Current through Register Vol. 49, No. 9, September, 2024
These guidelines concern the maintenance of water quality during
an underwater tank inspection or cleaning by divers, remote operated vehicles
(ROV), or rafts. They do not apply to newly constructed tanks, or tanks which
are removed from service and drained for cleaning or inspection.
Improperly disinfected divers, inspectors, and equipment can
contaminate the water. Additionally, tank sediment may contain microorganisms
which, if resuspended during the inspection or cleaning, can cause
contamination of the water.
Observing and measuring water quality, and taking the appropriate
actions if water quality is not maintained, including the notification of
customers, is the responsibility of the water utility. Advanced notice to the
Engineering Section, ADH is to be made by the utility of the proposed date of
an underwater inspection or cleaning. The availability of Engineering Section
staff for onsite water quality measurements is not guaranteed.
I.
Public Notification
A. Notification of the proposed tank entry is
to be provided to customers served by the affected tank in a manner appropriate
for the area and the utility.
II.
Tank Isolation
A. Isolation of the storage tank during
underwater inspection or cleaning is strongly recommended and may be required
for safety reasons. If operational conditions necessitate an underwater
inspection or cleaning without isolation, then the work should be done during
periods when positive flow into the storage tank is maintained, or flow rates
into or out of the tank are minimal.
III.
Water Quality Monitoring
A. Before entry - the chlorine residual and
turbidity of the tank contents shall be measured and recorded by the water
utility. Samples should be taken from several depths, if possible. At least one
bacteriological sample shall also be collected from the tank, analyzed by a
certified laboratory, and test negative for coliform bacteria (coliform
absent). If the chlorine residual is less than 0.5 mg/l, sufficient chlorine
solution or granules shall be added to raise the residual to at least 0.5 mg/l
but not to exceed 3 mg/l.
B. After
entry - the chlorine residual and turbidity of the tank shall be measured and
recorded at the same locations and at least one bacteriological sample
collected and analyzed for coliform bacteria.
IV.
Acceptable Water Quality
A. Water returned to the distribution system
from a tank which has undergone an underwater inspection or cleaning must meet
one of the following criteria:
1. If the tank
is isolated: A negative bacteriological analysis (coliform absent) from a
certified drinking water lab; and after-entry chlorine residual and turbidity
measurements that show no degradation when compared to the before-entry
measurements.
2. If the tank is not
isolated: After-entry chlorine residual and turbidity measurements that show no
degradation when compared to the before-entry measurements, as determined by an
onsite Engineering Section, ADH representative. The water utility shall also
collect and submit a sample from the tank for coliform analysis to a certified
drinking water laboratory, the results of which (24-48 hrs later) must be
negative (coliform absent).
Degradation is defined as a reduction in the chlorine residual
by 0.2 mg/l or more, or a turbidity increase of 2 NTU or more.
B. If after the tank
entry the water fails to meet these criteria, the utility shall immediately:
1. Isolate the tank, reestablish the chlorine
residual in the water in the tank, and collect subsequent bacteriological
samples until the results are negative (coliform absent); or,
2. Issue a Boil Water Advisory (BWA) for the
distribution area served by the tank. The BWA is to remain in effect until
bacteriological samples from the tank and the distribution system are negative
(coliform absent).
V.
Equipment and Personnel
Requirements
A. All equipment to be
used shall be available for inspection.
B. All equipment exposed to water shall be
dedicated for potable water storage facilities only and shall be stored in a
manner that prevents both chemical and bacteriological contamination.
C. All equipment shall be constructed and
maintained so that water quality is not affected.
D. Divers shall be completely encapsulated
with no bare skin exposed. There shall be no contact of the mouth or head with
the water.
E. Diving clothing shall
be of the dry-suit type, in good condition, and free from tears or other
imperfections that may impair the integrity of the suit.
F. Float down inspectors must wear a dry suit
that can be properly disinfected.
G. Unless explicitly approved by the utility
to do so, divers or ROV's shall not disturb tank sediment.
H. All personnel entering a storage tank
shall be free of communicable disease and shall not have been under a
physician's care within the previous 7 day period. No person who knowingly has
an abnormal temperature or symptoms of illness shall work in a storage
tank.
VI.
Disinfection of Equipment
A. All
equipment exposed to water shall be suitable for disinfection.
B. Before opening, the access hatch and its
immediate area shall be cleaned of all loose dirt and debris
C. A diver and clothing shall be disinfected
after the diver is suited up and on top of the tank.
D. A solution of 200 mg/l available chlorine
shall be applied to all surfaces immediately prior to entry to the water.
Application can be by submersion, spray, sponge, or brush and shall remain in
contact with the solution for at least 30 minutes. Any excess, runoff, or
spillage is to be controlled so that it does not enter the storage
tank.
E. Any equipment that makes
contact with the roof shall be redisinfected prior to entering the
tank.
VII.
Certifications
A. The contractor shall
have a comprehensive safety manual on site which addresses all potential
hazards for the particular storage tank. The manual shall include
certifications for onsite employees for diving, OSHA confined space entry,
first aid, and CPR.
B. The
contractor shall have a method and equipment readily available for extraction
and lowering of an injured diver.
VIII.
Logistics
A. A pre-job meeting involving the contractor
and water utility representatives shall be held to ensure that the personnel
understand the inspection or cleaning procedures, the configuration of the
reservoir, disinfection procedures, maintenance of water quality, and the
consequences if such quality is not maintained.
1 These guidelines are modeled on AWWA
C652-02 Disinfection of Water Storage Facilities and are only
meant to address the sanitary quality of the water before and after tank entry.
They are not meant to provide guidance on safety issues for confined space
entry and diving operations. Because of the hazardous nature of this work,
contractors must comply with all federal, state, and local regulations and
safety requirements.
