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City staff seeks diving inspection of 1985 outfall; contract expected back for consent
Summary
Public works staff reported corrosion and sedimentation problems on the city's 1985 wastewater outfall to the Spokane River and recommended contracting a professional diving firm for underwater inspection; staff will negotiate a contract and bring it to the council for approval under the consent calendar at a subsequent meeting.
Coeur d'Alene — City wastewater staff on March 4 told the City Council that the treatment plant outfall constructed in 1985 is showing corrosion and sedimentation and that further underwater inspection is required to determine the scope and cost of repairs.
Public works staffer Mike Becker presented drone footage and photos showing that several diffuser risers are buried or missing and that corrosion has affected other diffuser components. Becker said the outfall is a 30-inch diameter pipe with 10 diffuser holes and was originally designed to discharge 11.9–15.7 million gallons per day assuming all diffusers operate.
Becker proposed hiring a professional diving firm to inspect the pipe and riverbed to quantify sedimentation and the condition of diffusers. He said one firm's proposal covered an estimated six tasks for about $53,000 to $75,000 and that there are up to 11 additional unknown tasks that would be priced on a time-and-materials basis. "We do not believe it will exceed $100,000," Becker said, adding the project has an existing budget line and staff has authority to proceed with contracting negotiations.
Permitting and regulatory concerns: Becker told council that the investigative diving work does not require permits. He said maintenance or dredging that would remove substantial sediment could trigger permitting requirements and involvement by the U.S. Army Corps of Engineers and the Idaho Department of Environmental Quality (IDEQ). Becker also said an engineering firm (HDR) had done prior evaluation work but that underwater inspection is needed to complete the assessment.
Operational impact and timeline: Staff said there is currently no capacity issue; the plant is treating and discharging within permit limits. The purpose of the inspection is to identify what corrective work would be necessary to avoid a future sudden loss of capacity. Becker said staff will negotiate a lump-sum contract for defined tasks with time-and-materials pricing for unknown items, then present the contract to council at the next meeting for placement on the consent calendar if appropriate.
Council questions focused on hydraulics, permitting and future maintenance strategies. Councilmember Gookin asked whether a hydraulic engineer had been engaged; staff said HDR had performed earlier work and will be involved in developing recommendations alongside the diving firm. On permitting, Becker reiterated that the investigative dive does not require IDEQ or Army Corps permits but that dredging or more invasive repairs likely would.
Action taken: No formal council action was required at the March 4 meeting; staff will negotiate the contract and return it to council for approval under the consent calendar.
