Section 327IAC5-10-5. Small sanitary discharge

   (a) All discharges from continuous discharge sanitary wastewater treatment facilities with a design flow of five-hundredths (0.05) MGD or less (which are not considered to be lake or sinkhole dischargers as defined under section 4 of this rule) are subject to the following effluent limitations in the absence of a site-specific water quality modeled waste load allocation:

(1) Effluent limitations for CBOD₅, TSS, and dissolved oxygen (DO):

	Summer	Winter
Dilution Ratio (DR)	CBOD5/TSS/DO	CBOD5/TSS/DO
DR less than or equal to 1	15 /18 / 6	25 /30 / 5
DR greater than 1, less than or equal to 3	20 /24 / -	25 /30 / -
DR greater than 3	25 /30 / -	25 /30 / -

(2) Limitations for ammonia nitrogen shall be determined as follows:

(A) Effluent limitations for NH₃-N (ammonia nitrogen), calculated in accordance with subdivision (5)(C):

Summer	Winter
(May─November)	(December─April)
Ammonia nitrogen	Ammonia nitrogen
1.06 + 0.43 DR	1.58 + 0.69 DR

(B) When a properly designed and operated treatment facility qualifying for these limitations, which is not hydraulically or organically overloaded is of the type that is inherently capable of achieving the water quality standards for ammonia nitrogen, and ammonia nitrogen will not be discharged at a level that will cause, have the reasonable potential to cause, or contribute to an excursion above a water quality criterion for ammonia under 327 IAC 2-1 or 327 IAC 2-1.5, the commissioner, based on cost and other considerations, may exclude the ammonia nitrogen effluent limitations or monitoring requirements from the permit. Such action is not considered to be a variance from the applicable water quality standards.

(C) When DR exceeds 16:1 for the summer period and 10:1 for the winter period, ammonia nitrogen limitations will not be included in the permit, unless the commissioner can demonstrate that ammonia will be discharged at a level that will cause, have the reasonable potential to cause, or contribute to an excursion above a water quality criterion for ammonia under 327 IAC 2-1 or 327 IAC 2-1.5.

(3) The alternative limitations for total suspended solids applicable to waste stabilization lagoons as described under 327 IAC 5-5-3(b) may be applied to small sanitary discharges from properly designed, operated, and loaded waste stabilization lagoon treatment facilities in lieu of the limitations for TSS contained in subdivision (1).

(4) If deemed necessary to comply with water quality standards contained under 327 IAC 2-1 or 327 IAC 2-1.5, such as discharges to streams which are classified for cold water aquatic life, more stringent limitations for dissolved oxygen and ammonia nitrogen may be applied on a case-by-case basis.

(5) The following conditions apply within this subsection:

(A) All effluent limitations in subdivisions (1) and (2) are expressed in milligrams per liter.

(B) CBOD₅, TSS, and ammonia nitrogen limitations are monthly average concentrations. Weekly average limitations are one and five-tenths (1.5) multiplied by monthly average limitations, except where CBOD₅ equals twenty-five (25) milligrams per liter, in which case the weekly average is forty (40) milligrams per liter.

(C) Ammonia nitrogen limitations are derived using conservation of mass principles, applying one-half (½) stream flow (Q_7,10) and using the criteria contained in 327 IAC 2-1-6(b)(5)(A), using year-round stream pH of seven and eight-tenths (7.8) s.u., instream temperature of twenty-five degrees Celsius (25°C) summer, ten degrees Celsius (10°C) winter, and two-tenths (0.2) milligrams per liter background ammonia nitrogen year-round. If the discharge is in the Great Lakes system, ammonia nitrogen limitations shall be derived using the criteria for ammonia nitrogen contained in 327 IAC 2-1.5-8, the stream design flow, mixing zone, and background determined in accordance with 327 IAC 5-2-11.4, and the procedures to calculate WQBELs under 327 IAC 5-2-11.6.

(D) DR is calculated as Q_7,10 of receiving stream divided by the design flow of the discharge.

(6) In addition, water quality-based limitations for any other toxic substance may be included in the permit if the toxic substance is or may be discharged at a level that will cause, have the reasonable potential to cause, or contribute to an excursion above any applicable narrative or numeric water quality criteria or value promulgated under 327 IAC 2-1 or 327 IAC 2-1.5.

  (b) Continuous discharges include all discharges not designed, approved, and operated as controlled discharges from multicelled waste stabilization ponds.

  (c) Industrial plants with small sanitary discharges mixing with other nontoxic, nonorganic, nonnutrient containing wastewaters, such as cooling water, ash sluicing, etc. prior to discharge may use the other wastewaters as dilution in applying the criteria of subsection (a). (Water Pollution Control Division; 327 IAC 5-10-5; filed Feb 26, 1993, 5:00 p.m.: 16 IR 1773; filed Jan 14, 1997, 12:00 p.m.: 20 IR 1474; errata filed Aug 11, 1997, 4:15 p.m.: 20 IR 3380; readopted filed Jan 10, 2001, 3:23 p.m.: 24 IR 1518; readopted filed Nov 21, 2007, 1:16 p.m.: 20071219-IR-327070553BFA; readopted filed Jul 29, 2013, 9:21 a.m.: 20130828-IR-327130176BFA)