Hawaiian Electric Co. crews by late afternoon Wednesday had finished cleaning up an estimated 500-gallon oil spill that had leaked from an underground pipeline in Pearl City.

The incident was first reported at about 5:40 p.m. Tuesday by a Waiawa Road resident who saw the oil in his backyard. HECO — which owns and operates the pipeline — shut it down, notified the state Department of Health, and contained the spill. HECO also offered to relocate the affected residents. The leak occurred along a portion of the pipeline that runs behind three homes.

Crews, which worked overnight, monitored the odor but said there were no indications of public health hazards, according to HECO.

The utility said the fuel that leaked — low sulfur fuel oil — quickly hardens as it cools, making it easier to pick up.

“We have an ample supply of low sulfur fuel even if the pipeline is not in service,” HECO spokeswoman Shannon Tangonan said.

She said the company is still trying to determine the source of the leak and won’t know anything further until it excavates today.

The 8-inch steel pipeline, built in 2004, carries fuel from Barbers Point to the Waiau Power Plant in Pearl City.

The portion of the pipeline in the spill area is within the State Energy Corridor, which was established in 1972 to accommodate pipelines that transport petroleum products. Other entities, such as PAR Petroleum and The Gas Co., also have pipelines installed within the State Energy Corridor.

HECO owns another pipeline that runs from Barbers Point to the Kahe Power Plant in Kapolei. The closest it gets to a residential area is about 77 feet in Coconut Plantation in Ko Olina.