The rationale for retaining the existing underground Red Hill fuel tank system is thinning steadily, the most recent impediment being the position by state environmental regulators that the Navy has not made its case for doing so.

The issue has been a source of tension between the Navy and the local officials and advocates worried about the aging system of 20 tanks and its proximity to Oahu’s principal aquifers supplying much of the island’s drinking water. It’s festered for the past seven years, since a 27,000-gallon leak of jet fuel from one of the tanks put the longevity of the World War II-era system in question.

The latest development, paired with the state’s high rank in priority for investment of federal defense dollars, may be the nudge the Navy needs to find a permanent solution to the problem: replacement of the system altogether.

Last week’s finding of the state Department of Health (DOH) Environmental Health Administration was part of an ongoing contested case hearing over renewing the Navy’s five-year permit to continue operations of the facility, which stores fuel for its ships and jets serving the Pacific region.

Negotiations have directly involved the Health Department as well as the Environmental Protection Agency, but the Honolulu Board of Water Supply, along with Sierra Club Hawaii, have pressed hard to safeguard the nearby water aquifers.

State environmental regulators said last week that the Navy has not proved it can safely operate its underground Red Hill fuel tanks, which in recent years have been the subject of mounting concerns over leaks and groundwater contamination.

The conclusion, submitted by the Health Department agency as part of a contested case hearing, raises the possibility that the state might deny the Navy a five-year permit to continue operating the facility, or at least heavily condition the approval.

The statement, issued by James Paige, a deputy attorney general for the DOH administration, said definitively that the Navy “has not met its burden of demonstrating that this facility is protective of human health and the environment.”

The next step is uncertain, but the timing of the final decision could align with planning and financing of a solution that works for the long haul.

A hearings officer will recommend the order, after considering the positions of the parties in the case. The health director then will issue the final decision on the Navy’s permit request, but there could be a significant delay: There is no legal deadline for DOH to deliver one.

A conventional outcome would be an order setting strict conditions on a permit approval. At a minimum, the state should insist that the Navy implement a double-liner protection against future tank leaks.

However, this may be the time for the state to press the Navy for a better answer.

Hawaii has been on the receiving end of significant investments in defense infrastructure. The defense funding bill for fiscal year 2022 included — along with the big-ticket items such as $2.2 billion for Pearl Harbor Naval Shipyard and $75 million for a Hawaii missile defense system — $5 million to continue improving safety of the Red Hill tanks.

That could be a down payment for a long-term plan to relocate the tanks to a site that does not pose a threat to the precious aquifer. Hawaii is a crucial strategic base as security concerns for the Asia-Pacific region continue to mount.

It should be critical that its facilities be brought to a 21st-century level of safety, to support future needs. Oahu will be living with these decisions for decades to come — longer than these tanks might ever have been designed to last.