SEATTLE--The U.S. Coast Guard has found evidence of multiple safety and environmental violations in Shell Alaska's Noble Discoverer Arctic drilling rig and forwarded it to the Justice Department for a decision about possible civil or criminal penalties.

The action, which authorities confirmed Friday, is the latest setback for Shell's troubled Arctic drilling program, launched last summer off the coast of Alaska to tap one of the world's biggest remaining oil and gas deposits. The project has been plagued with logistical and mechanical troubles that raise questions about the company's ability to continue this year.

Already, the company's second Arctic drilling rig, the Kulluk, is facing substantial repairs after coming loose while under tow through the Gulf of Alaska and grounding on rocks near Kodiak Island. Now it appears that the Noble Discoverer also has problems, detailed in a Coast Guard report made available to the House Natural Resources Committee.

The Coast Guard found that a lack of preventive maintenance and "systematic failure" led the Discover to experience a loss of its propulsion system and an explosion in its exhaust system, according to a letter to Shell's president from Rep. Edward J. Markey, D-Mass., that detailed 16 reported deficiencies.

The letter also cited Shell's discovery of "possible unauthorized collected water discharges" outside the allowable period for drilling.

"The reports that Shell may have been drilling this summer using a drill ship with serious deficiencies in its safety and pollution control equipment raise additional and continued questions about whether Shell is able to drill safely offshore in the Arctic and raises serious questions regarding the nature and adequacy of Shell's compliance with applicable laws and regulations," Markey wrote.

The violations appear to be serious enough that Coast Guard officials in Alaska said they had referred the case to the Justice Department for review.

"The Coast Guard has referred some matters to us related to the Noble Discoverer, and we can't comment beyond that," said Kevin Feldis, assistant U.S. attorney in Anchorage.

The Coast Guard reportedly found that the Discoverer was not able to maintain sufficient speed at sea to maneuver safely in all sea conditions without the assistance of a tow, and that it had multiple dead-end wires and improper wire splices in the engine room and main engine cooling water contaminated with oil and sludge.

The vessel also experienced an abnormal propeller shaft vibration on the way back from the Arctic in November, requiring the crew to shut down the main engines and have the rig towed to the Port of Seward.

"It is imperative that any drilling operations in the Arctic Ocean occur with the highest levels of safety and environmental protections in place, and I am not convinced that these levels can ever be met given the extreme weather conditions, and Shell's performance thus far," Markey wrote.

Some of the reported deficiencies were described by the Coast Guard earlier, and Shell has said the owner of the vessel, Noble Corp., with which Shell has contracted for Arctic operations, already has moved to correct many of them.

"Of course, we take any deficiency very seriously, including those associated with the main propulsion system that surfaced after the Noble Discoverer had transited out of the Chukchi Sea," Shell spokesman Curtis Smith said. "At no time was the Noble Discoverer found or believed to be a danger to people or the environment while drilling in the Chukchi Sea in 2012. Had that been the case, we would have ceased all operations immediately."

The Kulluk and the Discoverer are scheduled to be transferred to a shipyard in Asia for inspections and repairs, and their return to operations in the Alaska Arctic depends on how much repair they need, Smith said.

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