AURORA — For a second straight day, the state’s Air Quality Control Commission heard from dozens of people — concerned residents, industry executives, respiratory doctors and elected officials — sounding off about strong new rules to regulate oil and gas emissions proposed by Gov. John Hickenlooper’s administration.

If approved without changes, the rules would make Colorado the first state in the country to regulate methane, a potent greenhouse gas known to cause climate change.

The rules would also increase the frequency of leak detection checks, forcing operators to use instrument-based monitoring — most likely, forward-looking infrared cameras — to check wells, tanks and pipelines once a month for chemical leaks.

The Commission is expected to issue a final rule by the end of the weekend; and while many believe the rule adopted will be very close to what the governor’s office wants — Hickenlooper already held a press conference celebrating that the state’s three largest oil and gas companies support his administration’s proposal — those watching the hearing closely believe that’s no slam dunk.

“We’re confident at the end of the day a strong rule will be adopted, but it’s far from assured at this point,” said Environmental Defense Fund’s Dan Grossman.

While Noble, Anadarko and Encana all support the proposal and addressed the Commission on Thursday, the industry’s main lobbying arm, the Colorado Oil and Gas Association, is pushing hard to weaken the rules, despite broad statements of commitment toward improving air quality.

“Like many other parties to the rule-making, we are hoping the Commission provides further clarity and modest changes to the rule that take into consideration all Colorado operators,” said COGA’s Doug Flanders. “Colorado is already a national leader in the regulation of air emissions from the oil and gas industry, and we are committed to continuing to partner with any and all stakeholders who are interested in having a solution-oriented conversation on this issue.”

COGA and other smaller operators it represents have pushed the Commission to apply the regulations only in “ozone non-attainment” areas, mostly along the Front Range, where current air quality levels are failing to meet federal standards.

“They’re couching what they’re asking for as ‘tweaks’ when, in reality, what they’re asking for would gut the rules,” said Grossman, who expressed his group’s support for the proposed rule before the Commission on Thursday morning.

“Applying these requirements in the non-attainment areas only would exempt about half of the wells in the state.”

The Commission heard from oil and gas companies, environmental groups and other interested parties on Thursday after the hearings opened on Wednesday with testimony from the public, a solid majority of which urged the AQCC to adopt a strong rule.

“As a doctor, I see the impacts that ground-level ozone has on lung health firsthand,” said Dr. Anthony Gerber, a respiratory specialist at National Jewish Medical Center in Denver. “Many of my patients with lung disease simply can’t function on the days with dangerously high levels of ozone.”

Conservationists made sure to put the rule-making in the context of the state’s ongoing oil and gas boom, with the industry investing billions of dollars to drill hundreds of new wells in the Denver-Julesberg Basin.

“Oil and gas drilling and development has mushroomed in our state and we must do all we can to provide cleaner air for our children and our communities,” said Pete Maysmith, the Director of Conservation Colorado. “The Commission needs to adopt the rules as they are and not give in to some in the industry who want to weaken them.”

The hearings also attracted numerous politicians, from Boulder County liberals to conservatives like state Sen. Greg Brophy, a farmer from Wray on the state’s eastern plains who’s running for the GOP’s gubernatorial nomination.

Brophy, a self-described “Prius-driving, gun-toting farmer”, told the Commission Wednesday that the expansion of natural gas is already leading to cleaner air and dismissed concerns about climate change as alarmist.

“Last week, John Kerry called those who deny climate change flat earthers. Please,” Brophy said. “The true flat earthers in the American energy debate are the extreme environmental groups who make wildly exaggerated claims about the climate impacts of greenhouse gases, while at the very same time doing everything in their power to stop natural gas development — the energy source that is actually reducing all emission types, including carbon.

“Flat earthers, thy name is the Sierra Club. In that sense, I hope this Commission won’t be swayed by the flat earthers here today arguing for a one size fits all air standard. This attempt to punish rural Colorado for the traffic congestion and smog in Denver and Boulder is part and parcel of a wider war that’s being waged against rural Colorado.”

Industry representatives have also complained about the cost of the new regulations, although 75 percent of the costs will be borne by the three biggest companies, which support the rule as it’s proposed.

The cost of the regulations is an estimated $42 million a year; that amounts to $820 per well per year (for context, the average well in Colorado produces $180,000 annually).

“Despite what COGA’s hired guns are saying, this is actually cost effective,” Grossman said. “We’re looking to pay about $500 per ton of pollution reduced.”