By Jeff Jensen
The Cape Breton Regional Municipal (CBRM) Water Utility in Nova Scotia supplies potable water to a population of 81,000, which is distributed over 770 km of pipeline. To do this, they operate, maintain and manage five water treatment plants, six pumping stations, 11 water storage tanks, eight supply sources, 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 biofilms. CBRM, like many municipalities of its size, uses a variety of conventional flushing methods for discharging stagnant water, including service “bleeder” lines (operating 365 days a year) and periodic manual hydrant flushing. This results in millions of litres of treated water going back into the environment.
Non-revenue water represents significant costs, when factoring in the expense of treating and pumping water throughout the distribution system. Real costs of non-revenue water are difficult to determine per flush event, as operational costs and asset depreciation are also difficult to ascertain. Quantifying the volume of water lost through conventional flushing methods versus an automated flushing device is the goal of this article.
When Greg Campbell, CBRM Water Utility’s Water Systems Engineer, viewed a presentation on automated programmable flushing in the spring of 2017, it became obvious to him that there was a relatively easy and inexpensive fix to significantly reduce the non-revenue water problem occurring at the MacLeod Street flush point in Sydney. The presentation showcased the neighboring town of New Glasgow’s “auto flushers” that save an average of 37 million litres per auto flusher annually. The town of New Glasgow had installed eight Hydro-Guard® HG-8 automated flushing devices.
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 an HG-8 to the MacLeod Street service bleeder line.
It was quickly determined that this would be an easy installation as 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 20 mm polyethylene tubing to the surface. The Hydro-Guard 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. By adding a new Mueller Oriseal® curb stop on the inlet connection of the automated flushing device and an adjustable arch base service box, the flushing unit was quickly connected. All that was left to do was return the gravel and softly compact the ground over the installation area.
During excavation, Louie Margettie, CBRM Water Utility Supervisor, found 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,” said Margettie.
It is important to ensure that flushing units are suitable for 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, internal components of the HG-8 are mounted on a movable platform that is connected to the inlet and outlet piping. 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 HG-8 installation is only 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 65 cm-diameter frame and cover. The HG-8 eliminates flushing noise and vibration, which means the public isn’t aware or concerned with flushing events, unlike other flushing approaches that visibly discharge water.
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. This unit alone is expected to save nearly 23 million litres of water annually.
There are many options for automated flushing, and most can be easily installed using existing water infrastructure. For example, discharge outlet lines can ideally 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 very 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.
If one 20 mm service line at 115 psi can displace over 23 million litres of water annually into the environment, imagine how many of these service lines and other bleeder or flush lines behave in a similar manner in other municipalities. These numbers become staggering when you look at non-revenue water as a global issue. With innovation on the part of CBRM and collaboration with local suppliers, a smart solution to conventional flushing became an instant success, saving the utility $2,284 annually per installation.
Jeff B. Jensen is with Mueller Canada. This article appears in ES&E Magazine’s June 2018 issue.