Ten days after an explosion at the Deepwater Horizon oil rig in the Gulf of Mexico killed 11 workers and started spewing 210,000 gallons of oil a day, the pressure is growing on BP to stop the leak. The oil giant’s proposal for the drilling operation, submitted to federal regulators February 2009, ruled out the possibility of serious environmental damage from an oil spill, according to The Washington Post:

The company said “it is unlikely that an accidental oil spill release would occur from the proposed activities.” While it acknowledged that a spill could “cause impacts to wetlands” and to beaches, it added that “due to the distance to shore (48 miles) and the response capabilities that would be implemented, no significant adverse impacts are expected.” It said any effects on fish or shellfish would be “sub-lethal.””

The complete failure of underwater shut-off valves was not considered in the planning stages, the Coast Guard told The Post. Now, in addition to cleaning up the spill, BP must figure out how to seal the leak. The Post illustrates three options, the quickest of which would activate a shut-off valve on the sea floor using remote-controlled robots. A second option calls for covering the leaks with a 100-ton steel dome and funneling the oil to the surface; the method would take a few weeks and has been effective at much shallower depths. A third option would dig a horizontal well to intercept oil away from the leaking well, reducing the pressure and making it possible to seal the leak. There is at least one drill ship already in place to start this months-long process.

As federal officials start to figure out how the accident happened, BP is pointing the finger at Transocean, which owned the oil rig. The Wall Street Journal details Transocean’s recent safety records, which are likely to come under scrutiny. Following four worker deaths in 2009, the Swiss-based company’s board of directors voted to withhold executive bonuses until there was an improvement in safety standards. None of the deaths last year were aboard Deepwater Horizon, which as of Februuary 2009 reported no serious accidents for six years, the Journal reports. Transocean received a safety award last year from the Minerals Management Service for its operations in one part of the Gulf of Mexico, and its 2009 safety record was above the industry’s average.

Update: The Coast Guard told the Los Angeles Times that it’s become difficult to estimate the size of the spill. “Any exact estimate is probably impossible at this time,” Coast Guard Adm. Thad Allen said. BP estimates about 5,000 barrels of oil are spilling each day, but an environmental group and a Florida oceanographer say the rate is at least five times greater. From the Times:

A glance at the charts compiled from the oil spill database of the Mineral Management Service shows there were 63 spills of more than 50 barrels in the gulf from 2004 to 2009. Some of those spills were a combination of oil, petroleum products and chemicals such as glycol and zinc bromide, according to MMS. Total barrels: 132.