No-Discharge Water Main Flushing

Posted on August 23, 2018

Residents, visitors, and businesses in Sonoma count on the City to deliver high quality, dependable water for a variety of community needs including consumption, irrigation, and fire protection. The water entering the distribution system is of very high quality. Water quality can deteriorate in water distribution mains, so flushing is conducted to remove impurities or sediment that may be present in the pipe. Regular flushing of the City’s water mains helps the City deliver safe and pleasant water for the City’s water customers to drink.

Flushing of the City’s water distribution system has typically been done by systematically opening fire hydrants and blowoff valves and dechlorinating the resultant discharges. This method of flushing wastes water, while the City encourages our customers to conserve water. It also discharges large volumes of water to storm drains that flow to creeks, which can negatively impact riparian ecosystems. In 2015, during the severe drought, the City contracted with ValveTek Utility Services to flush a portion of the City’s water mains with no discharge.

A no-discharge water main flushing system is to be used to flush the City’s water mains in 2018. A patented process (US Patent # 6,627,089 B1) by ValveTek Utility Services, Inc. utilizes a truck and trailer with an onboard filtering system to flush segments of the water distribution system without discharging water. Water flows from one fire hydrant, through the filtering system, and back into the water distribution system through another fire hydrant. This creates a temporary above ground loop in the water distribution system. A large pump circulates water through the loop at flushing velocity, typically 3-5 feet per second. The filters remove sediments and biofilms that may be present in the water system. When the section of water main designated for flushing has been filtered and tests clean, the system is shut down, hydrants are closed, and the truck and trailer move to the next location for flushing.

At least one-fifth (11 miles) of the City’s total length of water main (55 miles) is expected to be flushed using the no-discharge water main flushing system this year. If continued, the entire length of the City’s water mains will be flushed every 5 years.

Specific water mains to be flushed under the 2018-19 contract with ValveTek Utility Services are being determined by the City’s Water Operations Supervisor.   The highest priority areas are those in the southern areas of Sonoma, furthest from where water enters the distribution system at the north end of town.


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