Noise

A 130 MW battery storage facility runs continuously. The HVAC systems that cool the battery containers and the inverters that convert DC to AC both produce steady noise, day and night, for the life of the facility. The nearest homes are a few hundred feet away. The question for SEPA is not whether the facility will be audible; it is whether the record shows it will comply with King County’s noise limits at those homes. Right now it does not.

The applicant’s own study lands at the line

Jupiter Power’s Sound Study predicts a nighttime sound level of 42 dBA at R5, the closest home east of the site (Sound Study, Table 6). That is a prediction the applicant produced using its own equipment list, site layout, and assumptions.

King County Code Chapter 12.86, which adopts Washington’s WAC 173-60 noise framework, treats a 130 MW BESS as a Class C industrial source and the surrounding homes as Class A receivers. The nighttime limit is 50 dBA, reduced to 45 dBA where the source produces a pure tone, a narrow-band component that BESS inverters and cooling fans commonly generate. So the applicant’s own prediction sits at most 3 dBA under the limit, and against the stricter commercial limit the study itself chose to apply, exactly at the line with zero margin.

A result that close to the limit needs solid inputs to be trusted. These are not.

The prediction rests on placeholder data

• Substitute data for three of four equipment types. The Sound Study used sound data “for a similar unit” for the battery containers and both transformers, because the manufacturers provided none. Table 5 lists the manufacturer data as “Not Available” at every frequency band for all three. Only the power-conversion system used real manufacturer data, and the transformer values lean on a 1979 reference for equipment whose acoustic design has changed substantially since. Because the pure-tone penalty turns on exactly the frequency-band content this substitute data cannot supply, the error goes straight into the compliance prediction.
• Equipment the applicant has not selected. The study models equipment Jupiter has not committed to buying, and nothing in the record binds the equipment actually installed to the sound levels the model assumed.
• Ambient monitoring at the wrong place and time. The long-term monitor sat at the west boundary, which the report itself calls “not noise-sensitive,” and ran about one night. The two short-term samples were roughly 16-minute daytime measurements with noted interruptions (an ambulance, dog walkers, post-rain conditions). No nighttime baseline was measured at the homes to the east, which are the closest receivers and the ones the compliance question turns on.
• No cumulative analysis with the Mt. Si substation. The substation right next door is itself a continuous noise source. BESS noise would add to it at the nearest homes, but the study models only the BESS on its own. SEPA (WAC 197-11-330(3)(c)) requires cumulative impacts to be evaluated.

The “substation exemption” does not rescue it

Both the County’s Ordinance 19824 SEPA checklist and the staff memo suggest a BESS “integrated with” a substation might be exempt from the nighttime noise rules, each citing “K.C.C. 12.85.120.A.” That code section does not exist. The correct chapter is 12.86, and its actual substation exemptions are narrow: a substation is excused from the nighttime reduction and from the pure-tone penalty, and nothing more. Those carve-outs cover the substation’s own transformer hum. They do not cover the HVAC noise from a battery facility that happens to sit on the same parcel, and they do not waive the base sound limits at all. That two County documents reached the exemption conclusion by citing a code section that does not exist is a sign the question was not carefully analyzed.

What a comment should ask for

The fix here is front-end, before construction, not complaint-driven enforcement after a facility is already permitted and built. A strong comment asks King County to require, before any threshold determination:

• Manufacturer sound data for the equipment actually proposed, not substitute data from other projects
• A real nighttime baseline (14 or more days) measured at the homes immediately east of the site
• A pure-tone analysis demonstrating the 45 dBA nighttime limit is met
• A cumulative analysis that adds the adjacent Mt. Si substation
• A written legal determination of whether the substation exemption applies to BESS cooling noise, citing the actual code text
• Binding conditions making the modeled mitigation enforceable for the life of the facility, with post-construction verification

A zero-margin prediction built on placeholder inputs is not “information reasonably sufficient to evaluate the environmental impact of a proposal” (WAC 197-11-335). That gap is a reason for a full EIS.