Investigations into a pair of natural gas explosions that destroyed two homes in 2010 have now been closed, according to the State of Minnesota's Office of Pipeline Safety.
The office, known as MNOPS, said Monday a misunderstanding about a pair of natural gas lines was to blame for one of the blasts that leveled a home in Edina, Minn., near 50th and France.
In that case, a telephone contractor was installing cable underground. A gas line had been marked in the area, but another, abandoned line was not, according to the executive summary of the state report on the incident. The cable crew located the abandoned line, assumed it was the marked gas line and avoided it. Crews continued to dig and struck the nearby active gas line, which then ruptured.
The state said CenterPoint Energy took nearly eight hours after the rupture to shut off the gas supply, noting that was more than six hours after one home blew up and another filled with gas on Feb. 23. The Office of Pipeline Safety called the shutdown process "lengthy" and blamed the spacing of emergency valves for the delay.
CenterPoint had opted not to close a valve near the explosion, saying it would have cut off gas to more than a quarter million customers in the middle of winter.
"It would have been a massive outage," said Becca Virden, a spokeswoman for CenterPoint. "Unfortunately, it was too cold to do something different at that time without that massive outage - and, of course, you need your natural gas to make sure your house pipes don't freeze."
The Office of Pipeline Safety said CenterPoint has agreed to purchase new equipment to respond better to leaks. The company is reviewing the adequacy of its emergency valve locations. Last year it installed 78 new valves and has drawn up new engineering standards for valves in new construction. Citing those measures, state officials reduced CenterPoint Energy's fine from $1 million to $50,000.
Virden said that the company still has differences of opinion with state officials about the incident. "We are going to set aside our differences," Virden said. "Of course, we share the same goal, and that is operating a safe and efficient pipleline system in Minnesota."
In a second home explosion, on Feb. 1, 2010, a sewer contractor ran an auger into a gas line that years before had been inadvertently run through a sewer pipe leading to a home at 2014 Villard Ave. in St. Paul. The resulting leak let gas rush back into the house, where it ignited and blew up. A resulting fire burned the home to the ground, although the sewer worker and the homeowner escaped.
Bill Kaphing, senior director of gas governance and compliance for Xcel Energy, said the utility has spent the last three years inspecting gas service through the region, including nearly 50,000 homes in St. Paul and South St. Paul. He said utility installations are the reason for the focus on those two cities.
"Elevation changes are the number one reason, where the sewers are at their shallowest, and our gas mains are at the same depth," Kaphing said.
He said that has led to nearly 100 "cross-bore" incidents, where crews using hydraulic rams to shove pipe through the ground have unwittingly run the lines through sewer pipe. A total of nearly 100,000 service points in Minnesota and North Dakota have been inspected for cross-bores, he said, although some were simply ruled out by confirming the sewer and gas service were not in danger of intersecting.
The state initially levied a $1 million fine against NSP -- the legal name of Xcel Energy's gas business. The fine has been reduced to $20,000 "after MNOPS officials deemed NSP did have procedures for analyzing accidents and failures so the company could minimize the recurrence of cross-bores."