Crews are working to clean up roughly 500 gallons of oil that leaked from an underground pipeline in Pearl City.

The leak was first reported at around 5:40 p.m. Tuesday by a resident on Waiawa Road, who saw the oil in his backyard.

Gilbert Peter told KHON2 it came up to his home, contaminated a vegetable garden, and stopped right at the edge of Waiawa Stream.

“As I was going around the side of my house, I saw this black thing on my sidewalk there. I didn’t know what it was right away until I touched it with my slipper, and it was sticky,” he said.

The state Department of Health says a small amount of oil entered the stream.

“The oil is very viscous and slow-moving, so once it got into the water, they saw it right away and they could pretty much roll it up and take it on land,” said Liz Galvez from the Department of Health.

The 8-inch steel pipeline is owned and operated by Hawaiian Electric. It was built in 2004 and carries fuel from Barbers Point to the Waiau Power Plant.

Officials say the leak occurred along a portion of the pipeline that runs behind three homes. This is the first time the pipeline has leaked.

As soon as it was reported, HECO says personnel immediately shut down the pipeline, notified the Department of Health, and contained the spill.

The good news, according to officials, is that the pipeline carries low sulfur fuel oil, which hardens as it cools. Its thick, waxy consistency is slow to spread and easy to pick up.

“What they are doing is digging up the spill area, bagging it, and placing it in steel drums and taking it to another location,” said HECO spokeswoman Shannon Putnam.

Crews worked overnight to recover about 90 percent of the oil. Work continues to clean up the remaining oil.

They’re taking everything back to the Waiau Power Plant, where they will weigh the oil that has been collected to determine how much leaked.

HECO estimates about 500 gallons spilled, but it could be more or less as the investigation continues into the leak and when it started.

The Department of Health says the area where the leak occurred is safe. A spokeswoman told KHON2 that there were no detectable impacts to air quality. Soil and well water samples will be taken to make sure everything is safe.

HECO offered to relocated the affected residents, but they declined.

There is one other oil pipeline on Oahu “that goes from Barbers Point to our Kahe Power Plant,” said Putnam. “(The section of pipeline in Pearl City) is the closest it comes to any residential area. It doesn’t go under any homes.”

We asked what is the standard, minimum length a pipeline can be placed near homes and stream beds.

We’re told there is no limitation on how close it can be, but the permits to build a pipeline and where are approved by the state and U.S. Department of Transportation.

HECO tells us to its knowledge, the oil pipeline to Kahe Power Plant did leak in the past when Chevron used to own it. Ownership changed in 2015 under HECO.

The utility tells us staff walk through and inspect the pipelines every two weeks. A walk-through on the 12.75-mile pipeline was last conducted on Monday.

A more thorough internal inspection was just completed last month, but HECO is still waiting for the results.