PITTSBURGH, Pa. — Preliminary study results show that no chemicals used for fracking on natural gas drilling well sites have contaminated any drinking water aquifers at the site. Study officials, however, caution it is way too early to make any definite conclusions.

The study, funded through the U.S. Department of Energy, is being conducted by the National Energy Technology Laboratory in Pittsburgh.

It marks the first time a drilling company let government scientists inject special tracers into the fracking fluid and then continue regular monitoring to see whether it spread toward drinking water sources.

“NETL has been conducting a study to monitor for any signs of groundwater contamination as a result of hydraulic fracturing operations at a site on the Marcellus Shale formation in Pennsylvania,” said Shelley Martin, media relations manager for NETL in an e-mail.

Hydraulic fracturing is a process commonly used in oil development. It is a technique that cracks open rock layers to free natural gas.

The study site is in Greene County, which is located southwest of Pittsburgh.

After a year of monitoring, the researchers found the fluids, combined with chemicals used to free trapped gas during fracking, stayed below the shallower areas that supply drinking water.

Drilling fluids with markers were injected more than 8,000 feet below the surface, but were not found in a zone of 3,000 feet higher. It means that the chemical laced fluid used for fracking stayed away from the drinking water supplies.

Martin cautions this study is in the infancy stages and more research is needed.

“We are still in the early stages of collecting, analyzing and validating data from this site.

While nothing of concern has been found thus far, the results are far too preliminary to make any firm claims,” Martin said.

A final report on the results is expected by the end of the year.