The recent gushing on the edge of South Tempe at US 60 and McClintock Drive raised the ominous specter of a similar water main break flooding the nearby residential area and damaging homes.
If it happened there, what are the chances of it happening a few miles to the south?
Thin, according to Tempe officials.
The city’s water lines generally follow major thoroughfares and don’t go into residential neighborhoods, according to Mark Weber, acting deputy director of Tempe Municipal Utilities.
Water distribution lines in subdivisions are usually 6 to 8 inch distribution lines. The water main that broke May 7 and caused traffic nightmares as US 60 was closed for repairs was a 24-inch water main, which continues south on McClintock to to Guadalupe Road, where it connects to a wider line running out of Tempe’s South Water Factory south of Guadalupe to Price.
This does not mean that there might not be a water leak in a neighborhood.
There have been 1,100 in the system since 1998, when Tempe started tracking breaks.
“So we have a number of breaks every year,” Weber said. “We’ve had a few sporadic breaks in South Tempe, but the majority of the breaks are north of Baseline and mostly north of 60, and the breaks we’ve had are in our smaller lines.
“It’s pretty normal for utilities across the country to have breaks, depending on the age of the pipe, system materials and date of installation.”
The 24-inch transmission line break behind a retaining wall near the top of the westbound off-ramp from McClintock Drive to US 60 was Tempe’s first on a major pipeline, city officials said. They still don’t know what caused the cast iron pipe to fail, nor do they have an estimate of how much it will cost to repair.
South Tempe, comprising newer neighborhoods, has mostly ductile iron distribution pipe, the newer type in the system. The oldest pipes in the Tempe system are made of cast iron. Then came the asbestos-cement pipes.
Its entire water system is made up of about 860 miles of pipes, of which about 50 miles are large transmission lines like the one that recently failed.
SOUTH TEMPE WATER PIPE AGE
Monitoring every square inch of the system is daunting, but the city, recognizing that records of the oldest pipes are sketchy, implemented an identify and replace program eight years ago. So far, 38 miles of pipelines have been replaced.
“We have a replacement program on our distribution system, which is different from the pipeline that broke under the freeway,” Weber said, referring to smaller delivery pipes in neighborhoods. “Our replacement program is focused on these pipelines because that’s where all the breaks that we consider to be natural breaks, that is, due to age and material, have occurred.”
So it’s unlikely that anyone would be bodysurfing on a street in, say, Warner Ranch.
The majority of the 1,100 ruptures were in cast iron pipes, Tempe’s oldest which make up about 21% of its system but account for about 75% of ruptures, Weber said.
“We mainly look at the history of breakups, where they occur,” Weber said. “As the city develops, the developers build the water pipes and then hand them over to the city. Typically, if part of a neighborhood’s system fails, we consider that entire neighborhood a replacement project because it was built at the same time. »
The main transmission lines are another story.
“We’re in the planning stages of an assessment where we’re actually putting instruments in the lines so we can determine the structural condition of transmission lines like the one under 60 that broke,” Weber said. “To do that we need to build access into the pipes, so it’s going to take some time to get into all the pipes to structurally assess them all.”
While the line at McClintock and US 60 was torn apart, it received the new technology, according to Weber. If he failed there, the city wants to know if he’s vulnerable elsewhere.
“We just sent the first instrument (May 17) so we can see the condition of this one,” he said. “And there are additional instruments that come to look at another part of the pipe.”
The newly installed equipment includes a camera as well as electromagnetic instrumentation that examines the steel in the 50-year-old pipe, which Weber says typically has a life expectancy of around 75 years.
“Our main transmission assessment includes a detailed inventory of the exact types of hoses we have,” Weber said. “We didn’t have the best records over the years, so we don’t know precisely the exact details of each pipe. We will assess each of them individually.
“This transmission line is the first to break. We don’t know exactly what happened yet and we’re not going to speculate.
Tempe worked with the Arizona Department of Transportation to repair the flood-damaged highway. Eastbound lanes reopened on May 15. The more severely damaged westbound lanes reopened on May 23. ADOT earlier said the McClintock Drive overpass was structurally sound.
According to Chris Kabala, Tempe’s senior civil engineer, the concrete was poured by contractors hired by Tempe to rebuild the most badly damaged westbound lanes. Approximately 34,000 square feet of flood-damaged pavement has been removed.
Drivers had to make significant detours for more than two weeks while westbound lanes were closed from McClintock Drive to Loop 101.
“We clearly know it’s a really big challenge if you’re commuting,” Tempe Mayor Corey Woods said. “We know that’s absolutely a downside. But at the end of the day, I think people understood very well the fact that, unfortunately, sometimes things like this happen. »
Contractors hired by Tempe worked with ADOT personnel, examining areas under the freeway pavement to determine if the ground had shifted due to water pressure released from the broken water main. They wanted to provide ground stability and ensure the structural integrity of the McClintock Drive overpass.
ADOT and Tempe are reusing old concrete and asphalt pavement materials that were ripped out to make repairs as fill material in ADOT’s Interstate 10 Broadway Curve Improvement Project, which includes widening the freeway from Ray Road to the Interstate 17 split near downtown Phoenix and adding pedestrian bridges.
“Sustainability is very important to the city of Tempe,” Kabala said. “We’re glad this material is being used here and not being shipped off to a landfill somewhere.”