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Transcript of Distribution System Control Strategies. Tank Management/Operations Flushing Rerouting Water ...
![Page 1: Distribution System Control Strategies. Tank Management/Operations Flushing Rerouting Water Others optimizing existing booster chlorination.](https://reader036.fdocuments.us/reader036/viewer/2022062407/56649dc05503460f94ab5032/html5/thumbnails/1.jpg)
Distribution System Control Strategies
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Distribution System Control Strategies
Tank Management/Operations
Flushing
Rerouting Water
Others
optimizing existing booster chlorination (operation, control)
system modifications
tank modifications to enhance mixing, remove DBPs, adding booster chlorination
capital improvements after O&M options are exhausted/evaluated
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Tank Management/Operations
Basis for Considering: Tank spreadsheet estimates tank to have:
High water age
Poor mixing
Poor water quality based on sampling: In tank
Immediate vicinity of tank
Other options exist to provide system pressure (i.e., multiple tanks serve same
area, booster pump station, etc.).
Concerns/Implementation Considerations: Maintaining system pressure.
Ability to satisfy peak demands (e.g., fire protection, line breaks, and seasonal
variations).
Drawing tank down (at least initially) may release poor water quality into the
system.
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Tank
Man
agem
ent/
Ope
ratio
ns Level Modification
Change Fill Rate/Duration
Lower Max Level
Lower Min Level
Lower Both Levels
Faster Rate/ Shorter Duration
Slower Rate/Longer Duration
Remove Tank From Service
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Tank Level Modification
Lower Max Level Lower Min Level Lower Both Levels
Pros• Lowers water age (due
to reduced volume in tank)
• Maintains minimum system pressure
Cons• Less water for
fires/emergencies
• Possibly reduces mixing
Pros• Lowers water age
• Improves mixing
Cons• Less water for
fires/emergencies
• Lowers minimum system pressure
Pros• Lowers water age
• May improve mixing (depends on level fluctuation)
Cons• Lowers minimum
system pressure
• Less water for fires/emergencies
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Change Tank Fill Rate/Duration
Longer Fill Duration / Slower Fill Rate
Shorter Fill Duration /Faster Fill Rate
Pros• Increased water velocity to improve
mixing
• Tank filled fasterCons• Energy use considerations
• Uncertain impact on water quality
• Less water for fires/ emergencies
• Potential wear on control valve
• May not fill tank before next demand cycle
Pros• Longer mixing time
• Less stress on water mains
Cons• Energy use considerations
• Uncertain impact on water quality
• Possible over-pressurization of water mains
• Possible increased power bill
• May not fill tank before next demand cycle
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Remove Tank from Service
Cons• Possible reduced system pressure.
• Less water for fires/emergencies.
• Possible change in ISO rating when re-evaluated.
• Transferring demand to another tank could be a problem.
• Increased energy costs (i.e., pumping costs).
• Empty storage tanks are more vulnerable to weather (especially wind).
Pros• Lowers overall water age in system.
• Transfers demand to another tank (may improve operations of that tank).
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Operational Data
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Water Quality Data
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Flushing
Basis for Considering: Lower disinfectant residuals High disinfection byproducts Area is not influenced by a tank or tank operations cannot be
altered Dead-ends:
Physical Hydraulic
Concerns/Implementation Considerations: Lost revenue Discharge issues (e.g., dechlorination, water conservation)
Hydraulic limitations (e.g., pressure)
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Flu
shin
g Unidirectional
Automatic
Blow-Off
Conventional
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Flushing – Conventional
Cons• Labor intensive.
• Usually involves large volumes of water, relative to automated flushing.
• Can cause discolored water due to typical high water velocity.
• Usually not metered.
Pros• Immediate water quality improvement.
• Can obtain water quality data over time of flush.
• Can clean/scour the water main.
• Visual verification of water quality.
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Flushing – Unidirectional
Cons• Very time intensive/consuming.
• Usually involves large volumes of water, although tends to be less than conventional flushing.
Pros• Immediate water quality improvement.
• Scours/cleans biofilm and debris from mains.
• Controlled flushing, should not disturb adjacent lines.
• Can target specific flushing concerns.
• May reduce chlorine demand and DBP precursors in area.
• May use less water than conventional flushing.
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Flushing – Automatic
Cons• Typically, no water quality data is collected except for when
visited (monthly or less).
• Can be tampered with.
• Discharge issues (e.g., dechlorination and erosion).
• “Good” citizens (turning them off).
• If they fail, you don’t know until you visit the station.
Pros• Localized water quality improvement.
• Not labor intensive once installed.
• Water is typically metered.
• Flow is typically slow enough to avoid discolored water issues.
• Some installations can be hidden.
• Easy to control amount of water flushed.
• Reliable designs exist.
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Flushing – Blow-off
Cons• Typically no water quality data is collected except for when
visited (monthly or less).
• Can be tampered with.
• Discharge issues.
• “Good” citizens (turning them off).
• If they fail, you don’t know until you visit the station.
• Usually forgotten about.
Pros• Immediate water quality improvement.
• Constantly moving water.
• Flow is typically slow enough to avoid discolored water issues.
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Rerouting Water
Basis for Considering: Lower disinfectant residuals
High disinfection byproducts
Parallel lines and/or functional valves exist: to allow for changing the flow of water into/out of an area
to allow for a line to be taken out of service
single line capacity can handle required flow
Concerns/Implementation Considerations: May move problem from one area to another
Flushing may still be needed
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Rer
outin
g W
ater
Parallel Lines
Valve Changes
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Rerouting Water – Parallel Lines
Cons• One or more of the pipes is not in good condition.
• Required flow may be too much for one line to handle by itself.
• Must maintain adequate fire protection.
• Connecting the two lines could be difficult and/or expensive:• Required permits• Distance• Rock
Pros• Valve & reroute (assumes two different size parallel lines – i.e., 6” and 3”):
• majority of flow can be handled by larger line, reducing stress on smaller line.
• Rerouting flow through the larger line and into the smaller line helps keep water moving.
• Remove a line from service: reduce underground storage (water age).
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Rerouting Water – Valve Changes
Cons• Sufficient valves do not exist or locations of valves are unknown.
• Valves are old and may break when operated.
• No connection to other sections of the system.
• Line sizes are small and cannot handle the additional flow.
• If insufficient records are kept, problems could arise (i.e., hydraulic “bottleneck,” inadvertently opening the valve, etc.).
Pros• Sufficient control valves exist.
• Connections exist or are close enough to connect other areas of the system together.
• Lines are of sufficient size to handle the additional flow.
• Can reroute water through low demand areas, towards high demand area, to keep water moving.
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“Others”optimize booster chlorination, capital improvements
Not “primary strategies” because they are system- specific
(i.e., optimize booster chlorination) or not true optimization
strategies (i.e., cost $$).
Optimizing booster chlorination. Basis to consider:
System has booster chlorination and process monitoring/control capability.
Lower (or higher) disinfectant residuals in area of system influenced by
booster chlorine station.
Concerns/Implementation Considerations: May elevate DBP formation.
May still have high water age (i.e., require additional strategies discussed
previously).
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“Others”optimize booster chlorination, capital improvements
Capital improvements may include: Adding a mixer in a tank
DBP control in the distribution system
Adding booster chlorination
Others(?)
Should be considered advanced strategies once optimization (O&M) options are exhausted.
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Questions?