At the same time state officials are focused on the Red Hill fuel leak of 27,000 gallons, environmental activist Carroll Cox is pointing to a fuel release more than 10 times that amount at Pearl Harbor just 600 feet from the shoreline, originating from another aging tank.

A diesel fuel leak of 359,000 gallons from a 1-1/2-by 3-inch hole in the above-ground Tank 48 on Joint Base Pearl Harbor-Hickam was reported in 2007. Between World War II and the Tank 48 fuel spill, meanwhile, approximately 5 million gallons of petroleum spilled from the tank farm and remained in the subsurface, according to Navy reporting.

Most of that fuel is in the underground caprock, with the Navy saying the pre-Tank 48 release “was not migrating toward Pearl Harbor,” while the Tank 48 plume was “not likely” to reach the water’s edge.

But Cox, who obtained the “response action memorandum” for the Tank 48 spill, believes all the fuel should be cleaned up, and the fact that it hasn’t may be an indicator of what’s ahead for the Red Hill tank farm remediation.

“They need to address both (spills), and we shouldn’t trust anything they say up on (Red Hill), any promises made, because we see they can’t handle what’s downhill with the same ingredients, basically,” Cox said.

The Navy said Tank 48, built in 1925 and part of a complex of six above-ground tanks, is still active following a major overhaul in 2011. A small area on the bottom of the tank was weakened by corrosion and punctured by years of continuous pressure from the oil, the service said.

In an email, Navy Region Hawaii said subsurface oil under Joint Base Pearl Harbor-Hickam is not a new discovery.

“The Navy has been working with the Environmental Protection Agency and the state Department of Health on the Halawa-Main Gate Subsurface Fuel Plume since 1983,” the command said.

After the April 2007 Tank 48 release, the Navy assembled a unified command that included the EPA, the state Health Department and Coast Guard. The Navy said it spent approximately $3.2 million on emergency response.

The marine diesel fuel from the 2007 release seeped into the existing subsurface fuel plume. The Navy said it installed monitoring wells, a fuel recovery system and subsurface concrete barriers to monitor and prevent the migration of fuel products to Pearl Harbor, removing 14,647 gallons of petroleum products through an extraction trench.

The response action plan, signed by the Navy and state Health Department in 2013, said 87 groundwater monitoring wells, eight trench wells and four cutoff wall wells were initially gauged daily.

Petroleum hydrocarbon concentrations exceeding Health Department action levels were detected in two of nine groundwater samples, but fuel constituents in groundwater discharged into Pearl Harbor in the future were “likely to be well below screening criteria designed to protect human health and the environment,” the plan said.

Long-term monitoring was the recommended outcome. The Health Department said one of the problems in addressing the fuel plume is that utility lines cross the area, posing significant logistical challenges to remediation.

The Navy on Tuesday brought in members of the Honolulu Board of Water Supply and other officials to see the Red Hill Bulk Fuel Storage Facility as the EPA and state Health Department consider a proposed “Administrative Order on Consent” that would require the Navy and Defense Logistics Agency to take steps to minimize the threat of future fuel leaks at Red Hill.

The proposal commits the military to installing improved technologies for fuel release prevention and detection at the World War II facility. Supporting military operations in the Pacific, Red Hill includes 20 large underground fuel storage tanks built of reinforced concrete with steel liners surrounded by basalt bedrock.

Each storage tank has a capacity of 12.5 to 12.7 million gallons, with 18 of 20 tanks in use. In January 2014 while refilling Tank 5 after renovation, an estimated 27,000-gallon spill of JP-8 jet fuel was noted.

The leak was found to be the result of faulty work by a contractor, Rear Adm. John Fuller, commander of Navy Region Hawaii, said in an August opinion piece in the Honolulu Star-Advertiser.

But the spill touched off wider concerns about the aging facility and its proximity to Oahu drinking water sources. Sampling around Tank 5 indicated a spike in levels of hydrocarbons in soil vapor and groundwater while still remaining in compliance with federal and state regulations for safe drinking water, according to the EPA.

Some state and city officials have expressed concern about the continued use of Red Hill without more monitoring wells or double-lining of the steel tanks, something the Navy has said can be considered.

The proposed Administrative Order on Consent establishes a timeline for the Navy to “evaluate and remediate existing contamination to the extent practicable in the vicinity of the facility, as well as to evaluate and implement measures to prevent future releases,” the EPA said.

“Since 2006, the Navy and Defense Logistics Agency have invested more than $145 million to modernize Red Hill and for environmental testing, and we plan to invest another $70 million in upgrades,” Fuller said in the opinion piece. “This does not include any additional work that would be required by regulators through the Administrative Order on Consent.”