SAN FRANCISCO (Map, News) - Most of the workers who have cleaned Cosco Busan fuel from Bay Area shorelines are expected to be sent home by the end of this week, but officials have warned that toxic oil will remain on some coastal rocks.

Volunteers helped thousands of contractors clean oil from shorelines after the container ship spilled 58,000 gallons of fuel into the Bay on Nov. 7, but just 350 workers and no volunteers remained on the job Sunday, according to Department of Fish and Game official Rob Roberts, who has coordinated state cleanup efforts.

Cleanup efforts are expected to be finished by Friday, he said, but shoreline monitoring is expected to continue for months. The entire coastline will be surveyed for oil in January, Roberts said.

Locally, the remaining workers are painstakingly collecting oil on Treasure, Angel and Alcatraz islands, east of China Beach, and west of Aquatic Park, according to Roberts. He said workers are also spraying oiled rocks with hot water, then collecting the dislodged oil. “Sometimes we can get most of it,” Roberts said. “But it’s not 100 percent.”

Rocks that are too slippery to be safely walked on, or that are home to crabs, plants, barnacles and other organisms, such as some of the rocks on Alcatraz Island, are not pressure-washed. Instead, Roberts said, “We just let nature handle it.”

Hot water, according to UC Berkeley marine ecologist Tim Herrlinger, can be lethal to shoreline critters. “They’re more likely to die when the temperature goes up a little than if it went down a little,” he said.

Ecosystems on Alaskan rocks that were left in oil after the 1989 Exxon Valdez spill sometimes recovered better than ecosystems on rocks that were pressure-washed with hot water, according to Herrlinger.

Dennis Deaver fished Alaska’s Prince William Sound until the Exxon Valdez spill destroyed the inlet’s herring population. The commercial Bay fisherman said oil that was pressure-cleaned off Alaskan rocks was not always removed. “All it did was run down in the rocks and sand,” he said.

About 2 percent of Exxon’s oil remained on Alaskan shorelines three and a half years after the accident, researchers found.

The U.S. Coast Guard abandoned plans to use oil-lifting chemicals on rocks, according to U.S. Coast Guard spokesman Jonathan Cilley, because the chemicals left slippery residues after tests at UC Berkeley.

High-pressure, hot-water rock cleaning

Advantages

» Removes oil from rocks

» Organisms can repopulate cleaned rocks

» Removed oil is prevented from washing back into the Bay

Disadvantages

» Traces of oil are left behind

» Can kill animals, plants and other organisms

» Workers can slip as they clean oiled rocks

Source: Rob Roberts, California Department of Fish and Game

jupton@examiner.com