A crane used to drive test piles floats in Oura Bay at the site of a future U.S. Marine Corps runway at Camp Schwab, Okinawa, July 9, 2024. (Brian McElhiney/Stars and Stripes)

CAMP FOSTER, Okinawa — A construction vessel leaked oil at the site of a future Marine Corps airfield in northern Okinawa this week but caused no environmental damage, according to Japan’s coast guard.

Hydraulic oil spilled at 11:40 a.m. Wednesday from a drill on a vessel that was boring into the seabed in Oura Bay, according to a coast guard news release on the same day. The vessel was working on construction for the airfield in waters about 4,400 feet north-northeast of Cape Henoko in Nago city.

The airfield is under construction at the Marines’ Camp Schwab on reclaimed land to replace Marine Corps Air Station Futenma in densely populated Ginowan city. The U.S. and Japanese governments agreed to move the base in 1996, but the Okinawa prefectural government has repeatedly delayed construction.

Oil seepage was confirmed on the ocean surface around noon, and contractors installed an oil fence and an oil absorption mat to recover the spill, according to the release. Recovery work was successfully completed at 1:10 p.m.

An investigation is underway to determine the cause and how much oil was spilled, a coast guard spokesman said by phone Thursday.

Some Japanese officials speak to the press only on condition of anonymity.

Contractors hired by the Okinawa Defense Bureau, an arm of Japan’s Ministry of Defense, began ground improvement work in Oura Bay on Dec. 28, the bureau announced in a news release the previous day.

The work involves solidifying the soft seabed to ensure stability for the airfield by “laying sand at the required locations on the seabed and driving sand piles,” the bureau said.

In July, contractors drove test piles into the seabed to prepare the site for steel pipes that will support the seawall.

The construction zone is divided into two main sections: 279 acres on Schwab’s north side and 91 acres in the south, according to Okinawa Prefecture’s website.

Work on the Oura Bay side, or north side, had been on hold since April 21, 2020, when Okinawa Gov. Denny Tamaki, citing safety and environmental concerns, refused to approve design changes meant to solidify the seabed.

Tamaki filed, and lost, three lawsuits, culminating in a September 2023 defeat at the Supreme Court. Japanese Minister of Land, Infrastructure, Transport and Tourism Tetsuo Saito approved the construction permits Dec. 28, 2023, after Tamaki ignored a deadline from Fukuoka High Court.