The U.S. military will begin draining 1 million gallons of fuel from three pipelines at a World War II-era fuel storage facility that leaked petroleum into Pearl Harbor's tap water last year and sickened thousands of people.

The pipelines, which run about 3 miles from the Red Hill Bulk Fuel Storage Facility in the mountains above Pearl Harbor down to the military base, will be drained one by one beginning Tuesday. 

The operation is expected to last six days.

The fuel has been sitting in the pipes since the military suspended the use of the Red Hill facility last year after it leaked petroleum into a drinking water well serving 93,000 people in and around Joint Base Pearl Harbor-Hickam.

FLASHBACK: PEARL HARBOR WATER POISONED AFTER MULTIPLE ERRORS AT FUEL STORAGE FACILITY, NAVY REPORT SAYS

military officials walking through tunnel at facility

In this file photo provided by the U.S. Navy, Rear Adm. John Korka, Commander, Naval Facilities Engineering Systems Command (NAVFAC), and Chief of Civil Engineers, leads Navy and civilian water quality recovery experts through the tunnels of the Red Hill Bulk Fuel Storage Facility, near Pearl Harbor, Hawaii, on Dec. 23, 2021. (Mass Communication Specialist 1st Class Luke McCall/U.S. Navy via AP, File)

Nearly 6,000 people, mostly military personnel and their families, sought medical attention for rashes, sores, nausea and other ailments after drinking and bathing in the contaminated water.

above-ground oil tank

An above-ground fuel storage tanks stands at Joint Base Pearl Harbor-Hickam on Monday, Oct. 24, 2022. (AP Photo/Audrey McAvoy)

A Navy investigation found a series of mistakes over the course of six months caused the spill.

miners building fuel tank

In this file photo provided by the U.S. Army Corps of Engineers, this 1942 Navy photo shows miners building one of the 20 fuel tanks of Defense Logistics Agency's Red Hill Underground Fuel Storage Facility at Joint Base Pearl Harbor, Hawaii, which are connected by a miles-long tunnel. (U.S. Army Corps of Engineers via AP, File)

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Fuel from the three pipelines will go to above-ground storage tanks and fuel barges, which will then supply Air Force jets and Navy ships at the base, officials said.

The Associated Press contributed to this report.