Creates a new section in chapter 43.21C RCW and directs the Department of Ecology to add four specific elements to the SEPA environmental definitions in WAC 197-11-444 and WAC 197-11-960: climate change, carbon sequestration, treaty-protected resources, and exposures to environmental pollutants for overburdened communities and vulnerable populations. This is a procedural change to how state and local agencies implement SEPA, not a criminal or penalty change. The measure requires lead agencies to consider these four elements when applying chapter 43.21C RCW and obligates the Department of Ecology to adopt related guidance and rules. The bill specifies what lead-agency consideration must include for each element: for climate change, whether a proposed action may significantly increase life-cycle greenhouse gas emissions and whether it helps achieve state and local climate-related goals, with the Department required to define life-cycle emissions and significance thresholds; for carbon sequestration, whether an action would significantly reduce or benefit sequestration across various land and marine environments and to treat actions relying on mitigation or natural recovery taking more than 20 years as having potential adverse impacts; for treaty-protected resources, whether actions preserve, enhance, or adversely affect treaty-protected resources and whether tribal members exercising treaty rights could face contaminant exposure under reasonable maximum exposure scenarios developed with affected tribes; and for exposures to pollutants, whether actions would cause disproportionate adverse health effects on overburdened communities or vulnerable populations using screening or mapping tools and cumulative impact analysis. The measure defines "Department" as the Department of Ecology and adopts existing statutory definitions for "overburdened community," "vulnerable population," and "treaty-protected resources." Affected parties include the Department of Ecology, SEPA lead agencies, the Department of Health, the Environmental Justice Council, federally recognized tribes, and state and local jurisdictions. Important implementation details are not specified in the extracted text: the effective date is not stated, timelines and procedural steps for adopting guidance or rules are not given, the methodology and standards for "reasonable maximum exposure scenarios" are not defined, and the specific screening or mapping tools to be used are not identified.

If enacted, the Department of Ecology would be required to add four new topics to Washington’s SEPA review rules and write guidance and rules so that lead agencies must evaluate a project’s life‑cycle greenhouse gas emissions, its effects on carbon sequestration, impacts to treaty‑protected resources, and whether pollutant exposures disproportionately harm overburdened or vulnerable populations. Practically, that means more projects, permits, and some previously adopted plans or permits could need new analyses, threshold decisions, or reviews; lead agencies will spend more time and applicants will likely face higher study, consultation, and possible mitigation costs and delays. The Department of Ecology takes on the main new workload of producing guidance and rules, and federally recognized tribes gain a defined consultative role for exposure scenarios affecting treaty rights. Local and state agencies that set climate or land goals will be explicitly factored into reviews. Important details are unclear and will affect real costs and timing: the bill text does not specify an effective date, deadlines or processes for Ecology’s rulemaking, or the exact methods for the required exposure scenarios and screening tools.