The controversial findings of a new shale gas study commissioned by the U.S. Department of Energy (DOE) and conducted by the department's National Energy Technology Laboratory in Pittsburgh, Pennsylvania, are sure to lend additional fuel to the discussion of hydraulic fracturing. The DOE plans to release more details over the next several months.

After monitoring eight new horizontal wells in Pennsylvania's Marcellus Shale Basin, the government scientists said they found "no evidence" that chemicals from the hydraulic fracturing (fracking) process contaminated drinking water. In fact, the fracking fluid "stayed thousands of feet below the shallower areas that supply drinking water," says the study apparently released exclusively to the news agency Associated Press (AP).

In one of the tests, drilling fluids tagged with distinguishing chemical markers were injected more than 8,000 feet (2,438 meters) but the DOE said they could not be detected in a monitoring zone around 3,000 feet closer to the surface, which was "about a mile away from drinking water supplies."

The shale gas boom has led to tens of thousands of new wells being drilled, most of them in Pennsylvania, New York, Ohio and West Virginia. The eight wells in the test were monitored seismically, and one was injected with four different trackers at different stages of the fracking process, touching off small explosions to break the rock apart.

Calling the findings "landmark," the news agency noted that the DOE study can be expected to provide a boost for drilling companies in their long-running dispute with environmentalists and property owners. This marks the first time that a drilling company has allowed government scientists to inject tracers into the fracking fluid and continue regular monitoring.

Kathryn Klaber, CEO of the industry-backed Marcellus Shale Coalition told AP the study was "great news," adding that "it's important that we continue to seek partnerships that can study these issues and inform the public of the findings."

Rob Jackson, part of a Duke University team that collected data from nearly 700 wells in northeastern Pennsylvania, southern New York, central Arkansas, North Carolina, and West Virginia and has begun sampling in Texas, called the DOE findings "useful and important" but warned that a single study does not prove that fracking can't pollute, as geology and fracking practices vary.

In tests carried out in the Marcellus Basin - the results have been published in the Proceedings of the National Academy of Scientists (PNAS) - Jackson and his colleagues found no excess chemical concentration but did find higher than normal concentrations of methane, ethane and propane in drinking water of households less than 1 km from shale gas exploration sites. Ethane concentration was 23 times higher than that found elsewhere.

The Duke team said the "two simplest explanations for the higher dissolved gas

concentrations" could be faulty or inadequate steel casings of the fracking bores or imperfections in the cement sealing of the annulus or gaps between casings and rock that keep fluids from moving up the outside of the well. According to the PNAS paper, the Pennsylvania Department of Environmental Protection (DEP) issued 90 violations for faulty casing and cementing on 64 Marcellus shale gas wells in 2010, with 119 similar violations issued in 2011.