New Hampshire Code of Administrative Rules
Env - Department of Environmental Services
Subtitle Env-Ws - Division of Water
Chapter Env-Ws 300 - NEW HAMPSHIRE DRINKING WATER RULES
Part Env-Ws 380 - FILTRATION, DISINFECTION, TREATMENT PLANT AND WASTE RECYCLING
Section Env-Ws 380.10 - Disinfection for Systems Not Providing Filtration
Universal Citation: NH Admin Rules Env-Ws 380.10
Current through Register No. 13, March 27, 2025
(a) Each public water system owner that does not provide filtration treatment shall provide disinfection treatment as follows:
(1) The
disinfection treatment shall be sufficient to ensure at least 99.9 percent
inactivation of giardia lamblia cysts and 99.99 percent inactivation of
viruses, every day the system serves water to the public, except any one day
each month;
(2) Each day a system
serves water to the public, the owner shall calculate the CT value(s) from the
system's treatment parameters, using the procedure specified in
Env-Ws
380.14(f) and (g), and determine
whether this value(s) is sufficient to achieve the specified inactivation rates
for giardia lamblia cysts and viruses;
(3) If a system uses a disinfectant other
than chlorine, the owner shall demonstrate to the department, through the use
of on-site disinfection challenge studies or other information, that CT99.9
values other than those specified in Tables 380-8 and 380-9 or other
operational parameters are adequate to demonstrate that the system is achieving
minimum inactivation rates required by this paragraph;
(4) The disinfection system shall have
redundant components, including an auxiliary power supply with automatic
start-up and alarm to ensure that disinfectant application is maintained
continuously while water is being delivered to the distribution
system;
(5) The residual
disinfectant concentration in the water entering the distribution system shall
not be less than 0.2 mg/l for more than 4 hours.
(b) The residual disinfectant concentration in the distribution system shall be as follows:
(1)The residual disinfectant concentration
measured as total chlorine, combined chlorine, or chlorine dioxide shall not be
undetectable in more than 5 percent of the samples each month, for any 2
consecutive months that the system serves water to the public;
(2) Water in the distribution system with a
heterotrophic bacteria concentration less than or equal to 500/ml, measured as
HPC, is deemed to have a detectable disinfectant residual for purposes of
determining compliance with this requirement;
(3) The value "V" in the following formula
shall be calculated each month:
V = c + d + e/a + b x 100
(4) The terms in the formula in (b)(3) above
shall be as follows:
a. a = number of
instances where the residual disinfectant concentration is measured;
b. b = number of instances where the residual
disinfectant concentration is not measured but HPC is measured;
c. c = number of instances where the residual
disinfectant concentration is measured but not detected and no HPC is
measured;
d. d = number of
instances where the residual disinfectant concentration is measured but not
detected and where the HPC is >500/ml; and
e. e = number of instances where the residual
disinfectant concentration is not measured and HPC is >500/ml; and
(5)The value of "V" in (b)(3)
above shall not exceed 5 percent in one month for any 2 consecutive
months.
#5098, eff 3-18-91, EXPIRED 3-18-97
New. #6521, eff 6-4-97 (See Revision Note at chapter heading for Env-Ws 300); ss by #8352, eff 5-14-05 (formerly part of Env-Ws 380.15 )
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