PITTSBURGH — Hydraulic fracturing for natural gas hasn’t contaminated drinking water wells in Arkansas, according to a new study, but researchers said the geology there may be more of a natural barrier to pollution than in other areas where shale gas drilling takes place.

The most passionate critics and supporters of hydraulic fracturing, or fracking, often describe the process in extremes, suggesting it is either inherently dangerous for the environment or that it poses virtually no risk at all. But Avner Vengosh, a Duke University professor of geochemistry and water quality, said making generalizations about fracking in Arkansas, Pennsylvania and Colorado doesn’t make scientific sense.

“Each basin will have its own dynamics and its own rules,” he said of the possibility of contamination, adding that differences in well construction and regulations play a role, too.

Members of the U.S. Geological Survey were also part of the study, which examined 127 drinking water wells for evidence of pollution from methane gas or chemicals.

The study published Wednesday looked at an area of heavy drilling in north-central Arkansas known as the Fayetteville Shale. More than 4,000 new wells have been drilled there since 2004. The researchers did multiple tests to look for the presence of contamination from drilling.

Arkansas homeowners “typically had good water quality, regardless of whether they were near shale gas development,” said Robert Jackson, a professor of environmental sciences at Duke.

The Duke team has shown a willingness to report both positive and negative studies. In 2011 Duke researchers found higher concentrations of methane gas near drilling sites in Pennsylvania. State regulators denounced the findings even as environmental groups cheered them.

During fracking, large volumes of water, along with sand and hazardous chemicals, are injected into the ground to break rock apart and free the oil and gas trapped inside. In some areas fracking has been blamed for air pollution and gas leaks that have ruined well water, but the Obama administration and many state regulators say the practice is safe when done properly.