where:

a = number of instances where the residual disinfectant concentration is measured.

b = number of instances where the residual disinfectant concentration is not measured but heterotrophic bacteria plate count (HPC) is measured.

c = number of instances where the residual disinfectant concentration is measured but not detected and no HPC is measured.

d = number of instances where no residual disinfectant concentration is detected and where the HPC is > 500/ml.

e = number of instances where the residual disinfectant concentration is not measured and HPC is > 500/ml.

NR 810.31(2)(c)2. 2. If the department determines, based on site specific considerations, that a public water system has no means for having a sample transported and analyzed for HPC by a certified laboratory under the requisite time and temperature conditions required in s. NR 809.311 (1), Table F, and that the system is providing adequate disinfection in the distribution system, the requirements of subd. 1. do not apply.

NR 810.31 History History: CR 09-073: cr. Register November 2010 No. 659, eff. 12-1-10.

NR 810.32 NR 810.32 Disinfection profiling and benchmarking.

NR 810.32(1) (1) Requirements when making a significant change in disinfection practice.

NR 810.32(1)(a) (a) Following the completion of initial source water monitoring under s. NR 809.331, the water supplier for a public water system that plans to make a significant change to its disinfection practice, as defined in par. (b), shall develop disinfection profiles and calculate disinfection benchmarks for Giardia lamblia and viruses as described in sub. (2). Prior to changing the disinfection practice, the water supplier shall notify the department and shall include in this notice all of the following information:

NR 810.32(1)(a)1. 1. A completed disinfection profile and disinfection benchmark for Giardia lamblia and viruses as described in sub. (2).

NR 810.32(1)(a)2. 2. A description of the proposed change in disinfection practice.

NR 810.32(1)(a)3. 3. An analysis of how the proposed change will affect the current level of disinfection.

NR 810.32(1)(b) (b) Significant changes to disinfection practice are defined as any of the following:

NR 810.32(1)(b)1. 1. Changes to the point of disinfection.

NR 810.32(1)(b)2. 2. Changes to the disinfectants used in the treatment plant.

NR 810.32(1)(b)3. 3. Changes to the disinfection process.

NR 810.32(1)(b)4. 4. Any other modification identified by the department as a significant change to disinfection practice. Additional barriers with no change to existing disinfection practices may be exempt from these requirements.

NR 810.32(2) (2) Developing the disinfection profile and benchmark. Water suppliers for public water systems required to develop disinfection profiles under sub. (1) shall follow the requirements of this subsection:

NR 810.32(2)(a) (a) Water suppliers shall monitor at least weekly for a period of 12 consecutive months to determine the total logs of inactivation for Giardia lamblia and viruses. If water suppliers monitor more frequently, the monitoring frequency shall be evenly spaced. Systems that operate for fewer than 12 months per year shall be monitored weekly during the period of operation. Water suppliers shall determine log inactivation for Giardia lamblia through the entire plant, based on the CT99.9 (3 log) values in ss. NR 810.47 to 810.62. Water suppliers shall determine log inactivation for viruses through the entire treatment plant based on a protocol approved by the department.

NR 810.32(2)(b) (b) Water suppliers for systems with a single point of disinfectant application prior to entrance to the distribution system shall conduct the monitoring in subds. 1. to 4. Water suppliers for systems with more than one point of disinfectant application shall conduct the monitoring in subds. 1. to 4. for each disinfection segment. Water suppliers shall monitor the parameters necessary to determine the total inactivation ratio, using analytical methods in s. NR 809.563 (2), Table R.

NR 810.32(2)(b)1. 1. For systems using a disinfectant other than UV, the temperature of the disinfected water shall be measured at each residual disinfectant concentration sampling point during peak hourly flow.

NR 810.32(2)(b)2. 2. For systems using chlorine, the pH of the disinfected water shall be measured at each chlorine residual disinfectant concentration sampling point during peak hourly flow.

NR 810.32(2)(b)3. 3. The disinfectant contact times (“T”) shall be determined during peak hourly flow.

NR 810.32(2)(b)4. 4. The residual disinfectant concentrations (“C”) of the water before or at the first customer and prior to each additional point of disinfection shall be measured during peak hourly flow.

NR 810.32(2)(c) (c) In lieu of conducting new monitoring under par. (b), public water systems may elect to meet the following requirements:

NR 810.32(2)(c)1. 1. Water suppliers for systems that have at least one year of existing data that are substantially equivalent to data collected under par. (b) may use these data to develop disinfection profiles as specified in this section if the water system has neither made a significant change to its treatment practice nor changed sources since the data were collected. Water suppliers may develop disinfection profiles using up to 3 years of existing data.

NR 810.32(2)(c)2. 2. Water suppliers may use disinfection profile or profiles developed previously in lieu of developing a new profile if the water system has not made a significant change, as determined under sub. (1) (b), to its treatment practice or has not changed sources since the profile was developed. Water suppliers for systems that have not developed a virus profile shall develop a virus profile using the same monitoring data on which the Giardia lamblia profile is based.