Canadian community saves non-revenue water with automatic flushing unit
The Cape Breton Regional Municipal (CBRM) Water Utility in Nova Scotia supplies potable water to a population of 81,000 over 478 miles of pipeline. To do this, the utility operates, maintains and manages five water treatment plants, six pumping stations, 11 water storage tanks, eight sources of supply, 2,900 fire hydrants, 28,700 water meters and thousands of valves.
All municipal water distribution systems require flushing to maintain chlorine residual levels and prevent the buildup of biofilm. CBRM, like many municipalities of its size, use a variety of conventional flushing methods for discharging stagnant water, including service “bleeder” lines (operating year-round) and periodic manual hydrant flushing. This results in more than tens of millions of gallons of treated water going back into the environment.
The cost of non-revenue water (NRW) represents a significant cost when considering the expense of treating and pumping water throughout the distribution system. Real costs of NRW are difficult to determine per flush event, as operational costs and asset depreciation also are difficult to ascertain. Quantifying the volume of water lost through conventional flushing methods versus an automated flushing device was the goal of this project.
When Greg Campbell, water systems engineer for CBRM Water Utility, viewed a presentation on automated programmable flushing at the Municipal Public Works Assn. of Nova Scotia in the spring of 2017, he recognized there was a relatively easy and inexpensive fix to reduce the NRW problem occurring at the MacLeod Street flush point in Sydney. The presentation showcased the neighboring town of New Glasgow’s automatoic flushers that save an average of 8 million gal per flusher annually. The town of New Glasgow installed eight automated flushing devices within one year.
Mueller Canada consulted with the CBRM Water Utility in the months following the presentation and went to the site to better understand the logistics of adding a HydroGuard HG-8 system to the MacLeod Street service bleeder line. The existing service bleeder line used for conventional flushing had an old Mueller inverted key curb stop, which remained fully open, controlling the water flushed through a 3/4-in. polyethylene tubing to the atmosphere. The HG-8 was attached to the existing curb stop as a reliable connection for the flusher’s outlet line. Though a curb stop was not required for the automated flushing device’s outlet connection, the municipality did not want to jeopardize the service bleeder line’s integrity, as it had been dependable for years of daily use at a relatively high pressure.
The bleeder line essentially was completing a continual flush year-round, like leaving a hose running steady, and this project aimed to stop this continual loss of water and only flush when necessary.
A curb stop on the inlet connection of the automated flushing device and an adjustable arch base service box were installed to connect to the flushing unit, and gravel was returned and compacted over over the installation area.
Louie Margettie, CBRM water utility supervisor, left the site one hour after excavation revealed that the old Mueller inverted key curb stop and the relative service bleeder line were still in good working condition and could be used to connect the HG-8 automated flushing device. “At this point, it became clear that this was going to be an easy installation by using the existing curb stop and service bleeder line,” Margettie said.
It is important to ensure that flushing units are suitable to the environment in which they are operating. In colder climates, like Cape Breton, where winter temperatures can be consistently below freezing, it is necessary to place mechanical components in the ground below frost depths. This can add a degree of difficulty when it comes to accessibility. To overcome this challenge, the internal components of the flusher are mounted on a movable platform that is connected to the inlet and outlet pipe. This arrangement allows the platform to be easily raised to the surface by one person and then lowered back for normal operation. At the surface, the installation only is evidenced by its composite lid at ground level. If the municipality feels it is necessary, extra security from public tampering may be added by using a 30-in.-diameter frame and cover. The flusher eliminates flushing noise and vibration, which means the public is not aware or concerned with flushing events.
The water utility currently has the unit set to flush twice daily, instead of 24 hours per day, and is maintaining acceptable chlorine residuals. Flushing is scheduled when demand is low, which results in less disruption to water customers and still provides consistent, safe, clean drinking water. Automated flushing is less expensive, wastes less water and is safer and less visible to the public. This unit alone is expected to save nearly 5 million gal of water annually.
There are many options for automated flushing, and most can be installed using existing water infrastructure. For example, discharge outlet lines can be plumbed to storm sewer manholes or swales. Many automated flushing units also have the capability to add accessories for real-time analysis using two-way communication with existing SCADA systems. These options can be useful in times of unusual weather events like flooding or large snow accumulations. CBRM installed a Neptune positive displacement ND customer meter to the unit on MacLeod Street and can accurately measure flow at the flush point.
Cellular and SCADA communication options are available for automated flushing systems to provide operators real time information on water quality. Heavy rainfall can influence the turbidity or pH of the water, for instance, or warm weather can increase the rate of biofilm growth. Major snow events in Canada can make programming or re-programming less than convenient, and smart communication devices can notify operators when flush events happen, keeping the drinking water safe.
One ¾-in. service line at 115 psi can displace more than 5 million gal of water annually into the environment. These numbers become staggering when considering the NRW effect. CBRM’s solution and collaboration with local suppliers was successful, and saved the utility $2,284 annually. CBRM compared its water savings value to real water cost versus billed rate. Using this approach, return on investment of the flushing equipment will be realized in two years. However, in areas where water is scarce, any water saved can have the retail rate applied to calculate cost savings. The water recovered will generate more cost savings when it can be sold to paying customers.
This approach in Cape Breton saved thousands of dollars in excavation costs, prompting CBRM to address other service bleeder lines in its distribution systems. Not only is the municipality saving 5.7 million gal of drinking water per installation annually, it is practicing responsible environmental stewardship.
“As we continue to recover costs on non-revenue water at strategic flush points, we now have more resources to put forth in maintaining and repairing our aging distribution network,” said Louie Margettie.