on the original estimate of the long-term average production rate.

BOARD NOTE:  Derived from 40 CFR 403.6(c) (2005), as amended at 70 Fed. Reg. 60134 (Oct. 14, 2005).

(Source:  Amended at 47 Ill. Reg. 5083, effective March 23, 2023)