North Nehalem Hatchery

NAME: N Nehalem Hatchery
LOCATION: Tillamook County
MARKET: Water & Wastewater
SUBMARKET: Fish Ladders and Hatcheries

DESCRIPTION:  ODFW plans to reconstruct a series of fish hatchery rearing ponds at the Nehalem Fish Hatchery due to settlement beneath portions of Ponds 7 through 20 with the main impact being to Ponds 12 through 19. The ponds include a small curb extending above surrounding grades but are predominantly below existing grades at the site. The very loose to loose silty sand that underlies the organic soil is compressible and this variability in foundation conditions is believed to be the primary cause of the observed differential settlement in the ponds. The soil may also be susceptible to piping or erosion under seepage forces. Replacement of damaged walls and slabs may be required.

It was recommended to demolish the damaged portions of the ponds and fully mitigate the risk of future settlement by removing the compressible soil and replacing it with imported structural fill prior to reconstructing the ponds.

SERVICE: Foundation Engineering, Inc. was retained by ODFW to provide geotechnical consultation. Our scope of work included exploratory drilling, laboratory testing, and an engineering report. The report included a description of our work, a discussion of the site conditions, the boring logs, and laboratory test results. We also provided discussions of the geotechnical conditions contributing to the observed settlement and possible mitigation measures and identify a preferred mitigation approach.

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