An underground pipeline used to offload oil from a ship docked near Puget Sound apparently ruptured Sunday, spilling an estimated 400,000 gallons of Alaskan crude into a drainage ditch.

There were no immediate reports of damage to wildlife, oil company and Department of Ecology officials said.A small amount of oil seeped into Blair Waterway, where the ship was docked, said Bill Daberock, administrative services manager for U.S. Oil and Refining Co. "I don't think it's measurable."

The waterway leads to the sound's Commencement Bay more than a mile away.

Booms were rigged around the spill, and there was no immediate danger it would seep into the bay, Daberock said.

Most of the oil was trapped in a drainage ditch on Tacoma's Tideflats, which eventually drains into the waterway, Daberock said.

Crews used oil booms and other material to prevent the oil from seeping into the waterway, Ecology Department spokesman Ron Holcomb said. Vacuum trucks hired by the company were being used to remove the oil from the ditch.

"We have the entranceway (to the ditch) triple-boomed and have a skimmer there standing by," Daberock said. "If anything gets in there, we'll skim it out right away."

The leak was discovered about 9:25 a.m. on property not owned by U.S. Oil.

By calculating the amount of oil taken from the ship, the Overseas Alaska, and the amount that reached refinery storage tanks, company officials determined that roughly 10,000 barrels, or about 400,000 gallons, had spilled.