“TCEQ and RRC must properly address these intense emissions including, but not limited to, volatile organic compounds (VOCs), methane, and hydrogen sulfide,” Sharon Wilson, Earthworks’ thermographer, wrote in the letter.

It’s the latest example of mounting environmental concerns in the Permian Basin, where the extent of methane emissions from the oil and gas industry is largely unknown. Those concerns are being compounded by a collapse in crude prices that’s forced many producers into bankruptcy, sparking worries that they won’t be able to pay to maintain producing wells or properly plug ones that are abandoned. Methane emissions attract particular scrutiny because it’s a greenhouse gas far more potent than carbon dioxide.

TCEQ said in a statement that it will look into the issues raised in the letter. An enforcement case for complaints raised about MDC’s operations “is currently under development and will include the assessment of an administrative penalty and corrective actions, as needed,” the agency said. The RRC, whose website says MDC’s site is associated with a producing well, didn’t immediately have comment.

Earthworks first raised a complaint to TCEQ in December and MDC told regulators in April that it would fix and replace a faulty valve and broken tank hatch, according to an incident report obtained via a public records request by Earthworks. MDC also hired a third party to measure site-wide emissions, which were found to be higher than the quantities allowed by the agency and lacking a special permit. In May, TCEQ sent the company a message saying it would be issuing a notice of enforcement action. The agency also listed other violations, which MDC had until Aug. 10 to correct.

When Wilson revisited the site in September, however, she continued to record emissions, according to her letter.

Texas has taken a friendly stance toward the shale industry. But, more recently, some of the industry’s biggest investors, and even some oil producers, have called for stricter regulations. Another major environmental concern is the widespread industry practice of flaring in which producers burn off excess natural gas. Recent surveys by the Environmental Defense Fund found flares in the Permian are frequently unlit or malfunctioning, meaning methane is being released directly into the air.

MDC Energy’s parent company, owned by real estate developer Mark Siffin, filed for bankruptcy last October, owing more than $400 million in funded debt. The company is now seeking court approval to start a bankruptcy sale process while continuing to solicit offers to finance its way out of Chapter 11. Siffin didn’t immediately respond to an email seeking comment.