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County staff seeks direction on Mount St. Helens Spirit Lake tunnel alternatives; draft EIS comment window opens
Summary
Public works staff asked commissioners whether and how much the county should engage in commenting on the Forest Service draft EIS for Spirit Lake outflow, which lists two primary alternatives: restore the existing tunnel to roughly 550 CFS or install a pressurized pipe plus a natural overflow channel.
Public works staff asked commissioners how much county involvement and advocacy they want regarding the U.S. Forest Service draft Environmental Impact Statement (EIS) for Spirit Lake outflow options related to Mount St. Helens.
Staff summarized the Forest Service's two top alternatives: (1) repair and restore the existing tunnel to a capacity of about 550 cubic feet per second (CFS); or (2) install a pressurized steel pipe, perform minor tunnel rehabilitation and construct a natural overflow channel that would reconnect the North Fork (Toodle) to Spirit Lake while using the new pressure pipe as the primary outfall. "Their 2 top choices are 1 is repair of the tunnel... and then their other top choice is to install a pressure pipe, do minor rehabilitation of the tunnel, and start building an overflow channel," staff said.
Staff noted technical details recorded in the presentation: the historic tunnel is about 8,460 feet long and 11 feet in diameter; the current maximum outflow is roughly 400 CFS; the Forest Service candidate repairs would aim for 550 CFS if chosen; and the lake's surface area was described in discussion as about 3.5 square miles and about 100 feet deep. Staff also reported that the Forest Service's alternatives analysis leaves the final selection to the responsible official and that the U.S. Army Corps of Engineers would likely construct work if the Corps is the executing agent while the Forest Service retains ownership of the infrastructure.
Commissioners asked about seismic considerations and alternate outflows; staff said the pressure pipe option would generally be more resistant to seismic movement than a rehabilitated tunnel and that a natural channel would be more ‘‘mother‑nature‑resilient.'' Staff asked the board whether the county wants staff assistance preparing comment letters on the draft EIS (comments said to be due in October). "If we want a letter comment on this EIS, draft EIS... they're due the October. So we have a month for me to get a good information and get you guys some background," staff said and offered to prepare recommended positions when the board is ready.
No formal county position was adopted at the workshop. Staff recommended collecting background information and returning with a proposed county comment or recommendation when the board indicates which alternative it wishes to support.
