The chief engineer of an oil refueling ship is having to spend 30 days in a halfway house for ordering the dumping of more than 500 gallons of untreated bilge water into the ocean and attempting to conceal it from authorities.

Jeung Mun pleaded guilty in April to failing to record the release of two cubic meters of oily water from the 3,978-ton tanker B. Sky on the ship’s logs.

U.S. District Judge Leslie E. Kobayashi handed Mun the 30-day sentence Wednesday and fined him $1,500. Kobayashi had previously fined Mun’s employer, Doorae Shipping Co., $750,000 and ordered the South Korean-based company to contribute $200,000 to a charitable, nonprofit corporation to be used for coral reef preservation and restoration projects in Hawaii.

Doorae was operating the Vanuatu-flagged B. Sky in international waters in the Pacific Ocean in January when Mun ordered two separate discharges. The ship’s oil record book did not list the discharges when the B. Sky pulled into Honolulu in February, but a whistle-blower showed Coast Guard officials pictures of them when they boarded the vessel, said Mun’s lawyer, Rick Sing.

Mun and the rest of the B. Sky’s crew were prohibited from leaving Oahu while the Coast Guard investigated the case. Under the terms of an international treaty to prevent ships from polluting the world’s oceans and seas, Doorae was required to provide accommodations for its crew during the investigation.

The crew, except for Mun, was free to go, according to the terms of a plea agreement, when a company representative pleaded guilty on behalf of Doorae in April to charges in connection with the discharges. Sing said Mun has spent the past few months living in the Pagoda Hotel.

After Mun completes his 30-day sentence, he will be under court supervision for a year but will be able to return to South Korea during that time.

Bilge water contains fluid, solvents and water that collect in the lowest compartment of a ship and usually contains oil from the ship’s engine room.

The International Convention for the Prevention of Pollution from Ships requires operators of vessels from signatory countries to process bilge water through an oil-water separator to reduce the concentration of oil to an acceptable level before releasing the water into the ocean. The treaty also requires the recording of any and all discharges.