This year’s iteration of the annual defense funding bill making its way through Congress called on the Navy to conduct a technological review every five years to address safety concerns at the underground Red Hill Bulk Fuel Storage Facility.

The Navy built the facility near Honolulu during World War II, completing the tanks in 1943. The Navy placed the tanks underground beneath a mountain ridge to make them harder for Japanese military forces to strike. One of the largest fuel storage facilities in the country, it can store up to 250 million gallons of fuel.

But the tanks’ age, size, location and proximity to Oahu’s aquifer have provided unique challenges for maintenance. Over the facility’s long lifespan the tanks have occasionally leaked into groundwater, raising concerns for both local residents and officials.

Since 2006 the Navy has spent $260 million on efforts to upgrade the facility. The Navy has been working with University of Hawaii to look for ways to modernize the tanks.

In October the Navy proposed inventing a way to achieve “double wall equivalency” – a tank within a tank. The Environmental Protection Agency and Hawaii Department of Health rejected the plan calling it “deficient,” and asked the Navy to revise and resubmit its plan.