(1) In any multiyear rate plan filed by a large combination utility pursuant to RCW 80.28.425 and in accordance with this chapter, the large combination utility must include an updated depreciation study that reduces the gas rate base consistent with an approved integrated system plan, and the commission may adopt depreciation schedules that accelerate cost recovery and reduce the rate base for any gas plant. The commission shall approve a depreciation schedule that depreciates all gas plants in service as of July 1, 2024, by a date no later than January 1, 2050, in any multiyear rate plan, but the commission may adjust depreciation schedules for gas plants as necessary when considering future multiyear rate plans to address affordability provided all plants in service as of July 1, 2024, are fully depreciated by 2050.

(2) In any multiyear rate plan proposed by a large combination utility, the company may propose a merger of regulated gas and electric operations into a single rate base. The commission may approve the merger of electric and gas rate bases if the commission finds that the proposal will result in a net benefit to customers of the large combination utility and includes reasonable rate protections for low-income natural gas and electric customers.

(3) For a large combination utility that has merged gas and electricity rate bases, the large combination utility must monetize benefits received from any applicable federal and state tax and other incentives for the benefit of customers. These benefits must be separately accounted for and amortized on a schedule designed to mitigate the rate impacts to customers after the rate bases are combined. These credits may not be used for any other purpose, unless directed by the commission.

(4) For the first multiyear rate plan proposed by a large combination utility following commission approval or approval with conditions of the initial integrated system plan identified in RCW 80.86.020, the commission may for good cause shown extend the deadline for a decision set forth under RCW 80.04.130 by up to 60 days.

Findings—Intent—Effective date—2024 c 351: See notes following RCW 80.86.010.