State spill responders and Alyeska Pipeline Service Co. are responding to a "slow weeping of crude oil" discovered at a joint along a buried section of the 800-mile trans-Alaska pipeline between Glennallen and Delta Junction.

It's uncertain how long the coupling along the pipeline near Pump Station 10 has been seeping oil, but an estimated 10 or so gallons had spilled, according to an incident report issued by the Alaska Department of Environmental Conservation Friday.

The pipeline carries the crude oil that is the economic lifeblood for Alaska, moving an average of about 500,000 barrels of crude oil daily last month. The leak doesn't put the line in danger of shutting down, said Michelle Egan, director of corporate communications for Alyeska.

"It's not an imminent threat," Egan said. "It's something we're taking lots of caution around, but that's pretty much how we operate."

The trans-Alaska pipeline operator has recovered 5 yards of contaminated gravel from the area, she said. The company is monitoring the site around the clock, has installed containment protection to capture additional leaking, and has a vacuum truck on site as a precaution to remove oil if needed.

The leak was discovered last Friday, during standard maintenance required to assess the integrity of the pipeline. Oil had accumulated within the tar packing material that covered the coupling, the state said. The initial "weep rate" was about one drip per second, and "minor weeping" is still occurring, the incident report said.

Alyeska is investigating the cause and developing cleanup plans that will be approved by DEC regulators, the state said.

"(Alyeska) will continue to work closely with the State Pipeline Coordinator's Office to identify and correct the cause of the release, as well as developing protocols for assessing ... 21 isolation fittings located along the TAPS system," the state said.

Two previously scheduled maintenance shutdowns for the summer, including one in mid-June, offer a window for repairs, said Egan.