SEPA Outcomes for Washington BESS Projects

No battery energy storage project in Washington State has ever been required to complete a full Environmental Impact Statement. Every project that reached a SEPA threshold determination received a DNS or MDNS and was approved. The only formal appeal was denied.

That doesn’t mean the SEPA process is irrelevant. It means the realistic path runs through MDNS conditions, not project denial. The conditions other projects received show what’s possible, and what King County should be held to.

Summary

NextEra Mt. Vernon (200 MW, Skagit County)

The most detailed BESS conditions in the state. Hearing Examiner Rajeev Majumdar explicitly wrote conditions that “deviate from those proposed by the Department and agreed to by the Applicant, to better address a level of accountability, clarity, enforceability, and public concern.”

MDNS conditions (18)

The MDNS required compliance with fire codes (NFPA, NEC, IFC), UL 9540 and 9540A listing for all systems, hazard mitigation and emergency response plans, stormwater management, critical areas compliance, surface and groundwater protection, and an inadvertent discovery plan for archaeological resources.

Hearing examiner conditions (beyond MDNS)

The hearing examiner added requirements the county hadn’t proposed:

• 100% financial security bond (performance bond, letter of credit, or surety) for environmental mitigation, decommissioning, and site restoration, filed before building permit. King County’s Ordinance 19824 caps financial responsibility at $1 million regardless of facility size.
• Annual emergency response plan review by the fire authority. The plan must be amended whenever facility design, construction, operation, or maintenance changes.
• On-site emergency response coordinator as a single point of contact with required subject matter experts.
• All unredacted safety documents entered into the public record, including the Decommissioning Plan, Hazard Mitigation Analysis, and Fire Protection Technical Assistance Report.
• Spill Containment and Contingency Plan with monthly inspections and a designated employee.

The appeal

Stewards of Skagit filed an appeal in January 2025. It was heard by the Skagit County Commissioners on June 2, 2025, and denied unanimously.

The appeal argued that the hearing examiner didn’t fully understand the technology, that NextEra’s application had errors and omissions, that public noticing was inadequate, and that NextEra wasn’t forthright about risks.

It failed for structural reasons:

• The “clearly erroneous” standard requires appellants to prove the decision was not just wrong but unsupportable. That’s a high bar.
• Closed-record proceeding. No new facts or public comment allowed. The appeal was limited to the record that existed at the time of the original decision.
• No expert evidence in the record. The hearing examiner had already noted that opponents provided no “significant credible evidence, aside from hearsay anecdote.” Without expert testimony or technical data in the original comment record, there was nothing to appeal on.
• NextEra’s attorney characterized the appeal as “skepticism, displeasure and disagreement.”

The lesson is blunt: if the evidence isn’t in the SEPA comment record, it can’t support an appeal. The comment window is the whole ballgame.

Why Cascadia Ridge is different

Mt. Vernon was zoned Heavy Industrial. The hearing examiner said it was exactly the right place for this use. Cascadia Ridge is zoned UR (Urban Reserve), a residential-oriented zone. The zoning argument is much stronger here.

Mt. Vernon’s opponents had no expert evidence. We have PSE’s own 2021 siting study, which screened out Mt. Si. We have EPRI failure rate data. We have the Larsson HF study. And we have the fact that Jupiter Power already signed a $500M sodium-ion contract with Peak Energy for other projects.

Source: Hearing Examiner Decision (PDF, 26 pages)

Greenwater BESS (200 MW, Sumner)

MDNS issued August 2024 by the City of Sumner. Sumner had no BESS-specific code at the time and used SEPA as the primary tool for imposing conditions. After approval, Sumner adopted BESS development standards and restricted BESS to commercial/manufacturing zones only.

MDNS conditions (19)

Fire safety (6 conditions): Fire Response Plan approved by East Pierce Fire & Rescue, two new on-site fire hydrants, drive aisles to fire department turning radius standards, compliance with 2021 IBC/IFC and NFPA 855, hazard mitigation analysis per IFC Table 1207.6, decommissioning plan per IFC 1207.2.1.

Water well protection (3 conditions): The Dieringer Well sits on the BESS parcel itself, directly on the aquifer. Sumner required:

• Site plans must show the well, its protective radius, and public water mains
• Property within the well protective radius must be deeded to the City of Sumner with chain link security fence
• Hydrogeologic assessment required

The city explicitly stated that even a driveway within the sanitary control area was “unacceptable.”

Site containment (3 conditions): Secondary containment at substation, visual screening fence, paved surface with raised edge/curb for secondary site containment.

Cultural/tribal (2 conditions): Inadvertent discovery protocol with notification to the Puyallup and Muckleshoot Tribes. Immediate work stoppage if archaeological artifacts found.

Hazard and compliance (2 conditions): Recorded title notifications for five hazard areas (aquifer recharge, seismic, volcanic, wetlands, steep slope). General regulatory compliance.

Why the water conditions matter for Cascadia Ridge

A specific, documented environmental resource generates the most aggressive conditions. For Sumner, that was the Dieringer Well. For Cascadia Ridge, it’s Fisher Creek: a Type F (fish-bearing) stream running through the northwest portion of the primary parcel, less than 10 vertical feet below the development area, draining into the Snoqualmie River watershed where ESA-listed Chinook salmon, steelhead, and bull trout are present.

The well protection conditions (deeding land to the city, hydrogeologic assessment, secondary containment with raised curbs) are a model for what Fisher Creek protections should look like.

Source: Sumner MDNS (PDF)

Arlington SnoPUD (25 MW)

MDNS issued March 2025 by the City of Arlington. Zero public comments were received. No one attended the neighborhood meeting. The project sailed through because it checked every box: industrial zoning, existing utility campus, public utility as developer, small scale, no residential within 550 feet, and Arlington already had a comprehensive BESS ordinance (AMC 20.114).

Key conditions included remote surveillance for thermal runaway detection, secondary containment for battery and transformer contaminants, spill prevention and response plans, noise compliance limits, and notification to the Stillaguamish Tribe for ground disturbance.

Arlington’s BESS ordinance (AMC 20.114) is the most detailed municipal BESS code in the state. It covers installation, operations and maintenance, testing, commissioning, decommissioning, emergency planning, hazard mitigation, and NFPA/IFC/UL compliance. It could serve as a model for what King County’s Ordinance 19824 should have been.

Wautoma Solar + BESS (470 MW, Benton County, EFSEC)

The strongest institutional opposition of any Washington BESS project. Benton County’s prosecuting attorney intervened. The Confederated Tribes and Bands of the Yakama Nation raised cultural resource concerns. State legislators opposed it. The project was still approved by the governor through EFSEC.

What influenced conditions

The Yakama Nation’s cultural resource concerns produced specific, enforceable protections: 100-foot archaeological buffers around identified sites, DAHP permits, and ongoing monitoring. Wildlife habitat concerns led to a Habitat Restoration and Mitigation Plan with WDFW consultation and compensatory mitigation. Decommissioning concerns led to financial assurance requirements that cannot be reduced for salvage value.

The Site Certification Agreement also requires an Independent Environmental Monitor selected by EFSEC at the developer’s cost, with stop-work authority for environmental violations.

What didn’t work

Benton County argued that EFSEC should not preempt local land use and that the project improperly converts Agricultural Lands of Long-Term Commercial Significance. The county lost. At EFSEC, local zoning is overridden.

General opposition based on land use incompatibility did not change the outcome, even with the county prosecuting attorney as an intervenor. Comments that generated specific conditions were more effective than comments seeking project denial.

King County Ordinance 19824 DNS

In fall 2023, King County issued a Determination of Non-Significance for Ordinance 19824, the BESS regulatory framework. 192 people submitted comments arguing for a Determination of Significance and full EIS. No formal appeal was filed.

What commenters argued

Fire and explosion risk from lithium-ion. Toxic gas emissions affecting communities, schools, and hospitals. Water contamination (specifically Soos Creek, a salmon-bearing stream near the Kingfisher project). Wildlife impacts. Noise from 24/7 HVAC cooling systems. The ordinance being too permissive by allowing BESS as a permitted use in most zones.

How the county responded

The SEPA responsible official affirmed the DNS after consulting with the Prosecuting Attorney’s Office. The core argument: existing building and fire codes, plus the ordinance’s own provisions, provide sufficient mitigation. Individual BESS projects would still get project-level SEPA review for site-specific impacts.

That promise is important. The county justified skipping a programmatic EIS by saying site-specific analysis would happen at the project level. When Cascadia Ridge goes through SEPA, that’s the commitment we can hold them to. Every site-specific impact the ordinance DNS deferred (proximity to residences, schools, streams, valley atmospheric conditions, seismic risk) should be analyzed rigorously at the project level. That’s what the county said would happen.

What the county’s own checklist admits

The county’s 29-page SEPA checklist for the ordinance acknowledges risks that are directly relevant to Cascadia Ridge:

• Toxic gases: 100+ gaseous products from lithium-ion failure, including hydrogen fluoride
• Water contamination: Battery electrolyte “could conceivably contaminate soil or water” during failure events; firefighting water could contaminate soil and water
• Noise: Cited California studies showing 85-87 dBA at the system boundary from HVAC cooling
• Financial responsibility was weakened during adoption: The original draft required financial responsibility “based on a study of maximum potential damages.” The adopted version set a flat $1 million cap regardless of facility size.

Why Cascadia Ridge is different

Every Washington BESS project that went through SEPA was approved. But Cascadia Ridge has advantages no previous opposition has had:

PSE’s own consultant screened this site out. PSE’s 2021 Energy Storage System Location Study evaluated substations across their service territory and did not recommend Mt. Si. PSE selected it anyway four years later. No other BESS opposition in Washington has the developer’s own utility partner on record saying the site is unsuitable.

The developer already has a sodium-ion contract. Jupiter Power signed a $500M / 4.75 GWh deal with Peak Energy for sodium-ion batteries. They’re investing half a billion dollars in the technology that eliminates the primary risks this community has raised. The question is why they aren’t using it here.

Residential zoning, not industrial. Mt. Vernon was Heavy Industrial. Arlington was General Industrial. Cascadia Ridge is Urban Reserve, a residential-oriented zone. The hearing examiner in Mt. Vernon said the site was “exactly the right place” for a BESS. No one can say that about a site 1,500 feet from homes.

School proximity flagged by PSE’s own criteria. PSE’s siting study criteria explicitly identify schools within one mile as making a location less desirable. Cascade View Elementary is within that radius.

Valley inversion trapping. The Snoqualmie Valley is ridge-bounded. Temperature inversions in western Washington valleys can trap emissions close to the ground, unlike coastal or open-terrain sites where wind disperses them. No other Washington BESS project shares this atmospheric characteristic.

King County’s own SEPA checklist is on the record. The county’s 29-page non-project checklist puts hydrogen fluoride, water contamination, and 85-87 dBA noise on the record. At project level, they can’t walk that back. Demand specific analysis of what those impacts look like at this site.

What this means for your SEPA comment

The evidence has to be in the comment record or it can’t support an appeal. General opposition doesn’t work. The Mt. Vernon appeal failed because the opponents had no technical evidence to point to. The Wautoma opposition influenced conditions because the Yakama Nation and WDFW brought specific, documented environmental concerns.

When you write your SEPA comment, tie it to specific checklist elements, cite data, and ask for specific studies or conditions. Read our guide on how to write an effective SEPA comment.