Fracking chemicals do not cause water pollution, according to preliminary results of a U.S. Department of Energy (DOE) study on hydraulic fracturing in the Marcellus shale formation of Pennsylvania.

After a year of monitoring the aquifer near a drilling site in western Pennsylvania, DOE researchers could find no traces of the fluids that are laced with chemicals and injected thousands of feet below the surface, the Associated Press reported on July 19. In other words, the chemicals stayed where they were injected, 8,000 feet underground, rather than rising to pollute the aquifer, the DOE told the wire service.

To conduct the experiment, researchers tagged drilling fluids with marker chemicals that would identify them, then injected them underground, at the site of the gas well, AP said. But a year later they still had not been detected in a monitoring zone that was 5,000 feet below the surface 3,000 feet above where they had been placed. The Marcellus Shale formation is underneath sections of Pennsylvania, New York, Ohio and West Virginia. Hydraulic fracturing is the practice of injecting water mixed with various compounds into the shale and setting off small explosions to loosen the rock and liberate the natural gas. 

The researchers also checked how far the man-made fractures stretched, “and all were at least 6,000 feet below the surface,” the AP said.

The study is not over, so these are not final results. But they do represent “the first independent look at whether the potentially toxic chemicals pose a threat to people during normal drilling operations,” AP noted. “But DOE researchers view the study as just one part of ongoing efforts to examine the impacts of a recent boom in oil and gas exploration, not a final answer about the risks.”

"This is good news," said Rob Jackson, a scientist at Duke University who was not involved with the study, to AP. But he also said that the information, while useful, was not definitive. 

These results run counter, for instance, to an Environmental Protection Agency study released last September that found fracking compounds in the aquifer in Wyoming, near the Wind River Reservation. (Related: Wyoming Groundwater Again Tests Positive for Fracking-Related Chemicals on Wind River Reservation)

And fracking has been implicated in earthquakes as well, though the practice’s proponents are quick to point out that they are not major tremors. (Related: Fracking Suspected in Dallas-Area Earthquakes)

A study released in February 2012 suggested that any drinking-water pollution related to fracking is caused by the diligence and protocol of the fracker. In other words, fracking doesn’t pollute water; sloppy practices do, said researchers at the Energy Institute at the University of Texas at Austin, in the study they released at last year’s annual meeting of the American Association for the Advancement of Science. (Related: No Evidence That Fracking Contaminates Groundwater: Study)