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What is an environmental impact assessment? EIA steps, documents and US law

An environmental impact assessment (EIA) is the process of identifying, predicting, evaluating and mitigating the biophysical, social and other relevant effects of a development proposal before major decisions are taken[1]. In the US, federal agencies do it under NEPA, and states such as California under their own laws, like CEQA[2].

By Ilya Volodarsky. 20 sources, last read on . This page explains the law; it is not legal advice.

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    • A first draft of your NEPA or CEQA Document, 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
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    See how it compares

    Describe the project and ePlan proposes the level of review under NEPA or CEQA, then drafts the document, here an EA, from a reference document; every fact it can't confirm is marked for you.

    ePlan vs. by hand

    How ePlan compares to drafting a NEPA or CEQA Document by hand

    The same document, two ways to a first draft.

    ComparedePlan.aiBy hand
    Level of reviewePlan.aiProposes the NEPA level (CE, EA or EIS) or the CEQA document (exemption, negative declaration or EIR), for your team to confirmBy handWork it out from the statute, agency procedures and past projects
    Starting pointePlan.aiA plain-language project description, or the PDFs, Word files and GIS files (shapefile, GeoJSON, KML, GeoPackage) you already haveBy handA blank template, or last year's document retyped
    Precedent researchePlan.aiA research agent searches agency project pages, CEQAnet, the Federal Register, eCFR and EPA's EIS database for your project and up to two analog projectsBy handSearching each agency site and PDF library by hand
    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.

    The environmental impact assessment process, step by step

    The International Association for Impact Assessment's stages, grouped into six phases[1]; the outline below gives the document each phase produces under NEPA and CEQA.

    • Screening: does the proposal need an EIA, and how detailed
    • Scoping: the issues that matter, and the terms of reference
    • Alternatives and impact analysis: the options and their likely effects
    • Mitigation and significance: avoid, minimize or offset harm, then weigh what remains
    • Report and review: checked against the terms of reference and public concerns
    • Decision and follow-up: approve or reject, set conditions, monitor

    EIA in the United States: NEPA, CEQA and other state laws

    NEPA covers major federal actions[10]: an environmental impact statement when significant effects are reasonably foreseeable, an environmental assessment when they are not, and neither under a categorical exclusion[4]. Under CEQA, an initial study decides between a negative declaration and an EIR[6].

    An example under both laws: Valley Link Rail, 22 miles from Dublin/Pleasanton BART to Mountain House. Under CEQA came a notice of preparation in 2018, a draft EIR in 2020 and a subsequent EIR in 2024; under NEPA, an EA in December 2024 and FTA's FONSI in 2025, all under one State Clearinghouse number[11][12]. See CEQA and NEPA.

    Environmental and social impact assessment (ESIA)

    An ESIA adds impacts on nearby communities and workers to the physical, natural and cultural environment[9]. World Bank projects started on or after October 1, 2018 follow its Environmental and Social Framework[13], whose ESS1 requires borrowers to assess and manage those risks[8].

    ePlan does not prepare ESIAs or other countries' EIAs; it drafts US documents under NEPA and CEQA.

    Who does environmental impact assessment in the US?

    The deciding agency. Under NEPA, a sponsor may prepare the document, but the lead agency supervises it, evaluates it independently and is responsible for it[14]. Under CEQA, the public agency prepares it or contracts it out and reviews it independently[15].

    ePlan drafts NEPA and CEQA documents for agency staff and consultants; the agency still decides. For the work around the documents, see environmental planning.

    Outline

    How to do an environmental impact assessment in the US: NEPA and CEQA documents

    Each EIA stage and its document under each law[5][6]. For an Army Corps permit, the NEPA review informs the permit decision[16].

    1. Screening

      NEPA: a categorical exclusion if one fits[4]. CEQA: an exemption, if one applies[17].

    2. First-level assessment

      NEPA: an EA[4]. CEQA: an initial study[6].

    3. No significant effect

      NEPA: a finding of no significant impact (FONSI)[10]. CEQA: a negative declaration, or a mitigated one[7].

    4. Full assessment

      NEPA: an EIS, up to 150 pages (300 if extraordinarily complex)[14]. CEQA: an EIR, when a significant effect may occur[7].

    5. Public review

      NEPA: comments on the EIS notice of intent[14]. CEQA: 30 to 60 days on a draft EIR[18].

    6. Decision

      NEPA: a decision such as a record of decision[5]. CEQA: findings on each significant effect[19].

    7. Follow-up

      NEPA: carry out the decision's commitments[5]. CEQA: a mitigation reporting or monitoring program[20].

    Sources

    Where each statement comes from

    Show all 20 sources
    1. [1]Principles of Environmental Impact Assessment Best Practice. International Association for Impact Assessment (IAIA), with the Institute of Environmental Assessment, UK, January 1999. Read October 2, 2026.
    2. [2]State, Tribe, and Local Government Information. Council on Environmental Quality, nepa.gov. Read October 2, 2026.
    3. [3]42 U.S.C. 4332 - Cooperation of agencies; reports; availability of information; recommendations; international and national coordination of efforts. United States Code, 2023 edition (GovInfo). Read October 2, 2026.
    4. [4]42 U.S.C. 4336 - Procedure for determination of level of review. United States Code, 2023 edition (GovInfo). Read October 2, 2026.
    5. [5]The NEPA Process (flowchart). Council on Environmental Quality, nepa.gov, January 2026. Read October 2, 2026.
    6. [6]CEQA Guidelines, Cal. Code Regs., tit. 14, § 15063 - Initial study. Legal Information Institute (Cornell Law School), California Code of Regulations. Read October 2, 2026.
    7. [7]Cal. Public Resources Code § 21080 - Projects subject to CEQA; negative declarations; environmental impact reports. California Legislative Information (leginfo.legislature.ca.gov), September 17, 2025. Read October 2, 2026.
    8. [8]Environmental and Social Standards (ESS). World Bank. Read October 2, 2026.
    9. [9]Performance Standard 1: Assessment and Management of Environmental and Social Risks and Impacts. International Finance Corporation (IFC), World Bank Group, January 1, 2012. Read October 2, 2026.
    10. [10]42 U.S.C. 4336e - Definitions. United States Code, 2023 edition (GovInfo). Read October 2, 2026.
    11. [11]CEQAnet project page, SCH No. 2018092027: Valley Link Rail Project (8 documents). State Clearinghouse, LCI (CEQAnet). Read October 3, 2026.
    12. [12]Finding of No Significant Impact: Valley Link Rail Project. Federal Transit Administration (posted on CEQAnet), May 2025. Read October 2, 2026.
    13. [13]Environmental and Social Framework (ESF). World Bank. Read October 2, 2026.
    14. [14]42 U.S.C. 4336a - Timely and unified Federal reviews. United States Code, 2023 edition (GovInfo). Read October 2, 2026.
    15. [15]Cal. Public Resources Code § 21082.1 - Preparation of environmental documents; independent judgment; State Clearinghouse submission. California Legislative Information (leginfo.legislature.ca.gov), January 1, 2022. Read October 2, 2026.
    16. [16]33 CFR part 333 - Processing of Department of the Army Permits and 33 U.S.C. 408 Permissions, National Environmental Policy Act Implementing Procedures. Electronic Code of Federal Regulations (eCFR), current. Read October 2, 2026.
    17. [17]CEQA Guidelines, Cal. Code Regs., tit. 14, § 15061 - Review for exemption. Legal Information Institute (Cornell Law School), California Code of Regulations. Read October 2, 2026.
    18. [18]CEQA Guidelines, Cal. Code Regs., tit. 14, § 15105 - Public review period for a draft EIR or a proposed negative declaration or mitigated negative declaration. Legal Information Institute (Cornell Law School), California Code of Regulations. Read October 2, 2026.
    19. [19]Cal. Public Resources Code § 21081 - Findings required before approving a project with significant effects. California Legislative Information (leginfo.legislature.ca.gov), October 1, 1994. Read October 2, 2026.
    20. [20]Public Resources Code § 21081.6 - Mitigation reporting or monitoring program. California Legislative Information, October 1, 1994. 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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    • An EIA is the whole process of assessing a proposal's effects. An environmental impact statement is one document it can produce: the NEPA document for reasonably foreseeable significant effects.

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