Waterford — A supervisor and a welder for a private contractor working at the Millstone Power Station in 2014 unsuccessfully attempted to circumvent drug screening tests required to gain access to protected areas of the nuclear power plant, resulting in a violation of plant owner Dominion’s license agreement with the Nuclear Regulatory Commission.

The NRC on Tuesday notified Dominion that it determined after an investigation that a Level IV violation had occurred.

The violation is “of very low safety significance,” NRC spokesman Neil Sheehan said Wednesday, and Dominion has entered into a corrective action program.

The violation occurred when a supervisor for Cianbro Inc., a contractor working at the plant during a refueling outage for Unit 2 in 2014, did not administer a fitness-for-duty drug test on a Cianbro welder when he reported for duty after the welder told him he would probably fail the test because he had used narcotics a couple of weeks earlier, the NRC said in its letter to Dominion.

Instead, the supervisor told the welder to leave the site, drink a lot of water and return the next day to take the test. The welder followed the supervisor’s instructions, returned the next day and took the test. Despite his attempts to dilute the test results, he tested positive for drugs, the NRC said.

After Cianbro managers learned what happened, the supervisor was fired and Dominion canceled his access to Millstone.

The welder was never granted access to the site, the NRC said.

Officials at Cianbro, a national company with a regional office in Bloomfield, could not be reached for comment Wednesday.

Sheehan said Dominion was cited for a violation because “it is ultimately responsible for the actions of its contractors.”

“We did not find any fault on the part of Dominion,” Sheehan said. “Dominion did the right thing once they became aware of this.”

Nevertheless, he said, the NRC decided that formal notification of a violation would be prudent.

“We want to document that there was an attempt by a contractor to subvert the fitness-for-duty program,” he said.

Millstone spokesman Ken Holt said Dominion still uses Cianbro as a contractor.

He stressed that the welder never gained access to Millstone and that the supervisor has not been allowed back.

“Trying to cheat the test was a violation,” he said.

The NRC said that although the actions by the supervisor and welder were “willful,” they were determined to be isolated incidents that did not involve management, nor was it the result of a lack of management oversight.

Sheehan noted that the thresholds for the drug tests given in the fitness-for-duty program are “very conservatively set.”

The goal of the program, he said, is to ensure that everyone with access to the most sensitive areas of the plant is “trustworthy, reliable and not under the influence of any substance that would impair their ability to perform their duties.”

Overall, he added, the number of contractors and vendors who test positive for illegal drugs is much higher than the number of plant employees who test positive.

Nationwide in 2013, 907 staff of contractors and vendors at nuclear power plants failed the fitness-for-duty test for drug use, most frequently for use of marijuana.

That same year, 137 employees of the nation’s 100 nuclear power plants across failed the tests, most often for alcohol use, NRC data show.

j.benson@theday.com

Twitter: @BensonJudy