05:10 PM PST on Friday, March 17, 2006

KING5.com Staff and Wire Reports

SEATTLE - About 15 gallons of oil spilled into Seattle's Elliott Bay near Pier 70 but did not pose a threat to the environment or wildlife.

By late afternoon the spill had mostly evaporated.

Environmental teams placed absorbent pads in hopes up soaking up samples. But when crews on the water went to pick them up they found the pads barely soiled if at all.

Experts explained how one quart of oil can produce a sheen two acres in size. Then they announced the suspected source of the spill: not a pleasure boat, ferry or ship, but a sewer pipe.

KING

The spill was estimated 15 gallons.

They found an oily substance coming from a storm drain outfall on Harbor Island and that created a whole new mystery.

“We're not finding an obvious way petroleum product is getting into those storm drains, none-the-less we are finding petroleum in the storm drains," said Dick Walker of the Dept. of Ecology.

It could be that the substance was spilled into the newly installed drain system on Harbor Island, or contaminated groundwater could somehow be leaking into the system.

Puget Sound protection groups said it's time to shut off this source of contamination.

"I would just hope we that once we know of such known problems we could put in oil-water separators until we can get to the ultimate source of problem," said Fred Felleman.

The separators can actually treat contaminated water in sewer pipes before it's released into the bay but they are very expensive.

In the meantime, Seattle Public Utilities has agreed to send in crews Monday to search in depth for the cause in the storm drain system.

"We respond to about 400 spills of this nature every year," said Larry Altose, with the Department of Ecology. "Although the volume of the spill appears to be very small there is cumulative effect on the Sound. That's why it's so important to respond."