A composite photo illustration provided by NOAA, Boeing, and Coda Octopus shows a historic photo of the USS Independence, top, with a 3-D, low-resolution sonar image of the shipwreck, bottom, found in Monterey Bay National Marine Sanctuary off the coast of northern California. The outline of a possible airplane in the forward aircraft elevator hatch opening can be seen in the lower image.

HALF MOON BAY, Calif. (Tribune Content Agency) — In a ghostly reminder of the San Francisco Bay Area’s nuclear heritage, scientists announced Thursday they have captured the first clear images of a radioactivity-polluted World War II aircraft carrier that rests on the ocean floor 30 miles off the coast of Half Moon Bay.

The USS Independence saw combat at Wake Island and other decisive battles against Japan, and was later blasted with radiation in two South Pacific nuclear tests. The Navy deliberately sunk the contaminated ship in 1951 south of the Farallon Islands.

The rediscovery of the USS Independence offers a fascinating glimpse into American military history and raises old questions about the safety of the Farallon Islands Radioactive Waste Dump — a vast region overlapping what is now a marine sanctuary where the federal government dumped almost 48,000 barrels of low-level radioactive waste between 1946 and 1970.

The expedition to locate and survey the Independence was led by the National Oceanic and Atmospheric Administration with help from the Navy and Boeing, which mapped the wreck last month using a robotic underwater vehicle equipped with cutting-edge sonar capable of producing three-dimensional images.

The images, which show the hull of the ship remains remarkably intact, suggest the Independence lived up its nickname, “The Mighty I.”

The 623-foot-long ship took a remarkable degree of punishment in its 10-year career, said NOAA official James Delgado, chief scientist of the Independence mission. After World War II, the Independence was engulfed in a fireball and heavily damaged during the 1946 nuclear weapons tests at Bikini Atoll, transformed into a floating nuclear decontamination lab while stationed at Hunters Point Naval Shipyard in San Francisco, then finally towed out to sea laden with untold barrels of radioactive waste and scuttled with two torpedo warheads.

The Independence was sunk on Jan. 26, 1951, and came to rest 2,600 feet below the ocean surface.

The Navy withheld the location of the wreck for decades, but the U.S. Geological Survey found its likely resting place while mapping the sea floor in 1990. In 2004, a NOAA ship captured a distant image of what looked like a giant caterpillar stretched on the bottom of the ocean, said Delgado, who has led a two-year mission to find and study historic shipwrecks in and around the Gulf of Farallones National Marine Sanctuary.

“This ship is an evocative artifact of the dawn of the atomic age, when we began to learn the nature of the genie we’d uncorked from the bottle,” said Delgado, adding, “It speaks to the ‘Greatest Generation’ — people’s fathers, grandfathers, uncles and brothers who served on these ships, who flew off those decks, and what they did to turn the tide in the Pacific war.”

Delgado said he doesn’t know how many drums of radioactive material are buried within the ship — perhaps a few hundred. But he is doubtful that they pose any health or environmental risk. The barrels were filled with concrete and sealed in the ship’s engine and boiler rooms, which were protected by thick walls of steel, Delgado said.

The submarine that mapped the Independence got within 200 feet of the wreck, he said. Scientists tested the vehicle and the water on its instruments for radioactive isotopes and found only normal background radiation levels, he said.

But word of the Independence survey stirred up lingering concerns about the nuclear waste near the Farallon Islands, an area teeming with wildlife. Retired judge and state legislator Quentin Kopp, who many years ago demanded research into the Navy’s disposal of radioactive material off Northern California before 1970, said Thursday that the question of whether the waste posed a risk to humans and wildlife was never resolved.

“If I were an elected legislator, state or federal, I would be pounding the table,” Kopp said.

Kai Vetter, a University of California, Berkeley nuclear engineering professor who assisted the survey, said the ocean acts as a natural buffer against radiation. And the contaminated sites are small enough that they wouldn’t work their way into the broader food chain, he added.

“The risk here to have a public health impact is extremely small,” Vetter said.

Vetter said he hopes to obtain samples of the hull of the Independence in the next year to analyze the effects of radiation and other forces on the metal. Delgado said, however, there are no plans to further examine the wreck at this time.

The Gulf of Farallones sanctuary is a haven for wildlife, from white sharks to elephant seals and whales, despite its history as a dumping ground.

Richard Charter, a senior fellow at the Ocean Foundation, was involved in the creation of the sanctuary back in 1981. He said the radioactive waste is a relic of a dark age before the environmental movement took hold.

“It’s just one of those things that humans rather stupidly did in the past that we can’t retroactively fix,” he said.

©2015 San Jose (Calif.) Mercury News. Distributed by Tribune Content Agency, LLC.