It’s no longer just environmentalists who suspect hydraulic fracturing is contaminating groundwater.

Oil companies here in Oklahoma — ones that produce from older vertical wells — have raised that prospect as they complain about the practices of their larger brethren.

They say hundreds of their wells have been flooded by high-pressure fracturing of horizontal wells that blast fluid a mile or more underground. Some of those “frack hits,” they suspect, have reached groundwater.

“I’m convinced we’re impacting fresh water here,” Mike Majors, a small producer from Holdenville, said as he drove from well to well on a September afternoon. “If they truly impact the groundwater, we can kiss hydraulic fracturing goodbye.”

Majors found a burbling mess two years ago when he showed up at his friends’ oil well outside Holdenville.

Water was bubbling up around the wellhead of the well, named the I. Davis No. A-1, but also flowing out of a nearby embankment leading to a drainage.

A company called Silver Creek Oil & Gas LLC had been fracking a well about 2,000 feet away from the well. The frack fluid leaked out of its intended path and flooded into the well, which belongs to a company called Rayland Operating LLC.

The older wellbore, drilled in 1928, was not sealed off with cement casing deep enough to prevent the surging flow from reaching groundwater.

On a warm September afternoon, Majors, a lanky, chain-smoking veteran of the oil field, leaned on the hood of his pickup parked at the well site and explained that with thousands of pounds of upward pressure, there was nothing to stop the fluid from flooding into groundwater.

“Logic says it will impact [groundwater],” Majors said, looking out over the slight slope. “There was water coming out of the ground. There was enough pressure to bring it to surface.”

When the state inspector showed up at the well site in 2015, he had similar concerns about underground contamination. He ordered Silver Creek to drill a monitoring well to see if water had been contaminated.

It took months and the threat of a contempt charge to get the monitoring well drilled. The results, filed with the state and obtained by E&E News through state open records laws, shows that chlorides, sometimes a sign of oil and gas contamination, are low.

“A frack hit would cause elevated chlorides, and that’s what we’re most concerned with when it comes to groundwater protection,” said OCC spokesman Matt Skinner.

But there wasn’t a baseline to measure the chlorides against. And there was no test for fracking chemicals. A list of frack fluid ingredients Silver Creek filed with the FracFocus registry included chemicals such as isopropanol and naphthenic solvents.

The report is vague about where the samples were collected. It doesn’t list the depth of the monitoring well, or its location. It merely says the monitoring well is north of another well.

The monitoring well was drilled only to the depth of water likely to be used currently for drinking. Environmental laws generally require the protection of groundwater that isn’t used now but might be someday.

Mike Cantrell, co-chairman of the Oklahoma Energy Producers Alliance (OEPA), said the sampling should be taken deeply enough to find contamination that might not show up for years in drinking water.

“You may never see it,” he said. “It’s not a problem until it’s a problem.”