City planning staff presented proposed changes to Mill Creek’s Critical Areas Ordinance (CAO) on Nov. 26, telling the Planning Commission the updates are required under the Growth Management Act and must reflect best available science before the city’s compliance deadline of Dec. 31, 2025.

Staff Planner (Speaker 5) said the CAO amendments would update definitions, clarify treatment of nonconforming uses, require mitigation and monitoring for new trails, and move from a riparian buffer system to riparian management zones (RMZs) sized by site-potential tree height. "We are required by the Growth Management Act to protect critical areas," the presenter said, and noted the city used guidance from the Department of Ecology, the Department of Fish and Wildlife (WDFW) and the Department of Natural Resources in drafting the changes.

Major change: RMZs. Under the proposal, staff would use WDFW data to map site-potential tree height and set RMZ widths accordingly, with a minimum RMZ of 100 feet to account for pollution removal. Staff explained that the change would likely shrink the protected area along North Creek (where current buffers are relatively large) while expanding protections around many other streams; staff said most vacant, developable parcels would not be affected.

Other clarifications: Staff would allow redevelopment within existing impervious footprints (so lawfully established nonconforming buildings may be rebuilt on the same footprint) and set a one-time 1,000-square-foot allowance for limited expansions in some cases. Trails that were previously exempt would require mitigation measures (boardwalks, replanting) for impacts. Staff also proposed reducing the number of required mitigation-monitoring reports to reflect best available science.

Agency input and edits: Staff said they met with WDFW and incorporated minor changes; a letter of support from WDFW was received the afternoon of the commission meeting. Commissioners asked for clarifications on how unmapped or informal trails would be treated and whether existing site-specific approvals override the new subdivision language; staff said mapped or permitted trails would be treated differently and that they would add clarifying language to ensure nonconforming uses can be subdivided where intended.

Recommendation and vote: Under new business, Commissioner (Speaker 4) moved to adopt Planning Commission Resolution No. 2025-182 recommending City Council adopt the CAO updates. The commission approved an amendment to add a clarifying line about subdivisions and nonconforming uses, then approved the resolution as amended by voice vote.

What’s next: Staff said final adoption will most likely occur at the first City Council meeting in January (or Dec. 9 if timing allows), and staff will finalize language changes identified by the commission before forwarding the recommendation.