On occasion, the Livermore Municipal Water utility may need to clean sections of the water distribution system (the pipes and pumps that deliver water to customers). There are two important reasons cleaning is necessary – maintaining water quality and scheduled system maintenance. Cleaning is achieved by system flushing, a standard industry practice used by water agencies.
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 Department of Public Health.
Factors that may lower the chloramine residual and cause water quality to deteriorate include:
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 in the cleaning varies as necessary to improve the chloramine residual.
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.
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:
During distribution system maintenance, water service should not be interrupted although customers may temporarily experience slight cloudiness or discoloration of the water when air is entrained or sediment in the pipes and appurtenances is stirred up; this is normal and the water is safe to use. Cloudiness or discoloration is not likely to occur when the system is flushed for water quality reasons. Should this occur, run water taps briefly until the water clears.
During planned distribution system maintenance, the City uses an industry standard 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 scouring of the pipelines; less water is also used in unidirectional flushing than with conventional flushing methods. When flushing occurs to improve water quality, unidirectional flushing may or may not be used.
Maintaining water quality is the top priority for Livermore Municipal Water. While flushing may seem wasteful, it is only used when absolutely necessary to protect water quality. The average amount of water flushed by the Livermore Municipal Water each year is only about 0.2% (4.9 million gallons) of the total amount of water used each year by homes and businesses.
Livermore Municipal Water minimizes the amount of water flushed by:
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.
Discharged flushing water is generally channeled into storm drains, which lead to natural bodies of water. For this reason, discharged water is dechlorinated to protect wildlife and sensitive species. In most areas, this water feeds existing streams and wetlands, benefitting the health and well-being of those bodies of water.
The system flushing process is regulated by the California Regional Water Quality Control Board, which requires the following steps: 1) De-chlorination to remove chlorine residual before the water is released; 2) Use of Best Management Practices (BMPs) to prevent silt and debris from entering storm drains; and 3) Manage flow to creeks and streams to minimize impact on the surrounding environment.
Recapturing water discharged through flushing is difficult and not cost-effective. Effectively cleaning the pipes by flushing requires the water to run at high flow rates, which prevents capture. Using water trucks to collect and transport the water is neither cost effective, nor mechanically possible considering the necessary flow velocity and duration to adequately flush the system.