ANCHORAGE, Alaska (AP) — Members of a U.S. House committee are seeking answers about a natural gas release at a ConocoPhillips Alaska drill site on Alaska’s North Slope.

The company earlier this month reported it had identified and controlled the source of the gas release first detected on March 4.

Three Democrats on the U.S. House Natural Resources Committee sent a letter Tuesday to ConocoPhillips Chairman and CEO Ryan Lance seeking information about the incident, the Anchorage Daily News reported.

The letter, signed by Chair Raul Grijalva and Reps. Katie Porter and Alan Lowenthal, notes the committee has jurisdiction over oil and gas resources on public lands. It seeks responses by May 13.

“The ongoing leak and ConocoPhillips’ response raises a number of troubling questions, including how your company would respond to similar leaks at your proposed Willow project inside the National Petroleum Reserve-Alaska,” the letter states.

ConocoPhillips is pursuing the Willow oil project in the northeast portion of the National Petroleum Reserve-Alaska, but it has faced legal challenges from environmental groups. Rebecca Boys, a ConocoPhillips spokesperson, said the Willow project has undergone extensive environmental and permitting reviews.

Boys, by email, said the company was reviewing the letter. She also said lessons learned from the incident will be incorporated into future projects.

Boys on Tuesday said intermittent, trace amounts of gas that were trapped beneath underground obstructions are still finding their way to the surface and are being detected near wellhouses, which are structures enclosing the tops of wells.

The Alaska Oil and Gas Conservation Commission, which oversees oil and gas drilling in the state, in an update Tuesday said the company was continuing work to plug and abandon a waste disposal well that was being drilled when the leak occurred.

The lawmakers, among other things, want to know why it took the company a month to identify the source of the leak and how close the leak was to “becoming something more severe.”

ConocoPhillips continues investigating the cause and what happened at the field, where gas escaped at a drill site called CD1, according to the oil and gas commission.

The company has said it has not detected gas outside the gravel drill pad.