It took a spill of an estimated 27,000 gallons to draw attention to serious environmental risks that aging fuel tanks pose to Honolulu's drinking water.

Click here to watch Catherine Cruz's report.

Two years after that spill, there was still no cleanup, but the military agreed to a timeline and scope of work to reduce the threat. The plan gives a 20-year time frame to upgrade the 20 underground tanks.

"If we find that technology is appropriate and feasible as far as economics, that time frame could be shortened quite a bit,” said Keith Kawaoka, Deputy Environmental Director.

The settlement doesn't promise double-lined tanks nor does it say exactly how many additional monitoring wells will go in, but it does address studies that need to be done in the next two years to meet the 20-year timeline.

"One other thing that makes this unique is we have a regulatory agencies overseeing the Navy on a situation where wouldn't have been," said Dean Higuchi, EPA Region Hawaii.

The settlement also has language that leaves open improvements to leak detection systems and cleanup of past spills.

Navy officials say the spills can't be pumped, put out or dug out. The only other option? Finding ways to speed up the degrading process.

While the settlement says the military agrees to look at alternate fuel storage options and other locations, Navy officials were clear that moving the tanks isn't really doable.

The military points to the strategic importance of the facility to fueling the Pacific fleet's ships and planes, and being built into a mountainside provides the protections from outside threats and any power failure.

"Because of our off-the-grid nature, we are particularly not prone to any kind of cyberattacks. The combination of those elements make Red Hill unique and difficult to replicate in 2015 and up,” said Capt. Kenneth Epps, Fleet Logistics Center.

However, some still worry that the settlement doesn't go far enough to address the corrosion of the tanks and the transparency of a process that is up against national security.

"Actions need to be taken in a quicker time frame. This is a really old facility,” said Ernie Lau, Board of Water Supply Chief Engineer.

An old facility that even the military acknowledges the need for improvements that could cost hundreds of thousands of dollars even upwards of a billion dollars.

To view the full document on the Red Hill plans, please visit the “As Seen On” section of KITV.com.