An Oak Harbor couple did a little detective work last week and discovered that diesel fuel had been mistakenly placed in a premium unleaded fuel pump at the Safeway gas station.

Michelle Bois said her 2007 GMC Envoy was running on empty when she pulled into the Safeway gas station in Oak Harbor at about 1 p.m. in the afternoon of Jan. 10. After filling the tank, she drove away and immediately noticed that the vehicle was running rough.

The next morning, the SUV wouldn’t even start, so she had it towed to the GM dealership in Mount Vernon. That night, a mechanic called and said the tank was full of diesel fuel, which obviously caused the engine problems.

“Everyone kept asking me why I pumped diesel in the tank, but I knew I hadn’t,” she said.

Bois and her finance, North Whidbey firefighter and EMT Matt Buchholz, went down to the gas station and asked for a copy of her receipt. It showed that she had filled the tank from pump No. 8, which is an unleaded fuel pump.

Buchholz purchased a gas can from the store and filled it from the pump. He said he immediately could smell that it was diesel, so he alerted the gas station attendant. The pump was shut down.

“Safeway was fantastic,” Buchholz said. “Everyone was very helpful.”

Yet he worries about others who may have pumped diesel into their unleaded-only cars and didn’t realize it.

“I don’t know how many people were affected,” he said. “Hopefully we stopped more people from getting diesel.”

Buchholz said he received calls from the Safeway corporate office and then the fuel supplier. He was told the mix-up was an accident and that the fuel supplier would handle the damages.

As for the Envoy, Buchholz said the mechanic had to drain the tank and completely flush the system. The couple got the vehicle back after six days with a large bill, but they were warned that the diesel may have harmed the fuel pump, the catalytic converter, the oxygen sensor or other engine parts.

“We don’t know what this will cost us in the long-run,” he said.

Such fuel mix-ups aren’t unheard of at gas stations, according to Jerry Buendel, the weights and measures program manager at the Washington State Department of Agriculture. The agency is responsible for investigating complaints about fuel at gas station. Common allegations, he said, are about faulty meters at the pump, water in gas or regular unleaded being sold as premium.

Buendel said he didn’t receive any complaints about the incident at Safeway in Oak Harbor, but he said that’s not unusual. Normally, the gas station would work with customers to compensate them, so the customers don’t usually call Buendel to complain. He said there’s no way of knowing how often fuel is mixed up, but he said it’s simply a matter of human error. It doesn’t happen often, but sometimes truck drivers pump fuel into the wrong tank.

“There’s always an opportunity for human error,” he said.

A corporate Safeway spokesperson said the fuel distributor is handling the complaints and that all submitted claims have been paid. The manager at the Safeway store in Oak Harbor did not return a call for comment.