[Code of Federal Regulations]
[Title 40, Volume 22]
[Revised as of July 1, 2005]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR141.72]
[Page 443-445]
TITLE 40--PROTECTION OF ENVIRONMENT
CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
PART 141_NATIONAL PRIMARY DRINKING WATER REGULATIONS--Table of Contents
Subpart H_Filtration and Disinfection
Sec. 141.72 Disinfection.
A public water system that uses a surface water source and does not
provide filtration treatment must provide the disinfection treatment
specified in paragraph (a) of this section beginning December 30, 1991,
unless the State determines that filtration is required in writing
pursuant to Sec. 1412 (b)(7)(C)(iii). A public water system that uses a
ground water source under the direct influence of surface water and does
not provide filtration treatment must provide disinfection treatment
specified in paragraph (a) of this section beginning December 30, 1991,
or 18 months after the State determines that the ground water source is
under the influence of surface water, whichever is later, unless the
State has determined that filtration is required in writing pursuant to
Sec. 1412(b)(7)(C)(iii). If the State has determined that filtration is
required, the system must comply with any interim disinfection
requirements the State deems necessary before filtration
[[Page 444]]
is installed. A system that uses a surface water source that provides
filtration treatment must provide the disinfection treatment specified
in paragraph (b) of this section beginnng June 29, 1993, or beginning
when filtration is installed, whichever is later. A system that uses a
ground water source under the direct influence of surface water and
provides filtration treatment must provide disinfection treatment as
specified in paragraph (b) of this section by June 29, 1993, or
beginning when filtration is installed, whichever is later. Failure to
meet any requirement of this section after the applicable date specified
in this introductory paragraph is a treatment technique violation.
(a) Disinfection requirements for public water systems that do not
provide filtration. Each public water system that does not provide
filtration treatment must provide disinfection treatment as follows:
(1) The disinfection treatment must be sufficient to ensure at least
99.9 percent (3-log) inactivation of Giardia lamblia cysts and 99.99
percent (4-log) inactivation of viruses, every day the system serves
water to the public, except any one day each month. Each day a system
serves water to the public, the public water system must calculate the
CT value(s) from the system's treatment parameters, using the procedure
specified in Sec. 141.74(b)(3), and determine whether this value(s) is
sufficient to achieve the specified inactivation rates for Giardia
lamblia cysts and viruses. If a system uses a disinfectant other than
chlorine, the system may demonstrate to the State, through the use of a
State-approved protocol for on-site disinfection challenge studies or
other information satisfactory to the State, that CT99.9
values other than those specified in tables 2.1 and 3.1 in Sec.
141.74(b)(3) or other operational parameters are adequate to demonstrate
that the system is achieving minimum inactivation rates required by
paragraph (a)(1) of this section.
(2) The disinfection system must have either (i) 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,
or (ii) automatic shut-off of delivery of water to the distribution
system whenever there is less than 0.2 mg/l of residual disinfectant
concentration in the water. If the State determines that automatic shut-
off would cause unreasonable risk to health or interfere with fire
protection, the system must comply with paragraph (a)(2)(i) of this
section.
(3) The residual disinfectant concentration in the water entering
the distribution system, measured as specified in Sec. 141.74 (a)(2)
and (b)(5), cannot be less than 0.2 mg/l for more than 4 hours.
(4)(i) The residual disinfectant concentration in the distribution
system, measured as total chlorine, combined chlorine, or chlorine
dioxide, as specified in Sec. 141.74 (a)(2) and (b)(6), cannot be
undetectable in more than 5 percent of the samples each month, for any
two consecutive months that the system serves water to the public. Water
in the distribution system with a heterotrophic bacteria concentration
less than or equal to 500/ml, measured as heterotrophic plate count
(HPC) as specified in Sec. 141.74(a)(1), is deemed to have a detectable
disinfectant residual for purposes of determining compliance with this
requirement. Thus, the value ``V'' in the following formula cannot
exceed 5 percent in one month, for any two consecutive months.
[GRAPHIC] [TIFF OMITTED] TC15NO91.131
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 the residual disinfectant concentration is
measured but not detected and where the HPC is 500/ml; and
e=number of instances where the residual disinfectant concentration is
not measured and HPC is 500/ml.
(ii) If the State determines, based on site-specific considerations,
that a system has no means for having a sample
[[Page 445]]
transported and analyzed for HPC by a certified laboratory under the
requisite time and temperature conditions specified by Sec.
141.74(a)(1) and that the system is providing adequate disinfection in
the distribution system, the requirements of paragraph (a)(4)(i) of this
section do not apply to that system.
(b) Disinfection requirements for public water systems which provide
filtration. Each public water system that provides filtration treatment
must provide disinfection treatment as follows.
(1) The disinfection treatment must be sufficient to ensure that the
total treatment processes of that system achieve at least 99.9 percent
(3-log) inactivation and/or removal of Giardia lamblia cysts and at
least 99.99 percent (4-log) inactivation and/or removal of viruses, as
determined by the State.
(2) The residual disinfectant concentration in the water entering
the distribution system, measured as specified in Sec. 141.74 (a)(2)
and (c)(2), cannot be less than 0.2 mg/l for more than 4 hours.
(3)(i) The residual disinfectant concentration in the distribution
system, measured as total chlorine, combined chlorine, or chlorine
dioxide, as specified in Sec. 141.74 (a)(2) and (c)(3), cannot be
undetectable in more than 5 percent of the samples each month, for any
two consecutive months that the system serves water to the public. Water
in the distribution system with a heterotrophic bacteria concentration
less than or equal to 500/ml, measured as heterotrophic plate count
(HPC) as specified in Sec. 141.74(a)(1), is deemed to have a detectable
disinfectant residual for purposes of determining compliance with this
requirement. Thus, the value ``V'' in the following formula cannot
exceed 5 percent in one month, for any two consecutive months.
[GRAPHIC] [TIFF OMITTED] TC15NO91.132
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; and
e=number of instances where the residual disinfectant concentration is
not measured and HPC is 500/ml.
(ii) If the State determines, based on site-specific considerations,
that a system has no means for having a sample transported and analyzed
for HPC by a certified laboratory under the requisite time and
temperature conditions specified in Sec. 141.74(a)(1) and that the
system is providing adequate disinfection in the distribution system,
the requirements of paragraph (b)(3)(i) of this section do not apply.
[54 FR 27527, June 29, 1989, as amended at 69 FR 38855, June 29, 2004]