For more than two decades, the City of Mankato, Minn., has prided itself on taking a proactive approach to maintaining and repairing its water distribution and fire protection system.
The commitment to providing residents with the highest-quality drinking water and fire protection includes a five-part system of fire hydrant maintenance, fire flow testing, water main valve testing, valve and line repairs and water loss surveys.
Like spokes in a wheel, each component serves its own critical function and also is essential to the overall health of the distribution system. Mankato, a growing community of 35,500 in south central Minnesota, has seen consistent urban development and redevelopment during the past decade. With a customer base of 10,000, the 200-mile distribution system needs constant care and monitoring.
Comprised of lines ranging from 4 to 36 inches, consisting of cast iron, ductile iron and PVC, the system is much like those of most smaller cities. The difference is that the terrain is hilly, rock strewn and prone to “hot soils.” These features, along with extreme freeze-thaw cycles, create stress on pipes, valves and hydrants. A component-based, scheduled approach helps the Department of Public Works and its Utilities Division manage the system effectively.
Fire protection
Mankato has about 1,900 hydrants. Twice per year, crews flush and test them, performing a detailed check by operating them, checking the caps, and pressure testing. If any problems are found, repairs are scheduled according to priority, based on severity. External obstructions such as debris or vegetation that could impede access or functioning are removed during testing.
Whenever a new business that needs a fire sprinkler system is to be built in the city, a crew performs a fire flow test on the distribution system to make sure water volume and pressure are adequate to protect the building. Crews also perform fire flow testing routinely at about 100 locations per year to make sure the fire protection system is in optimum working order.
“We perform fire flow testing in specified areas throughout the year, dividing the city into three sections with the goal of testing the entire system over a three-year cycle,” explains Anthony Talamantez, infra-structure superintendent. “We open up one hydrant and measure its flow using a peto gauge, then open another and measure its pressure.
“This tells us how much pressure we lose when there is a maximum amount of water coming from the system and how much fire protection we actually have at those hydrants,” he says. “It also tells us, in the event of a fire, what level of water could safely be pulled without collapsing pipes or creating other infrastructure issues.”
These proactive measures have earned the city an ISO 3 fire protection rating, one of the highest rankings among Minnesota cities. The high rating means potential savings on residential and commercial fire insurance premiums.
Testing the valves
Water main valve health is also essential to a healthy distribution system. All of Mankato’s more than 5,400 valves are tested every five years. The testing involves manual exercising using bell keys, or in the case of larger valves, an automatic Pow-R-Drive system from by E.H. Wachs Co.
In either case, crew members log numerous details about each valve, such as number of turns, ease of turning, and physical defects. All of this data is then input into the city’s asset management system from Infor Public Sector (formerly Hansen Information Technologies).
The Hansen system provides many benefits through its ability to track information about the system and the various tests. One case in point: Certain types of valves throughout the system indicated large water losses.
“One of the biggest things we found by looking at the report history was a high incidence of leaky valves that have regular bolts on them,” Talamantez says. “We were losing a lot of water with those types of valves. As a result of having information about the system, we now require everything to have stainless steel fittings. This was a huge find.”
The system also helps management prioritize and schedule repairs. Mankato has a diligent but small crew, and being able to set priorities helps them meet their goals. “Each year there are more things laid out for us to accomplish or keep track of and complete with the same number of people,” says Mary Fralish, deputy director of Public Works. “You need to prioritize, and having a system to analyze and track information and generate work orders has helped a lot.”
Main and valve repairs
Of course, not all repairs can be neatly scheduled. Sudden problems do occur, often through the freeze-thaw cycle. “Our record keeping helps us keep ahead of those areas that we’ve tracked as problematic and we’ll replace lines,” Talamantez says. “But the freeze-thaw cycle creates movement, and that’s when sudden cracks in the cast-iron pipe can occur.”
In those cases, the city uses stainless steel sleeves by the Ford Meter Box Co. Inc. that require minimal trenching to install. The sleeves are fitted with rubber gaskets and are placed on the cracked section of the pipe, much like bandages, to seal the gaps. For pipes that are split lengthwise and require a section to be removed and replaced, crews use PowerMax solid repair sleeves by PowerSeal Pipeline Products Corp.
The city completes the majority of repairs with in-house crews, but occasionally calls outside contractors to help on large-scale repairs or replacements. Mankato has used Ditch Witch directional boring technology from the Charles Machine Works Inc. for pipe replacement and rehabilitation in hard-to-reach areas or where excavation would be cost-prohibitive or logistically impossible. To date, the city has rehabilitated 12,000 feet of pipe with the technology.
Tracking water losses
Going beyond repairs, the city’s water-loss survey program is aimed at resource conservation and cost containment. It includes monthly monitoring of water use, sounding surveys and data logging surveys.
Every month, the city monitors the amount of water produced by its treatment plant and compares that with the amount actually billed to customers. Differences indicate the level of water that is not accounted for and the revenue the system is potentially losing.
To pinpoint potential water losses, the city uses 10 Permalog leak detectors by Fluid Conservation Systems. These devices are attached underground by a magnet to a water valve’s bell nut. For the survey process, the detectors are deployed in a specific area for about one week. They are set to “listen” and record data during the early morning hours (starting at about 1 a.m.) for 15- to 20-second intervals.
Each morning during the survey period, crews go to each of the detector positions and pick up all data recordings from the previous evening. The results are then compiled and analyzed to find suspected leaks.
“We perform the survey for a week at this early hour to eliminate any random water use that could be misinterpreted as a leak,” says Talamantez. “If we detect a leak sound consistently throughout the week-long test, we’ll deploy more sophisticated leak detection devices to pinpoint the nature, location and severity of the problem.”
Where a Permalog device detects a potential leak, a correlator/sub-surface leak detection system by Fuji Tecom Inc. is the next step. The correlator is attached to two points (hydrants or valves). The device takes a reading between those two points and gives the location of the leak.
Locations for water-loss surveys are focused in specific areas known to have problems or are situated in rocky terrain. “In rocky areas, when there is a leak, many times the water will not come up to the surface,” explains Fralish. “It will just remain underground and run through the rocks. So those areas are critical spots for detecting potential water loss.”
In addition to its own surveys, Mankato uses an independent contractor to perform loss surveys using advanced listening devices. The contractor checks throughout the city over a two-week period and records any potential problems or water-loss areas. All these efforts have reduced water loss by 15 percent.
Leading by example
The Department of Public Works’ proactive approach aligns well with the city’s motto: Leading the Way. It illustrates how individual, innovative practices can combine to create a leading-edge method for maintaining a water distribution system.
“Our leadership philosophy has accompanied every type of job in the city, and our water distribution maintenance program is just one example of how we are leading the way,” says Fralish. “By being proactive with our water-loss surveys and making sure that maintenance is done on a routine, scheduled manner so that nothing is missed, we can feel confident about our system and its ability to serve our community.”
