"Three hundred sixty years from now, in the core part of the USS Arizona, the oil bunkers here will still have significant structural integrity," he said.

Another example is the SS Jacob Luckenbach. A freighter carrying military supplies, it left San Francisco in July 1953, headed for Korea, when it struck another vessel in fog. It sank just 17 miles off the coast, settling in 180 feet of water with 457,000 gallons of bunker fuel on board.

In the early 1990s, Californians began to notice mysterious, intermittent oil spills on their beaches. Over the next decade, more than 51,000 shorebirds were covered with oil and died. Oil and tar balls floated onto the beaches.

Investigators sampled the goo and tried to match it to fuel in the bunkers of passing ships. "But we couldn't figure out where it was coming from," Symons said.

It wasn't until 2002 that the state's technical dive community — recreational divers who used advanced technologies to reach more challenging sites — came forward and said they knew a shipwreck in the area that had been leaking oil for years, Symons said. It was the Luckenbach.

Cleanup and wildlife rehabilitation cost $2 million. Salvage of 100,000 gallons of the ship's oil eventually cost another $20 million, said Dagmar Schmidt-Etkin of Environmental Research Consulting. The rest remains on board.

Identifying wrecks that pose a serious risk of leaks and extracting the fuel before an incident occurs is costly, she said. But there is a cost to doing nothing, too: the economic losses to fisheries and tourism; monitoring wrecks for signs of spills; maintaining the personnel, equipment and supplies needed to respond when needed; cleaning the shoreline and oiled wildlife; and disposing of the oil.

Her study estimated the costs of dealing with an oil spill from a shipwreck at $1 million to $5 million for a small spill at a protected location, to $20 million to $100 million for a big, complex spill recovery in a difficult, or open-water location.

Symons said there are many more ships like the Luckenbach off North Carolina, Virginia and Maryland, "and all the way up the seaboard, with the potential for having significant pollutants on board. We can wait until one of these vessels breaks apart, or we can try to be proactive."

Scott Wahl, public information officer for the New Jersey beach town of Avalon, said at the conference that his town has just 2,000 year-round residents. But its beach economy is dependent on clean and healthy beaches.

"Every job along the beach is dependent on clean beaches," he said. "Without that sand on the beach, we don't have an economy. Without a clean environment, we don't have an economy." Preventing spills from shipwrecks, he said, "is not a cost; it's an investment."

frank.roylance@baltsun.com

http://twitter.com/froylance

Maryland weather blog: Frank Roylance on meteorology

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