Debris unleashed from March’s Japanese earthquake and tsunami will land on beaches in the main Hawaiian Islands as early as spring 2013, but how much will arrive and how it will be disposed of remain a mystery.

An estimated 5 million to 20 million tons of debris was dragged out to sea by the March 11 tsunami, said Jan Hafner, a scientific computer programmer at the University of Hawaii’s School of Ocean and Earth Science and Technology who is helping UH oceanographer Nikolai Maximenko track the path of the debris.

It’s unknown how much tonnage continues to bear down on Midway Island, the Hawaiian Islands and eventually the West Coast of the mainland, Hafner said.

But the loose assortment of debris stretches 2,000 miles long and 1,000 miles wide, he said.

From Sept. 21 through 28, the crew of the Russian training ship STS Pallada sailed into the debris field and retrieved a boat and saw a television set, refrigerator, other home appliances, drums, wash basins, fishing buoys, wood and lots of plastic bottles, Hafner said.

"Everything that can float can possibly be in that field," Hafner said. "The common misconception is that people think you can walk on it. It’s just the opposite. It’s very diluted and very patchy. One day they (the crew of the Pallada) could hardly see any debris, even from inside the garbage patch."

Tests on the debris found no danger of radiation, Hafner said, because it likely flowed to sea before Japan’s nuclear catastrophe.

"They did not measure any elevated levels," he said. "All normal."

Gary Gill, the Health Department’s deputy director for the environment, said, "The Department of Health is anticipating and is prepared for the possibility that there may be debris from the Japan tsunami that could be tainted with radiation, and our radiological response team is already sampling ocean debris and anything that comes ashore and testing it for radioactivity. We have not found anything above background levels at this point. We don’t anticipate finding anything significant any time soon, but we are monitoring and are ready to respond if any debris comes ashore."

It could be "months to years" before any of the Japanese debris arrives in Hawaii, Gill said.

"From my own life experience, I don’t anticipate that we’re going to see a huge debris field coming in all at once," he said.

City Councilwoman Tulsi Gabbard co-founded the Healthy Hawaii Coalition, an environmental nonprofit group, and helped pick up medical waste that poured out of the Waimanalo Gulch landfill and washed back ashore during January’s heavy rain.

"To my knowledge, no one here in Hawaii has really stepped up at this point in terms of coming up with a plan for all this (Japanese) debris, and that’s crucial," Gabbard said. "When we look at our vital natural resources here that we must preserve, we can’t afford to wait until this comes to our shores before taking action. We need to ensure that our reefs and beaches will not be affected and that this will not negatively affect our economy and tourism industry, let alone our fishing and other industries that rely on our waterways."

Gabbard wants the city to work with state and federal agencies to come up with a plan to retrieve and dispose of the Japanese debris.

"It’s not a matter if we’ll be affected, because we will," Gabbard said. "We need to be prepared. Where all of this debris and waste will be put is definitely an issue."

Stuart Coleman, Hawaii regional coordinator for the Surfrider Foundation, agrees with Gill that "it won’t be a mountain of garbage."

But Surfrider Foundation volunteers currently sweep Hawaii’s beaches of tons of refuse each year, and bits and pieces of Japanese debris will only add to the tonnage, Coleman said.

"We’re very concerned," he said. "We should see a dramatic increase in the tons of debris we already collect."

The Surfrider Foundation’s Oahu chapter has applied for a grant to organize volunteers to clean up heavy marine debris and pay for disposal fees, Coleman said.

"But our landfills are already overfilled and have been extended beyond their original life span," he said.

Maximenko’s computer models anticipate that the debris field will hit the Midway Islands directly this winter, followed by an unknown amount that will land on each of Hawaii’s populated islands by spring or winter 2013, Hafner said.

"Most of it will pass north of Hawaii," Hafner said. "Some of it — the very patchy pieces of the southern flank — will end up in Hawaii in the first wave and reach all beaches that currently receive garbage."

The first pieces of light debris will hardly be noticed, Hafner said.

They’ll likely be plastic bottles and similar items being pushed ahead of the main debris field by ocean winds, Hafner said.

"It will be gradual and difficult to tell," Hafner said. "There might be just one bottle, and the next day there’ll be two bottles, then gradually more."

But when television sets, refrigerators and other appliances start landing on Hawaii’s famous beaches, Hafner said, "that’s when you’ll know it’s most likely from the tsunami."

The rest of the debris will then move north around the main Hawaiian Islands and head for Oregon, Washington, Canada and Alaska before turning south-southwest back down the West Coast.

Whatever is left of the Japanese debris will then merge with the infamous "North Pacific Garbage Patch" swirling between California and Hawaii, Hafner said.

"That’s the final destination of all debris and garbage floating in the Pacific Ocean," he said.