        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

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               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,


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               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


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               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

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               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

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               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

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               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.

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               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


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               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


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               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
