Arborist Report: Port Of Seattle Industrial Wastewater Treatment Plan – AGB Site, Sea-Tac, WA

A June 2025 arborist report by Tree Solutions Inc. inventoried and assessed 181 trees across ten Port of Seattle parcels at the AGB Site near SeaTac Airport, finding the site largely dominated by red alders, black cottonwoods, and invasive plant species following demolition of previous buildings. The report identifies one notable high-value western redcedar (Tree 470, 31.8 inches in diameter) and outlines tree replacement requirements under Port of Seattle Resolution 3821, which mandates a 4-to-1 replacement ratio for any regulated trees removed during future construction. The report is preliminary, as no design or construction plans had been reviewed at the time of writing.

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Tree Solutions Inc. arborist report (Project No. TS-9736) prepared by Tyler Bunton (ISA PN-8715A) and Lindsay Osborn (ISA PN-10281A), reviewed by Sean Dugan (RCA #457, ISA PN-5459B), for HBB Landscape Architecture c/o Aaron Luoma. Inventory and assessment of 181 on-site trees and 49 right-of-way/adjacent private property trees at Port of Seattle Industrial Wastewater Treatment Plant AGB Site, SeaTac, WA 98148, parcels 3223049306, 3223049021, 3223049286, 3223049313, 3223049314, 3223049315, 3223049263, 3223049303, 3223049034, 3223049304, 3223049033. Site inspections conducted May 21 and June 12, 2025. Dominant species include red alder (Alnus rubra), black cottonwood (Populus trichocarpa), and western redcedar (Thuja plicata, Tree 470, DSH 31.8 inches). Invasive species noted: Himalayan blackberry (Rubus bifrons), invasive ivy (Hedera sp.), tansy ragwort (Jacobaea vulgaris). Discusses Port of Seattle Resolution No. 3821 tree retention and replacement requirements (4:1 ratio for regulated trees ≥6-inch DSH) within the Airport Activity Area, and SEA Tree Replacement Standards and Land Stewardship Plan.

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