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City begins stormwater comprehensive-plan work to address climate, permit changes and urbanization
Summary
Environmental Services presented the start of a stormwater comprehensive plan that will respond to new permit requirements, climate-change design needs, urban densification and community priorities; staff said only about 10% of stormwater runoff is currently treated and outlined next steps for modeling, outreach and funding options.
Environmental Services staff presented progress on a stormwater comprehensive plan and described how new permit obligations, climate-change impacts and increased urban impervious surface under the city’s housing and growth strategies will affect flooding, conveyance and water-quality needs.
Dana De Leon and staff said the city does not currently have a single stormwater comprehensive plan and that the new document will build on prior community engagement and the Urban Watershed Protection Plan. Staff summarized outreach conducted in recent years and said future engagement will begin in February to refine priorities and align solutions with neighborhood needs.
Presenters noted regulatory changes in the Municipal Stormwater Permit (referred to in the meeting as the city's MPDS permit) and forthcoming EPA work on the Puyallup River/Tideflats area. Staff said Ecology’s permit expectations and the city’s permit obligations now include additional monitoring, street sweeping requirements and attention to contaminants of emerging concern such as PFAS and tire-related 6PPD-quinone. Environmental Services said it is collaborating with Ecology on laboratory methods and a stormwater characterization program.
Staff highlighted system scale and condition: many stormwater conveyance assets were built primarily for flood control and not treatment; staff estimated only about 10% of stormwater runoff currently receives treatment before entering waterways. A calibrated model for a 4,510-acre basin draining to Thea Foss Waterway outfalls showed that increased impervious surface associated with higher-density growth would increase the number of manholes with capacity exceedances, indicating more localized flooding unless mitigated.
To respond, staff outlined strategies including updating stormwater design standards for climate-change design storms, requiring on-site management for redevelopment in higher-growth areas, expanding fee-in-lieu and regional facility options for low-opportunity sites, and evaluating system development charges and other funding mechanisms. Staff emphasized tree canopy and green infrastructure (rain gardens, pervious surfaces, distributed facilities) as part of the toolbox; staff noted a currently under-resourced rain-garden assistance program that could be expanded.
On funding, staff said they will model long-term needs, consider incremental rate changes to reduce ratepayer impacts, pursue new revenue sources such as SDCs and expand fee-in-lieu programs. Staff aims to produce a draft stormwater comprehensive plan later in 2025 and return to the committee with funding and prioritization options.
Committee members asked about green‑infrastructure programs, the interaction between developer-required off‑site improvements and proposed SDCs or fees, and how street‑level programs and regional facilities would be coordinated. Staff said they would present options and coordination work in future committee briefings.
