Feasibility study shows trestle replacement would remove creosote pilings but could cost $62M–$102M; design and funding next steps discussed

A feasibility study presented to the Anacortes City Council on April 7 recommended further design and stakeholder work to advance replacement of the Tommy Thompson (Thompson Trail) trestle. The study — funded by a mix of Recreation and Conservation Office grants, congressional appropriations to the Samish Indian Nation, and partner contributions — examined environmental sampling, geotechnical borings, hydrodynamic modeling and conceptual designs.

Todd Woodard of the Samish Indian Nation and Hansen Professional Services consultant Lauren Schroeder outlined the study findings. The report found more than 1,600 creosote pilings supporting the existing trestle, with additional buried pilings inside the causeway; consultants counted 1,360 pilings visible at the lowest tide during the survey and noted there may be as many as 2,300 additional buried pilings. Geotechnical borings showed very soft bay-floor soils in much of the crossing, requiring deep pile foundations: one boring encountered firmer materials only at about 43 feet below grade and another at about 70 feet.

Environmental soil testing returned mostly ‘‘clean’’ results at one boring and residual contamination at shallow depths in another; consultants did not find soils that met state dangerous-waste thresholds in this limited sampling. The firm that performed hydrodynamic modeling observed that the primary channel location has been relatively stable since historic mapping and that restoring tidal circulation by removing portions of the causeway could help inner-bay sediment processes and habitat.

Consultants presented three structural alternatives and analyzed two in greater detail: a precast concrete deck-girder bridge (100-foot spans) and a prefabricated truss with fiberglass grated decking. The concrete girder option had an opinion of probable construction cost of about $62,000,000; the truss with fiberglass decking was estimated at about $102,000,000. A large portion of the cost reflects removal and proper disposal of creosote-contaminated soils and pilings, assumed at a conservative landfill type suitable for creosote-impacted material, and installation of new piling (the study proposed roughly 32 new piles and 43 long spans to replace the existing piling field).

Presenters described potential phasing approaches. Phase priorities could emphasize trestle replacement first to remove water-exposed creosote pilings, or begin by removing the causeway to restore circulation and then address the trestle. The team said phased construction would be constrained by marine fish-window permitting and could stretch over multiple years; the study estimated a three-year construction timeline for the full scenario but noted that phasing, permitting and seasonal windows could extend the schedule.

Council members asked about environmental tradeoffs, permitting uncertainties and funding strategies. Councilmember Walters stressed the urgency of positioning the project before potential regulatory mandates require removal; he noted that trestle removal costs alone were estimated at roughly $15 million and that the city’s annual general revenue would not cover the projected construction cost. Presenters said earlier feasibility work indicates a range of potential funding sources — state Recreation and Conservation Office grants, tribal funds, DNR assistance and federal appropriations — and recommended reconvening stakeholders to determine a desired end state and pursue the next design and permitting steps.

No council action was taken; the item was presented as a discussion to inform next steps and possible grant or design efforts. Presenters recommended additional geotechnical and bathymetric work, refinement of hydrodynamic and wave modeling (including storm surge), environmental permits consultation, and advancing preliminary design to a shovel‑ready stage to improve competitiveness for future infrastructure funding.