Washington Administrative Code
Title 246 - Health, Department of
WATER SYSTEMS
Chapter 246-290 - Group A public water supplies
Part 6 - SURFACE WATER TREATMENT
Subpart B - Requirements for Filtered Systems
Section 246-290-664 - Monitoring for filtered systems
Universal Citation: WA Admin Code 246-290-664
Current through Register Vol. 24-18, September 15, 2024
(1) Source coliform monitoring.
(a) The purveyor shall ensure that source
water samples of each surface or GWI source are:
(i) Collected before the first point of
disinfectant application and before coagulant chemical addition; and
(ii) Analyzed for fecal coliform density in
accordance with methods acceptable to the department.
(b) At a minimum, the purveyor shall ensure
source samples are collected for fecal coliform analysis at a frequency equal
to ten percent of the number of routine coliform samples collected within the
distribution system each month under WAC
246-290-300, or once per calendar
month, whichever is greater up to a maximum of one sample per day.
(c) With written approval from the
department, purveyors of filtered water systems serving less than ten thousand
people may collect twenty-six consecutive monthly fecal coliform samples
instead of collecting E. coli samples every two weeks for
twelve months as specified in
40 C.F.R.
141.701(a)(3)(i). The fecal
coliform levels that will trigger Cryptosporidium monitoring
will be the same as the E. coli levels specified in
40 C.F.R.
141.701(a)(4)(i), (ii), or
(iv).
(2) Source turbidity monitoring.
(a) The purveyor using conventional, direct,
or in-line filtration shall measure source turbidity at least once per day on a
representative sample collected before disinfection and coagulant
addition.
(b) Grab sampling or
continuous turbidity monitoring and recording may be used to meet the
requirement specified in (a) of this subsection.
(c) Purveyors using continuous turbidity
monitoring shall record continuous turbidity measurements at equal intervals,
at least every four hours, in accordance with a department-approved sampling
schedule.
(d) Purveyors using an
approved alternative filtration technology may be required to monitor source
water turbidity at least once per day on a representative sample as determined
by the department.
(3) Filtered water turbidity monitoring.
(a) The
purveyor using direct, conventional, or in-line filtration shall:
(i) Continuously monitor turbidity on
representative samples from each individual filter unit and from the system's
combined filter effluent, prior to clearwell storage;
(ii) For systems serving at least ten
thousand people, record continuous turbidity measurements from each individual
filter unit at equal intervals of at least every fifteen minutes, and for all
systems, from the combined filter effluent at equal intervals of at least every
four hours, in accordance with a department-approved sampling
schedule;
(iii) Systems serving
less than ten thousand people shall record continuous turbidity measurements
from each individual filter unit at equal intervals of at least every fifteen
minutes;
(iv) Systems serving less
than ten thousand people and consisting of two or fewer filters may record
continuous turbidity measurements from the combined filter effluent at equal
intervals of at least fifteen minutes in lieu of recording individual filter
turbidity measurements; and
(v)
Conduct monitoring in accordance with the analytical techniques under WAC
246-290-638.
(b) The purveyor using slow sand or
diatomaceous earth filtration shall:
(i)
Continuously monitor turbidity on representative samples from each individual
filter unit and from the system's combined filter effluent, prior to clearwell
storage;
(ii) Record continuous
turbidity measurements from the combined filter effluent at equal intervals of
at least every four hours in accordance with a department-approved sampling
schedule; and
(iii) Conduct
monitoring in accordance with the analytical techniques under WAC
246-290-638.
(c) Purveyors using an alternative filtration
technology approved under WAC
246-290-676 shall provide
monitoring in accordance with the technology-specific approval conditions
determined by the department.
(d)
Purveyors using slow sand filtration or an alternative filtration technology
may reduce filtered water turbidity monitoring to one grab sample per day with
department approval. Reduced turbidity monitoring shall be allowed only where
the purveyor demonstrates to the department's satisfaction that a reduction in
monitoring will not endanger the health of consumers served by the water
system.
(4) Monitoring the level of inactivation and removal.
(a)
Each day the system is in operation, the purveyor shall determine the total
level of inactivation and removal of Giardia lamblia cysts,
viruses, and Cryptosporidium oocysts achieved.
(b) The purveyor shall determine the total
level of inacti-vation and removal based on:
(i)
Giardia lamblia cyst,
Cryptosporidium oocyst, and virus removal credit granted by
the department for filtration; and
(ii) Level of inactivation of Giardia
lamblia cysts and viruses achieved through disinfection.
(c) At least once per day,
purveyors shall monitor the following to determine the level of inactivation
achieved through disinfection:
(i)
Temperature of the disinfected water at each residual disinfectant
concentration sampling point used for CT calculations; and
(ii) If using chlorine, pH of the disinfected
water at each chlorine residual disinfectant concentration sampling point used
for CT calculations.
(d)
Each day during peak hourly flow (based on historical information), the
purveyor shall:
(i) Determine disinfectant
contact time, T, to the point at which C is measured; and
(ii) Measure the residual disinfectant
concentration, C, of the water at the point for which T is calculated. The C
measurement point shall be located before or at the first consumer.
(e) The department may reduce CT
monitoring requirements for purveyors that demonstrate to the department's
satisfaction that the required levels of inactivation are consistently
exceeded. Reduced CT monitoring shall only be allowed where the purveyor
demonstrates to the department's satisfaction that a reduction in monitoring
will not endanger the health of consumers.
(5) Monitoring the residual disinfectant concentration entering the distribution system.
(a) Systems serving more than thirty-three
hundred people per month.
(i) The purveyor
shall continuously monitor and record the residual disinfectant concentration
of water entering the distribution system and report the lowest value each
day.
(ii) If the continuous
monitoring equipment fails, the purveyor shall measure the residual
disinfectant concentration on grab samples collected at least every four hours
at the entry to the distribution system while the equipment is being repaired
or replaced. The purveyor shall have continuous monitoring equipment back
online within five working days following failure.
(b) Systems serving thirty-three hundred or
less people per month.
(i) The purveyor shall
collect grab samples or use continuous monitoring and recording to measure the
residual disinfectant concentration entering the distribution system.
(ii) Purveyors of community
systems choosing to take grab samples shall collect:
(A) Samples at the following minimum
frequencies:
| Population Served | Number/day |
| 25 - 500 | 1 |
| 501 - 1,000 | 2 |
| 1,001 - 2,500 | 3 |
| 2,501 - 3,300 | 4 |
(B) At least one of the grab samples at peak
hourly flow; and
(C) The remaining
samples evenly spaced over the time the system is disinfecting water that will
be delivered to the public.
(iii) Purveyors of noncommunity
systems choosing to take grab samples shall collect samples for disinfectant
residual concentration entering the distribution system as directed by the
department.
(iv) When grab samples
are collected and the residual disinfectant concentration at the entry to
distribution falls below 0.2 mg/L, purveyors shall collect a grab sample every
four hours until the residual disinfectant concentration is 0.2 mg/L or
more.
(6) Monitoring residual disinfectant concentrations within the distribution system.
(a) The purveyor shall measure the residual
disinfectant concentration at representative points within the distribution
system on a daily basis or as otherwise approved by the department.
(b) At a minimum, the purveyor shall measure
the residual disinfectant concentration within the distribution system at the
same time and location that a routine or repeat coliform sample is collected
under WAC
246-290-300(3)(e) through
(g).
(c) The purveyor may measure HPC within the
distribution system in lieu of measuring the residual disinfectant
concentration under this subsection.
Statutory Authority: RCW 70.119A.180 and 43.20.050. 08-03-061, § 246-290-664, filed 1/14/08, effective 2/14/08. Statutory Authority: RCW 43.20.050 and 70.119A.080. 04-04-056, § 246-290-664, filed 1/30/04, effective 3/1/04. Statutory Authority: RCW 43.20.050(2) and (3) and 70.119A.080. 03-08-037, § 246-290-664, filed 3/27/03, effective 4/27/03. Statutory Authority: RCW 43.02.050 [43.20.050]. 99-07-021, § 246-290-664, filed 3/9/99, effective 4/9/99. Statutory Authority: RCW 43.20.050. 94-14-001, § 246-290-664, filed 6/22/94, effective 7/23/94; 93-08-011 (Order 352B), § 246-290-664, filed 3/25/93, effective 4/25/93.
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