Located underneath Pearl Harbor’s Halawa gate is an environmental problem that’s nothing new, but still majorly concerning.

One of more than 700 documented areas of contamination on the base is a murky plume of bunker fuel and other petroleum products, . These hazardous materials - some of which the Navy claims dates back to World War II - have been leaking from a tank farm and collecting in the water for decades.

What used to be an important fishing area has now been on the of hazardous waste sites since 1992. In 1998, by the health department to warn people against eating fish or shellfish caught in the harbor. The Navy has been working with the EPA and the Hawaii Department of Health since 1983 to monitor and remedy the situation.

“The state agrees with our assessment that the plume is table,” Navy Region Hawaii spokesman Tom Clements . “It is not a threat to drinking water and it does not appear to be moving towards the ocean.”

Despite reassurances, many islanders remain understandably concerned.

This photo shows a general view of Joint Base Pearl Harbor-Hickam on Friday, June 29, 2012 in Pearl Harbor, Hawaii.

(Kent Nishimura/AFP/GettyImages)

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“This is the most egregious, the most harmful environmental issue there is,” environmental activist Carroll Cox . “Oil should not be in the ground, diesel should not be in the ground because they are contaminants.”

Current records issued by the Navy indicate that the subsurface oil plume now . Because it lies underneath a maze of utility lines, clean-up efforts face extreme difficulty. Estimates for cleanup costs run into the tens of millions of dollars.

“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,” the Navy . They also shared that they continue long-term monitoring of the plume and that all reports are being provided to the state’s health department.

The plume , a tar-like substance used by ships. Additionally, it contains weathered jet fuel and diesel. Because bunker fuel is so heavy, the state health department does not believe that the oil is moving and that it will not seep into the water soon.

However, if it were to seep into the water, it would cause a significant amount of marine and environmental damage.

“I think the most important thing is transparency. This is something that has been happening for years both for this incident and others,” said State Representative Chris Lee, D-Kailua, who stated that . “We need to know if there is a risk posed by these tanks and others around the state because we need to stop this before [another] leak happens.”

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