Section 327IAC8-2.6-10. Developing the disinfection profile and benchmark; disinfection profiling and benchmarking requirements; enhanced treatment for Cryptosporidium

   (a) A PWS required to develop a disinfection profile under section 9 of this rule shall follow the requirements of this section, including the following:

(1) A PWS shall monitor at least weekly for a period of twelve (12) consecutive months to determine the total log inactivation for Giardia lamblia and viruses as required under subdivision (4).

(2) If a PWS monitors more frequently than required under subdivision (1), the monitoring frequency must be evenly spaced.

(3) A PWS that operates for fewer than twelve (12) months per year shall monitor weekly during the period of operation.

(4) Each PWS shall determine log inactivation for the following:

(A) Giardia lamblia through the entire plant based on CT_99.9 values (where C is the residual disinfectant concentration and T is the disinfectant contact time) in Tables 1.1 through 1.6, 2.1, and 3.1 of 40 CFR 141.74(b)* as applicable.

(B) Viruses through the entire treatment plant based on a protocol approved by the commissioner.

  (b) Disinfectant monitoring requirements to develop a disinfection profile are as follows:

(1) A PWS with a single point of disinfectant application prior to the entrance to the distribution system shall monitor according to this subsection.

(2) A PWS with more than one (1) point of disinfectant application shall monitor according to this subsection for each disinfection segment.

(3) A PWS shall monitor the parameters necessary to determine the total inactivation ratio using analytical methods in 327 IAC 8-2-8.7.

(4) A PWS using a disinfectant other than UV shall measure the temperature of the water at:

(A) each residual disinfectant concentration sampling point during peak hourly flow; or

(B) an alternative location approved by the commissioner.

(5) A PWS using chlorine shall measure the pH of the disinfected water at:

(A) each chlorine residual disinfectant concentration sampling point during peak hourly flow; or

(B) an alternative location approved by the commissioner.

(6) A PWS shall determine the disinfectant contact time or times (t) during peak hourly flow.

(7) A PWS shall measure the residual disinfectant concentration or concentrations (C) of the water before or at the first customer and prior to each additional point of disinfectant application during peak hourly flow.

  (c) In lieu of conducting new monitoring under subsection (b), a PWS may elect to meet the requirements of either of the following:

(1) A PWS that has at least one (1) year of existing data that are substantially equivalent to data collected under the requirements of subsection (b) may use these data to develop disinfection profiles as specified in this section if the PWS has not:

(A) made a significant change to the treatment practice; or

(B) changed sources;

since the data were collected. A PWS may develop a disinfection profile using up to three (3) years of existing data.

(2) A PWS may use a disinfection profile developed under section 2 or 2.1 of this rule in lieu of developing a new profile if the system has not:

(A) made a significant change to the treatment practice; or

(B) changed sources;

since the profile was developed. A PWS that did not develop a virus profile under section 2 or 2.1 of this rule shall develop a virus profile using the same monitoring data on which the Giardia lamblia profile is based.

  (d) A PWS shall calculate the total inactivation ratio for Giardia lamblia according to the following:

(1) A PWS using only one (1) point of disinfectant application may determine the total inactivation ratio for the disinfection segment based on either of the following methods:

(A) Determine one (1) inactivation ratio (CTcalc/CT_99.9) before or at the first customer during peak hourly flow.

(B) Determine successive (CTcalc/CT_99.9) values, representing sequential inactivation ratios, between the point of disinfectant application and a point before or at the first customer during peak hourly flow. The PWS shall calculate the total inactivation ratio by determining CTcalc/CT_99.9 for each sequence and use the sum of the (CTcalc/CT_99.9) values to determine ∑(CTcalc/CT_99.9).

(2) A PWS using more than one (1) point of disinfectant application before the first customer shall determine the CT value:

(A) of each disinfection segment immediately prior to the next point of disinfectant application; or

(B) for the final segment, before or at the first customer;

during peak hourly flow. The (CTcalc/CT_99.9) value of each segment and ∑(CTcalc/CT_99.9) must be calculated using the method in subdivision (1)(B).

(3) A PWS shall determine the total logs of inactivation by multiplying the value calculated in subdivision (1) or (2) by three and zero-tenths (3.0).

(4) A PWS shall calculate the log of inactivation for viruses using a protocol approved by the commissioner.

  (e) A PWS shall use the following procedures to calculate a disinfection benchmark:

(1) For each year of profiling data collected and calculated under subsections (a) through (d), a PWS shall determine the lowest mean monthly level of both Giardia lamblia and virus inactivation. A PWS shall determine the mean Giardia lamblia and virus inactivation for each calendar month for each year of profiling data by dividing the sum of daily or weekly Giardia lamblia and virus log inactivation by the number of values calculated for that month.

(2) For a PWS with:

(A) one (1) year of profiling data, the disinfection benchmark is the lowest monthly mean value; or

(B) more than one (1) year of profiling data, the disinfection benchmark is the lowest monthly mean values of Giardia lamblia and virus log inactivation in each year of profiling data.

  * Tables 1.1 through 1.6, 2.1, and 3.1 of 40 CFR 141.74(b) are incorporated by reference and are available for review and copying at the Indiana Department of Environmental Management, Office of Water Quality, 100 North Senate Avenue, Room N1255, Indianapolis, Indiana 46204. (Water Pollution Control Division; 327 IAC 8-2.6-10; filed May 7, 2010, 9:30 a.m.: 20100602-IR-327080198FRA)