HARRISBURG - John Quigley, a longtime environmental advocate and fixture in Pennsylvania politics, resigned Friday as the state's top environmental officer, days after a private email he wrote stoked the latest controversy over his tenure.

The Wolf administration would not say why Quigley abruptly left his post as secretary of the Department of Environmental Protection. Gov. Wolf named the DEP's policy director, Patrick McDonnell, as acting secretary.

"I thank John Quigley for his service to the commonwealth, and I look forward to working with Patrick McDonnell," the governor said in a statement.

Quigley was not available for comment. A longtime and prominent environmental activist before taking office, he is the third member of Wolf's cabinet to leave in less than a year.

His departure came as Wolf was examining whether an email the DEP secretary sent last month to advocacy groups compromised his objectivity, according to a source close to the administration.

The source described that message as "the straw that broke the camel's back," and said Quigley's strained relationships with the legislature and even with administration officials had become a political liability.

In the email, sent from a private account, Quigley expressed frustration about delays both in updates he wanted in the state's oil and gas drilling regulations, as well as in plans for clean air regulation changes, the source said. The changes have been a point of contention between industry officials and environmental and citizen groups.

Two people familiar with the email said Quigley had urged the groups in the message to mobilize and press for action on the regulations.

Shortly after receiving the email, which was first disclosed Thursday by the Capitolwire news service, several advocacy groups, including PennFuture, PennEnvironment, and the Natural Resources Defense Council, used print and radio advertisements to urge an end to some of the delays, supported by Republican and Democratic state senators.

The ads took aim at Democratic Sen. John Yudichak (D., Luzerne), the ranking Democrat on the Senate Environmental Resources and Energy Committee.

The Senate is considering a bill that would extend the amount of time legislators can take to review and require changes to state regulators' plans for cutting power plant carbon emissions - and Yudichak joined all but one Democrat in voting with Republicans on the committee to send the legislation to the Senate floor.

Angered by the ads, Yudichak asked Wolf to determine if they were spurred by Quigley's email to environmental groups.

Yudichak would not discuss the matter Friday, except to say in a statement: "I can only confirm that serious concerns have been raised about the conduct of DEP Secretary John Quigley. I am working with the administration to secure all relevant facts before I make any further comment on this sensitive matter."

According to the source who read it, Quigley's email did not single out legislators or urge running ads as a course of action.

Quigley, a 56-year-old Democrat, is from Hazleton, where he once served as mayor.

Before being tapped by Wolf to lead the DEP, he served as secretary for the Department of Conservation and Natural Resources under Gov. Ed Rendell. Before and after his time in the Rendell administration, he worked for PennFuture - one of the advocacy groups that aired the ads against Yudichak.

He became the third high-profile administration official to leave Wolf's administration. Wolf's former policy secretary, John Hanger, stepped down this year during the state budget impasse, saying he wanted to spend more time with his family. Last summer, Katie McGinty, Wolf's former chief of staff, resigned to launch her campaign for the U.S. Senate.

Quigley's determination to revise the state's oil and gas drilling regulations reflects a long-fought battle.

The DEP has spent years crafting wide-ranging revisions that include changes to add protections for public resources near well sites, improve standards for cleaning up spills, and require companies to search for abandoned wells near the sites of new wells.

Oil and gas industry representatives contend the regulations would impose unjustified and expensive burdens, while environmental and citizen groups support the changes but also want greater protections.

The state's Independent Regulatory Review Commission approved the update in a divided vote in April. But there has been resistance in the legislature, with a House committee voting this month to block the new rules from taking effect. The full House and Senate would have to approve the resolution to stop the changes.

Legislators who want the rules scrapped - Republicans as well as some Democrats - have argued that the agency did not meet a requirement to differentiate between large-scale shale drilling operations and the shallow oil and gas wells operated by small businesses, and that it failed to meet procedural requirements.

Democratic legislators who have backed the measures have characterized them as commonsense public health protections.

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