Colorado Explosion in April Blamed on Leak Near Anadarko Well -- 2nd Update

An explosion that killed two people and severely injured another at a Colorado home two weeks ago was caused by natural gas leaking from an abandoned line that remained attached to a nearby well owned by Anadarko Petroleum Corp., authorities said Tuesday.

Theodore Poszywak, chief of the Frederick-Firestone Fire Protection District, said unrefined and odorless gas appears to have leaked from a more than 20-year-old vertical natural gas well operated by Anadarko, via an abandoned gas line that intersected a corner of the home's foundation. The gas went into the soil before migrating into the home through a French drain and sump pit, he said.

The well was drilled in 1993 by Gerrity Oil & Gas Corp. and later acquired by Anadarko, a Houston-based oil-and-gas producer, in 2014.

The single-family home, 178 feet from the well in the town of Firestone about 30 miles north of Denver, was built in 2015.

"It would appear an unusual and tragic set of circumstances occurred here, including circumstances around the proper identification of and proper maintenance of the related abandoned flow lines," Mr. Poszywak said.

The April 17 explosion killed homeowner Mark Martinez and Joey Irwin, Mr. Martinez's brother-in-law. Mr. Martinez's wife, Erin, was also seriously injured.

Amy Follweiler, Mark Martinez's sister, said Tuesday evening that her family was "in shock still" after reading the latest updates on the explosion.

"We appreciate all the prayers for Erin and the kids," she said. "My brother was a great guy."

Following the blast, Anadarko voluntarily shuttered more than 3,000 wells of the same vintage that it operates across northeast Colorado.

Mr. Poszywak said the investigation is now being turned over to the Firestone Police Department, which will conduct a death investigation. Those findings will be turned over the Weld County district attorney's office.

Following the news, Colorado Gov. John Hickenlooper on Tuesday called for a statewide review of existing oil and gas operations. The Colorado Oil and Gas Conservation Commission notified producers that they would be required to reinspect any existing flow lines and pipelines within 1,000 feet of a building by May 30.

"Our thoughts and prayers are with the Martinez and Irwin families at this difficult time," said Mr. Hickenlooper, a Democrat who formerly worked in the oil-and-gas industry.

Anadarko, which also reported a first-quarter net loss of $318 million Tuesday afternoon, saw its shares fall more than 3% in after-hours trading.

Anadarko's chief executive, Al Walker, offered his company's thoughts and prayers to the Martinez and Irwin families Tuesday and said he hopes the shuttering of Anadarko's vertical wells in the area provides "some additional reassurance to the community in the wake of this tragedy."

"The safety of our employees and the people who live and work in the communities in which we operate is our number one priority," he said.

Anadarko has said it will continue to work with authorities and the Colorado Oil and Gas Conservation Commission.

Write to Erin Ailworth at Erin.Ailworth@wsj.com

Theodore Poszywak, chief of the Frederick-Firestone Fire Protection District, said unrefined and odorless gas appears to have leaked from an abandoned gas line that bisected a corner of the home's foundation, and was attached to a more than 20-year-old vertical natural gas well operated by Anadarko. The line had been cut at some point and the gas went into the soil before migrating into the home through a French drain and sump pit, he said.