Pearl Harbor was once known as Oahu's "bread basket" because it was such an important fishing area, teeming with ocean life. But since the construction of the iconic U.S. military base, the pristine harbor has been marred by environmental disaster.
The 12,600 acres of land and water that make up the Pearl Harbor Naval Complex were added to the Environmental Protection Agency's National Priority List of hazardous waste sites in 1992. This list identified the area as a Superfund site, or one that could harm local people or ecosystems due to hazardous waste. In 1998, the health department had issued an advisory to warn people against eating shellfish and fish caught in Pearl Harbor.
One of the base's more than 700 documented areas of contamination sits beneath Joint Base Pearl Harbor-Hickam's Halawa-Main Gate. There, bunker fuel and other petroleum products -- some of which the Navy says date back to World War II -- have been leaking from a tank farm and collecting in a large underground plume for decades.
Current estimates put the amount of spilled fuel at around 5 million gallons, or nearly half the volume of the 1989 Exxon Valdez oil spill in Alaska, Hawaii News Now reported earlier this month. The plume is approximately 20 acres, or 15 football fields, in size, according to the Navy.
The subsurface oil "is not a new discovery," Navy Region Hawaii said in an email to The Huffington Post.
The Navy has been working with the EPA and Hawaii Department of Health since 1983 to monitor and address the situation.
"The state agrees with our assessment that the plume is stable," Tom Clements, a spokesman for Navy Region Hawaii, told HuffPost by phone. "It is not a threat to drinking water and it does not appear to be moving toward the ocean."
The plume is extremely difficult to access, and estimates for cleanup costs run in the tens of millions of dollars, Hawaii News Now reports. It is on a water table that is not a current or future source of groundwater, and reportedly lies 5 to 40 feet below ground, under a maze of utility lines.
Although the Navy reports the plume is stable, many islanders are still concerned.
Even State Sen. Mike Gabbard (D), who serves as chair of the committee on Water, Land, and Agriculture, didn't know about the plume before this month, telling HuffPost he was "shocked" to learn about the contamination.
"This news unfortunately adds to the mistrust in our government," he wrote in an email.
Carroll Cox, president of Honolulu-based environmental group EnviroWatch Inc., called it "the most egregious, the most harmful environmental issue there is."
Kyle Kajihiro, a board member of Hawaii Peace & Justice, said that while he knew about the plume before reading the most recent reports, he had not realized the scale and encourages an aggressive cleanup effort.
"What's interesting for me is how something so serious and egregious and large of a problem can be hidden in plain sight," he said.
French Peter via Getty ImagesPearl Harbor: USS Missouri foreground, USS Arizona Memorial background.
The military certainly has its skeptics in Hawaii.
Marti Townsend, director of the Sierra Club Hawaii Chapter, said that while she has huge concerns about the plume at Halawa Gate, a larger concern is the context of contamination.
"There's so much military contamination in Hawaii, it boggles the mind," she said.
In 2014, for example, an estimated 27,000 gallons of jet fuel leaked at Red Hill Bulk Fuel Storage Facility. The U.S. military plans to upgrade the Red Hill underground fuel storage tanks over the next 20 years as part of a new agreement with the EPA and the state health department.
But the Red Hill incident was just the latest of dozens of leaks over the last 70 years.
While the Navy says most of the oil in the Pearl Harbor plume was released from fuel storage, handling and transfer activities prior to the 1980s, 359,000 gallons of marine diesel fuel spilled in 2007 from an above-ground storage tank and seeped into the existing subsurface plume.
The Navy spent approximately $3.2 million on the 2007 emergency response. It installed monitoring wells, a fuel recovery system and subsurface concrete barriers to monitor and prevent the migration of fuel product to Pearl Harbor. It also removed approximately 11,000 gallons of spilled petroleum through an extraction well.
A larger emergency response would likely be needed if the massive Halawa Gate plume suddenly became unstable.
The Navy told HuffPost it continues long-term monitoring of the plume and that all reports are provided to the state's health department.
"To date, all well monitoring data shows that the plume is stable and not moving and does not pose a threat to human health or the environment," it said.
But the military recognizes that there are natural and man-made situations that could potentially cause the plume to move. "Although these situations are considered to be unlikely, if movement of product is observed, the Navy would immediately take mitigation measures to contain and recover any recoverable free product as practical to ensure the safety of human health and the environment," it said.
That effort would likely include strategically placed extraction systems or subsurface barrier walls.
"My main concern," Gabbard noted, "is that we do everything in our power to prevent the fuel from getting into our water."