A Pitt professor resigned Saturday after he said that his beliefs concerning environmental… A Pitt professor resigned Saturday after he said that his beliefs concerning environmental advocacy and public health clashed with those of the University.

Conrad “Dan” Volz Jr. said that he is resigning over a “difference of opinion between the University and me of the proper advocacy in the world of public health.”

Volz, the director of the Center for Healthy Environments & Communities at the Graduate School of Public Health, is an open critic of Marcellus Shale drilling. He said the University has not allowed him to openly voice his dissent, although he did not cite specific instances.

But Volz emphasized, “I’m not leaving because I’m being forced out. I’m leaving entirely of my own choice.”

Donald Burke, dean of the Graduate School of Public Health, directed requests for comment to UPMC spokeswoman Allison Schlesinger.

Schlesinger said that Volz left by his own choice. She would not offer additional comment on the matter.

Volz published research last month saying that Marcellus Shale drilling is leading to contamination of drinking water. The drilling process known as “fracking” involves shooting sand, water and chemicals into the shale to break it up to provide easy access to the gas.

The research in the report showed high levels of bromide in the Josephine brine treatment facility, located in Indiana County, Pa. Volz’s report says the treatment facility accepts water from the oil and gas industry, including the “flowback water from Marcellus Shale gas extraction operations.”

Representatives for the Josephine Facility could not immediately be reached for comment Sunday. Critics in the Canada Free Press newspaper claimed that the research Volz published misstated and misrepresented facts.

Volz wrote a revised report following the criticisms, but said that his overall conclusions did not change.

He will testify in Washington, D.C., on Tuesday before the U.S. Senate Committee on Environment and Public Works. The hearing will be called “Natural Gas Drilling: Public Health and Environmental Impacts.”

Volz said the reason he is testifying is not directly because of the issues surrounding his resignation, but there is “a relationship.”