What We're Asking

We support Washington’s clean energy goals and recognize that battery storage is part of the state’s strategy for meeting the Clean Energy Transformation Act (CETA) requirements. PSE needs grid storage, and the Mt. Si substation next door is a real interconnection point.

But this site has serious problems. PSE’s own 2021 siting study screened all 382 substations and did not recommend Mt. Si. It did not even pass initial screening. Four years later, PSE signed a tolling agreement for a 130 MW facility at the location its own consultant rejected. From constrained valley topography and seismic hazards to limited evacuation routes, unproven emergency response capacity, and proximity to schools and thousands of homes, the questions about whether a battery storage facility can operate safely here are too significant for a checklist-level environmental review to answer. That is why we are asking King County to issue a Determination of Significance and require a full Environmental Impact Statement (EIS) before making a threshold determination on this project.

We are not asking King County to deny the project. We are asking for the level of review that a project of this scale, in this location, requires. An EIS is the process designed to answer these questions. A SEPA checklist is not.

Why a full EIS is necessary

The proposed facility would be the largest BESS in western Washington, sited in a constrained river valley adjacent to thousands of homes. The site raises questions across multiple environmental categories that a checklist cannot credibly evaluate:

Toxic gas dispersion in a constrained valley

Battery energy storage systems using lithium-ion and most other commercially available chemistries can undergo thermal runaway, a self-sustaining chemical reaction that produces hydrogen fluoride (HF) and other toxic gases. HF is immediately dangerous to life and health at 30 ppm (NIOSH). Larsson et al. (2017) measured 20-200 mg of HF per Wh of capacity; even a fire involving a small fraction of this facility could produce quantities of HF that exceed IDLH concentrations over a significant area.

The Snoqualmie Valley’s topography, a ridge-bounded river valley subject to frequent temperature inversions, traps airborne emissions close to the ground rather than dispersing them. No atmospheric dispersion modeling has been conducted for this site. Nobody has studied what toxic gas concentrations would look like at nearby schools, along Snoqualmie Parkway, or in surrounding neighborhoods during a fire event under inversion conditions.

School proximity

Cascade View Elementary is approximately half a mile from the proposed facility. District school bus routes on Snoqualmie Parkway pass within 500 feet of the site boundary. PSE’s own 2021 siting study flagged schools as making a location “less desirable” for energy storage, and Mt. Si was screened out of that study’s recommended locations.

No BESS-specific emergency preparedness assessment has been conducted for the school district.

Emergency response and evacuation

Eastside Fire & Rescue Chief Will Aho stated in writing on April 6, 2026 that “Eastside Fire & Rescue cannot confirm that we are fully prepared today to mitigate an incident of this type and scale.”

The City of Snoqualmie’s ESF #16 Evacuation Plan (November 2017) does not contemplate an industrial toxic release from an adjacent facility. The plan acknowledges that school buses “may not have staffing to operate them” during an evacuation and that “there may be times where there is too little or too late of notice to successfully evacuate all or certain parts of the population.” Snoqualmie Ridge has two primary evacuation routes, and unincorporated residents downhill of the site have even fewer options.

Seismic hazard

The Snoqualmie Valley is exposed to the Southern Whidbey Island Fault (mapped through the valley, M6.5-7.4), the Seattle Fault (M7.0-7.5), and the Cascadia Subduction Zone (M9.0+). USGS Fact Sheet 2025-3050 puts the 50-year probabilities for the Puget Sound region at 85% for a M6.5+ deep earthquake and 17% for a M6.5+ crustal fault earthquake. Nobody has modeled the full chain: earthquake damages cells, thermal runaway, fire, contaminated runoff into Fisher Creek, all while evacuation routes may be damaged.

Groundwater and private wells

The project site is surrounded by dozens of private domestic wells (31 in the quarter section downhill to the southwest alone). Contaminated firefighting runoff from a battery fire could migrate through soil to groundwater. No hydrogeologic assessment has been submitted.

What we are asking King County to do

  1. Issue a Determination of Significance and require a full Environmental Impact Statement, including atmospheric dispersion modeling for toxic gases under valley inversion conditions with receptor points at Cascade View Elementary and along school bus routes.

  2. Require an alternatives analysis covering battery chemistry, site configuration, and alternative locations, so the community and permitting authority can evaluate whether public safety can be assured under any project configuration.

  3. Require a site-specific emergency response plan developed in coordination with the school district, Eastside Fire & Rescue, and the City of Snoqualmie, with provisions for school notification, shelter-in-place activation, and evacuation during school hours.

  4. Scale financial responsibility with facility size. The current requirement is the same $1 million whether the facility is 5 MW or 130 MW adjacent to thousands of homes. An earlier draft of Ordinance 19824 required financial responsibility “based on a study of maximum potential damages.” The Moss Landing cleanup required EPA to invoke CERCLA (Superfund) authority. Financial responsibility should scale with facility capacity and proximity to residential areas.

  5. Require permanent fenceline air quality monitoring for facilities adjacent to residential areas.

  6. Retain existing trees on the west side of the site, facing the backyards of homes on Bracken Place SE and SE Center Street, where no critical area buffer protection exists.