Two natural gas leak explosions that leveled homes in Edina and St. Paul three years ago occurred when workers punctured gas lines either because of confusion or lack of information, the state Office of Pipeline Safety reported Monday.

No one died in the unrelated blasts, but the sewer contractor who nicked the St. Paul gas line suffered burns to his face, neck and hands.

In both cases, the state wound up slashing the initial $1 million fines it had levied against CenterPoint Energy and Northern States Power-Minnesota (NSP), a subsidiary of Xcel Energy Co.

State regulators said Monday that they recently closed their investigations of the blasts, which happened three weeks apart in February 2010.

The Edina explosion was blamed on confusion over two pipelines — one abandoned and the other active — that were stacked atop one another, regulators said.

The blast at 50th Street and Arden Avenue was attributed soon afterward to St. Paul-based TD&I Cable Maintenance, which hit a CenterPoint Energy line while laying phone line under the home of Matt and Jen Auguston and their two children.

Matthew Augustson walked through the wreckage after a natural-gas explosion destroyed his home in Edina in 2010. The family rebuilt at the same address.

Regulators said that TD&I had contacted state-required Gopher State One Call before digging, and that CenterPoint responded by flagging the location of an active underground gas line.

TD&I found what it thought was the active line, when in fact it was the inactive line sitting above the one holding gas. The crew resumed digging below the one line it was aware of and punctured the active line, prompting the leak and then the blast two hours later.

CenterPoint, which reached a financial settlement with the state that reduced the utility's fine to $50,000, insisted Monday that it had done nothing wrong and directed blame at the contractor.

The state said it reduced the fine after being satisfied with the company's changes in procedures, relevant equipment and how it responds to such emergencies.

The state levied the lower fine for the company's response to the leak in shutting off service to the area. One minor line was shut off immediately after the blast, a second more than three hours later and a third about six hours later. CenterPoint chose not to use its emergency valves to stem the flow, which would have left far more customers without service.

Utility spokeswoman Rebecca Virden said the "controlled outage" was preferred because the gas was "going harmlessly" in the air.

She also said TD&I should have realized that the line it came upon was inactive because it was made of steel. Knowing that the active line was made of plastic, the crew should have halted work and sought more information from CenterPoint. Tim Stanke, president of TD&I, declined to comment.

The blast under the 70-year-old home valued at more than $500,000 was heard and felt six blocks away, and insulation was found up to a mile away. The family has since rebuilt at the same address.

In the St. Paul explosion, a sewer contractor punctured a natural gas line that he didn't know had been inserted through a sewer pipe, a procedure called a cross bore. The line break caused gas to leak into a house on Villard Avenue in the Highland Park district, sparking an explosion.

State regulators fined NSP $1 million for failure to prevent the explosion, but later cut the fine to $20,000 after finding the company already analyzed accidents to reduce cross bores. The lower fine was for not giving the gas line enough clearance to ease maintenance and avoid damage.

The state required NSP to develop a plan with timelines to eliminate cross bores. Since the explosion, NSP has inspected more than 97,000 state sewer lines for cross bores.

More than half of those inspections were in St. Paul and South St. Paul, where the predominance of sloped lots increase the chances of a collision between gas and sewer lines.

NSP has fixed 92 so-called "conflicts" in St. Paul and four in South St. Paul since 2010. It plans to do another 30,000 inspections in St. Paul before wrapping up the project next year.

Lee Moey, the sewer contractor in the St. Paul explosion, had been trying to unclog a sewer pipe when he hit the gas line. He rushed to get the homeowner and her two dogs out of the house after he smelled gas.

paul.walsh@startribune.com • 612-673-4482 kevin.duchschere@startribune.com • 651-925-5035