*Updated 8/30 to clarify next steps for addressing nutrients in stormwater.
The state Department of Ecology is considering a new regulation for wastewater treatment plants that discharge into marine water, including four in Skagit County.
The Puget Sound Nutrients General Permit would require treatment plants to reduce the amount of nutrients — largely nitrogen and carbon found in such items as feces and soap — they release into the water.
Ecology Water Quality Communications Manager Colleen Keltz said a similar regulation in the Chesapeake Bay region has had success in improving water quality.
Ecology is accepting public comment on the proposed permit until Oct. 21.
After the comment period, Ecology will review the input received and decide whether to proceed with developing the permit.
If written, the permit might apply to the Anacortes, La Conner, Mount Vernon and Big Lake treatment plants, along with dozens of others in Western Washington.
Keltz said those treatment plants would be included because they discharge directly into marine waters or into the Skagit River not far upstream of Skagit Bay.
The problem with nutrients that come from those types of wastewater treatment plants is that they provide a food source for marine plants and algae, which can deplete oxygen in the water as their populations grow.
Excess nutrients can also cause acidity harmful to shellfish, lead to the growth of algae that harms eelgrass and even kill fish, according to Ecology.
Ecology is currently focusing on the connection between nutrients and oxygen in the water, called dissolved oxygen, which is needed at certain levels in order for marine life to thrive.
Currently, oxygen levels in much of Puget Sound dip below the state’s water quality standard of 4 to 7 milligrams per liter, according to an Ecology study released in January.
In some areas, including in the Whidbey Basin that includes Skagit Bay, oxygen levels can remain low for more than three months, according to the study.
Whidbey Basin also has the largest area that experiences low oxygen levels and the second most days each year with low levels, behind only the Tacoma-Olympia area.
Keltz said low water circulation in the Whidbey Basin allows nutrients to build up and their impacts to intensify.
That study found that if the amount of nutrients coming from treatment plants was reduced, oxygen levels in the marine waters would improve.
Under existing conditions, about 20% of Puget Sound does not meet the state’s dissolved oxygen standards. That’s about 136,000 acres, or an area about 17 times the size of the city of Mount Vernon.
Improvements at wastewater treatment plants could cut the number days with low oxygen levels in half, as well as the amount of area impacted by 40 to 50%, according to the study.
Further work will be needed to address other sources of nutrients that impact oxygen levels, such as animal waste and fertilizer washed into Puget Sound by stormwater.
While Ecology is currently focused on managing treatment plants, it also plans to consider ways to reduce those stormwater sources in the future.
This year, Ecology plans to begin a study where it will evaluate combinations of treatment plant and stormwater source reductions.