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City seeks underwater inspection contract after corrosion and sedimentation discovered at wastewater outfall
Summary
Public works staff told the council they will negotiate a contract with a diving firm to investigate a corroded 1985 wastewater outfall on the Spokane River and that the work will be presented for consent at a future meeting; the system currently meets discharge needs but several diffusers are buried or missing.
Coeur d'Alene — Wastewater staff informed the council that the city’s primary treated-effluent outfall, constructed in 1985, shows corrosion and sedimentation that have left some diffuser risers buried or missing and that staff plan to negotiate a contract with a specialized diving firm to gather more information for engineering recommendations.
Mike Becker, who presented the staff report, said the outfall is a 30-inch diameter pipe with 10 diffusers and diffuser boots intended to disperse treated effluent into the Spokane River. A 2022 drone inspection and subsequent engineering review showed roughly half the diffusers appear above the riverbed while others are buried or not operational; one diffuser was recorded as missing. Becker said the outfall was designed for a discharge capacity of 11.9 to 15.7 million gallons per day when all diffusers are functioning.
Becker said the city solicited proposals for a professional diving firm and received one proposal from a Spokane-based firm experienced with outfalls and underwater pipeline work. The firm provided estimated costs for a subset of tasks (about $53,000 and $75,000 figures were reported in staff materials) and noted numerous unknowns that could require additional time-and-materials work. Becker said the current investigations and potential work would be negotiated as a lump sum "not to exceed" for six tasks and time-and-materials for the remaining items; staff said they do not expect the total to exceed $100,000 and that budget authority exists in a planned line item.
Operational impact and permitting: Wastewater staff emphasized the system currently has no capacity shortfall and is meeting permit obligations, but they want to avoid a failure. The work is investigative and does not require permitting; any future substantial dredging or removal would trigger coordination with the Army Corps of Engineers and IDEQ. Councilmember Gookin asked whether HDR (the city’s previous engineering consultant) has evaluated hydraulic effects and whether a maintenance schedule could be developed; staff said HDR had been engaged earlier but more on-water data was needed and that future work would consider timing and permitted maintenance windows.
Next steps: Becker told council he will negotiate the diving contract and present it for consent at a subsequent meeting; no formal council action was taken at this session. The staff report included plans to combine dive findings with consultant engineering to scope any repair or maintenance, and staff said they would confer with regulatory agencies about activities in the Spokane River.
