At a hearing in Anchorage, Alaska, Rear Adm. Thomas Ostebo and Shell Alaska Vice President Pete Slaiby both said it would be inappropriate to comment on an ongoing investigation, the Anchorage Daily News reported Thursday.
But Ostebo did say the Coast Guard was concerned with "potential Marpol violations," which is short-hand for "Marine Pollution," which would be a violation of the International Convention for the Prevention of Pollution from Ships, the newspaper said.
Slaiby said Shell's operations in arctic waters in 2012, "were completed safely and successfully."
"It was while leaving the theater of operations that issues with the Discoverer were identified by the Coast Guard and the Kulluk ran aground," Slaiby said.
The concerns stem from the grounding of the Kulluk drilling rig, which occurred off the coast of Kodiak Island after a New Year's Eve storm.
The rig was being towed to Seattle for maintenance when it ran aground. Shell said the Kulluk departed for Singapore on a dry-tow vessel Wednesday morning for inspection and repairs.
Shell also had trouble with the drilling rig the Noble Discoverer, which the Coast Guard cited for 16 code violations, including a claim that the vessel did not have the capacity to move fast enough in hazardous waters to remain safe.
Shell spent more than $4.5 billion in its arctic drilling and ended up with two partially drilled wells for its investment.
Shell's top executive in charge of arctic drilling and exploration has announced he is retiring, the Daily News said.
The Interior Department has also stepped in, revoking the company's permission to drill in Alaskan waters until it can show it has plans to manage an operation in the rough arctic conditions.
Interior Secretary Ken Salazar recently gave the company a succinct judgment. "Shell screwed up in 2012," he said.