Sierra Club v. County of Fresno ( 2018 )


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    IN THE SUPREME COURT OF
    CALIFORNIA
    SIERRA CLUB et al.,
    Plaintiffs and Appellants,
    v.
    COUNTY OF FRESNO et al.,
    Defendants and Respondents;
    FRIANT RANCH, L.P.,
    Real Party in Interest and Respondent.
    S219783
    Fifth Appellate District
    F066798
    Fresno County Superior Court
    11CECG00726, 11CECG00706, 11CECG00709
    December 24, 2018
    Justice Chin authored the opinion of the court, in which Chief
    Justice Cantil-Sakauye and Justices Corrigan, Liu, Cuéllar,
    Kruger, and Robie* concurred.
    *
    Associate Justice of the Court of Appeal, Third Appellate
    District, assigned by the Chief Justice pursuant to article VI,
    section 6 of the California Constitution.
    SIERRA CLUB v. COUNTY OF FRESNO
    S219783
    Opinion of the Court by Chin, J.
    We granted review to determine whether an
    Environmental Impact Report (EIR), issued as part of a master
    plan to develop a partial retirement community in Fresno,
    California, violates the California Environmental Quality Act
    (CEQA) for failing to include sufficient information on topics the
    Act requires. (Pub. Resources Code, § 21000 et seq.)1 Our task
    is to review specific challenges to the final EIR2 that defendant
    County of Fresno (County) and its Board of Supervisors adopted,
    and the trial court approved. As we explain, we affirm in part
    and reverse in part the Court of Appeal’s judgment.
    FACTUAL AND PROCEDURAL BACKGROUND
    The Friant Ranch project (Project) consists of real party in
    interest Friant Ranch, L.P.’s (real party) planned development
    of the Central Valley’s first master-planned “pedestrian
    friendly” community on a 942-acre site (formerly zoned
    agricultural) that sits adjacent to the unincorporated
    community of Friant in north central Fresno County, just south
    1
    All further statutory references are to CEQA provisions as
    codified in Public Resources Code sections 21000-21177 unless
    otherwise indicated. Where applicable, the CEQA guidelines
    (Cal. Code Regs., tit. 14, §§ 15000-15387) will be noted as
    “Guidelines” throughout the text to distinguish between the
    Public Resources Code and the Code of Regulations.
    2
    All references to the EIR are to the final EIR unless
    otherwise indicated.
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    of the San Joaquin River. The County is the local governmental
    entity that acted as the lead agency for the CEQA review and
    for preparation of the Project’s EIR.
    The Project includes the Friant Ranch Specific Plan
    (Specific Plan), which contemplates the construction of
    approximately 2,500 single and multi-family residential units
    that are age restricted to “active adults” age 55 and older, other
    residential units that are not age restricted, a commercial
    village center, a recreation center, trails, open space, a
    neighborhood electric vehicle network, and parks and parkways.
    The Project also includes 250,000 square feet of commercial
    space on 482 acres and the dedication of 460 acres to open space.
    An additional Friant Community Plan Update expands the
    Specific Plan area and adds policies that are consistent with the
    Specific Plan and the County’s General Plan. The Project’s
    construction is divided into five phases with an estimated 10-
    year build-out.
    Through its Board of Supervisors, the County received
    written comments to the draft EIR, held a public hearing, and
    prepared responses to the comments. After making the findings
    required under section 21081, subdivision (a), for each
    significant effect noted in the draft, the County issued a
    Statement of Overriding Considerations (Statement) that is
    required in CEQA approved projects to show that the Project’s
    significant environmental effects have been identified, and
    avoided or mitigated, or that unmitigated effects will be
    outweighed by the Project’s benefits. (§§ 21002, 21002.1, 21081;
    Guidelines, §§ 15091-15093.) The Statement noted: “The
    Project implements and furthers important plans and public
    policies adopted and endorsed by the County related to urban
    growth.” The Statement also observed that the County “made a
    2
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    reasonable and good faith effort to eliminate or substantially
    mitigate the environmental impacts resulting from the Project
    by requiring implementation of the environmentally superior
    alternative—Project Alternative No. 3: Northeast Development
    Configuration and the Beck Property alternative wastewater
    treatment plant location—and various mitigation measures,
    goals and policies identified in the EIR, General Plan, the
    proposed Friant Community Plan Update, and the proposed
    Friant Ranch Specific Plan.”
    On February 1, 2011, the County’s Board of Supervisors
    approved Project Alternative 3, certified the EIR, and approved
    a version of the Specific Plan that prohibited the discharge of
    treated effluent into the river from the wastewater treatment
    plant. The County also adopted a Mitigation Monitoring
    Program (MMP), which noted in part that compliance with the
    mitigation measures would be “enforced through subsequent
    conditions of approval for future discretionary actions,”
    including use permits and tentative subdivision maps for the
    Specific Plan area. By petition for writ of mandamus filed in the
    trial court, plaintiffs Sierra Club, Revive the San Joaquin, and
    League of Women Voters of Fresno (collectively, plaintiffs)
    challenged the County’s certification of the EIR, alleging that it
    violated CEQA in several respects. (Code Civ. Proc., §1094.5
    [challenge to public agency’s determination based on alleged
    CEQA noncompliance requires administrative mandamus
    proceeding].) The trial court rejected plaintiffs’ challenges and
    approved the Project, noting in its judgment that in reviewing
    CEQA decisions, “it may not exercise its independent judgment
    on the evidence, but must determine only whether the act or
    decision is supported by substantial evidence.” In reviewing the
    EIR, the court agreed with County’s findings on traffic impact,
    3
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    biological resources, wastewater treatment, and air quality
    impact, among other considerations. It stated that the court
    “does not pass on the correctness of any EIR’s environmental
    conclusions, but instead determines whether the EIR is
    sufficient as an informational document. All conflicts in the
    evidence and reasonable inferences must be resolved and drawn
    in favor of the agency’s decisions and findings. The reviewing
    Court does not reweigh the evidence.”
    The court’s judgment also observed that regarding air
    quality impacts, the County explained why the EIR’s mitigation
    measures would reduce the Project’s greenhouse gas emissions.
    The court agreed with the County that plaintiffs did not cite to
    the record in sufficient detail to show any error.
    At the end of its judgment, the court noted that it retained
    jurisdiction to allow the County a reasonable amount of time to
    circulate a Park Impact analysis on the Project’s effect on
    adjoining parks, including Lost Lake Park and Millerton Lake.
    This analysis is not at issue here. Otherwise, the court denied
    all of plaintiffs’ claims and entered judgment in favor of real
    party.
    Plaintiffs appealed the judgment before the County could
    implement the mitigation measures. They claimed in relevant
    part that the Project’s EIR failed to comply with CEQA because
    its discussion of air quality impacts was inadequate.
    The Court of Appeal agreed with plaintiffs’ contentions
    involving the EIR’s consideration of the Project’s air quality
    impacts on the following grounds: “(1) the EIR was inadequate
    because it failed to include an analysis that correlated the
    [P]roject’s emission of air pollutants to its impact on human
    health; (2) the mitigation measures for the [P]roject’s long-term
    4
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    air quality impacts violate CEQA because they are vague,
    unenforceable and lack specific performance criteria; and (3) the
    statement that the air quality mitigation provisions will
    substantially reduce air quality impacts is unexplained and
    unsupported. These defects must be cured by the preparation of
    a revised EIR.” The Court of Appeal reversed the trial court’s
    judgment on those grounds only.3
    We granted real party’s petition for review on the issues
    concerning the Court of Appeal’s reversal of the trial court
    judgment upholding the air quality impact findings and
    conclusions in the EIR’s chapter 3 (discussing air quality
    impacts). The scope of our review concerns how courts should
    determine the adequacy of an EIR’s discussion, including: What
    standard of review a court must apply when adjudicating a
    challenge to the adequacy of an EIR’s discussion of adverse
    environmental impacts and mitigation measures, and whether
    CEQA requires an EIR to connect a project’s air quality impacts
    to specific health consequences. We must also decide whether a
    3
    Plaintiffs had also argued that the EIR’s discussion of
    treated effluent from the proposed wastewater treatment
    facilities was inadequate and that the EIR was inconsistent with
    land use and traffic policies in the County’s General Plan. The
    Court of Appeal concluded that the amount and location of
    wastewater use and disposal, and the hydrogeology of the site
    chosen for the wastewater treatment plant, were addressed in
    sufficient detail during the environmental review process. The
    Court of Appeal also concluded that the development plan was
    consistent with the land use element (as changed from
    agricultural to residential by amendment), and that the traffic
    policy issues had not been properly exhausted during the
    administrative process. The parties do not dispute the Court of
    Appeal’s judgment on these issues, and we do not address that
    aspect of the court’s opinion here.
    5
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    lead agency impermissibly defers mitigation measures when it
    retains the discretion to substitute later adopted measures in
    place of those proposed in the EIR, and whether a lead agency
    may adopt mitigation measures that do not reduce a project’s
    significant and unavoidable impacts to a less-than-significant
    level.
    We conclude as follows: When reviewing whether a
    discussion is sufficient to satisfy CEQA, a court must be
    satisfied that the EIR (1) includes sufficient detail to enable
    those who did not participate in its preparation to understand
    and to consider meaningfully the issues the proposed project
    raises (Laurel Heights Improvement Assn. v. Regents of
    University of California (1988) 
    47 Cal. 3d 376
    , 405 (Laurel
    Heights I)), and (2) makes a reasonable effort to substantively
    connect a project’s air quality impacts to likely health
    consequences. As explained below, the EIR in this case failed to
    do so. The EIR should be revised to relate the expected adverse
    air quality impacts to likely health consequences or explain in
    meaningful detail why it is not feasible at the time of drafting to
    provide such an analysis, so that the public may make informed
    decisions regarding the costs and benefits of the Project.
    We further conclude that a lead agency may leave open the
    possibility of employing better mitigation efforts consistent with
    improvements in technology without being deemed to have
    impermissibly deferred mitigation measures. A lead agency
    may adopt mitigation measures that do not reduce the project’s
    adverse impacts to less than significant levels, so long as the
    agency can demonstrate in good faith that the measures will at
    least be partially effective at mitigating the Project’s impacts.
    6
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    We therefore affirm the Court of Appeal’s judgment
    finding the EIR’s analyses of the Project’s air quality impacts
    inadequate. However, we reverse the Court of Appeal’s
    judgment that the EIR improperly deferred mitigation
    measures by proposing to substitute more effective measures if
    available in the future, and that the mitigation measures
    proposed were impermissibly vague and unlikely to reduce
    adverse health impacts to less than significant levels.
    DISCUSSION
    A. Adequacy of the EIR’s discussion of health impacts of
    the Project’s long-term effects on air quality
    Plaintiffs claim that the EIR was insufficient as an
    informational document because it failed to adequately explain
    how the air pollutants the Project generated would impact
    public health. To address that claim, we must first decide what
    standard of review applies to a challenge to the adequacy of an
    EIR’s discussion of a required topic.
    1. Standard of review
    “The foremost principle under CEQA is that the
    Legislature intended the act ‘to be interpreted in such manner
    as to afford the fullest possible protection to the environment
    within the reasonable scope of the statutory language.’ ” (Laurel
    Heights 
    I, supra
    , 47 Cal.3d at p. 390, quoting Friends of
    Mammoth v. Board of Supervisors (1972) 
    8 Cal. 3d 247
    , 259.)
    “With narrow exceptions, CEQA requires an EIR whenever a
    public agency proposes to approve or to carry out a project that
    may have a significant effect on the environment. [Citations.]”
    (Laurel Heights 
    I, supra
    , 47 Cal.3d at pp. 390-391; see
    Guidelines, § 15002, subd. (f).) The basic purpose of an EIR is
    7
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    to “provide public agencies and the public in general with
    detailed information about the effect [that] a proposed project is
    likely to have on the environment; to list ways in which the
    significant effects of such a project might be minimized; and to
    indicate alternatives to such a project.”          (§ 21061; see
    Guidelines, § 15003, subds. (b)-(e).)4 “Because the EIR must be
    certified or rejected by public officials, it is a document of
    accountability. If CEQA is scrupulously followed, the public will
    know the basis on which its responsible officials either approve
    or reject environmentally significant action, and the public,
    being duly informed, can respond accordingly to action with
    which it disagrees.” (Laurel Heights 
    I, supra
    , at p. 392.) The
    EIR “protects not only the environment but also informed self-
    government.” (Ibid.)
    The standard of review in a CEQA case, as provided in
    sections 21168.5 and 21005, is abuse of discretion. Section
    21168.5 states in part: “In any action or proceeding . . . to attack,
    review, set aside, void or annul a determination, finding, or
    decision of a public agency on the grounds of noncompliance
    with this division, the inquiry shall extend only to whether there
    was a prejudicial abuse of discretion.” (See § 21005, subd. (a)
    [noncompliance with information disclosure requirements may
    “constitute a prejudicial abuse of discretion”].) Our decisions
    have thus articulated a procedural issues/factual issues
    dichotomy. “[A]n agency may abuse its discretion under CEQA
    either by failing to proceed in the manner CEQA provides or by
    reaching factual conclusions unsupported by substantial
    4
    A “significant effect” is defined as “a substantial, or
    potentially substantial, adverse change in the environment.”
    (§ 21068.)
    8
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    evidence. (§ 21168.5.) Judicial review of these two types of error
    differs significantly: While we determine de novo whether the
    agency has employed the correct procedures, ‘scrupulously
    enforc[ing] all legislatively mandated CEQA requirements’
    (Citizens of Goleta Valley v. Board of Supervisors (1990) 
    52 Cal. 3d 553
    , 564 [
    276 Cal. Rptr. 410
    , 
    801 P.2d 1161
    ]), we accord
    greater deference to the agency’s substantive factual
    conclusions.     In reviewing for substantial evidence, the
    reviewing court ‘may not set aside an agency’s approval of an
    EIR on the ground that an opposite conclusion would have been
    equally or more reasonable,’ for, on factual questions, our task
    is ‘not to weigh conflicting evidence and determine who has the
    better argument.’ (Laurel Heights 
    I, supra
    , 47 Cal.3d at p. 393.)”
    (Vineyard Area Citizens for Responsible Growth, Inc. v. City of
    Rancho Cordova (2007) 
    40 Cal. 4th 412
    , 435 (Vineyard).)
    This distinction between de novo review and substantial
    evidence review has worked well in judicial review of agency
    determinations. In most cases, the question whether an agency
    has followed proper procedures will have a clear answer. Did
    the agency provide sufficient notice and opportunity to comment
    on a draft EIR? (§ 21092; Guidelines, § 15087.) Did the agency
    omit the required discussion of alternatives? (Guidelines,
    § 15126.6.) As to these legal requirements, the agency has no
    discretion, and courts will invalidate an EIR that fails to meet
    them. In that sense, judicial review is de novo.
    But the question whether an agency has followed proper
    procedures is not always so clear. This is especially so when the
    issue is whether an EIR’s discussion of environmental impacts
    is adequate, that is, whether the discussion sufficiently
    performs the function of facilitating “informed agency
    decisionmaking and informed public participation.” (California
    9
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    Native Plant Society v. City of Santa Cruz (2009) 
    177 Cal. App. 4th 957
    , 988 [relying on Laurel Heights 
    I, supra
    , 47
    Cal.3d at pp. 404-405].) The review of such claims does not fit
    neatly within the procedural/factual paradigm.
    This court’s decision in Laurel Heights I illustrates how a
    court should assess a claim of inadequate discussion. The case
    involved a challenge to an EIR’s discussion of alternatives to the
    proposed construction of the University of California, San
    Francisco’s (UCSF) Laurel Heights campus.              This court
    concluded that the discussion was inadequate:             “UCSF’s
    treatment of alternatives was cursory at best. The draft EIR
    identified three types of alternatives: no project anywhere,
    alternative sites on the UCSF Parnassus campus, and
    alternative sites off-campus. The three categories received a
    scant one and one-half pages of text in an EIR of more than 250
    pages. The EIR stated the obvious conclusion that the ‘no
    project’ alternative, i.e., no relocation to Laurel Heights, would
    not have the environmental effects identified in the EIR. It then
    stated in a mere two-sentence paragraph that ‘. . . no alternative
    sites on [the Parnassus] campus were evaluated as possible
    candidates for the location of the basic science units of the
    School of Pharmacy.’ This is not a sufficient discussion of on-
    campus alternatives; it is merely an admission that such
    alternatives were not considered.” (Laurel Heights 
    I, supra
    , 47
    Cal.3d at p. 403.)
    Laurel Heights I continued: “Even if the Regents are
    correct in their conclusion that there are no feasible alternatives
    to the Laurel Heights site, the EIR is nonetheless defective
    under CEQA. As we stated in a context similar to CEQA, there
    must be a disclosure of the ‘analytic route the . . . agency
    traveled from evidence to action.’ (Topanga Assn. for a Scenic
    10
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    Community v. County of Los Angeles (1974) 
    11 Cal. 3d 506
    , 515
    [construing requirements of Gov. Code, § 65906 for zoning
    variances]; [citation].) The EIR prepared by UCSF contains no
    analysis of any alternative locations. An EIR’s discussion of
    alternatives must contain analysis sufficient to allow informed
    decision making. (San Bernardino Valley Audubon Society, Inc.
    v. County of San Bernardino (1984) 
    155 Cal. App. 3d 738
    , 751
    [
    202 Cal. Rptr. 423
    ].)” (Laurel Heights 
    I, supra
    , 47 Cal.3d at
    p. 404.)
    In Laurel Heights I this court was clear that its inquiry
    was not a matter of reviewing the record for substantial
    evidence: “The Regents also contend the [project opponents]
    failed to point to any evidence in the record that demonstrates
    reasonable alternatives to moving the School of Pharmacy
    research units to Laurel Heights. This argument is somewhat
    disingenuous given the Regents’ own failure to provide any
    meaningful information regarding alternatives. It is the project
    proponent’s responsibility to provide an adequate discussion of
    alternatives.     (Guidelines, § 15126, subd. (d).)           That
    responsibility is not dependent in the first instance on a showing
    by the public that there are feasible alternatives. If the project
    proponent concludes there are no feasible alternatives, it must
    explain in meaningful detail in the EIR the basis for that
    conclusion.” (Laurel Heights 
    I, supra
    , 47 Cal.3d at p. 405.)
    Recently, in Cleveland National Forest Foundation v. San
    Diego Assn. of Governments (2017) 3 Cal.5th 497, 514–515
    (Cleveland National Forest), this court made a similar point that
    the adequacy of an EIR’s discussion of environmental impacts is
    an issue distinct from the extent to which the agency is correct
    in its determination whether the impacts are significant. “[A]n
    EIR’s designation of a particular adverse environmental effect
    11
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    as ‘significant’ does not excuse the EIR’s failure to reasonably
    describe the nature and magnitude of the adverse effect. (See
    Berkeley Keep Jets Over the Bay Com. v. Board of Port Cmrs.
    (2001) 
    91 Cal. App. 4th 1344
    , 1371 [
    111 Cal. Rptr. 2d 598
    ] [‘The
    EIR’s approach of simply labeling the effect “significant”
    without accompanying analysis of the project’s impact on the
    health of the Airport’s employees and nearby residents is
    inadequate to meet the environmental assessment
    requirements of CEQA.’]; Galante Vineyards v. Monterey
    Peninsula Water Management Dist. (1997) 
    60 Cal. App. 4th 1109
    ,
    1123 [
    71 Cal. Rptr. 2d 1
    ].) An adequate description of adverse
    environmental effects is necessary to inform the critical
    discussion of mitigation measures and project alternatives at
    the core of the EIR. (See Guidelines, § 15151 [‘An EIR should
    be prepared with a sufficient degree of analysis to provide
    decisionmakers with information which enables them to make a
    decision which intelligently takes account of environmental
    consequences.’].)” (Ibid.)
    However, there are instances where the agency’s
    discussion of significant project impacts may implicate a factual
    question that makes substantial evidence review appropriate.
    For example, a decision to use a particular methodology and
    reject another is amenable to substantial evidence review, as
    Sierra Club concedes. But whether a description of an
    environmental impact is insufficient because it lacks analysis or
    omits the magnitude of the impact is not a substantial evidence
    question. A conclusory discussion of an environmental impact
    that an EIR deems significant can be determined by a court to
    be inadequate as an informational document without reference
    to substantial evidence.
    12
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    Our Courts of Appeal have consistently recognized that
    adequacy of discussion claims are not typically amenable to
    substantial evidence review. As the court explained in County
    of Amador v. El Dorado County Water Agency (1999) 
    76 Cal. App. 4th 931
    , 945-946, “Substantial evidence challenges are
    resolved much as substantial evidence claims in any other
    setting: a reviewing court will resolve reasonable doubts in
    favor of the administrative decision, and will not set aside an
    agency’s determination on the ground that the opposite
    conclusion would have been equally or more reasonable.
    [Citations.] [¶] A claim that an agency failed to act in a manner
    required by law presents other considerations. Noncompliance
    with substantive requirements of CEQA or noncompliance with
    information disclosure provisions ‘which precludes relevant
    information from being presented to the public agency . . . may
    constitute prejudicial abuse of discretion within the meaning of
    Sections 21168 and 21168.5, regardless of whether a different
    outcome would have resulted if the public agency had complied
    with those provisions.’ (§ 21005, subd. (a).) . . . [W]hen an
    agency fails to proceed [as CEQA requires], harmless error
    analysis is inapplicable. The failure to comply with the law
    subverts the purposes of CEQA if it omits material necessary to
    informed decisionmaking and informed public participation.
    Case law is clear that, in such cases, the error is prejudicial.
    (Sierra Club v. State Bd. of Forestry (1994) 
    7 Cal. 4th 1215
    , 1236-
    1237 [
    32 Cal. Rptr. 2d 19
    , 
    876 P.2d 505
    ]; Fall River Wild Trout
    Foundation v. County of Shasta (1999) 
    70 Cal. App. 4th 482
    , 491-
    493 [
    82 Cal. Rptr. 2d 705
    ]; Kings County Farm Bureau v. City of
    Hanford (1990) 
    221 Cal. App. 3d 692
    , 712 [
    270 Cal. Rptr. 650
    ];
    East Peninsula Ed. Council, Inc. v. Palos Verdes Peninsula
    Unified School Dist. (1989) 
    210 Cal. App. 3d 155
    , 174 [258
    13
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    Cal.Rptr. 147] (East Peninsula); Rural Landowners Assn. v. City
    Council (1983) 
    143 Cal. App. 3d 1013
    , 1021–1023 [
    192 Cal. Rptr. 325
    ].)” (Italics added.) The court in that case concluded that
    the EIR was insufficient because among other things it failed to
    adequately describe environmental baseline conditions.
    (County of Amador, at pp. 952–956.)
    We also affirm that in reviewing an EIR’s discussion, we
    do not require technical perfection or scientific certainty:
    “ ‘ “[T]he courts have looked not for an exhaustive analysis but
    for adequacy, completeness and a good-faith effort at full
    disclosure.” ’ ” (California Native Plant Society v. City of Santa
    
    Cruz, supra
    , 177 Cal.App.4th at p. 979; accord Laurel Heights 
    I, supra
    , 47 Cal.3d at p. 406; see Guidelines, § 15151 [“An
    evaluation of the environmental effects of a proposed project
    need not be exhaustive, but the sufficiency of an EIR is to be
    reviewed in the light of what is reasonably feasible.”].)
    Three basic principles emerge from our decisions and
    those of the Court of Appeal: (1) An agency has considerable
    discretion to decide the manner of the discussion of potentially
    significant effects in an EIR. (2) However, a reviewing court
    must determine whether the discussion of a potentially
    significant effect is sufficient or insufficient, i.e., whether the
    EIR comports with its intended function of including “ ‘ “detail
    sufficient to enable those who did not participate in its
    preparation to understand and to consider meaningfully the
    issues raised by the proposed project.” ’ ” (Bakersfield Citizens
    for Local Control v. City of Bakersfield (2004) 
    124 Cal. App. 4th 1184
    , 1197 (Bakersfield).) (3) The determination whether a
    discussion is sufficient is not solely a matter of discerning
    whether there is substantial evidence to support the agency’s
    factual conclusions.
    14
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    The ultimate inquiry, as case law and the CEQA
    guidelines make clear, is whether the EIR includes enough
    detail “to enable those who did not participate in its preparation
    to understand and to consider meaningfully the issues raised by
    the proposed project.” (Laurel Heights 
    I, supra
    , 47 Cal.3d at
    p. 405; see Berkeley Keep Jets Over the Bay Com. v. Board of Port
    
    Cmrs., supra
    , 91 Cal.App.4th at p. 1356 [“Whether an EIR will
    be found in compliance with CEQA involves an evaluation of
    whether the discussion of environmental impacts reasonably
    sets forth sufficient information to foster informed public
    participation and to enable the decision makers to consider the
    environmental factors necessary to make a reasoned decision.”];
    Guidelines, § 15151 [“An EIR should be prepared with a
    sufficient degree of analysis to provide decisionmakers with
    information which enables them to make a decision which
    intelligently takes account of environmental consequences.”].)
    The inquiry presents a mixed question of law and fact. As such,
    it is generally subject to independent review. However,
    underlying factual determinations—including, for example, an
    agency’s decision as to which methodologies to employ for
    analyzing an environmental effect—may warrant deference.
    (Cf. Mountain Air Enterprises, LLC v. Sundowner Towers, LLC
    (2017) 3 Cal.5th 744, 751; Crocker National Bank v. City and
    County of San Francisco (1989) 
    49 Cal. 3d 881
    , 888.) Thus, to
    the extent a mixed question requires a determination whether
    statutory criteria were satisfied, de novo review is appropriate;
    but to the extent factual questions predominate, a more
    deferential standard is warranted. (Connerly v. State Personnel
    Bd. (2006) 37 Cal.4th 1169,1175.)
    Real party draws a distinction for standard of review
    purposes between claims that a required discussion has been
    15
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    omitted altogether and claims that a required discussion is
    insufficient, with the former subject to de novo review and the
    latter subject to substantial evidence review. But such a
    distinction is neither consistent with our precedent (see Laurel
    Heights 
    I, supra
    , 47 Cal.3d at pp. 403–405) nor logically
    defensible. Whether or not the alleged inadequacy is the
    complete omission of a required discussion or a patently
    inadequate one-paragraph discussion devoid of analysis, the
    reviewing court must decide whether the EIR serves its purpose
    as an informational document.
    2. The EIR’s air quality discussion
    The Court of Appeal’s opinion presents a concise summary
    of the EIR’s discussion regarding the Project’s air quality
    impacts on public health.
    “The EIR’s discussion of Impact No.3.3.2, the long-term
    area and operational emissions, estimated that, at build-out, the
    proposed Friant Community Plan would emit approximately
    117.38 tons per year of PM10 [particulate matter 10 microns in
    diameter or smaller], 109.52 tons per year of reactive organic
    gases (ROG), and 102.19 tons per year of nitrogen oxides (NOx).
    Estimates were made for ROG and NOx because they are
    precursors to ozone, which is formed when ROG and NOx
    undergo chemical reactions in the presence of sunlight.
    “The Air District’s thresholds of significance are 15, 10 and
    10 tons per year for PM10, ROG and NOx, respectively. Because
    the project’s estimated emission of PM10, ROG and NOx were
    from seven to 10 times larger than that of the thresholds of
    significance, the EIR concluded these air pollutants would have
    a significant adverse effect on air quality. Because Mitigation
    Measure 3.3.2 could not reduce these emissions below the Air
    16
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    District’s thresholds of significance, the EIR concluded that the
    significant impacts were unavoidable.
    “The draft EIR included a page of background information
    about ozone and nearly a page of background information about
    PM10. Each included a paragraph about the adverse health
    effects associated with the pollutant. The discussion of the
    adverse health effects, however, was not connected to the levels
    of the pollutant that would be emitted by the completed project.
    Instead, the discussion of adverse health effects was general in
    nature. For example, the description of the health effects of
    ozone noted that the effects were primarily to the respiratory
    system and stated:
    ‘Exposure to ambient levels of ozone ranging from 0.10 to
    0.40 [parts per million] for 1 to 2 hours has been found to
    significantly alter lung functions by increasing respiratory rates
    and pulmonary resistance, decreasing tidal volumes, and
    impairing respiratory mechanics.’
    “As to PM10, the EIR stated its adverse health effects
    depended upon ‘the specific composition of the particulate
    matter.’ The EIR, however, provided no information about the
    composition of the particulate matter that was expected to be
    produced by the Project.”
    3. Adequacy of the EIR’s discussion of public health
    impacts from air pollutants that the Project is
    expected to generate
    Real party contends that the EIR satisfied all CEQA
    requirements because it analyzed the Project’s air quality
    impacts and disclosed the Project’s likely general health
    impacts. Plaintiffs argue that the EIR failed to satisfy
    Guidelines section 15126.2, subdivision (a), which requires an
    17
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    EIR to “analyze any significant environmental effects the project
    might cause by bringing development and people into the area
    affected.” In other words, they argue, the Project’s health effects
    must be “clearly identified” and the discussion must include
    “relevant specifics” about the environmental changes
    attributable to the Project and their associated health outcomes.
    The Court of Appeal held that the EIR’s analysis of air
    quality impacts was inadequate because it did not connect the
    raw particulate numbers and their effect on air quality with
    specific adverse effects on human health in the built
    environment. (See 
    Bakersfield, supra
    , 124 Cal.App.4th at p.
    1193.) Bakersfield considered EIRs relating to the construction
    and operation of two shopping centers in the City of Bakersfield.
    (Ibid.) The shopping centers featured a Wal-Mart Supercenter
    as their primary tenant and anchor. (Id. at p. 1194.) Both EIRs
    concluded that the projects would have “significant and
    unavoidable adverse impacts on air quality.” (Id. at p. 1219.)
    But neither EIR specifically identified the health impacts that
    would result from the adverse air quality effects. The appellate
    court criticized the EIRs because they lacked an
    “acknowledgement or analysis of the well-known connection
    between reduction in air quality and increases in specific
    respiratory conditions and illnesses. After reading the EIRs, the
    public would have no idea of the health consequences that result
    when more pollutants are added to a nonattainment basin.” (Id.
    at p. 1220.) Bakersfield concluded that brief references to
    adverse health impacts on human respiratory health rendered
    the EIRs in that case inadequate as a matter of law because they
    failed to connect the adverse air impact with negative health
    effects. (Ibid.) The court held that “the health impacts resulting
    18
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    from the adverse air quality impacts must be identified and
    analyzed in the new EIRs.” (Ibid., italics added.)
    The Court of Appeal acknowledged that the EIR at issue
    here went “much further than” the Bakersfield EIRs, noting that
    the EIR not only listed the type and tons per year of the
    pollutants the Project is expected to produce, but also provided
    a general description of each pollutant and how it affects human
    health. The Court of Appeal found, however, that the EIR was
    inadequate under CEQA because its analysis failed to correlate
    the increase in emissions that the Project would generate to the
    adverse impacts on human health.
    Real party had argued below that “the reader can infer
    from the provided information that the Project will make air
    quality and human health worse.” But the Court of Appeal
    concluded that “although the better/worse dichotomy is a useful
    starting point for analyzing adverse environmental impacts,
    including those to human health, more information is needed to
    understand that adverse impact.”
    The EIR does include some discussion of the health
    impacts of various pollutants and attempts to provide an
    explanation for its lack of specificity. It offers a general
    discussion of adverse health effects associated with certain
    Project-related pollutants. Notably, it also recognized that
    Fresno County suffers from the “most severe” ozone problems in
    the state and acknowledged the relationship between adverse
    ambient air quality and certain health risks to the respiratory
    system that could affect asthmatics, children, and healthy
    adults. These adverse effects, the draft EIR observed, could
    include “breathing and respiratory symptoms, aggravation of
    existing respiratory and cardiovascular diseases, alterations to
    19
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    the immune system, carcinogenesis, and premature death.” The
    EIR explained, however, that a more detailed analysis of health
    impacts is not possible at this early planning phase. According
    to the EIR, “Health Risk Assessments are typically prepared for
    inclusion in development specific project EIRs when certain
    types of development commonly known to have the potential to
    result in a human health risk are being proposed (automobile
    fueling stations [for example]). Due to the broad nature of the
    planning approvals analyzed in this EIR, it is impossible to
    conduct a human health risk assessment based on specific
    proposed uses at specific locations within the boundaries of the
    Project Area because such specific information has not been
    determined.”
    We agree with the Court of Appeal that the EIR’s
    discussion of health impacts found in Impact No. 3.3.2 is
    inadequate as an informational document, similar to what the
    court found in 
    Bakersfield, supra
    , 124 Cal.App.4th at p. 1220.
    The EIR’s discussion of health impacts of the named pollutants
    provides only a general description of symptoms that are
    associated with exposure to the ozone, particulate matter (PM),
    carbon monoxide (CO), and nitrogen dioxide (NOx), and the
    discussion of health impacts regarding each type of pollutant is
    at most a few sentences of general information. The disclosures
    of the health effects related to PM, CO, and sulfur dioxide fail to
    indicate the concentrations at which such pollutants would
    trigger the identified symptoms. As in Bakersfield, “[a]fter
    reading the EIRs, the public would have no idea of the health
    consequences that result when more pollutants are added to a
    nonattainment basin.” (
    Bakersfield, supra
    , 124 Cal.App.4th at
    p. 1220.) And as mentioned above, a sufficient discussion of
    significant impacts requires not merely a determination of
    20
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    whether an impact is significant, but some effort to explain the
    nature and magnitude of the impact. (See Cleveland National
    
    Forest, supra
    , 3 Cal.5th at pp. 514–515.) The EIR in this case
    fails to meet the standards articulated in Bakersfield and
    Cleveland National Forest.
    Even in the one area in which the EIR goes into some
    detail about health effects––ozone––the analysis is inadequate.
    The EIR states: “Exposure to ambient levels of ozone ranging
    from 0.10 to 0.40 [parts per million of ozone] has been found to
    significantly alter lung functions by increasing respiratory rates
    and pulmonary resistance, decreasing tidal volumes, and
    impairing respiratory mechanics. Ambient levels of ozone above
    0.12 [parts per million] are linked to symptomatic responses
    that include such symptoms as throat dryness, chest tightness,
    headache, and nausea.”
    At first glance, this information appears to potentially
    illuminate the health impacts of ozone produced by the Project.
    But the EIR presents no evidence of the anticipated parts per
    million (ppm) of ozone as a result of the Project. Rather, the EIR
    provides the estimated tons per year of reactive organic material
    (ROG) and NOx, the two components that react with sunlight to
    form ozone (i.e., ROG + NOx + sunlight → ozone). The raw
    numbers estimating the tons per year of ROG and NOx from the
    Project do not give any information to the reader about how
    much ozone is estimated to be produced as a result. Therefore,
    the disclosure of the health impacts associated with exposure to
    0.10 to 0.40 ppm of ozone is not meaningful within the context
    of the Project because the reader has no idea how much ozone
    will be produced (i.e., whether the amount of ozone resulting
    from the ROG and NOx pollution will bring the ozone ppm
    within the 0.10 to 0.40 range).
    21
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    Guidelines section 15126.2, subdivision (a) is instructive.
    It mandates that an EIR “identify and focus on the significant
    environmental effects of the proposed project . . . examin[ing] []
    changes in the existing physical conditions in the affected area,”
    that it identify and describe “[d]irect and indirect significant
    effects of the project on the environment,” and that the
    discussion should include, among other things, “relevant
    specifics of . . . health and safety problems caused by the
    physical changes.” It also suggests that a connection be drawn
    between the two segments of information presented in the
    EIR—potential project emissions and human health impacts.
    Such a connection would meet CEQA’s requirements.
    Relying on various amici curiae briefs submitted to the
    court, the County and real party attempt to explain why the
    connection between emissions and human health that plaintiffs
    seek cannot be provided given the state of environmental science
    modeling in use at this time. The parties may be correct; we
    express no view on the question, except to note that scientific
    certainty is not the standard. But if it is not scientifically
    possible to do more than has already been done to connect air
    quality effects with potential human health impacts, the EIR
    itself must explain why, in a manner reasonably calculated to
    inform the public of the scope of what is and is not yet known
    about the Project’s impacts. Contained in a brief, such
    explanation is directed at the wrong audience. The relevant
    informational document here is the EIR, and the EIR must
    communicate not to the reviewing court, but “the public and the
    government officials deciding on the project.” 
    (Vineyard, supra
    ,
    40 Cal.4th at p. 443.) For purposes of supplementing the EIR
    and bringing it in conformance with CEQA, the information
    contained in the briefs “is irrelevant [] because the public and
    22
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    decision makers did not have the briefs available at the time the
    project was reviewed and approved.” (Ibid. [“That a party’s
    briefs to the court may explain or supplement matters that are
    obscure or incomplete in the EIR [] is irrelevant . . . . The
    question is [] not whether the project’s significant
    environmental effects can be clearly explained, but whether
    they were.”].)
    We further reject real party’s argument that the EIR
    sufficiently accounted for its lack of specificity by explaining
    that a “Health Risk Assessment” is typically prepared later in
    the CEQA process, in connection with development-specific
    EIRs. A “Health Risk Assessment” is defined in the Health and
    Safety Code as a type of analysis undertaken in connection with
    the siting of hazardous substances, “a detailed comprehensive
    analysis . . . to evaluate and predict the dispersion of hazardous
    substances in the environment and the potential for exposure of
    human populations and to assess and quantify both the
    individual and population wide health risks associated with
    those levels of exposure.” (Health & Saf. Code, § 44306.)
    CEQA does not mandate such an in-depth risk
    assessment. CEQA requires that the EIR have made a
    reasonable effort to discuss relevant specifics regarding the
    connection between two segments of information already
    contained in the EIR, the general health effects associated with
    a particular pollutant and the estimated amount of that
    pollutant the project will likely produce. This discussion will
    allow the public to make an informed decision, as CEQA
    requires. Because the EIR as written makes it impossible for
    the public to translate the bare numbers provided into adverse
    health impacts or to understand why such translation is not
    possible at this time (and what limited translation is, in fact,
    23
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    possible), we agree with the Court of Appeal that the EIR’s
    discussion of air quality impacts in this case was inadequate.
    The Court of Appeal identified several ways in which the
    EIR could have framed the analysis so as to adequately inform
    the public and decision makers of possible adverse health
    effects. The County could have, for example, identified the
    Project’s impact on the days of nonattainment per year. But the
    Court of Appeal was clear that, ultimately—though the EIR
    must provide an analysis that is adequate to inform (Guidelines,
    § 15151)—the “County has discretion in choosing what type of
    analysis to provide . . . .” We agree. The task for real party and
    the County is clear: The EIR must provide an adequate analysis
    to inform the public how its bare numbers translate to create
    potential adverse impacts or it must adequately explain what
    the agency does know and why, given existing scientific
    constraints, it cannot translate potential health impacts further.
    To be sure, “ ‘courts have looked not for perfection but for
    adequacy, completeness, and a good faith effort at full
    disclosure.’ ” (In re Bay-Delta etc. (2008) 
    43 Cal. 4th 1143
    , 1175.)
    But basic CEQA principles dictate there must be a reasonable
    effort to put into a meaningful context the conclusion that the
    air quality impacts will be significant. Although the EIR
    generally outlines some of the unhealthy symptoms associated
    with exposure to various pollutants, it does not give any sense
    of the nature and magnitude of the “health and safety problems
    caused by the physical changes” resulting from the Project as
    required by the CEQA guidelines. (Guidelines, § 15126.2, subd.
    (a).) Perhaps it was not possible to do more. But even in that
    case, we would have found the EIR insufficient because it failed
    to explain why it was not feasible to provide an analysis that
    connected the air quality effects to human health consequences.
    24
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    B. Mitigation measures
    1. “Substantially reduce air quality impacts”
    At the outset of the discussion of proposed Mitigation
    Measure 3.3.2 (discussed more fully in part D below), the EIR
    stated that “Implementation of the following mitigation
    measures will substantially reduce air quality impacts related
    to human activity within the entire Project area but not to a
    level that is less than significant.”
    The Court of Appeal concluded that the EIR’s use of the
    term “substantial” to describe the impact the proposed
    mitigation measures would have on reducing the Project’s
    significant health effects, without further explanation or factual
    support, amounted to a “bare conclusion” that did not satisfy
    CEQA’s disclosure requirements.
    We agree with the Court of Appeal on this point. (See
    Laurel Heights 
    I, supra
    , 47 Cal.3d at pp. 404 - 405 [“ ‘To
    facilitate CEQA’s informational role, the EIR must contain facts
    and analysis, not just the agency’s bare conclusions or opinions.’
    ”].) Here, the EIR included no facts or analysis to support the
    inference that the mitigation measures will have a quantifiable
    “substantial” impact on reducing the adverse effects. The EIR
    must accurately reflect the net health effect of proposed air
    quality mitigation measures. (Cleveland National 
    Forest, supra
    ,
    3 Cal.5th at p. 514 [“an EIR’s designation of a particular adverse
    environmental effect as ‘significant’ does not excuse the EIR’s
    failure to reasonably describe the nature and magnitude of the
    adverse effect”].)
    2. Deferral of mitigation measures
    We next decide whether, as the Court of Appeal concluded,
    the County, as the lead agency, impermissibly deferred
    25
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    mitigation measures when it approved real party’s EIR, which
    included mitigation measures to “at least partially reduce” the
    Project’s air quality impacts, as well as a substitution clause for
    future mitigation methods. Plaintiffs contend that the Project’s
    EIR is insufficient, because “the mitigation analysis is devoid of
    criteria for measuring the effectiveness of mitigation measures.”
    (Guidelines, §15126.4, subd. (a)(1)(B); see Sundstrom v. County
    of Mendocino (1988) 
    202 Cal. App. 3d 296
    , 306-307 [improper to
    defer formulation of mitigation measures until after project
    approved].)     Plaintiffs agree with the Court of Appeal’s
    conclusion that the formulation of future substitutions in this
    case was improperly deferred.
    The general rule is that an EIR is required to provide the
    information needed to alert the public and the decision makers
    of the significant problems a project would create and to discuss
    currently feasible mitigation measures. Mitigation measures
    need not include precise quantitative performance standards,
    but they must be at least partially effective, even if they cannot
    mitigate significant impacts to less than significant levels.
    (Laurel Heights 
    I, supra
    , 47 Cal.3d at p. 404; §§ 21051, 21100;
    Guidelines, § 15370.)5
    5
    Guidelines section 15370 provides that legally adequate
    mitigation measures must be capable of “(a) Avoiding the impact
    altogether by not taking a certain action or parts of an action.
    [¶] (b) Minimizing impacts by limiting the degree or magnitude
    of the action and its implementation. [¶] (c) Rectifying the
    impact by repairing, rehabilitating, or restoring the impacted
    environment. [¶] (d) Reducing or eliminating the impact over
    time by preservation and maintenance operations during the life
    of the action. [¶] (e) Compensating for the impact by replacing
    or providing substitute resources or environments.”
    26
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    In the present matter, the Project’s EIR noted that the air
    quality impacts will be significant and unavoidable. But the
    EIR’s 12 mitigation measures in Mitigation Measure 3.3.2 were
    designed to reduce the Project’s air quality impacts by providing
    shade trees, utilizing efficient PremAir or similar model
    heating, ventilation, and air conditioning [HVAC] systems,
    building bike lockers and racks, creating bicycle storage spaces
    in units, and developing transportation related mitigation that
    will include trail maps and commute alternatives.
    Mitigation Measure 3.3.2 includes a substitution clause
    that allows the lead agency to “substitute different air pollution
    control measures for individual projects, that are equally
    effective or superior to those propose[d] [in the EIR], as new
    technology and/or other feasible measures become available
    [during] build-out within the [Project].” In other words, the
    County retains the discretion to modify or substitute the
    adopted mitigation with equally or more effective measures in
    the future as better technology becomes available, unless the
    changes increase a project’s significant impacts.             (See
    Guidelines, § 15162, subd. (a)(3).)
    The County concluded that the Project’s air quality
    impacts will be significant, and that the 12 mitigation measures
    set forth in the Specific Plan should be at least partially effective
    in reducing the significant impacts. The substitution clause will
    allow for additional and presumably better mitigation measures
    when they become available and it should be encouraged. (See
    Napa Citizens for Honest Government v. Napa County Bd. of
    Supervisors (2001) 
    91 Cal. App. 4th 342
    , 357−358 [recognizing
    county must have power to modify land use plans].) Allowing
    future substitutions for equal or more efficient technology to
    mitigate a project’s acknowledged significant effects promotes
    27
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    CEQA’s goal of environmental protection and is not an
    impermissible deferral of mitigation or an abuse of discretion.
    It is simply a recognition that substitutions of adopted
    mitigation measures may be implemented to further minimize
    the Project’s environmental impacts.
    3. Failure to reduce impacts to less than significant
    levels
    Plaintiffs also ask us to decide whether a lead agency
    violates CEQA when its proposed mitigation measures will not
    reduce a significant environmental impact to less than
    significant levels. We conclude that as long as the public is able
    to identify any adverse health impacts clearly, and the EIR’s
    discussion of those impacts includes relevant specifics about the
    environmental changes attributable to the project, the inclusion
    of mitigation measures that partially reduce significant impacts
    does not violate CEQA.
    We have stated that protection of the environment and of
    California’s resources has long been considered of the utmost
    importance. However, in enacting CEQA to protect the
    environment, the Legislature did not seek to prevent all
    development. Section 21081, subdivision (b) allows a project to
    continue even if there are significant environmental effects that
    have not been mitigated, if “the public agency finds that specific
    overriding economic, legal, social, technological, or other
    benefits of the project outweigh the significant effects on the
    environment.”
    If, after the feasible mitigation measures have been
    implemented, significant effects still exist, a project may still be
    approved if it is found that the “unmitigated effects are
    outweighed by the project’s benefits.” (Laurel Heights 
    I, supra
    ,
    28
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    47 Cal.3d at p. 391.) Even when a project’s benefits outweigh its
    unmitigated effects, agencies are still required to implement all
    mitigation measures unless those measures are truly infeasible.
    (City of San Diego v. Board of Trustees of California State
    University (2015) 
    61 Cal. 4th 945
    , 967.) We recently held that
    “the lead agency must adopt feasible mitigation measures or
    project alternatives to reduce the effect to insignificance; to the
    extent significant impacts remain after mitigation, the agency
    may still approve the project with a statement of overriding
    considerations. [Citations.]” (Center for Biological Diversity v.
    Department of Fish & Wildlife (2015) 
    62 Cal. 4th 204
    , 231.) The
    inclusion of a mitigation measure that reduces an
    environmental impact is permitted even if the measure will not
    reduce the impact to a level below the threshold of significance.
    4. Enforceability of mitigation measures
    Plaintiffs argue that mitigation measures involving the
    installation of HVAC systems and tree planting, and any
    required mitigation efforts that “are fully enforceable through
    permit conditions, agreement, or other measures,” are
    unenforceable. (§ 21081.6, subd. (b).) We note that the
    measures referred to in this section are proposed as “guidelines”
    that “shall be used by the County during review of future
    project-specific submittals for non-residential development . . .
    with [the] intent that specified measures be required where
    feasible and appropriate.”
    The Court of Appeal found the EIR mitigation “provision
    about equipping HVAC units with a catalyst system does not
    identify who will determine if the system is ‘reasonably
    available and economically feasible’ ” and is unenforceable. In
    its analysis, the court omitted the next sentence, “[c]atalyst
    29
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    systems are considered feasible if the additional cost is less than
    10% of the base HVAC cost.” This definition of what constitutes
    “economically feasible” catalyst systems eliminates the need to
    have individuals make such determinations. The Court of
    Appeal also found the phrase “ ‘PremAir or similar catalyst
    system’ ” vague for not defining what performance criteria must
    be met to be a “ ‘similar catalyst system.’ ” The term is not
    vague. PremAir is a brand name for an HVAC catalyst system.
    The individuals proposing new projects, or those tasked with
    evaluating the proposals for approval, would necessarily have
    knowledge of HVAC systems and catalyst systems, including
    PremAir. It is also impossible to require specific performance
    criteria, given that the type, size, model, and efficiency levels of
    the HVAC systems being installed in these future projects are
    unknown. Given the uncertainty of these future proposed
    projects, the language “ ‘PremAir or similar catalyst system’ ” is
    sufficient under CEQA to provide an enforceable mitigation
    measure for any HVAC systems associated with those projects.
    The Court of Appeal similarly found that the mitigation
    measure requiring trees be selected to provide shade did not
    specify the person(s) responsible for selecting which trees to
    plant. The measure instructs that “ ‘[t]rees selected to shade
    paved areas should be varieties that will shade 25% of the paved
    area within 20 years.’ ” The instruction provides sufficient
    guidance for selecting appropriate shade trees. Any plan that
    the County approves must be complete, and must contain
    information about the trees selected for this mitigation
    measure. It seems clear that the person(s) selecting the trees
    would be the individuals or entity submitting the plans to the
    County for approval. The measure is not vague.
    30
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    In finding the mitigation measures cannot be enforced
    through permit conditions, agreements, or other measures, the
    Court of Appeal also misinterpreted section 21081.6, subdivision
    (b) and its significant effects provision, which provides that a
    public agency may set forth conditions of project approval
    required to avoid significant effects in “referenced documents
    which address [or incorporate the] required mitigation
    measures . . . into the plan.” (§ 21081.6, subd. (b).) The Project’s
    MMP places the burden of enforcement on the County to “ensure
    that all construction plans and project operations conform to the
    conditions of the mitigated project.”         The Specific Plan
    additionally states that “The County shall monitor compliance
    with the Specific Plan and mitigation measures,” and it provides
    the stages of planning at which certain mitigation measures
    must be completed. These measures are not vague as to how
    they will be enforced; the County will enforce them during the
    approval process of future nonresidential development.6 Indeed,
    6
    The Statement and MMP have this language: “The
    following guidelines shall be used by the County during review
    of future project-specific submittals for non-residential
    development within the Specific Plan area and within the
    Community Plan boundary in order to reduce generation of air
    pollutants with intent that specified measures be required
    where feasible and appropriate.” To clarify, this aspect of the
    Statement and MMP deals with the specific air quality issues
    discussed in the EIR, which issues are considered “non-
    residential.” The off-site created HVAC catalyst systems (that
    are eventually inserted into each home), tree planting, bicycle
    trails, and any other mitigation that affects air quality and
    comprises this aspect of the MMP are considered “non-
    residential development” for architecture and engineering
    planning purposes. Of course, they each are part of the greater
    “residential development” in the project, but for EIR purposes
    31
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    if the County were to approve a project that did not include a
    feasible mitigation measure, such approval would amount to an
    abuse of discretion, which could be corrected in a court
    mandamus proceeding. (See Rominger v. County of Colusa
    (2014) 
    229 Cal. App. 4th 690
    , 727 [holding dust control mitigation
    measures left to the county’s discretion are enforceable through
    a judicial writ of mandamus]; see also, e.g., California Oak
    Foundation v. Regents of University of California (2010) 
    188 Cal. App. 4th 227
    , 247.)
    CONCLUSION
    In our view, the EIR’s air quality impacts discussion and
    its mitigation measures meet CEQA requirements for specificity
    and enforceability with one exception: The EIR fails to provide
    an adequate discussion of health and safety problems that will
    be caused by the rise in various pollutants resulting from the
    Project’s development. At this point, we cannot know whether
    the required additional analysis will disclose that the Project’s
    effects on air quality are less than significant or unavoidable, or
    whether that analysis will require reassessment of proposed
    mitigation measures. Absent an analysis that reasonably
    informs the public how anticipated air quality effects will
    adversely affect human health, an EIR may still be sufficient if
    it adequately explains why it is not scientifically feasible at the
    time of drafting to provide such an analysis. Otherwise, the EIR
    is generally clear about the potential environmental harm under
    the Specific Plan, and it outlined mitigation measures to address
    those effects with factual support and scientific consensus.
    are considered “non-residential” since they involve cleaning the
    air, planting trees, and creating bicycle trails.
    32
    SIERRA CLUB v. COUNTY OF FRESNO
    Opinion of the Court by Chin, J.
    Based on the foregoing analysis, we affirm in part and
    reverse in part the Court of Appeal’s judgment and remand the
    matter for additional proceedings consistent with this opinion.
    CHIN, J.
    We Concur:
    CANTIL-SAKAUYE, C. J.
    CORRIGAN, J.
    LIU, J.
    CUÉLLAR, J.
    KRUGER, J.
    ROBIE, J.*
    *
    Associate Justice of the Court of Appeal, Third Appellate
    District, assigned by the Chief Justice pursuant to article VI,
    section 6 of the California Constitution.
    33
    See last page for addresses and telephone numbers for counsel who argued in Supreme Court.
    Name of Opinion Sierra Club v. County of Fresno
    __________________________________________________________________________________
    Unpublished Opinion
    Original Appeal
    Original Proceeding
    Review Granted XXX 
    226 Cal. App. 4th 704
    Rehearing Granted
    __________________________________________________________________________________
    Opinion No. S219783
    Date Filed: December 24, 2018
    __________________________________________________________________________________
    Court: Superior
    County: Fresno
    Judge: Rosendo Pena, Jr.
    __________________________________________________________________________________
    Counsel:
    Law Office of Sara Hedgpeth-Harris, Sara Hedgpeth-Harris; Brandt-Hawley Law Group and Susan Brandt-
    Hawley for Plaintiffs and Appellants.
    Chatten-Brown & Carstens, Jan Chatten-Brown, Douglas P. Carstens and Amy C. Minteer for Association
    of Irritated Residents, Medial Advocates for Healthy Air and Coalition for Clean Air as Amici Curiae on
    behalf of Plaintiffs and Appellants.
    Michael W. Graf for Center for Biological Diversity as Amicus Curiae on behalf of Plaintiffs and
    Appellants.
    Law Offices of Stephan C. Volker, Stephan C. Volker and Daniel P. Garrett-Steinman for North Coast
    Rivers Alliance as Amicus Curiae on behalf of Plaintiffs and Appellants.
    Ashley E. Werner and Phoebe S. Seaton for Leadership Counsel for Justice and Accountability as Amicus
    Curiae on behalf of Plaintiffs and Appellants.
    Kevin B. Briggs, County Counsel, and Bruce B. Johnson, Principal Deputy County Counsel, for
    Defendants and Respondents.
    Remy Moose Manley, James G. Moose, Tiffany K. Wright and Laura M. Harris for Real Party in Interest.
    Catherine T. Redmond and Annette Ballatore-Williamson for San Joaquin Valley Unified Air Pollution
    Control District as Amicus Curiae on behalf of Defendants and Respondents and Real Party in Interest.
    The Sohagi Law Group, Margaret M. Sohagi and Philip A. Seymour for League of California Cities,
    California State Association of Counties, California Special Districts Association and Association of
    California Water Agencies as Amici Curiae on behalf of Real Party in Interest.
    Brownstein Hyatt Farber Schreck and Lisabeth D. Rothman for California Building Industry Association
    and Building Industry Legal Defense Foundation as Amici Curiae on behalf of Real Party in Interest.
    Page 2 – S219783 – counsel continued
    Counsel:
    Best Best & Krieger, Jason M. Ackerman and Fernando Avila for California Association of Environmental
    Professionals and American Planning Association California Chapter as Amici Curiae on behalf of Real
    Party in Interest.
    Kurt R. Wiese and Barbara Baird for South Coast Air Quality Management District as Amicus Curiae.
    Counsel who argued in Supreme Court (not intended for publication with opinion):
    Sara Hedgpeth-Harris
    Law Office of Sara Hedgpeth-Harris
    2115 Kern Street, Suite 1
    Fresno, CA 93721
    (559) 510-1259
    Susan Brandt-Hawley
    Brandt-Hawley Law Group
    P.O. Box 1659
    Glen Ellen, CA 95442
    (707) 938-3900
    James G. Moose
    Remy Moose Manley
    555 Capitol Mall, Suite 800
    Sacramento, CA 95814
    (916) 443-2745