SPRINGDALE – Supply chain bottlenecks have struck again.
Springdale’s water utilities require local contractors to lay ductile iron pipe to supply water and sewage to homes and buildings. But right now, ductile iron pipes are hard to come by. The lead time is nearly a year, say Northwest Arkansas utility directors.
The Springdale Water and Sewer Commission, which oversees the utility, has given the utility workers permission to authorize the use of PVC pipe – or polyvinyl chloride, a plastic product. The commission also said staff can change the requirements for iron pipes on a case-by-case basis without the commission’s approval each time.
Springdale Water Utilities executive director Heath Ward said small projects and small pipe diameters could justify the replacement.
Experts said they don’t see much of a difference in the overall quality of the two types of pipe, and they don’t expect any further leaks, ruptures or other problems.
Customers are unlikely to notice any difference in their service no matter what happens underground, said Wen Zhang, associate professor of civil engineering at the University of Arkansas, Fayetteville.
Ductile iron — a type of cast iron — is known for its resistance to fatigue and wear, according to the Ductile Iron Pipe Research Association website. It doesn’t break easily on impact, the website says.
Carbon is added to the cast iron during the melting process. Spherical graphite structures in the metal make the iron ductile.
PVC offers affordability, faster and more flexible installation, and durability, according to the Plastic Pipe and Fittings Association website.
PVC in the United States is made from natural gas and salt, according to the website.
“I still prefer ductile iron, but we’ll accept something else as long as we can sleep at night,” Ward said. “I’m not worried about whether we have one pipe or 50 pipes made of PVC.”
About 60% of the utility’s system uses PVC pipe, said Rick Pulvirenti, the utility’s chief operating officer and engineer.
But when the supply chain returns to normal, the utility will return to its iron pipes, Ward said.
DUCTILE VS. PVC
PVC pipe costs less than ductile iron pipe under normal market conditions, Ward said. However, PVC requires a special bedding surrounding the pipe. Properly installed, the bedding will even out the pressure points of the water being pumped through the pipe – especially if the pipe will be there for a long time.
Ductile iron is stronger than PVC, Pulvirenti said. But iron is subject to erosion, which the utility found in pipes buried around the utility’s water tank farm in the eastern part of town, Ward said.
The utility has taken steps to curb erosion by placing sacrificial anodes on the pipe to attract the electrical charges that are eroding the metal, he added.
PVC currently costs about $95 for a 100-foot length of 8-inch diameter pipe, Pulvirenti said. Ductile iron cost about the same, he said.
Engineers and contractors must consider the lifetime costs of the two pipe materials. That includes maintenance, repair and replacement, Pulvirenti said.
Zhang said PVC pipe is a very good choice for pipelines. It is not subject to corrosion. She said that today’s PVC pipe should last about 70 years. The typical lifespan for any type of pipe is 50 to 100 years, she said.
Ward said he will always use PVC for deep sewers – with pipes buried at a depth of 15 feet. Digging that deep for repairs risks collapsing the walls.
The longstanding standard for the city’s water and sewer lines is ductile iron lined with epoxy, Pulvirenti said. But the liner can spall away, leaving exposed metal subject to erosion, he said.
Utility crews replaced the liner with a cast-in-place, quick-drying fiberglass pipe, Pulvirenti said.
This liner is on the inside of sewer pipes, but outside of water pipes, so epoxy doesn’t get into drinking water, Ward noted.
TO THE CODE
Many materials are available for casting pipe – ductile iron, cast iron, copper, steel and various plastic products.
Ben Peters, director of the city’s engineering department, said the city’s stormwater drainage system runs through concrete pipes.
Clay is a good material and has been used throughout history, Ward said, citing aqueducts of ancient Rome. The 19 BC The Acqua Vergine, built in the 4th century BC, has been restored several times and supplies water to the Trevi Fountain in the heart of the modern city.
But clay pipes have been known to leak at joints, Ward said.
City ordinance allows many types of pipe for individual construction projects, explained Mike Chamlee, director of the Springdale Building Department. Most of the pipes that run from the city’s main lines to individual buildings are already made of PVC, he said.
Nodular iron is used for main lines that can withstand a lot of pressure, he explained.
Numerous homeowners have found that the rocky ground of Northwest Arkansas will settle against a PVC pipe when a sharp edge of the rock punches a hole in the pipe.
Ward was one of those homeowners, and it cost nearly $4,000 to repair, he said.
The problem could be alleviated by using thicker PVC, burying the pipe to the correct depth and installing proper bedding, he said.
A 10-month wait for ductile iron pipe can significantly delay a project. PVC suppliers are telling local officials the lead time for their products is a few weeks, Ward said.
Ward said he understands the dilemma faced by engineers and contractors trying to complete much-needed projects — particularly single and multi-family projects.
“They’re under pressure in the market, but we don’t want anything inferior,” he said.
The utility’s current project on Emma Avenue will use PVC pipe, allowing the project to complete more quickly and allowing the city of Emma to reopen to traffic, Ward said.
Kevan Inboden, Beaver Water District’s chief operating officer, said the new western water penstock will be laid with steel pipe. Officials don’t see a significant supply problem, he said.
“But we are proceeding with our normal start date as supply issues will not delay the project,” he said.
Inboden said the water supply infrastructure should be completed by the end of 2025. When fully expanded, it will be able to pump 70 million gallons of water per day.
Local towns will be connected to the pumping station to deliver water to the western reaches of Washington and Benton counties.