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

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.

Tank Management/ Operations 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

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

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 faster Cons 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

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).

Operational Data

Water Quality Data

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)

Flushing Unidirectional Automatic Blow-Off Conventional

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.

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.

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.

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.

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

Rerouting Water Parallel Lines Valve Changes

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).

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.

“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).

“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.

Questions?