WAC 246-290-692
Disinfection for unfiltered systems. (1) General requirements.
(a) The purveyor without a limited alternative to
filtration shall:
(i) Provide continuous disinfection treatment to ensure
at least 99.9 percent (3 log) inactivation of Giardia lamblia
cysts and 99.99 percent (4 log) inactivation of viruses at all
times the system serves water to the public.
(ii) Failure to provide the required inactivation level
on more than one day in any calendar month shall be considered
a treatment technique violation.
(b) The purveyor with a limited alternative to filtration
shall meet the treatment requirements in WAC 246-290-630(11)
at all times the system serves water to the public.
(c) The purveyor may be required to provide greater
levels of inactivation of Giardia lamblia cysts, other
pathogenic microorganisms of public health concern, and
viruses to protect the health of consumers.
(2) Determining the level of inactivation.
(a) Each day the system without a limited alternative to
filtration serves water to the public, the purveyor, using
procedures and CT99.9 values specified in 40 CFR 141.74, Vol.
54, No. 124, (published June 29, 1989), shall determine:
(i) CT values using the system's treatment parameters and
calculate the total inactivation ratio achieved by
disinfection; and
(ii) Whether the system's disinfection treatment process
is achieving the minimum levels of inactivation of Giardia
lamblia cysts and viruses required by the department. For
purposes of determining compliance with the inactivation
requirements specified in subsection (1) of this section, no
credit shall be granted for disinfection applied to a source
water with a turbidity greater than 5.0 NTU.
(b) Each day the system with a limited alternative to
filtration serves water to the public, the purveyor, using
appropriate guidance, shall determine:
(i) CT values using the system's treatment parameters and
calculate the total inactivation ratio achieved by
disinfection; and
(ii) Whether the system's treatment process is achieving
the minimum levels of inactivation of Giardia lamblia cysts,
viruses, or other pathogenic organisms of health concern
including Cryptosporidium oocysts that would be greater than
what would be expected from the combination of filtration plus
chlorine disinfection.
(c) The purveyor shall be considered in compliance with
the daily inactivation requirement when a total inactivation
ratio equal to or greater than 1.0 is achieved.
(d) The purveyor of a system using a disinfectant or
combination of disinfectants may use CT values lower than
those specified in (a) of this subsection, if the purveyor
demonstrates to the department's satisfaction that the
required levels of inactivation of Giardia lamblia cysts,
viruses, and, if providing a limited alternative to
filtration, any other pathogenic organisms of public health
concern including Cryptosporidium oocysts, can be achieved
using the lower CT values.
(e) The purveyor of a system using preformed chloramines
or adding ammonia to the water before chlorine shall
demonstrate to the department's satisfaction that the system
achieves at least 99.99 percent (4 log) inactivation of
viruses.
(3) The purveyor using either unfiltered or "limited
alternative to filtration" treated sources shall ensure that
disinfection facilities provide either:
(a) Redundant components, including an auxiliary power
supply with automatic start up and alarm, to ensure continuous
disinfection. Redundancy shall ensure that both the minimum
inactivation requirements and the requirement for a 0.2 mg/L
residual disinfectant concentration at entry to the
distribution system are met at all times water is delivered to
the distribution system; or
(b) Automatic shutoff of delivery of water to the
distribution system when the residual disinfectant
concentration in the water is less than 0.2 mg/L. Automatic
shutoff shall be allowed only in systems where the purveyor
demonstrates to the department's satisfaction that automatic
shutoff will not endanger health or interfere with fire
protection.
(4) Disinfectant residual entering the distribution
system.
(a) The purveyor shall ensure that water entering the
distribution system contains a residual disinfectant
concentration, measured as free or combined chlorine, of at
least 0.2 mg/L at all times the system serves water to the
public; and
(b) Failure to provide a 0.2 mg/L residual at entry to
distribution for more than four hours on any day shall be
considered a treatment technique violation.
(5) Disinfectant residuals within the distribution
system.
(a) The purveyor shall ensure that the residual
disinfectant concentration in the distribution system,
measured as total chlorine, free chlorine, combined chlorine,
or chlorine dioxide, is detectable in at least ninety-five
percent of the samples taken each calendar month.
(b) The purveyor of a system that purchases completely
treated surface or GWI water as determined by the department
shall comply with the requirements specified in (a) of this
subsection.
(c) Water in the distribution system with an HPC level
less than or equal to 500 organisms/ml is considered to have a
detectable residual disinfectant concentration.
[Statutory Authority: RCW 70.119A.180 and 43.20.050. 08-03-061, § 246-290-692, filed 1/14/08, effective 2/14/08. Statutory Authority: RCW 43.20.050 (2) and (3) and70.119A.080
. 03-08-037, § 246-290-692, filed 3/27/03,
effective 4/27/03. Statutory Authority: RCW 43.02.050
[43.20.050]. 99-07-021, § 246-290-692, filed 3/9/99,
effective 4/9/99. Statutory Authority: RCW 43.20.050.
94-14-001, § 246-290-692, filed 6/22/94, effective 7/23/94;
93-08-011 (Order 352B), § 246-290-692, filed 3/25/93,
effective 4/25/93.]