Authority: IC 13-13-5; IC 13-14-8; IC 13-14-9; IC 13-15-1-2; IC 13-15-2-1; IC 13-18-3

Affected: IC 13-11-2; IC 13-18-4

Sec. 6. (a) Disinfection is required of all sanitary wastewater discharges on an annual basis for the period of April 1 through October 31 except multicelled waste stabilization ponds that are:

1. (1) adequately designed and operated;
2. (2) not either hydraulically or organically overloaded; and
3. (3) in compliance with the provisions of section 3(c) of this rule.

(b) Disinfection is not required and is not expected to be practiced on an annual basis for the period of November 1 through March 31, except as necessary to comply with one (1) or more of the following:

1. (1) ORSANCO requirements (for discharges directly to the Ohio River).
2. (2) The requirements of other states for interstate waters.
3. (3) The provision of section 4(c) of this rule.

In cases where chlorination must be practiced during this period, for example, to maintain sand filters, the maximum effluent limitation and monitoring requirements for chlorine remain in effect.

(c) The following are requirements for facilities using chlorine or other halogenated compounds as a disinfectant:

1. (1) For those sanitary wastewater dischargers designated as minor facilities (generally those with a population equivalent (PE) of less than ten thousand (10,000)), the following requirements must be met:

   1. (A) Residual chlorine concentration after disinfection (but prior to dechlorination) is to be maintained at a minimum of five-tenths (0.5) milligram per liter.
   2. (B) The final effluent must comply with subsection (e).

2. (2) For those sanitary wastewater dischargers designated as major facilities (those with a PE of ten thousand (10,000) or greater), the following requirements must be met:

   1. (A) No minimum residual chlorine limitation applies.
   2. (B) The final effluent must comply with subsection (e).

3. (3) Dechlorination is to be practiced for all:

   1. (A) sanitary wastewater discharges using chlorine or bromine compounds as a disinfectant; or
   2. (B) filter or other equipment maintenance at any time;
4. so that the concentration of total residual chlorine (TRC) or, where bromine is used, TRO in the final effluent does not exceed water quality-based effluent limitations. If these water quality-based limitations are below the LOQ, compliance with the water quality-based effluent limitations will be determined using the applicable procedures contained under 327 IAC 5-2-11.1 or 327 IAC 5-2-11.6.

(d) Facilities using a disinfectant other than chlorine or other halogen compounds shall ensure that the final effluent complies with subsection (e) during the applicable recreation season as indicated in the facility's NPDES permit.

(e) Sanitary wastewater dischargers shall ensure the following:

1. (1) The concentration of E. coli in the undiluted discharge does not exceed one hundred twenty-five (125) cfu or MPN per one hundred (100) milliliters as a geometric mean of the effluent samples taken in a calendar month.
2. (2) Not more than ten percent (10%) of all samples when not less than ten (10) samples are taken and analyzed for E. coli in a calendar month exceed two hundred thirty-five (235) cfu or MPN per one hundred (100) milliliters as a daily maximum. Under this subdivision, the calculation of ten percent (10%) of the samples taken shall be limited to the lowest whole number result.

(Water Pollution Control Division; 327 IAC 5-10-6; filed Feb 26, 1993, 5:00 p.m.: 16 IR 1774; filed Jan 14, 1997, 12:00 p.m.: 20 IR 1475; readopted filed Jan 10, 2001, 3:23 p.m.: 24 IR 1518; readopted filed Nov 21, 2007, 1:16 p.m.: 20071219-IR-327070553BFA; filed Mar 18, 2008, 2:26 p.m.: 20080416-IR-327060573FRA; readopted filed Jul 29, 2013, 9:21 a.m.: 20130828-IR-327130176BFA; readopted filed Jun 14, 2019, 1:59 p.m.: 20190710-IR-327190246BFA; readopted filed Oct 18, 2024, 1:57 p.m.: 20241113-IR-327230810RFA)