Dr. Brantley described the geology in northern Pennsylvania as being similar to a layer cake with numerous layers that extend down thousands of feet to the Marcellus Shale. The vertical fractures are like knife cuts through the layers. They can extend deep underground, and can act like superhighways for escaped gas and liquids from drill wells to travel along, for distances greater than a mile away, she said.

Katie Brown, an energy consultant with Energy in Depth, an advocacy group for the Independent Petroleum Association of America, said the authors had no evidence that the small traces they found of 2BE, which is also used in many household items, came from a drilling site.

“The entire case is based around the detection of an exceedingly small amount of a compound that’s commonly used in hundreds of household products,” Ms. Brown wrote in an email. “The researchers suggest the compound is also found in a specific drilling fluid, but then tell us they have no evidence that this fluid was used at the well site.”

Garth T. Llewellyn, a hydrogeologist with Appalachia Hydrogeologic and Environmental Consulting and the lead author of the report, said that when his team sampled water wells that were farther away from the drilling sites, they did not find any of the compounds found in the three households. “When you include all of the lines of evidence, it concludes that that’s the most probable source,” he said. Mr. Llewellyn had previously provided the families with environmental consulting during their civil case with Chesapeake Energy.

Victor Heilweil, a hydrogeologist from the University of Utah who was not involved with the study but reviewed its details, said it was noteworthy for showing “the detailed geologic fabric explaining how these contaminants can move relatively long distances from the depth to the drinking well.”

An environmental scientist from Stanford University, Rob Jackson, who also reviewed the paper, said it “clearly shows an impact of oil and gas drilling on water quality.” But he emphasized that this instance was an exception.

The dates of the incident were not surprising to Scott Anderson, a senior policy analyst with the environmental advocacy group Environmental Defense Fund, who said that well integrity was generally poor around 2008 and 2009. He said that using casings of steel and cement at depths below 1,000 feet was a good idea in this region. But he also noted that the industry has strengthened its practices since then, including increased use of intermediate casings.

“Industry knows how to construct wells properly, but the fact is that they don’t always do so,” Mr. Anderson said. “My hope would be that papers like this will encourage industry and its regulators to do a better job of doing what they already know they are supposed to do.”