An oil and gas company that sought to drill underneath the long-shuttered Rocky Flats nuclear weapons plant announced Thursday it will drop its plans after a loud outcry from Superior residents worried about the potential disturbance of buried plutonium.

Highlands Natural Resources Corp., registered in the United Kingdom, issued a statement saying “the best course of action is to withdraw all of the Colorado Oil and Gas Conservation Commission spacing and permit applications” related to the 6,200-acre Rocky Flats site northwest of Denver.

“This determination comes after extensive discussions with communities and other stakeholders, including people who live in the project area, mineral owners, county, state and federal representatives, U.S. Fish and Wildlife Service, COGCC and others,” the company said. “Highlands appreciates the concerns and debate raised by its Jefferson County development plans and is taking the conscious step back from its development plans to affirm its commitment to being a responsible and transparent operator within the state of Colorado.”

The company already had announced this week that it would withdraw applications it had submitted to the Colorado Oil and Gas Conservation Commission for 31 wells inside Superior at the corner of Colorado 128 and McCaslin Boulevard, but Highlands hung on to plans for a multiwell pad along Colorado 93 that would rely on horizontal drilling to reach hundreds of feet underground into the refuge.

Plans for that remaining pad were put on ice Thursday.

The company’s Rocky Flats drilling proposal, first revealed in late October, triggered a fierce reaction from nearby Superior residents, who packed town hall Monday night to condemn the plan and express concern about the proposed wells’ proximity to a town water tank. Superior Mayor Clint Folsom told The Denver Post that he had “never seen a crowd of that size” in town hall before.

“There’s a great amount of concern among our residents about any type of use at Rocky Flats,” the mayor said. “In terms of severity of concern, the prospect of drilling in an area with possible plutonium contamination was unprecedented.”

Highlands’ proposal came to light just days before the Nov. 6 election, in which voters rejected a highly controversial ballot measure that would have dramatically increased the distance new oil and gas wells would have to be situated from homes, schools, lakes and rivers. Monday’s meeting in Superior occurred less than a week after Highlands withdrew applications to drill for oil and gas under Standley Lake and a popular dog park in Westminster.

Superior, with a population of 13,000 on Boulder County’s southern border, long has had concerns about any activity — be it construction of the Jefferson Parkway or the public opening of the Rocky Flats National Wildlife Refuge — that might disturb the soil at Rocky Flats, where triggers for nuclear warheads were manufactured for four decades starting in the early 1950s.

The plant, notorious for fires and ground contamination from leaking barrels of plutonium-laced waste stored on site, had to undergo a $7 billion, decade-long cleanup before it could open to the public. A core 1,350-acre area in the middle of the refuge where weapons production occurred is still an active Superfund site that is off limits to visitors.

Officials with the U.S. Fish and Wildlife Service and the U.S. Department of Energy, which oversees the core “central operable unit” at Rocky Flats, repeatedly have pointed to testing over the last couple of decades that they say shows that levels of any contaminants at the sprawling site north of Arvada are well within health and safety limits.

But allowing drilling and hydraulic fracturing — in which a mixture of water, sand and chemicals is injected under high pressure underground to fracture rock and loosen oil and gas deposits to flow back up to the surface — so close to where plutonium-contaminated sections of buildings remain buried in place was a red flag too far for many.

Even though those building slabs are buried a dozen or so feet deep, and while drilling typically goes down thousands of feet, David Abelson, executive director of the Rocky Flats Stewardship Council, said not enough is known about how intensive industrial activity like drilling might affect the refuge’s wider hydrology and whether it might increase chances for exposure to contaminants.

“Any proposal to conduct oil and gas operations that either are on or under the Rocky Flats refuge merit a discussion of what is legal and what the potential risks are,” Abelson said.

A quick reading of closure documents published after the plant cleanup makes it clear that “excavation, drilling, and other intrusive activities below a depth of three feet are prohibited, without prior regulatory review and approval pursuant to the Soil Disturbance Review Plan.” But Abelson said those regulations were put into place before horizontal drilling — where wells can extend underground laterally for a mile or two from where the well was drilled at the surface — became widespread.

What about a plan, like the one Highlands put forward, where drilling takes place outside refuge boundaries and reaches back into the refuge thousands of feet below the surface?

“There is a clear prohibition on drilling inside the old production area, but the new element of horizontal drilling raises questions about how that prohibition might be interpreted,” Abelson said.

Highlands likely faced rigorous vetting by multiple agencies before it would have been able to proceed with drilling and fracking. The Colorado Department of Public Health and Environment told The Post that the agency’s Hazardous Materials and Waste Management Division would likely have gotten involved with a “regulatory review” of any proposal involving drilling under the central operable unit.

And a spokeswoman with the Denver office of the U.S. Environmental Protection Agency, which oversees Superfund sites in the United States, said it was ready to coordinate “closely with CDPHE in reviewing proposed activities, technical information, and potential impacts or concerns” before any oil and gas operations commence.

Jeremy Jackson, a three-year resident of Superior who helped spearhead citizen opposition to Highlands’ plans, said people were concerned not only about soil disturbance at the surface but also about possible “seismic activity well above the drilling depths.”

He said within days of hearing about the proposal, a group called Safe Superior Citizens Action Group sprung up and quickly gathered more than 500 followers.

“Asking residents to have faith that no accidents can possibly occur when the repercussions of an accident happening on a site like that are life-and-death is a hard pill to swallow,” he said. “Also, it’s not necessary. We’re not experiencing an energy shortage. There are other sites to drill that aren’t through a national Superfund site.”