Why can't they plug the leak?
To plug the leak, Remotely Operated Vehicles (ROVs) have been deployed to try to trigger the blowout preventer (BOP), a valve that, when activated, would secure the leak, Terrell explained. The valve is located at the well head on the ocean floor.
"Right now, what the ROVs are doing is pumping a hydraulic fluid into the blowout preventer, in hopes to build pressure [to] close the hydraulic valve," Terrell told LiveScience. "The valve is supposed to work automatically, so now we're trying to come up with different ways to activate the blowout preventer manually."
The BOP's malfunction in this case — something that Terrell said is uncommon — will be part of ongoing investigations into the incident.
The ROV robot subs, manufactured by a company called Oceaneering, have been an integral part of the effort to control the leaking oil.
"The ROVs are our eyes and our hands down there," Terrell said. "We can't just go down 5,000 feet and work in that environment. So, they are definitely playing the biggest role."
The ROVs are controlled by personnel on land. So far, their attempts to activate the shut-off valve have been unsuccessful.