Snoqualmie plans Thompson Avenue street-tree rebuild; city pilots soil-amendment approach

Superintendent Jason Battles gave the committee an update on the Urban Forest Improvement Program and the 2026 street-tree replacement work on April 7, 2026.

Battles said the city's inventory includes 110 SR1 streets with inadequate soil volumes and poor drainage that leave trees with only shallow rooting and increase the chance of failure and sidewalk damage. To improve durability and canopy benefits, staff is targeting roughly 300 cubic feet of engineered soil per street tree and will install drainage or dry wells where needed so trees can develop structural roots.

For 2026, Thompson Avenue is the highest-priority project (score 82): staff plans to replace about 1,500 linear feet of planter strip and plant an estimated 60 80 street trees to increase canopy cover in a census block the 2025 canopy assessment identified as having the least coverage. Battles said the updated 2026 prioritization adds resident concerns about aphid damage and an assessment of existing canopy cover to the previous criteria of tree condition and infrastructure damage.

On funding, Battles said the city has used outside grants before (an earlier grant funded 300 downtown street trees) and will pursue similar opportunities. He described a cost-saving pilot: instead of exporting all glacial till and importing new soil, crews exported half the existing soil, amended the remainder and will use a vacuum inspection to check conditions and retained water after one year. Battles said the pilot aims to reduce the greatest cost factor (soil export/import) while still achieving adequate soil volume for tree health.

Battles also described the city's ongoing street-tree program that performs single-tree or small-scale structural improvements in areas (including SR2 streets, which already have improved soil volumes). When asked about specific species, Battles indicated he would phase out problematic linden trees where appropriate.

What's next: Thompson Avenue work is programmed for 2026, staff will proceed with mobilizing contractors and will bring project outcomes and larger program summaries to the full council when schedules allow.