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Expert: revised biological evaluation and noise mitigations sharply reduce pile‑driving risk to fish
Summary
The city's biological evaluator testified that at the request of the Army Corps and National Marine Fisheries the Biological Evaluation (Ex. 12) will be revised to remove upland analyses and reflect noise‑attenuation measures (timber block, bubble curtains) that shrink modeled injury and disturbance zones for pile driving.
Mister Callow, the city's testifying biologist, told the hearing that federal and state agencies asked the city to narrow the Biological Evaluation (Exhibit 12) to work below the ordinary high water mark and to reassess potential harms from pile driving. He said National Marine Fisheries and the Army Corps asked that the BE remove references to upland work and clarify why impact pile driving might cause injury or mortality to listed fish.
Callow said the project will drive piles with a vibratory hammer and then proof them with an impact hammer; the Washington Department of Fish and Wildlife (WDFW) HPA requires noise‑attenuating measures during proofing. "WDFW is requiring…a large wooden block between the top of the steel piles and the steel impact hammer during those proofing activities, and that helps to reduce the sound generated," he testified. He also described bubble curtains — perforated hose lines that create a ring of bubbles around piles — as a standard mitigation measure to reduce underwater noise.
Using NMFS' modeling tool and incorporating the mitigation measures, Callow testified that the previously large injury and disturbance distances in the draft BE shrink dramatically. Where the BE had reported behavioral disturbance and potential injury extending thousands of feet, Callow said the adjusted modeling shows injury thresholds of only a few feet (for example, injury to fish <2 grams decreases to roughly 9 feet, to larger fish to about 5 feet) and a behavioral disturbance radius dropping to about 152 feet once attenuation measures are applied. On that basis, he said, "the determination in the BE will be revised from a 'may affect likely to adversely affect' to a 'may affect not likely to adversely affect.'"
Callow added that the most restrictive fish‑window (set by WDFW or the Corps) will apply and that, together, timing limits and noise attenuation make the likelihood of fish injury insignificant. He also noted the HPA conditions and stated the replacement piles will be steel (not treated wood), which reduces toxic leachate concerns compared with some removed timber piles.
What happens next: Callow said the BE will be revised consistent with agency requests and the HPA conditions, and the record will be updated accordingly. The parties flagged that WDFW and NMFS remain parties with authority to require further conditions under their permits.
