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Storage Tank Management
Water & Wastewater Utility Operation andManagement for Tribes
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Water Storage
Why? What kind? Inspection Maintenance Corrosion control Cold weather considerations
EPA publication 816-K-03-002 Koester Associates, Inc.
www.westsussexda.fsnet.co.uk
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Water Storage Purpose Why?
Supply & demand equalizing Power cost savings Emergency & fire needs Surge relief Chlorine detention time increase Blending water from different sources Convenience!
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Storage Types Elevated Tanks
Dunham Engineering
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Storage Types Reservoirs
Dunham Engineering
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www.aquastore.com
Storage Types Standpipes
www.waterworld.com
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Storage Types Pneumatic Tanks
Dunham Engineering
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Who Should do the Inspection?
You? A professional?
Modern Technology?
tankdiver.files.wordpress.com
potablewatertankcleaning.com
www.ronperrin.com
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Inspection Items
Foundation: settling, cracks, deterioration Overflow pipe and valve Interior and exterior coating systems Water quality Water level indicator Surface tanks:
Roofs
Air vents Ladders Hatches
Pressure tanks
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Foundation/Containment Structure
Check for: Subsidence and uneven settlement Corrosion (cracking & spalling) Cracks
Other deterioration
inspectapedia.com geerassociation.org Dunham Engineering
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Overflow Pipe and Valve
Sufficient size Condition
Supported pipe Corrosion
Obstruction Screening (avoid animals/insects)
Valve: Accessible Operable/functional
Drainage Sufficient size
Erosion control
Dunham Engineering
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Altitude Valve
Controls tank level Refill tank Prevent overflow
Can be 1- or 2-way
Similar issues to theoverflow valve Sizing Condition Access Operation
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Interior & Exterior Coating
Steel reservoirs or tanks: Inside/outside paint prevents corrosion
Concrete tanks: Waterproofing can seal surface cracks
Protective coating systems: Adhesion Peeling or rusting areas Materials (lead?) Ice or other damage (e.g., from
welding or gunshots) Meet NSF Standard 61 if in
contact with potable water Dunham Engineering
inspectapedia.com
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Water Quality
Water sampling (e.g., at drain connection) Suspended solids Turbidity (cloudy?) Odor
Birds, rodents, and insects at access points orwithin the tank
Bottom sediment or sludge
potablewatertankcleaning.com
AWWA
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Water Level Indicator
Pressure gauge Reading in psi or feet of water Adequate reading for tank height
Float-style indicator Cable access opening protected Float moves freely Target reads properly
Supervisory Controland Data Acquisition(SCADA)
Horsley Witten Group
Dunham Engineering
Dunham Engineering
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Roofs
Low spots where water may pond Min. 0.75/12 slope (AWWA D100) Recommend 1/12 slope & thick
Holes along seams
Support columns, rafters, and connections
Dunham Engineering tankdiver.files.wordpress.com
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Air Vents
Proper design Min. 24 Downward-facing cover
Screened to keep animals
and birds out #16 mesh No hardware cloth
Sealed edges & seams Gaps < 1/16 No holes in vent cover
Dunham Engineering
tankdiver.files.wordpress.com
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Access Ladders
Ladder rungs 12 apart Safety:
Cage around ladder Rail-type safety system
Above ground restrict access Ladders supports spaced 10 apart max.
Dunham Engineering
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Hatches
Proper design 30 diameter (or square) opening 4 raised curb
Closes properly (no gaps)
Locks
Dunham Engineering www.swregional.net
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Hydro-pneumatic Tanks
Take inspections seriously!
Annual pressure tank inspections must ensure: Pressure release device is working properly Pressure gauge is working properly Air-water ratio is maintained at the adequate level Rubber gasket is replaced
meridithcorp.com www.frwa.net
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Maintenance: Cleaning & Disinfection
Disinfect tanks after inspection and cleaning
AWWA Standard C652-92 Disinfection of Water-StorageFacilities
Procedure similar to disinfecting water mains
Add chlorine to water filling tank Maintain chlorine residual of at least 50 mg/L for 6
hours minimum Carefully dispose of the disinfection water
For large tanks: Collect samples while filling, or Spray walls with highly chlorinated water
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Maintenance: Steel Tank Issues
Repair and replacement of protective coatings Lead abatement
Containment Competent Person
Corrosion damage Repair/replacement
of rafters Repair/replacement of hatches and appurtenances Repair of pitting to
> Prevent leaks> Maintain structural integrity
Dunham Engineering
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Maintenance: Concrete Tank Issues
Leak repairs Cracking and spalling of concrete over time Concrete doesnt rust, but reinforcement does Typically costs more to build, but less to
maintain
Dunham Engineering Dunham Engineering
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Corrosion Why does it happen?
Corroding water tank is like a battery: Walls = anode provides electrons Water = cathode receives electrons Tank corrodes as electrons leave the steel wall
The electrons (-) in
the steel tank
move into the water
causing corrosion
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Cold Weather Considerations - Ice
Keep water moving! Overflow pipe
Keep clear of ice If clogged, water will flow from
the air vent and freeze, the addedweight could topple the tower
Water tower riser Protect it from freezing If pipe large enough, may partially
freeze on the outside and stillallow flow inside
LA Times
gtluke.com
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Cold Weather Considerations - Ice
Ground-level tanks less likely to freeze Elevated tank
If frozen, costly to thaw Ice can deform walls
If drained, must be disinfected
Koester Associates, Inc.
Keep water moving!
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What Have We Learned?
Various types of tanks
Inspection & Maintenance
Corrosion control
Cold weather issues