By Melanie Petrucci, Senior Community Reporter
Shrewsbury – The Board of Selectmen held a joint meeting at its Oct. 8 meeting with representatives of Tate & Howard, a Marlborough-based water consulting firm that has been working on Shrewsbury’s water quality for 20 years.
Jeff Howland, DPW director, introduced Paul Howard, co-founder, and associate Justine Carroll, who provided an overview of initiatives relevant to “uni-directional” flushing and the hexavalent chromium pilot program that will begin again next spring.
Regarding the town’s water treatment plant, Howard said that were treating manganese to below detectable levels and the plant is running very well and exceeds expectations.
Carroll explained that uni-directional flushing is a system of flushing hydrants one-way directionally, and is considered an industry best practice.
She added that the Mass. Department of Environmental Protection recommends the practice be done annually. It removes as much sediment as possible and when done regularly it allows more water to flow once deposits are removed.
“To accomplish this, you have to go out to the system and close valves so that you start from the water treatment plant or the water storage tank and basically continue to use clean water to flush the mains that you haven’t reached yet. It’s a systematic approach,” Carroll explained.
Conventional flushing is inadequate as it just moves the deposits somewhere else in the system but with unidirectional flushing the water moves with higher velocity to push sediment completely through.
Valves are opened and closed in sequences throughout the system to prevent deposits to travel back to cleaned pipes. Less water is ultimately used.
Tata & Howard has mapped all hydrants and valves as per the town’s plan. They have digitized valve locations.
In executing the first flushing it will be important to avoid isolating customers from their water supply. Also, the will need to maintain velocities and water pressures by not closing too many valves at once.
Elements of implementation included notifying customers of potential water quality concerns and notifying the fire department that low pressures may cause fire suppression system alarms.
“The first time you implement this the flushing times are likely going to be longer to clean the pipes out,” Carroll said. “The key piece of information that is going to drastically impact this time is the condition of the valves. Shrewsbury historically hasn’t had a valve exercising program so many of the valves haven’t been operated unless there has been a main break.”
The plan is to get started with a contractor who is qualified to do the flushing and also do any repair work that might be needed
Selectman Jim Kane inquire what the suspected the failure rate would be of the valves since they have not been exercised regularly.
Howland replied that he suspected 20 percent would need to be replaced.