The Navy announced this week that recent tests show that the drinking water supply in the Red Hill area around its aviation fuel tank facility is safe, just as the Honolulu Board of Water Supply sent out letters to its 170,000 customers expressing leeriness in the aftermath of a leak that released roughly 27,000 gallons of fuel into the ground.

The U.S. Environmental Protection Agency announced last week that it has reached a tentative agreement with the Navy and state Department of Health on a plan to improve the Red Hill Bulk Storage Facility, a plan that involves further study, more frequent testing and upgrades to all 20 of the 12.5 million-gallon aviation fuel tanks at Red Hill.

In January 2014, officials said that roughly 27,000 gallons of aviation fuel had leaked from one of the facility’s tanks. While tests on drinking water samples taken since the incident have been within acceptable federal and state levels, state and city officials have voiced serious reservations about the continued use of the storage tanks.

The agencies will hold a public hearing on the draft report of the Administrative Order on Consent, 6:30 to 8:30 p.m. Thursday at Moanalua Middle School’s cafeteria.

In a news release issued Wednesday, the Navy Region Hawaii office said samples drawn from the Red Hill Shaft drinking water well showed a “non-detect” level of fuel contamination. Similar lab tests have been conducted at least quarterly since the January 2014 leak, with results consistently within federal and state guidelines — “most often as non-detect, or no presence of fuel contamination in drinking water wells,” the release said.

Capt. Dean Tufts, regional engineer for Navy Region Hawaii, said, “While the facility’s value to our nation remains vital as America rebalances its forces to the Indo-Asia Pacific, the Navy considers the availability of safe drinking water on Oahu to be a nonnegotiable requirement.”

The Board of Water Supply, which did not participate in negotiating and drafting the administrative order, expresses less confidence about the situation in its letter to customers.

Pointing out that the World War II-era fuel tanks are located 100 feet above the groundwater aquifer that BWS uses to provide about 25 percent of the supply used for customers from Moanalua to Hawaii Kai, the letter notes in boldface print, “The BWS is testing its wells in the area and wants to assure our customers that our water is safe to drink.”

It continues, “However, Navy studies show that fuel leaks from the Red Hill tanks have occurred in the past, and the groundwater underneath the tanks are already contaminated with fuel. These findings describe a situation that poses a serious threat to the aquifer’s long-term ability to provide safe drinking water.”

The city agency said it is “working to obtain more information about the facility,” maintaining contact with the state Health Department and the EPA, and conducting its own groundwater studies.

The letter advises customers to “be concerned” about the existing situation, stay informed and voice any concerns.

“This contamination, if not cleaned up, has the potential to migrate to neighboring wells in the area because the groundwater is always moving,” the letter said.

Further, the letter said, BWS will continue to urge the Navy to double-line tanks, install advanced leak detection and tank corrosion protection, and clean up existing fuel beneath the tanks “so that the contamination does not reach our wells.”

The draft administrative order calls for a feasibility study to be submitted within two years that will spell out a range of tank upgrade options. Each of the tanks would then need to be upgraded over the next 20 years. Additionally, the Navy is to double the frequency of its tank testing.

The BWS website delves further into the matter, noting that “a catastrophic fuel release could occur as the result of structural failure of the tanks caused by an earthquake. This could result in more than 1.2 million gallons of fuel released into the groundwater and 6.3 million gallons to Halawa Stream and Pearl Harbor.”

Regarding the BWS letter to customers, agency spokeswoman Shawn Nakamoto said, “This is our effort to inform our customer base to make them aware of the situation, to let them know what we’re doing to protect the water source.”

She added, “We’re not saying that our wells are contaminated, because they’re not. But the fact that there are fuel tanks, and they are old fuel tanks, sitting atop of that aquifer just barely 100 feet above is concerning to us as a water utility.”