Intermountain Gas is asking the state for permission to speed the replacement of a kind of aging plastic natural-gas pipe that has caused fires and explosions in some states.
The Boise-based utility is seeking regulatory approval for a maintenance program to accelerate replacement of aging infrastructure, including 600 miles of the pipe, which can become brittle and crack, causing leaks.
The pipe, a DuPont product known as Aldyl-A, has been responsible for a handful of fires and explosions across the country, though none in Idaho.
Intermountain Gas says it is replacing four to five miles a year of Aldyl-A manufactured before 1984. At that rate, it would take 120 years to complete the replacement. The company wants to finish the job in 20 years.
The work is estimated to cost $158 million at today's prices. But company spokeswoman Cheryl Imlach said the impact on customers' bills would be "negligible." The utility serves 355,000 Idahocustomers in 26 counties,
"This particular pipe was identified by the manufacturer and the industry as pipe that could pose potential problems, " Imlach said.
The pipe, she said is located across the company's service area in Southern Idaho. The 600 miles of Aldyl-A represents less than 5 percent of Intermountain Gas' 12,700 miles of pipeline.
About 45 percent of the Aldyl-A pipe is within the company's Capital District, which includes Boise, Garden City, Star and Kuna. Half is within an area from Mountain Home to Payette, which represents 82 percent of the company's customers.
"It's reasonable to say it's in every town in our service territory," Imlach said. "Because Boise is our largest service territory and has the most customers, percentage-wise there's probably more of it in Boise than other areas."
If the application is approved by theIdaho Public Utilities Commission, Intermountain Gas would file an annual proposed recovery amount to the PUC in May, with any approved adjustment to rates to go into effect each Oct. 1.
Concerns about Aldyl-A pipe have been raised for nearly four decades.
DuPont issued a letter to its customers in 1982 warning of the pipe developing cracks. After a series of pipe failures caused by cracking, the National Transportation Safety Board in 1998 conducted an investigation and concluded that many of the plastic pipelines manufactured from the 1960s to the early 1980s might be susceptible to cracking.
Two people were injured during a December 2008 natural gas fire and explosion caused by the plastic pipe that damaged a garage in Odessa, Washington, southwest of Spokane. State regulators fined Avista, which provides natural gas service in Washington, North Idaho and Southern Oregon, $200,000.
In 2005, a Spokane explosion triggered by a leaking natural gas line engulfed a man trying to light incense in flames. Avista later paid the man $500,000.
In 2011, an explosion and fire raged through a home in Cupertino, California. It was caused by a crack in a Pacific Gas & Electric gas line made from Aldyl-A. The pipe was also blamed for a 2003 explosion that killed a Missouri fairgrounds worker.
In 2000, Tucson Gas & Electric in Arizona reached a $25 million settlement from problems stemming from its pipeline that used Aldyl-A.
Avista, headquartered in Spokane, Washington, serves about 80,000 customers in six North Idaho counties. It began replacing Aldyl-A pipe earlier this decade and has replaced 32 miles in Idaho and has 109 miles remaining, said Michael Whitby, an Avista project manager.
The 141 miles of Aldyl-A pipe in Idaho represented 18 percent of the company's 737 miles. Avista began replacing its pipe in 2014 and plans to have the project completed by 2034.
Avista said it's paying for its pipe replacement through its regular rate structure.
Both Intermountain Gas and Avista say most breaches in their lines occur when someone digs on a property without checking for the presence of underground lines.
"That's why it's always so important to call 811 before you do any digging projects," Imlach said.
811 is a free service that identifies the location of natural gas lines and other underground utilities before someone digs.