Section 327IAC5-2-11. Considerations in the calculation and specification of effluent limitations

   (a) The following definitions and averaging procedure apply throughout this section:

(1) "Average monthly discharge" means the total mass or flow-weighted concentration of all daily discharges sampled or measured during a calendar month on which daily discharges are sampled and measured, divided by the number of daily discharges sampled and/or measured during such month. The average monthly discharge limitation is the highest allowable average monthly discharge for any calendar month.

(2) "Average weekly discharge" means the total mass or flow-weighted concentration of all daily discharges during any calendar week on which daily discharges are sampled or measured, divided by the number of daily discharges sampled and/or measured during such calendar week. The average weekly discharge limitation is the maximum allowable average weekly discharge for any calendar week.

(3) "Continuous discharge" means a discharge that occurs without interruption, except for infrequent shutdowns for maintenance, process changes, or other similar activities, throughout the operating hours of the facility.

(4) "Daily discharge" means the total mass of a pollutant discharged during the calendar day or, in the case of a pollutant limited in terms other than mass pursuant to subsection (e), the average concentration or other measurement of the pollutant specified over the calendar day or any twenty-four (24) hour period that reasonably represents the calendar day for the purposes of sampling. The maximum daily discharge limitation is the maximum allowable daily discharge for any calendar day.

(5) The average of discharge data shall be determined as follows:

(A) For fecal coliform, the average monthly discharge and average weekly discharge, as concentrations, shall be calculated using a geometric mean.

(B) For E. coli, the average monthly discharge, as a concentration, shall be calculated using a geometric mean.

(C) For all other parameters, calculations that require averaging of sample analyses or measurements of daily discharges shall use an arithmetic mean unless otherwise specified or approved by the commissioner.

  (b) All permits shall impose final and, where necessary, interim effluent limitations under sections 8 and 10 of this rule for each outfall or discharge point of the permitted facility, except as otherwise provided under section 10(7)(B) of this rule and subsection (h).

  (c) Production-based limitations requirements shall be as follows:

(1) For dischargers other than POTWs, permit effluent limitations which are based on production rates (or another measure of operation) shall be calculated on the basis of a reasonable measure of the actual production of the facility. The time period of the production rate shall correspond to the time period of the calculated permit limitations, for example, monthly production shall be used to calculate average monthly limitations. The commissioner may include a condition establishing alternate permit limitations, standards, or prohibitions based upon anticipated increases (not to exceed maximum production capacity) or decreases to production levels.

(2) A discharger whose permit limitations are determined through a waste load allocation procedure, for example, to maintain water quality above applicable standards, may request the commissioner to calculate the discharger's load allocation, relative to the load allocations of other dischargers, on the basis of the design production capacity of the discharger's facility. The commissioner may grant such a request if the commissioner determines that a reasonable probability exists that the discharger will attain the design production capacity for significant periods during the expected lifetime of the waste load allocation. Even if a discharger's load allocation is established on the basis of design production, the commissioner shall consider the discharger's current actual production in calculating current permit limitations.

(3) In the case of POTWs, permit limitations shall be calculated based on design flow unless good cause exists for utilizing a different basis, for example, effluent limitations for a POTW designed to treat industrial wastes under section 10 of this rule would be based on actual production.

  (d) For continuous dischargers, all interim and final permit effluent limitations, including those necessary to achieve water quality standards, shall be stated, unless impracticable, as maximum daily and average monthly discharge limitations for all dischargers, except that, for POTWs average weekly and average monthly discharge limitations shall be used for BOD₅, TSS, and ammonia nitrogen. For discharges within the Great Lakes system, limitations for ammonia shall be stated as maximum daily and average monthly discharge limitations for all dischargers.

  (e) All pollutants limited in permits shall have effluent limitations expressed in terms of mass except:

(1) for pH, temperature, radiation or other pollutants, and flow that cannot be appropriately expressed by mass;

(2) where applicable, promulgated effluent guideline limitations, standards, or prohibitions are expressed in terms other than mass, for example, as concentration levels; or

(3) if, in establishing permit limitations on a case-by-case basis, limitations expressed in terms of mass are infeasible because the mass of the pollutant discharged cannot be related to a measure of operation (for example, discharges of total suspended solids (TSS) from certain mining operations) or are inadequate to assure continuous compliance with applicable water quality standards, and permit conditions ensure that dilution will not be used as a substitute for treatment.

Pollutants limited in terms of mass additionally may be limited in terms of other units of measurement, and the permit shall require the permittee to comply with both limitations.

  (f) Except as provided as follows or in section 11.1(g) or 11.6(i) of this rule, effluent limitations imposed in permits shall not be adjusted for pollutants in the intake water:

(1) Upon request of the discharger, technology-based effluent limitations imposed in a permit shall be calculated on a net basis, that is, adjusted to reflect credit for pollutants in the discharger's intake water, if each of the following conditions are met:

(A) The applicable effluent limitations guidelines or standards promulgated under the Clean Water Act (CWA) specifically provide that they shall be applied on a net basis or the discharger demonstrates that pollutants present in the intake water will not be essentially removed by the properly installed, maintained, and operated intake and wastewater treatment systems operated by the discharger.

(B) The discharger's intake water is drawn from:

(i) the same body of water into which the discharge is made; or

(ii) a body of water containing ambient concentrations of pollutants for which net limitations are desired that are no greater than the upstream ambient concentrations for the pollutants in the body of water receiving the discharge.

(C) The pollutants in the intake water do not vary significantly in physical, chemical, or biological nature from the pollutants limited by the permit nor are they concentrated by the discharger to such a degree that their discharge would significantly degrade the quality of the receiving body of water.

(2) Adjustments to a discharger's effluent that allow for the application of effluent limitations on a net basis shall be calculated as follows, and the amount of pollutants present in the intake water limited by the permit shall be reduced:

(A) To reflect removal of such pollutants by any treatment of the intake water performed by or for the discharger.

(B) To reflect any further removal of such pollutants by the wastewater treatment technology employed by the discharger.

The amount of such pollutants remaining after the reductions may be applied as an adjustment to the gross amount of the pollutants in the discharge prior to its evaluation for compliance with applicable effluent limitations. If the discharger can demonstrate that pollutants are present in the intake water in sufficient quantities to significantly reduce the efficiency of the discharger's wastewater treatment system, the amount of the adjustment calculated under this subsection may be modified to the extent necessary to compensate for the reduction in treatment efficiency.

(3) If the application of effluent limitations on a net basis is authorized under this subsection, the permit shall specify the method of calculating adjustments to the gross effluent and shall contain conditions requiring the permittee to conduct additional monitoring, for example, for flow and concentration of pollutants, as necessary to determine continued eligibility for and compliance with any such adjustments. The discharger shall notify the commissioner if this monitoring indicates that eligibility for an adjustment under this section has been altered or no longer exists. In such case, the permit shall be modified or revoked and reissued under section 16 of this rule.

(4) Credit for generic pollutants such as biochemical oxygen demand (BOD) or TSS shall not be granted unless:

(A) the permittee demonstrates that the constituents of the generic measure in the effluent are substantially similar to the constituents of the generic measure in the intake water; or

(B) appropriate additional limits are placed on process water pollutants either at the outfall or elsewhere.

(5) Credit shall be granted only to the extent necessary to meet the applicable limitation or standard, up to a maximum value equal to the influent value. Additional monitoring may be necessary to determine eligibility for credits and compliance with permit limits.

  (g) Discharges that are not continuous, as defined in subsection (d), shall be particularly described and limited, considering the following factors, as appropriate:

(1) Frequency.

(2) Total mass.

(3) Maximum rate of discharge of pollutants during the discharge.

(4) Prohibition or limitation of specified pollutants by mass, concentration, or other appropriate measure.

  (h) Where permit effluent limitations imposed at the point of discharge are impractical or infeasible (such as where the final discharge point is practicably inaccessible, the wastes at the point of discharge are so diluted as to make monitoring impracticable, or interferences among pollutants at the point of discharge would make detection or analysis impracticable), effluent limitations for discharges of pollutants may be imposed on internal waste streams prior to mixing with other waste streams or cooling water streams. In such instances, the effluent limitations shall be adjusted to reflect any removal of pollutants occurring between the point at which the limitation is imposed and the point of discharge, and the monitoring, recording, and reporting required by sections 13 through 15 of this rule shall be applied to the internal waste streams at the closest practicable or feasible point to the point of discharge unless the permittee and the commissioner agree that another location is more suitable. Intermediate waste streams that constitute input to other industrial processes (excluding treatment processes) shall not be considered internal waste streams for purposes of this subsection.

  (i) Where part of a discharger's process wastewater is not being discharged into waters of the state because it is disposed into a well, into a POTW, or by land application, applicable effluent limitations and standards for the discharge shall be adjusted in the permit to reflect the reduced raw waste resulting from such disposal, including the following:

(1) Adjusted effluent limitations and standards in the permit shall be calculated by one (1) of the following methods:

(A) If none of the waste from a particular process is discharged into waters of the state and effluent limitations guidelines provide separate allocation for wastes from that process, all allocations for the process shall be eliminated from calculation of permit effluent limitations or standards.

(B) In all cases other than those described in clause (A), effluent limitations shall be adjusted by multiplying the effluent limitation derived by applying effluent guidelines to the total waste stream by the amount of wastewater flow to be treated and discharged into waters of the state, and dividing the result by the total wastewater flow. Effluent limitations and standards so calculated may be further adjusted under 327 IAC 5-6 to make them more stringent if discharges to wells, POTW, or by land application change the character or treatability of the pollutants being discharged to receiving waters.

(2) Subdivision (1) shall not apply where promulgated effluent limitations guidelines:

(A) control concentrations of pollutants discharged, but not mass; or

(B) specify a different specific technique for adjusting effluent limitations to account for well injection.

(3) Subdivision (1) does not alter a discharger's obligation to meet any more stringent requirements otherwise established under this rule.

  (j) Technology-based permit effluent limitations, standards, or prohibitions for a metal shall be expressed in terms of total recoverable metals as defined in 40 CFR 136 unless:

(1) an applicable effluent standard or limitation has been promulgated under the CWA and specifies the limitation for the metal in the dissolved, valent, or total form;

(2) in establishing permit limitations on a case-by-case basis under 327 IAC 5-5-2, it is necessary to express the limitation on the metal in the dissolved, valent, or total form to carry out the provisions of the CWA; or

(3) all approved analytical methods for the metal inherently measure only its dissolved form, for example, hexavalent chromium.

(Water Pollution Control Division; 327 IAC 5-2-11; filed Sep 24, 1987, 3:00 p.m.: 11 IR 625; filed Feb 26, 1993, 5:00 p.m.: 16 IR 1746; filed Jan 14, 1997, 12:00 p.m.: 20 IR 1429; errata filed Aug 11, 1997, 4:15 p.m.: 20 IR 3378)