Honolulu would face some serious pain if the aging tanks that store some 187 million gallons of Navy jet and diesel fuel at Red Hill were to suffer a catastrophic leak.

The aquifer that lies 100 feet below the 78-year-old Red Hill Bulk Fuel Facility could become unusable for decades, officials with the Honolulu Board of Water Supply warn.

It would also render useless Oahu’s largest and most productive well, the Halawa shaft, which sits less than a mile from Red Hill. The Ha­lawa shaft produces 20% of the water — 10 million to 20 million gallons of water a day — for some 450,000 residents and other customers from metropolitan Honolulu to Waikiki and all the way to Hawaii Kai.

And that would likely lead to a decade or more of mandatory Honolulu water conservation mandates, weakened water pressure, a construction moratorium and higher water rates across the island.

“It could go on for a very long time,” said Erwin Kawata, chief of the Honolulu Board of Water Supply water quality division. “Because to try to install a water source to replace the Halawa shaft would not occur overnight. It would take several years to design, construct and fund a replacement equal to the Halawa shaft. It could take hundreds of millions of dollars.”

Ernie Lau, the board’s manager and chief engineer, said he hopes never to have to experience this worst-case scenario.

“We hope that people will wake up and make the right decisions to prevent a major disaster from happening,” he said.

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The Red Hill facility actually sits on the border between the Waimalu and Moanalua aquifer systems. Together, the aquifers produce a combined 61 million gallons of water a day.

What exactly is an aquifer?

Chris Shuler, a groundwater researcher with the University of Hawaii’s Water Resources Research Center, says there are a lot of misconceptions out there.

“It is not an underground lake or river,” Shuler said. “It’s not a closed system where you can easily draw boundaries.”

Generally speaking, an aquifer in Hawaii is the mass of volcanic lava rock that holds fresh water in its nooks, crannies and cracks. The fresh water floats on layers of denser brackish and salt water that is connected to the ocean.

The aquifer recharges itself from rain that trickles and filters down into the lava rock, and it can take decades for a raindrop to reach the aquifer.

The state Commission on Water Resource Management has divided the island’s aquifer into 26 aquifer systems that are all connected to each other, though water flows between some systems more than others.

Shuler said that while the geology of the island and its aquifers makes it extremely unlikely a major spill at Red Hill would contaminate the groundwater on the other side of the Koolau, or on the North Shore or Leeward coast, the complex geology in the Honolulu-Pearl Harbor region also makes it difficult to predict exactly where or how far any pollution would travel.

The Honolulu Board of Water Supply uses four shafts, 12 tunnels and 84 well stations around the island to tap water from the aquifers. Water from the tunnels and wells is fed into nearly 2,000 miles of transmission pipes that go to water users.

Sustainable yields are defined in the State Water Code as the maximum rate at which water may be withdrawn from a water source without impairing the utility or quality of the water source. The total sustainable yield on Oahu, according to the Board of Water Supply, is 407 million gallons per day. One 1 mgd serves about 2,000 homes.

There was a time when contamination of Hawaii’ s groundwater was thought to be unlikely, because of the depth of the water table and the extensive percolation and filtering action required for the water to join up with the aquifer.

However, in the early 1980s insecticide chemicals were discovered in various Central Oahu wells, proving that Hawaii’s aquifers are indeed vulnerable.

Among the polluters was Del Monte’s 3,000-acre pineapple plantation at Kunia, which was designated an Environmental Protection Agency Superfund site after chemicals from fumigants used in the 1940s were found fouling the groundwater. While a section of the plantation has been removed from the list, contamination remediation continues at the site.

The Board of Water Supply continues to treat a combined 20 mgd of groundwater with agricultural chemicals in it from sources in Waipahu, Kunia and Waialua.

It’s an expensive process, officials said, but the water is treatable. Unknown is whether water contaminated with petroleum chemicals can be feasibly treated for drinking water.

Navy studies have already indicated the groundwater underneath and within close proximity to the Red Hill tanks is already contaminated with petroleum chemicals. Documents also show leaks dating back to 1947, plus ongoing corrosion of the tank liners.

An earthquake could easily cause a structural failure of the tanks and trigger a large fuel release, sending more than a million gallons of fuel into the groundwater and potentially several million gallons into Halawa Stream and Pearl Harbor, officials said.

If that were to happen, according the Board of Water Supply’s website, the agency would immediately shut down its Halawa shaft and Moanalua wells and then impose a water moratorium in Honolulu.

The Navy’s Red Hill shaft also would be closed, causing a water shortage for Pearl Harbor. A large fuel leak would render the groundwater aquifer unfit for drinking for decades, officials said.

In an interview, Lau said his agency would immediately look for a replacement water source, but a well field of that size would take seven to 10 years to get online.

There would be exploratory wells to determine capacity, and then the infrastructure and pumps needed to develop the wells, including the electrical systems and connecting pipelines, would need to be designed. A small water tank might also be needed to stabilize pressure.

“It’s a lot of effort,” Lau said. “The permit process could be extensive. We would also have to complete an environmental assessment or an environmental impact statement.”

Lau said the cost of spending $100 million for a new water source was not factored into the board’s 2016 30-year master plan.

“It is not a trivial effort,” he said.

The Navy is requesting to operate at Red Hill through 2045 and to gradually upgrade the facility over time.

“But it’s already 78 years old. As each year passes, the risk of a major release increases,” Lau said.

With Lau, the veteran water manager, at the helm, the Honolulu Board of Water Supply for eight years has been urging the Navy to either double-line the Red Hill tanks or move them elsewhere.

On Friday, when Lau announced in a news conference that the board was temporarily shutting its Halawa well down to safeguard its water source against the Navy’s fuel contamination, he grew emotional.

“It’s time for action now. It is time … ,” he said before pausing to compose himself. “We cannot wait any longer. The water resource is precious, it’s irreplaceable, it’s pure. There is no substitute for pure water, and our lives are dependent on it.”

Hawaii’s water cycle by Honolulu Star-Advertiser