A slow-motion environmental disaster may be in the making with the discovery Saturday that 42,000 gallons a day of crude oil is spewing from a well on the bottom of the Gulf of Mexico near where a huge drilling rig sank last week ï¿½ and it could be months before it's stopped.

The spill, which a day earlier Coast Guard officials believed was contained within a 16-square-mile area on the surface, now covers some 400 square miles ï¿½ slightly bigger than the city of Dallas ï¿½ and could grow as the well continues to leak, Rear Adm. Mary Landry, commander of Coast Guard District 8, said Saturday.

ï¿½This is a very serious spill,ï¿½ she said at a press conference, adding that governments of Texas, Louisiana, Alabama, Mississippi and Florida had been warned about the threat of oil coming ashore and invited to participate in the response.

Word of the expanding spill came as the Deep­water Horizon drilling rig was found capsized and lying on the sea floor about 1,500 feet northwest of the well, located roughly 40 miles off the coast of Louisiana.

The semi-submersible rig, which is owned and operated by Swiss-based Transocean and under lease to BP, sank Thursday morning after an apparent blowout late Tuesday night sent the facility up in flames. Of the 126 on board at the time, 11 are still missing and presumed dead; the rest were evacuated safely.

Friday evening, the Coast Guard suspended the search for the 11 workers amid growing signs they had perished in the initial blast.

Since then, attention has turned to the huge environmental cleanup effort and what Landry called a ï¿½very extensiveï¿½ investigation by the Coast Guard and U.S. Minerals Management Service into how the accident happened.

As part of that effort, robot submarines equipped with cameras have been deployed in recent days to survey the wreckage and ensure the well was no longer leaking oil.

The Coast Guard said it had not detected oil coming from the well Friday and assumed post-accident efforts to activate the blowout preventer ï¿½ a huge stack of valves sitting atop the wellhead on the sea floor ï¿½ had been successful.

But later trips by the remotely operated vehicles, called ROVs, discovered oil shooting from the end of the pipe-like riser that had connected the rig to the blowout preventer.

A second, smaller leak was found in a section of drill pipe near the wellhead.

That 21-inch-diameter riser had become detached from the rig when it sank. In the process, it was folded over at a 90-degree angle just above the wellhead, which had the effect of kinking it like a garden hose and constraining the flow of oil from the well. It now sits in a long, meandering mess on the ocean bottom. This helps explains why oil was not initially thought to be seeping.

Challenging situation

It also highlights the challenges of trying to comb an accident scene nearly one mile below the surface of the water.

ï¿½In 5,000 feet of water, it does add some complexity,ï¿½ said Lars Herbst, region director of the Gulf of Mexico for the U.S. Minerals Management Service, the arm of the Interior Department that regulates offshore drilling in federal waters.

Doug Suttles, chief operaing officer for BP exploration and production, said while the Coast Guard works to clean up oil at the surface, the company has mobilized some 700 employees and contractors to figure out a solution for sealing the well at the sea floor.

The preferred option, he said, is still to find a way to engage the blowout preventer. That fix, if it works, could be handled in a matter of days, he said.

But if that doesn't work, the other option is to drill a deep ï¿½reliefï¿½ well into the damaged well and stem the flow of oil, though that option could take several months, Suttles acknowledged. He said his team would spend the next several days trying to determine the best method.

So far, the cleanup effort has vacuumed more than 33,000 gallons of oily water mix from the surface of the Gulf of Mexico, Landry said. No estimate was available about how much remained. Also onboard the submerged rig is an estimated 700,000 gallons of diesel fuel that has not been retrieved.

Sidney Coffee, former chair of Louisiana's Coastal Protection and Restoration Authority, said any oil can pose a threat to marine habitats, and she is watching the Deepwater Horizon situation. ï¿½But with the technology they have, they can usually get it under control pretty quickly.ï¿½

Rough seas, rain and winds temporarily halted the cleanup Saturday. Storms produced waves 8 to 10 feet high, forcing the Coast Guard to call ashore five oil-skimming boats, three work barges and five planes involved in the efforts. They will resume when the weather improves.

brett.clanton@chron.com