HONOLULU — Navy officials “didn’t have enough understanding” of the risks of keeping massive fuel storage tanks on top of a drinking water well at Pearl Harbor, where they spilled poisoned jet fuel more than 6,000 people in 2021, a US military watchdog said Thursday.

That lack of awareness came even though officials had engineering drawings and environmental studies describing the risks, the U.S. Defense Department’s inspector general said.

The finding was among a long list of Navy failures identified by the inspector general in two reports that follow a years-long investigation into fuel leak at the Red Hill bulk fuel storage facility. The investigators said it was imperative that the Navy address the management of fuel and water systems at Joint Base Pearl Harbor-Hickam and recommended that the Army evaluate leak detection systems at other Navy fuel facilities.

“DoD must take this action, and others, to ensure that tragedies like the one in November 2021 are not allowed to happen again,” Inspector General Robert P. Storch said in a statement.

The Army built the Red Hill fuel tanks on the side of a mountain in the early 1940s to protect them from air attack. There were a total of 20 tanks, each as high as a 25-story building, with the capacity to store 12.5 million gallons (47.3 million liters). The site was in the hills above Pearl Harbor and above an aquifer equipped with wells that supplied drinking water to the Navy and Honolulu’s municipal water system.

Fuel spills at Red Hill have occurred before, including in 2014, prompting the Sierra Club of Hawaii and the Honolulu Board of Water Supply to ask the military to move tanks to a place where they would not threaten Oahu’s water. But the Navy refused, saying the island’s water was safe.

The 2021 spill gushed from a ruptured pipeline in May of that year. Most of it leaked into a firefighting drainage system, where it sat unnoticed for six months until a cart hit a line holding the liquid. Crews thought they had cleaned up most of this fuel, but were unable to recover about 5,000 gallons (19,000 liters). Around Thanksgiving, the fuel leaked into a drain and drinking water supply that provided water to 90,000 people at Joint Base Pearl Harbor-Hickam.

The inspector general’s report noted that 4,000 families were forced to move from their homes for months because they were unable to drink or bathe in the water. The military spent more than $220 million housing residents in hotels and responding to the spill. Congress appropriated an additional $2.1 billion, some of which helps the Navy close the Red Hill facility according to the year order from Hawaii regulators.

Among the inspector general’s other findings:

Hawaii’s congressional delegation, which requested the investigation in 2021, issued a joint statement saying the reports made clear that the Navy and Army failed to manage fuel and water operations at Red Hill and Pearl Harbor to a standard that protects the health and safety of the people of Hawaii.

“This is outrageous and unacceptable,” said the statement from U.S. Sens. Mazie Hirono and Brian Schatz and U.S. Reps. Ed Case and Jill Tokuda, both Democrats.

They called on the Navy to take “full responsibility” for its failures and immediately implement the inspector general’s recommendations.

A Navy spokesman said in a statement that the inspector general’s findings align with previous assessments and support the corrective actions the Navy is implementing.

“We are committed to constant improvement to ensure the highest standards of operation, maintenance, safety and oversight in all of our facilities at all times,” the statement said.

Navy last year issued written reprimands to three retired military officers for their roles in the fuel spill, in a move the Sierra Club called a “slap on the wrist.”

Hawaii Gov. Josh Green said he welcomed the inspector general’s findings, which he said underscored what environmental advocates have long argued.

“We will continue to push for transparency and accountability around the Red Hill issue because all people living in Hawaii deserve pure, clean drinking water,” Green said in a statement.

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