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Washington SEPA guide: the environmental checklist, threshold determinations and EIS

Washington SEPA, the State Environmental Policy Act, requires state and local agencies to consider environmental impacts before deciding on a proposal[1]. Unless it is exempt, the lead agency reviews a SEPA environmental checklist and makes a threshold determination: a DNS, a mitigated determination of nonsignificance (MDNS), or a determination of significance (DS) requiring an EIS[2][3].

By Ilya Volodarsky. 28 sources, last read on . This page explains the law; it is not legal advice.

Draft a SEPA Checklist for Infill Housing

    ePlan gets you

    • A first draft of your SEPA Checklist, from a project description or the files you already have
    • Precedent research: analog projects and their documents, found for you
    • Every fact ePlan can't confirm, marked for your team to fill in
    • A Word download, plus tasks and a Gantt timeline on Pro and Max
    See how it compares

    Describe the project and ePlan drafts the SEPA Checklist answers, question by question, from your description and files, for the lead agency to review; every fact it can't confirm is marked for you.

    ePlan vs. by hand

    How ePlan compares to drafting a SEPA Checklist by hand

    The same document, two ways to a first draft.

    ComparedePlan.aiBy hand
    Starting pointePlan.aiYour project description and files, following the checklist form you upload or it findsBy handEcology's Word template, answered question by question
    Precedent researchePlan.aiResearches agency project pages for your project and up to two similar onesBy handSearch the SEPA Register by hand for comparable checklists
    Missing factsePlan.aiEvery fact ePlan can't confirm stays a highlighted [INSERT] placeholder until someone fills itBy handGaps surface in review, or not at all
    Cost to startePlan.aiScoping letters are free. EAs, EIRs and decision memos are on Max at $199 a monthBy handStaff or consultant hours for every draft

    ePlan.ai as of October 2026. “By hand” means a Word template, past documents and agency PDFs. Your team reviews, edits and signs every draft.

    When is a SEPA checklist required?

    SEPA applies to agency decisions such as permits for private projects, public facilities, and new regulations, policies and plans[12]. For a nonexempt proposal, the lead agency bases its threshold determination on a checklist in the form of WAC 197-11-960[13]. Exempt projects need none[14].

    The first agency to receive an application determines the lead agency[15]. When a private project also needs a county or city license, it is the county or city with the largest share of the site[16].

    Which projects are exempt from SEPA?

    Categorically exempt projects need no threshold determination or EIS. By default, minor new construction is exempt up to four single-family or four multifamily units, a 10,000-square-foot farm building, or a 4,000-square-foot office, school, commercial or storage building with 20 parking spaces; local limits may be higher. The exemption does not apply on lands covered by water or where a nonexempt license is needed[17].

    Exemptions added since 2023[18]:

    • SB 5412: housing in urban growth areas, after an environmental analysis of the area[19]
    • HB 1491: housing and mixed use near rail and bus rapid transit stations, with exceptions[19]
    • SB 5445: solar over parking lots, on capped landfills or reclaimed mines, and small arrays on disturbed land[20]

    Threshold determination: SEPA DNS, MDNS or DS

    A DNS finds no probable significant adverse impacts[21]; an MDNS, that the applicant changed or conditioned the proposal to include the lead agency's mitigation[22]. Every MDNS gets 14 days of comment, as does a DNS when another agency has jurisdiction, the proposal includes nonexempt demolition or grading, or it is a GMA action[21][6].

    A DS starts scoping, with 21 days for comment[23][24]. Example: the EIS for the Millennium coal terminal in Longview found unavoidable significant impacts in nine areas and assumed full greenhouse gas offsets. The company offered to offset about 0.5 percent, and Cowlitz County's hearing examiner denied its shoreline permits, citing SEPA. The Court of Appeals affirmed in 2020[25].

    How to fill out the SEPA environmental checklist

    Answer briefly from your own observations or plans, cover every part of the proposal, and write "does not apply" or "do not know" where true, saying why[3][26]. Agencies may not delete questions[27].

    Ecology publishes a Word version with help links, plus DNS, MDNS and DS templates; agencies may use their own forms[28].

    Outline

    What the SEPA environmental checklist asks

    The questions in WAC 197-11-960[3], each explained in Ecology's guidance[26]. SEPA is one of the state environmental policy acts.

    1. A. Background (questions 1 to 12)

      Applicant, timing, prior studies, pending applications, approvals needed, description and location maps[3].

    2. B.1 to B.3 Earth, air and water

      Slopes, soils, erosion, impervious surface, emissions, surface water within 200 feet, floodplain, groundwater, stormwater[3].

    3. B.4 to B.7 Plants, animals, energy and environmental health

      Vegetation, listed and invasive species, wildlife, energy, contamination, hazardous chemicals, pipelines, noise[3].

    4. B.8 and B.9 Land and shoreline use; housing

      Current uses, farm and forest land, zoning and shoreline designations, critical areas, displacement, and housing by income level[3].

    5. B.10 to B.13 Aesthetics, light, recreation and historic resources

      Height and views, light and glare, recreation, structures over 45 years old, cultural resources[3].

    6. B.14 to B.16 Transportation, public services and utilities

      Access, transit, new roads, daily and peak vehicle trips, public services and utilities[3].

    7. C. Signature

      The signer certifies the answers are true and complete[3].

    8. D. Supplemental sheet for nonproject actions

      Seven questions for plans, policies and regulations only[3].

    Sources

    Where each statement comes from

    Show all 28 sources
    1. [1]RCW 43.21C.031: Significant impacts. Washington State Legislature (app.leg.wa.gov). Read October 2, 2026.
    2. [2]WAC 197-11-310: Threshold determination required. Washington State Legislature (app.leg.wa.gov), September 1, 2003. Read October 2, 2026.
    3. [3]WAC 197-11-960: Environmental checklist. Washington State Legislature (app.leg.wa.gov), January 20, 2023. Read October 2, 2026.
    4. [4]RCW 43.21C: State Environmental Policy Act (chapter). Washington State Legislature (app.leg.wa.gov). Read October 2, 2026.
    5. [5]Chapter 197-11 WAC: SEPA rules. Washington State Legislature (app.leg.wa.gov). Read October 2, 2026.
    6. [6]State Environmental Policy Act (SEPA) Handbook, 2025 Update (Publication 25-06-009). Washington State Department of Ecology, Shorelands and Environmental Assistance Program, September 2025. Read October 2, 2026.
    7. [7]RCW 43.21C.033: Threshold determination to be made within ninety days after application is complete. Washington State Legislature (app.leg.wa.gov). Read October 2, 2026.
    8. [8]WAC 197-11-455: Issuance of DEIS. Washington State Legislature (app.leg.wa.gov), April 4, 1984. Read October 2, 2026.
    9. [9]WAC 197-11-460: Issuance of FEIS. Washington State Legislature (app.leg.wa.gov), April 4, 1984. Read October 2, 2026.
    10. [10]WAC 197-11-508: SEPA register. Washington State Legislature (app.leg.wa.gov), May 10, 2014. Read October 2, 2026.
    11. [11]Statewide SEPA register. Washington State Department of Ecology. Read October 2, 2026.
    12. [12]State Environmental Policy Act (SEPA). Washington State Department of Ecology. Read October 2, 2026.
    13. [13]WAC 197-11-315: Environmental checklist. Washington State Legislature (app.leg.wa.gov), January 28, 2013. Read October 2, 2026.
    14. [14]RCW 43.21C.503: Exempt projects: environmental checklist not required. Washington State Legislature (app.leg.wa.gov). Read October 2, 2026.
    15. [15]WAC 197-11-924: Determining the lead agency. Washington State Legislature (app.leg.wa.gov), April 4, 1984. Read October 2, 2026.
    16. [16]WAC 197-11-932: Lead agency for private projects requiring licenses from more than one agency, when one of the agencies is a county/city. Washington State Legislature (app.leg.wa.gov), April 4, 1984. Read October 2, 2026.
    17. [17]WAC 197-11-800: Categorical exemptions. Washington State Legislature (app.leg.wa.gov), January 20, 2023. Read October 2, 2026.
    18. [18]SEPA laws and regulations: current & historical revisions. Washington State Department of Ecology. Read October 2, 2026.
    19. [19]RCW 43.21C.229: Infill and housing development: categorical exemptions from chapter. Washington State Legislature (app.leg.wa.gov), July 27, 2025. Read October 2, 2026.
    20. [20]RCW 43.21C.560: Solar energy generation projects exempt from this chapter. Washington State Legislature (app.leg.wa.gov), July 27, 2025. Read October 2, 2026.
    21. [21]WAC 197-11-340: Determination of nonsignificance (DNS). Washington State Legislature (app.leg.wa.gov), November 10, 1997. Read October 2, 2026.
    22. [22]WAC 197-11-350: Mitigated DNS. Washington State Legislature (app.leg.wa.gov), April 4, 1984. Read October 2, 2026.
    23. [23]WAC 197-11-360: Determination of significance (DS)/initiation of scoping. Washington State Legislature (app.leg.wa.gov), April 4, 1984. Read October 2, 2026.
    24. [24]WAC 197-11-408: Scoping. Washington State Legislature (app.leg.wa.gov), November 10, 1997. Read October 2, 2026.
    25. [25]Millennium Bulk Terminals-Longview, LLC v. Department of Ecology, No. 52215-2-II (unpublished opinion). Washington State Court of Appeals, Division II, March 17, 2020. Read October 3, 2026.
    26. [26]SEPA checklist guidance. Washington State Department of Ecology. Read October 2, 2026.
    27. [27]RCW 43.21C.460: Environmental checklist: authority of lead agency, limitations of section. Washington State Legislature (app.leg.wa.gov). Read October 2, 2026.
    28. [28]SEPA document templates (forms). Washington State Department of Ecology. Read October 2, 2026.

    Written by

    Ilya Volodarsky

    Ilya Volodarsky founded ePlan.ai. He co-founded Segment and is co-founder and CEO of Wildfires.org.

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    FAQ

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    • Yes. Before the threshold determination you may ask, then change or condition the proposal to mitigate the impacts, which can lead to an MDNS instead.

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