updated 10/17/2006 5:25:04 PM ET 2006-10-17T21:25:04

A $31 million system designed to collect runoff from de-icing fluid sprayed on planes at Portland International Airport in winter is causing problems for fish.

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The collection system, which the Port of Portland began using in November 2003, has worked fine. But officials say it was based on two faulty assumptions that have led to dozens of water-quality violations, an $82,500 state fine and an agreement signed this month that the Port will build a new treatment and discharge system by 2012.

Discharges containing the de-icing fluid — variations of glycol, similar to antifreeze — are harmful to fish and other aquatic life. Bacteria break down the fluid, robbing fish of oxygen in the Columbia Slough, where the water is emptied.

As glycol-laden water passes into the lower portion of the slough, it encounters habitat for juvenile coho and chinook salmon, members of the Columbia Slough Watershed Council wrote the state Department of Environmental Quality in 2004.

Susan Aha, a Port water-quality manager, said the chief problem with the current system was that it was based on models indicating that water flows in the slough ran 100 cubic feet per second.

"Since then we've come to realize that flows are much lower," Aha said, averaging 50 to 60 cubic feet per second. Many days there is no measurable flow at all.

The result of lower water flows is that the concentration of glycol in the slough is not sufficiently diluted.

The Port is looking at piping discharges directly into the Columbia River as part of enhancing its system. Current discharges eventually get there anyway, after passing from the slough to the Willamette River and then to the Columbia.

The Port began contacting advocacy groups recently to discuss such a possibility.

"To its credit, the Port came to us, acknowledged a problem, and we're talking," said Brent Foster, executive director of Columbia Riverkeeper. "But I can tell you we're not excited about a new discharge into the Columbia."

A second flaw in the current system is that a holding tank was constructed to a capacity that, on most days, causes it to contain four times more biodegradable material than the city of Portland is willing to accept for treatment. That forces more de-icing material into a holding pond and later the slough.

The cost and details of beefing up the current system have yet to be determined. Although the Port is a public agency, airline usage fees ultimately pay the bills for such a system.

The Port de-ices runways on extremely cold days, and airlines spray down their planes to prevent ice buildup that can make them unsafe to fly.

Copyright 2006 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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