Study: Wastewater polluting Sound

Sewage-treatment plants, not rivers,

By John Dodge | The Olympian • Published January 29, 2009

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Treated wastewater from sewage-treatment plants spills much more nitrogen into south Puget Sound in late summer than rivers do, according to a state Department of Ecology study of what's causing dissolved oxygen problems in South Sound.

In September 2007, treatment plants south of the Tacoma Narrows bridges contributed four times as much nitrogen to the marine waters as the rivers did, according to the study. The contribution was even greater from treatment plants compared with rivers in central Puget Sound from Tacoma to Edmonds.

These nitrogen levels might be contributing to low dissolved oxygen levels in South Sound that can stress or kill marine life, or cause aquatic life to flee oxygen-depleted habitat. The nitrogen triggers algae blooms, which suck oxygen from the water when they die.

But Ecology scientists said more study and computer modeling of water circulation patterns in south and central Puget Sound is needed before water-quality regulators could tell sewer utilities and their ratepayers they must install costly nitrogen-removal systems at their treatment plants.

"We need to know how the water moves around before deciding if it's worth spending hundreds of millions of dollars on upgrading wastewater treatment plants," Ecology environmental engineer Mindy Roberts said.

The $1.5 million, four-year Ecology study is slated for completion in June 2010.

"I'm not sure waiting is a good idea," said Taylor Shellfish spokesman Bill Dewey, who is a member of the South Sound study's technical advisory committee. "There's no question in our minds, as users of the South Sound water body, that we're seeing dramatic changes from too much nitrogen in the water."

The excess nutrients in the water are like too much of a good thing, providing so much food for oysters that they grow too fast and experience higher mortality rates, he said.

LOTT rules

The LOTT Alliance treatment plant in downtown Olympia is the only one in the Puget Sound basin where Ecology requires nitrogen to be removed before the effluent is discharged. It has been a condition of the LOTT operating permit since 1994.

Ironically, about 50 percent of the water-quality violations for dissolved oxygen levels recorded in the study occurred in Budd Inlet.

That's not to say that the $47 million LOTT investment in nitrogen removal 15 years ago wasn't a good idea, Roberts said.

"It just means it didn't solve the entire problem in an inlet with multiple sources and poor water circulation," she said.

Other sources of nitrogen include septic systems, marine sediments, air deposition and the Pacific Ocean, the study shows.

Population growth in the Puget Sound watershed has contributed to a doubling of nitrogen entering South Sound in recent years. The computer models should be able to assess how much of the nutrient loading in South Sound is delivered from Tacoma-Seattle area of Central Puget Sound, Roberts said.

Tackling low dissolved oxygen levels in South Sound is identified as a top priority in the Puget Sound Partnership's plan to restore Puget Sound health by 2020, partnership executive director David Dicks said.

John Dodge covers the environment and energy for The Olympian. He can be reached at 360-754-5444 or jdodge@theolympian.com.