The north and south beaches at Seattle’s Discovery Park will close Wednesday and Thursday due to construction work at the West Point Treatment Plant.

The West Point Lighthouse, beachside parking, nearby trails and road access to the area will also close, as crews begin replacing a pipe that serves a critical purpose for the plant.

The pipe, nearly 30-years-old, is at the end of its life and needs to be swapped out. The replacement process will release biogas — emitting a sulfur or rotten egg-like smell in the area, but visitors won’t be able to smell it, said Marie Fiore, a spokesperson with the King County Wastewater Treatment Division.

“The contractor is going to have a temporary waste gas burner on site,” Fiore said. “So we’re actually gonna burn the gas instead of venting it directly into the atmosphere.”

If park users do notice a strong smell, they are advised to turn around until they no longer detect the odor. The beach closure will be enforced by the Seattle Police Department.

Construction is expected to begin 3 a.m. Wednesday and last until Thursday. Crew members will monitor for any impact on air quality.

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The 56-year-old West Point Treatment Plant is part of a regional water treatment network and treats wastewater from Seattle, Shoreline, north Lake Washington, northern parts of King County and some southern parts of Snohomish County.

The plant processes about 90 million gallons of wastewater a day in the summer. During rainy months, the plant treats as much as 300 million gallons a day, up to 80% of which can be stormwater. The excess water brought by rain and storms can strain the sewage system.

In February 2017, wastewater overflowed West Point, causing a catastrophic flood at the treatment plant. The plant ended up dumping an estimated 235 million gallons of untreated wastewater into Puget Sound. The Washington Department of Ecology fined King County $361,000 for mismanagement that led to the incident.

In January 2021, the West Point plant and four other regional plants spilled more than 10 million gallons of untreated wastewater into Puget Sound after being hit with considerable rainfall and a power outage at the same time, according to the Bothell-Kenmore Reporter. Approximately two million gallons of the untreated wastewater was sewage.

In response, King County officials took a $96.8 million loan from the U.S. Environmental Protection Agency to design and build an underground storage tunnel that can hold millions of gallons of excess stormwater to alleviate pressure on sewage system, including the West Point plant.