The trans-Alaska pipeline is scheduled to shut down again this weekend for about 36 hours while workers install new piping to fix a leak that prompted a four-day emergency shutdown, company officials and regulators said.

The 800-mile line restarted at reduced flow on a short-term basis Tuesday night. The line was carrying oil from the North Slope oil fields on Wednesday at about two-thirds of its normal rate: roughly 400,000 barrels per day.

Federal and state regulators are allowing Alyeska Pipeline Service Co. to pump oil through the line even though it is causing more oil to leak from the faulty pipe encased in concrete at Pump Station 1 that prompted the shutdown on Saturday.

The ranking Democrat on the U.S. House Natural Resources Committee sent a letter to Alyeska on Wednesday with a battery of questions about the leak -- why it happened and whether the decision to restart the 800-mile line has created new spill risks.

Rep. Edward Markey of Massachusetts reminded Alyeska in his letter that the company testified to Congress in 2007 that accelerated corrosion was not a threat for the 800-mile line. The company also testified that it had added new corrosion monitoring locations at Pump Station 1, he wrote.

"It would appear those new monitoring locations were insufficient," Markey wrote. He requested a response to his letter by next Tuesday.

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