Buried ancient forest clogs Fife sewer project

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FIFE - Crews building a sewer line in east Pierce County have run into a stand of really old-growth trees - an ancient forest buried 16 feet deep by a mudflow probably triggered by an eruption on Mount Rainier 1,100 years ago.

While geologists are excited by the find, it's no walk in the woods for sewer workers who face months of extra work to dig through the water-soaked logs.

A major arterial, 70th Avenue East between Valley Avenue East and 20th Street East, was supposed to reopen last October.

But the sewer contractor, Tydico of Renton, began to uncover the well-preserved and saturated logs.

Crews also uncovered hard, claylike soils formed from volcanic ash that trapped unexpected water, said Tydico project manager Kathleen Wilcox.

The work stalled as crews tried to remove the additional water and jumbled logs.

The logs are likely part of a forest buried by a mudflow from the White River Valley, triggered by a volcanic eruption on Mount Rainier, said Pat Pringle, a state Department of Natural Resources geologist.

The trees are preserved because of the large amounts of water, Pringle said. He has obtained samples and will carbon-date and study them for climate and environmental histories.

"It's fantastic," he said. "It's like a time capsule."

Such buried forests "are everywhere" in the Puyallup Valley, Pringle said.

What's good for science isn't necessarily nice for sewers.

"It was unexpected," said Ron Garrow, Fife public-works director. "The cedar logs are well preserved. Some of the wood is spongy. You can squeeze it, and it contracts and expands like a sponge."

The underground logs will take more equipment and time to get out, he said. The sewer line must be laid 20 feet underground, 4 feet below where the forest was found.

Fife officials estimated the additional work could take as long as 3-1/2 months, instead of the few weeks originally thought. Tydico estimated it could cost an extra $600,000 to $800,000 to do the removal work and install the sewer lines next summer, when the ground is drier.