City’s newer water mains suffer from ‘premature’ breaks
In Prescott’s lengthy history, the underground pipes that carry the community’s water have been known to last 75 years or longer.
“The pipes in the downtown area are pushing 100 years now,” Prescott Public Works Director Craig Dotseth said, adding that water mains ideally should have a lifespan of at least 50 to 70 years.
While that standard is applicable to the city’s historic water mains, it is not holding true for many of the mains that were installed later, starting in about the 1980s.
In recent years, the city has been dealing with a series of “premature” water-main failures in its newer subdivisions, Dotseth said.
Among them: the Marvin Garden Lane area of the 1980s-era Cliff Rose subdivision, where eight waterline breaks have occurred over the past decade or so.
Breaks have also occurred in other subdivisions from that timeframe, including The Ranch, the Country Park area, and the Eagle Ridge/Cedarwood area.
For the most part, those premature breaks have happened in PVC (polyvinyl chloride) pipes that were put down directly on rock.
Current standards call for the pipes to be surrounded by a 6-to-12-inch layer of bedding that consists of a mixture of small rocks, gravel and sand, Dotseth said.
The bedding serves as a buffer between the pipe and the sharp rocks that are common in Prescott.
Since new city engineering standards went into effect in about 2016-17, Dotseth said city inspectors ensure that the proper bedding is applied.
Still, the city must now deal with the water mains that were the product of less stringent standards and/or less city inspection.
Just in the past year, city crews have responded to four water main breaks on Marvin Gardens (as well as several more in previous years), including the most recent break that happened this past weekend, April 6-7.
Those successive breaks have been enough to convince Public Works to launch a major water main replacement project on Marvin Gardens, Dotseth said Monday, April 8.
“We have it on our radar,” Dotseth said of the Marvin Gardens waterline. He plans to propose that project design begin soon, and that the replacement be done as an “emergency project” within this calendar year.
Still to be determined is how extensive the replacement will need to be and its estimated cost. Dotseth said the project would be considered “emergency” because it is not included in the city’s budget. Reserve funding is available cover such projects, he added.
Of the Marvin Gardens pipeline, which is only about 30 years old, and other premature pipe replacements in the city, Dotseth said, “It’s a shame we have to do it with pipe that hasn’t even met one-half its lifetime.”
Also up for possible discussion this year is the city’s General Engineering Standards document, which still allows developers to use PVC for water mains.
Dotseth said the city uses exclusively ductile iron pipes for its own public water main projects, and a number of other Arizona communities, such as Flagstaff and Scottsdale, require ductile iron pipes in all developments.
The General Engineering Standards document is up for review this year, and Dotseth said requiring ductile iron water mains “has been discussed” in the past.