A long-delayed public health study commissioned by Colorado regulators found that oil and gas drilling poses health risks at distances greater than current minimum "setback" distances, a development that is poised to send shockwaves through a regulatory environment already in a state of transition and uncertainty.

"Exposure to chemicals used in oil and gas development, such as benzene, may cause short-term negative health impacts…during 'worst-case' conditions," the Colorado Department of Public Health and Environment said in a press release. "The study found that there is a possibility of negative health impacts at distances from 300 feet out to 2,000 feet."

The state's current rules require new oil and gas wells to be at least 500 feet from single-family homes and 1,000 feet from high-occupancy buildings. Proposition 112, the statewide ballot measure pushed by environmental groups and defeated by Colorado voters in 2018, would have imposed a 2,500-foot minimum.

State toxicologist Kristy Richardson said in a press conference Thursday afternoon that the results of the study are consistent with the health impacts that have been reported by Colorado residents near oil and gas sites in recent years.

“We’ve received, since 2015, about 750 health concerns that have been reported through our hotline,” Richardson said. “About 60 percent of those concerns reported to us are things like headaches, nosebleeds, respiratory issues, skin irritation.”

The study, conducted by consulting firm ICF International, is one of the most comprehensive analyses of its kind, and was submitted for peer review and publication in the Journal of the Air and Waste Management Association. Its modeling is based on air samples collected near oil and gas sites along the Front Range and in Garfield County on the Western Slope.

“I haven't come across any data like this in the world,” state epidemiologist Mike Van Dyke told CPR News when the study was first announced in 2017.

"This study is the first of its kind because it used actual emissions data to model potential exposure and health risks," John Putnam, the CDPHE's environmental program director, said in a statement on the study's release.

The study is also consistent with a large body of existing health and environmental research finding risks associated with oil and gas development. A 2016 analysis published in the scientific journal PLOS One reviewed nearly 700 peer-reviewed studies on the health impacts of fracking and found that 84 percent of them “contain findings that indicate public health hazards, elevated risks, or adverse health outcomes.”

As it faced repeated delays over the past two years, the study achieved a somewhat mythical status in environmental-advocacy circles. Anti-fracking activists were suspicious when the study’s initial release was pushed back until after the 2018 election, when Coloradans voted on Proposition 112.

Oil and gas groups, in turn, speculated earlier this year that the study’s release was being delayed until Democrats could pass Senate Bill 181, a package of oil and gas reforms that strengthened health and safety protections and granted local governments greater authority to regulate drilling.

In a separate press conference held later on Thursday, representatives of the oil and gas industry downplayed the study, and objected to the fact that it drew its conclusions from computer modeling. Dan Haley, president of the Colorado Oil and Gas Association, also stressed that the air samples on which the modeling study was based were collected in 2016.

“The technology has changed,” Haley said. “What’s happening out in the field, the standards that were used in 2014, 2015, are no longer used.”

The Colorado Oil and Gas Conservation Commission, which is already undertaking an extensive overhaul of its rules following the enactment of SB 181, issued a response to the study that outlined a series of immediate changes to its review processes.

“Working with our partners and CDPHE, we will immediately enact stricter and safer precautionary review measures to protect public health, safety, welfare, the environment,” COGCC director Jeff Robbins said in a statement.

Those measures include ensuring that "a protective review will occur for all wells under 2,000 feet from well to building unit." Following the passage of SB 181, the agency had already said it would subject permits under 1,500 feet to additional review.

Anti-fracking group Colorado Rising, which has called on the state to impose a moratorium on new drilling permits, said the study highlights the inadequacy of the state’s approach to regulating oil and gas. Anne Lee Foster, the group’s communications director, pointed to cases in which residents impacted by fracking have undergone blood tests showing elevated levels of benzene — which researchers wrote was the “critical toxic effect” identified by the study.

“We have a lot of corroborative data showing people, especially children, with very high levels of benzene in their blood,” says Foster. “I think this goes to support the case that we need to pause the permits. We don’t know what level of harm is being done, especially when it comes to cumulative impacts.”

The COGCC said the study's findings will impact the SB 181 rulemaking process, and the agency will continue to work with CDPHE to review health impacts from oil and gas development.

"This study just reinforces what we already know: We need to minimize emissions from oil and gas sources," Putnam said.