An eroded sewer pipe sprung a leak at the southern end of Lincoln Park, forcing King County to haul sewage by truck from Fauntleroy to the Alki storm water treatment plant.

A crew from the King County Wastewater Treatment Division (formerly known as Metro) found a leak in the sewer line Jan. 17. It had washed away sand and gravel under the paved path, causing part of the asphalt surface to collapse west of the park restrooms with the tube-shape skylights.

Asphalt in the same section of the walkway caved in five days earlier, when water from an unknown source washed away about 1 foot of sand and gravel beneath the path.

The pressurized, 30-inch sewer line is buried about 4 feet beneath the walkway along the Fauntleroy Cove shoreline. Workers replaced approximately 70 linear feet of the sewer pipe, said Gary Larson, Wastewater Treatment Division spokesman.

Lincoln Park's south parking lot became a construction staging area heaped with tall, orderly piles of sand and gravel, and lined with rumbling dump trucks.

There are no estimates of how much sewage escaped into Puget Sound but the leak continued for a few hours before it was stopped, Larson said. Orange signs from Public Health-Seattle and King County were posted on the beach near where the leak occurred warning people not to drink or play in the water.

Workers dug a trench down to the sewer line and snaked a small television camera through the pipe for an inside look, which revealed much of the 50-year-old pipe eroded, Larson said. King County officials theorize the concrete-and-steel pipe has been worn thin by sand, rocks and street grit that washes into the pipe during heavy rainstorms.

They also found several storm water drainage pipes cross the sewer line.

While repair work was underway, sewage was hauled by truck to the Murray Avenue pump station, located at Lowman Beach Park. That proved to be a nuisance to people living nearby, so the county hauled the sewage farther north to the Alki storm water treatment plant, Larson said.

Some sewage mixed with storm water was pumped into Puget Sound temporarily, from the Barton Street pump station to an outfall about 620 feet offshore.

Normally, sewage from Fauntleroy and surrounding areas is pumped northward through the Barton Street pump station, which is underground next to the Fauntleroy Ferry Terminal. Sewage continues north along the water side of Lincoln Park to another pump station beneath Lowman Beach Park.

Sewage continues to flow north to a tunnel that runs eastward beneath the Admiral District to Harbor Avenue. Another pump station there sends the sewage south and then east under the Duwamish River to a main line in South Seattle. It eventually goes to the West Point sewage treatment plant off Discovery Park in Magnolia.

Repair of the sewer leak is expected to be completed this week, Larson said.

Tim St. Clair can be reached at 932-0300 or tstclair@robinsonnews.com