Scott Pruitt, whom the Senate confirmed Friday, 52-46, doesn’t fit either mold. His focus is neither expanding nor reducing regulation. “There is no reason why EPA’s role should ebb or flow based on a particular administration, or a particular administrator,” he says. “Agencies exist to administer the law. Congress passes statutes, and those statutes are very clear on the job EPA has to do. We’re going to do that job.” You might call him an EPA originalist.

Not that environmentalists and Democrats saw it that way. His was one of President Trump’s most contentious cabinet nominations. Opponents objected that as Oklahoma’s attorney general Mr. Pruitt had sued the EPA at least 14 times. Detractors labeled him a “climate denier” and an oil-and-gas shill, intent on gutting the agency and destroying the planet. For his confirmation hearing, Mr. Pruitt sat through six theatrical hours of questions and submitted more than 1,000 written responses.

When Mr. Pruitt sat down Thursday for his first interview since his November nomination, he spent most of the time waxing enthusiastic about all the good his agency can accomplish once he refocuses it on its statutorily defined mission: working cooperatively with the states to improve water and air quality.

“We’ve made extraordinary progress on the environment over the decades, and that’s something we should celebrate,” he says. “But there is real work to be done.” What kind of work? Hitting air-quality targets, for one: “Under current measurements, some 40% of the country is still in nonattainment.” There’s also toxic waste to clean up: “We’ve got 1,300 Superfund sites and some of them have been on the list for more than three decades.”

Such work is where Washington can make a real difference. “These are issues that go directly to the health of our citizens that should be the absolute focus of this agency,” Mr. Pruitt says. “This president is a fixer, he’s an action-oriented leader, and a refocused EPA is in a great position to get results.”

That, he adds, marks a change in direction from his predecessor at the EPA, Gina McCarthy. “This past administration didn’t bother with statutes,” he says. “They displaced Congress, disregarded the law, and in general said they would act in their own way. That now ends.”

Mr. Pruitt says he expects to quickly withdraw both the Clean Power Plan (President Obama’s premier climate regulation) and the 2015 Waters of the United States rule (which asserts EPA power over every creek, pond or prairie pothole with a “significant nexus” to a “navigable waterway”). “There’s a very simple reason why this needs to happen: Because the courts have seriously called into question the legality of those rules,” Mr. Pruitt says. He would know, since his state was a party to the lawsuits that led to both the Supreme Court’s stay of the Clean Power Plan and an appeals court’s hold on the water rule.

Will the EPA regulate carbon dioxide? Mr. Pruitt says he won’t prejudge the question. “There will be a rule-making process to withdraw those rules, and that will kick off a process,” he says. “And part of that process is a very careful review of a fundamental question: Does EPA even possess the tools, under the Clean Air Act, to address this? It’s a fair question to ask if we do, or whether there in fact needs to be a congressional response to the climate issue.” Some might remember that even President Obama believed the executive branch needed express congressional authorization to regulate CO 2 —that is, until Congress said “no” and Mr. Obama turbocharged the EPA.

Among Mr. Pruitt’s top priorities is improving America’s water infrastructure. “I’m going to be advancing this with the president, this idea that when we talk about investing in infrastructure, we need to look more broadly than bridges and roads,” he says. “Look at what happened in Flint,” the Michigan town where lead was found in the water supply. “Look at what is happening in California,” where the Oroville Dam’s failure endangers tens of thousands of homes. [...]

He faults President Obama’s EPA for its “attitude that the states are a vessel of federal will. They were aggressive about dictating to the states and displacing their authority and letting it be known they didn’t trust the states.” Mr. Pruitt has numbers to back up the claim: During the combined presidencies of George H.W. Bush, Bill Clinton and George W. Bush, the EPA imposed five federal air-quality implementation plans on states. Mr. Obama’s EPA imposed 56.

States’ rights were the motivating impulse behind Mr. Pruitt’s lawsuits against the Obama administration, and he has plenty of examples of the benefits of letting states take the lead on pressing environmental problems. He mentions the progress that a state coalition has made on improving the habitat of the lesser prairie chicken, a threatened species. States have also clubbed together to tackle water pollution in the Chesapeake Bay.

“There is this attitude that has grown of late that Oklahomans and Texans and Coloradans really don’t care about the air they breathe or the water they drink,” he says. “That’s just not the case.” As a demonstration of his commitment to the devolution of power, he pledges to vigorously defend the portion of the EPA’s annual $7 billion budget—roughly half—that goes to the states as funds and grants: “This is the front line of a lot of the work on air and water quality and infrastructure, and its very important that money continue.”

Mr. Pruitt argues that his renewed focus on statutes and federalism will help produce regulatory certainty, which will be good for business: “The greatest threat we’ve had to economic growth has been that those in industry don’t know what is expected of them. Rules come that are outside of statutes. Rules get changed midway. It creates vast uncertainty and paralysis, and re-establishing a vigorous commitment to rule of law is going to help a lot.”

Full interview