HOUSTON -- Choppy weather is delaying efforts to find the source of an oil sheen floating at the site of the 2010 Gulf of Mexico oil spill.

Coast Guard and BP PLC officials said a plan to use a remotely operated vehicle (ROV) to investigate equipment lying at the bottom of the Gulf by the Macondo well site was delayed last week but would restart this week.

Investigators had initially planned to take a look beginning Dec. 3 after the Coast Guard approved a proposal by BP and Transocean Ltd., the company that owned and operated the Deepwater Horizon offshore drilling rig (EnergyWire, Dec. 3).

Rough weather yesterday could have delayed operations further, but Coast Guard Ensign Glenn Sanchez said teams planned to proceed with the ROV deployment this week and would work as conditions allowed.

The continuing presence of an oil sheen at the site of the spill is leading to fears that some of the wrecked equipment could still be leaking crude oil. BP said multiple inspections have confirmed that the Macondo well itself is secured, remaining capped and sealed in concrete and showing no signs of further leakage.

Caps to relief wells drilled to intervene in the 2010 spill are also maintaining their integrity, according to the company.

BP spokesman Brett Clanton said there are no additional updates in the ongoing investigation of what's causing the surface sheen. The company had discovered a small leak from a massive containment dome left at the bottom, but workers sealed that leak weeks ago.

The Coast Guard is the lead on this week's investigation, Clanton said. He added that BP would defer to the Coast Guard to issue new updates and information on the investigation, but that the company was pledging to do everything it could to cooperate and get to the bottom of what's causing the sheen at the Mississippi Canyon 252 offshore lease.

"After recently confirming for a third time with ROV video inspection that the Macondo well and its associated relief wells are secure, BP capped and plugged an abandoned piece of subsea equipment known as a cofferdam that was identified as a potential source of sheen," Clanton said. "A further ROV survey is planned to inspect the Deepwater Horizon rig, riser, wells, cofferdam and associated wreckage from the accident.

"BP will work with the Coast Guard and Transocean on any further steps, as needed, to address the results of the next ROV survey," he added.

The Coast Guard cautions that it may take days or weeks to post updates on the subsea investigation.

"The information won't be put out until it's been vetted and authorized by headquarters," Sanchez said.

Lawmakers press Coast Guard for details

The presence of the sheen is attracting interest from lawmakers in Washington who are requesting more details into the investigation and even video of the ROV sweep of the Deepwater Horizon disaster wreckage.

Last week Reps. Ed Markey (D-Mass.) and Henry Waxman (D-Calif.) sent a joint letter to Coast Guard Adm. Robert Papp asking that he provide detailed answers to a set of six questions on the ROV inspection by Dec. 21.

In the letter, both congressmen complain that BP did not to respond to an earlier written request asking for a briefing on the investigation into the sheen. The lawmakers want to know whether the ROV inspection under way this week will skip over some of the remaining equipment lying at the bottom, and if so, why.

The lawmakers also want to know whether the planned survey includes an inspection of the seafloor itself, to determine whether crude oil is leaking through fissures. In the letter, they also express concerns about crude oil that may be trapped in the crumpled riser pipe and whether anything can be done about it.

"BP has failed to adequately respond to questions concerning these issues that we had posed to the company in correspondence from October 16, 2012," the lawmakers wrote. "BP has also failed to provide any documents and non-public information that we requested in our letter.

"It is imperative that BP take all available actions to mitigate further environmental damage from its oil spill."

So far, the Coast Guard says the oil sheen being looked at does not seem to pose any threat to nearby coastal regions. Investigators also believe cleaning up the sheen wouldn't be feasible for the time being.