Current through September 17, 2024
011.01 Systems
required to develop disinfection profiles must follow the requirements of 179
NAC 25-011. Systems must monitor at least weekly for a period of 12 consecutive
months to determine the total log inactivation for Giardia lamblia
and viruses. If systems monitor more frequently, the monitoring
frequency must be evenly spaced. Systems that operate for fewer than 12 months
per year must monitor weekly during the period of operation. Systems must
determine log inactivation for Giardia lamblia through the
entire plant, based on contact time (CT)99.9 values in
Tables 13.1 through 13.8 of 179 NAC
13-007.02C5 as
applicable. Systems must determine log inactivation for viruses through the
entire treatment plant based on a protocol approved by the
Department.
011.02 Systems with a
single point of disinfectant application prior to the entrance to the
distribution system must conduct the monitoring in 179 NAC 25-011.02A through
011.02D. Systems
with more than one point of disinfectant application must conduct the
monitoring in 179 NAC 25-011.02A through
25-011.02D for
each disinfection segment. Systems must monitor the parameters necessary to
determine the total inactivation ratio, using analytical methods in 179 NAC
13-007.01.
25-011.02A For systems using a
disinfectant other than UV, the temperature of the disinfected water must be
measured at each residual disinfectant concentration sampling point during peak
hourly flow or at an alternative location approved by the Department.
25-011.02B For systems using chlorine, the pH
of the disinfected water must be measured at each chlorine residual
disinfectant concentration sampling point during peak hourly flow or at an
alternative location approved by the Department.
25-011.02C The disinfectant contact time(s)
(t) must be determined during peak hourly flow.
25-011.02D The residual disinfectant
concentration(s) (C) of the water before or at the first customer and prior to
each additional point of disinfectant application must be measured during peak
hourly flow.
011.03 In
lieu of conducting new monitoring under 179 NAC
25-011.02, systems may elect to
meet the following requirements:
25-011.03A
Systems that have at least one year of existing data that are substantially
equivalent to data collected under the provisions of 179 NAC
25-011.02 may use these data to
develop disinfection profiles as specified in this section if the system has
neither made a significant change to its treatment practice nor changed sources
since the data were collected. Systems may develop disinfection profiles using
up to three years of existing data.
25-011.03B Systems may use disinfection
profile(s) developed under 179 NAC
17-004 or 179 NAC 19-007.01 through
19-007.07 in lieu of developing a new profile if the system has neither made a
significant change to its treatment practice nor changed sources since the
profile was developed. Systems that have not developed a virus profile under
179 NAC
17-004 or 179 NAC 19-007.01 through
19-007.07 must develop a virus profile using the same monitoring data on which
the Giardia lamblia profile is based.
011.04 Systems must calculate the total
inactivation ratio for Giardia lamblia as specified in 179 NAC
25-011.04A through
25-011.04C.
25-011.04A Systems using only one point of
disinfectant application may determine the total inactivation ratio for the
disinfection segment based on either of the following methods:
1. Determine one inactivation ratio
(CTcalc/CT99.9) before or at the first customer during
peak hourly flow.
2. Determine
successive CTcalc/CT99.9 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 system must
calculate the total inactivation ratio by determining
(CTcalc/CT99.9) for each sequence and then adding the
(CTcalc/CT99.9) values together to determine
[[SIGMA](CTcalc/CT99.9)]
25-011.04B Systems using more than one point
of disinfectant application before the first customer must determine the CT
value of each disinfection segment immediately prior to the next point of
disinfectant application, or for the final segment, before or at the first
customer, during peak hourly flow. The (CTcalc/CT99.9)
value of each segment and [[SIGMA](CTcalc/CT99.9)] must
be calculated using the method in 179 NAC
25-011.04A item
2.
25-011.04C The system must
determine the total logs of inactivation by multiplying the value calculated in
179 NAC
25-011.04A or
25-011.04B by
3.0.
25-011.04D Systems must
calculate the log of inactivation for viruses using a protocol approved by the
Department.
011.05
Systems must use the procedures specified in 179 NAC
25-011.05A and
25-011.05B to
calculate a disinfection benchmark.
25-011.05A For each year of profiling data
collected and calculated under 179 NAC 25-011.01 through
25-011.04, systems must determine
the lowest mean monthly level of both Giardia lamblia and
virus inactivation. Systems must 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.
25-011.05B The disinfection
benchmark is the lowest monthly mean value (for systems with one year of
profiling data) or the mean of the lowest monthly mean values (for systems with
more than one year of profiling data) of Giardia lamblia and
virus log inactivation in each year of profiling data.
