Water Distribution System Maintenance Program

Water Distribution System Maintenance Program

Livermore’s water distribution system includes 147 miles of pipe; 2,758 valves; 1,578 hydrants, and 376 other appurtenances such as air release and blow-off valves. Routine distribution system maintenance practices occur on a continuous three-year cycle throughout the City for water quality protection, general maintenance, and emergency preparedness.

Routine distribution system maintenance includes inspection and testing of fire hydrants, location of all system valves, exercising the valves to ensure they are working properly, and any necessary repairs or replacements identified through this process. Distribution system maintenance also includes cleaning by sending water through the main pipelines and appurtenances to flush any accumulated sediment to preserve water quality.

Maintaining Water Quality

Livermore Municipal Water conducts weekly water quality tests at nine sites throughout the water distribution system to ensure the safety of the water being delivered to its customers. If test results show that chloramine residual levels are lower than required, cleaning may need to occur within the system.

Chloramine is a disinfectant used in water treatment. Maintaining safe chloramine residual levels in the water distribution system helps to protect the quality of the water as it moves through the pipelines to customers.  Maintaining safe chloramine residual levels is a requirement of the United States Environmental Protection Agency and the California State Water Resources Control Board Department of Drinking Water.

Factors that may lower the chloramine residual and cause water quality to deteriorate include:

  • Distance from the Water Treatment Plant;
  • Proximity to dead-end water mains where the water does not circulate as well as in looped water mains; and
  • Water usage and flow. 

System Cleaning (Flushing)

On occasion, the Livermore Municipal Water utility may need to clean sections of the water distribution system (pipes and pumps that deliver water to customers).  There are two important reasons cleaning is necessary - maintaining water quality and scheduled system maintenance.  Clean is achieved by system flushing, a standard industry practice used by water agencies.

Over time, small particles of rust and sediment accumulate inside water main pipes, which could harbor colonies of bacteria that may harm water quality. By pushing flushing water through at a high velocity from a specific point in the system to a discharge point, the water:

  • Scours the insides of the pipes to remove residue;
  • Eliminates "aged" water;
  • Increases chloramine residuals;
  • Removes sediment; and
  • Reduces taste and odor problems.

The location of cleaning to maintain water quality is limited to the area of the system where the decline in chloramine residual is occurring.  The amount of water used the in the cleaning varies as necessary to improve the chloramine residual.

Dead-End Flushing 

The routine maintenance technique that the City uses most often is "dead end flushing."  Dead end water mains experience the greatest effect of water age in the distribution system due to lower flow rates and high water age.  These factors are dependent on the length of the dead end and the number of services that draw water from it.  Dead end flushing targets the cleaning to dead end water mains to bring fresh water into the area and remove sediment buildup in the pipes, while minimizing the amount of water used for flushing.  Flushing is done until the water main runs clear.  The water used for dead end flushing is discharged into sanitary sewer pipes for return to the Livermore Water Reclamation Plant.  There, the flushing water is treated along with wastewater, and becomes available for use as recycled water for fire suppression and irrigation purposes.

Unidirectional Flushing 

Where cleaning of a larger area is required, the City uses a technique known as unidirectional flushing.  This method involves closing valves in a specific sequence to create water movement in one direction, while opening specific fire hydrants at the end of that sequence.  This creates higher flow velocities by isolating certain sections of water mains.  The higher the water velocity, the better the cleaning of the pipelines.

Because greater water volumes and velocities are used in unidirectional flushing, the flushing water cannot be discharged to the sanitary sewer system.  Instead, the flushing water is channeled into storm drains which lead to natural bodies of water.  The system flushing process requires the following steps:  1)  De-chlorination to remove an chloramine residual before the water is released; 2)  Use of Best Management Practices (BMPs) to prevent silt and debris from entering storm drains; and 3)  Management of flow to creeks and streams to minimize impact on the surrounding environment.  These steps protect wildlife and sensitive species.  In most areas, the water feeds existing streams and wetlands, benefitting the health and well-being of those bodies of water.

Pressure Changes and Cloudy/Discolored Water

During distribution system maintenance, water service should not be interrupted.  During the flushing process, customers may experience a temporary decrease in water pressure.  The pressure changes may cause air or fine sediment in service lines to be disturbed, resulting in water first run from the tap to have a cloudy or discolored appearance.  If this occurs, run the tap briefly until it clears.