STATE OF CALIFORNIA
Pete Wilson, Governor
GOVERNOR'S OFFICE OF PLANNING AND RESEARCH
1400 Tenth Street
Sacramento, CA 95814
(916) 445-483 1
Lee Grissom, Director, Office of Planning and Research
Robert Cervantes, Chief, Planning Unit
Antero Rivasplata, Chief, State Clearinghouse
Thresholds of Significance
Appendix: Excerpts from the Public Resources
Code and the CEQA Guidelines
OPR thanks and recognizes Ron Bass and Al Herson of Jones and Stokes for
their pioneering work on this topic as well as their assistance on this
paper. Much of what is contained in these pages was previously discussed
by them in one form or another at workshops and classes they have conducted
throughout California. We also sincerely thank John Watts for generously
sharing his research and opinions on thresholds.
In addition, we thank the following people who reviewed the draft of this
advisory memo and offered their comments and suggestions. Although the final
version of Thresholds of Significance does not always reflect their
views, we appreciate their thoughtful contributions.
Curtis Alling, Dames and Moore
DeAnn Baker, California State Association of Counties
Mike Chiriatti, State Clearinghouse
Brad Eckhardt, City of Mountain View
Ann B. Hix and Sean Cardenas, City of San Diego
Supervisor Gary Patton, Santa Cruz County
Barbara Shelton, County of Santa Barbara
Ernie Silva, League of California Cities
Bruce Smith, County of Ventura
Michael Zischke, Landels, Ripley, and Diamond
Determining whether or not a project may result in a significant adverse
environmental effect is one of the key aspects of the California Environmental
Quality Act (CEQA). Thresholds of Significance discusses how public
agencies, including cities, counties, and special districts, may adopt quantitative
or qualitative thresholds which represent the point at which a given environmental
effect will be considered significant. Enacting thresholds helps ensure
that during the initial study phase of environmental review significance
determinations will be made on a consistent and objective basis.
Neither CEQA nor the CEQA Guidelines describes specific thresholds
of significance or how they may be used. Appendix G of the Guidelines
lists a variety of potentially significant effects, but does not provide
a means of judging whether they are indeed significant in a given set of
circumstances. Appendix I, the environmental checklist, prompts project
reviewers to examine a spectrum of potential environmental effects, but
leaves the determination of significance to the lead agency. Instead of
dictating a one-size-fits-all approach, CEQA authorizes local governments
to adopt by "ordinance, resolution, rule or regulation" their
own "objectives, criteria, and procedures for the evaluation of projects"
(Section 21082). Clearly, this enables local governments to adopt thresholds
which will assist in determining the environmental significance of a project.
By explaining thresholds of significance and the practical advantages to
public agencies, the Office of Planning and Research hopes to encourage
more local agencies to use them. This advisory paper is not a mandate of
any kind. It does not replace, nor does it amend, the CEQA Guidelines.
All citations refer to the Public Resources Code unless otherwise noted.
Return to top
Thresholds of Significance
Thresholds of significance are principally used to determine whether a project
may have a significant environmental effect. They are not intended to be
stand alone environmental policies, although they should certainly reflect
the agency's policies. Thresholds are an analytical tool for judging significance.
When examining a project that is not exempt from CEQA, the Lead Agency usually
prepares an initial study to determine whether the project may have a significant
adverse effect on the environment. If no potential significant effects are
identified, a negative declaration is prepared (Section 21080(c)). A mitigated
negative declaration is called for if there are potential effects, but these
can be mitigated to a level of insignificance (Section 21064.5). An EIR
is equired if there are significant environmental effects which cannot be
avoided or mitigated (Sections 21100 and 21151). The CEQA Guidelines
defines "significant effect on the environment" as: "a substantial,
or potentially substantial, adverse change in any of the physical conditions
within the area affected by the project including land, air, water, minerals,
flora, fauna, ambient noise, and objects of historic or aesthetic significance"
(Guidelines Section 15382).
The "threshold of significance" for a given environmental effect
is simply that level at which the Lead Agency finds the effects of the project
to be significant. "Threshold of significance" can be defined
Ideally, a threshold of significance provides a clear differentiation of
whether or not the project may result in a significant environmental effect.
More practically, a threshold will assist the Lead Agency in making this
determination. In either case, thresholds do not substitute for the agency's
use of careful judgment in determining significance (CEQA Guidelines
- A quantitative or qualitative standard, or set of criteria, pursuant
to which the significance of a given environmental effect may be determined.
A threshold may be based on standards such as the following:
- A health-based standard such as air pollutant emission standards,
water pollutant discharge standards, or noise levels.
- Service capacity standards such as traffic level of service, water
supply capacity, or waste treatment plant capacity.
- Ecological tolerance standards such as physical carrying capacity,
impacts on declared threatened or endangered species, loss of prime farmland,
or wetland encroachment.
- Cultural resource standards such as impacts on historic structures
or archaeological resources.
- Other standards relating to environmental quality issues, such as
those listed in the Guidelines' Initial Study Checklist or Appendix
G of the Guidelines.
Adopting thresholds of significance promotes consistency, efficiency, and
predictability in the initial study process.
Thresholds enable the Lead Agency to make consistent determinations of significance.
Once thresholds have been adopted, every project in a given locale will
be subject to a known set of impact assessment criteria. Project reviews
undertaken by different staff members or at different times will employ
a standard methodology. This increases certainty for both the agency and
the applicant, as well as the fairness of the process.
The Lead Agency's efficiency in preparing an initial study may be improved
when the anticipated effects of a project can be examined pursuant to standard
thresholds. Standardizing review criteria reduces duplication of effort.
It may also offer some assurance that a comprehensive review has been made.
Standard threshold criteria are also valuable as a method of "scoping"
a proposed project. They may assist the Lead Agency in identifying Responsible
Agencies, as well as focusing its environmental analysis on effects expected
to be significant.
A threshold provides a rational basis for significance determinations. This
complies with the CEQA Guidelines' requirement that a Lead Agency's
determination of significance be "based to the extent possible on scientific
and factual data" (Guidelines Section 15064). In this same vein,
thresholds based on substantial evidence of significance bolster the defensibility
of the determination.
The existence of a threshold may encourage project proponents to incorporate
mitigation into the design of the project prior to submitting an application
or a project's public review. The advantages of this are clear: the Lead
Agency receives a project which has minimized its environmental impact;
the project sponsor may avoid the need to prepare an EIR; when an EIR is
required, it is properly focused on pertinent issues. Similarly, a threshold
offers a target for revisions or mitigation actions which, if integrated
into the project, would allow the preparation of a mitigated negative declaration
rather than an EIR.
At least one court has shown a willingness to defer to local thresholds
in order to decide a marginal situation where disagreement among experts
or serious public controversy based on substantial evidence of a significant
effect might require preparation of an EIR. In Citizens Action to Serve
All Students v. Thornley (1990) 222 Cal.App.3rd 748, the City of Hayward's
traffic impact thresholds played some part in convincing the court that
evidence did not exist to support the existence of a significant impact
Return to top
Only a few agencies have formally adopted a comprehensive set of significance
thresholds as part of their local CEQA guidelines. Many others utilize in-house
criteria which have not been adopted by the governing body (i.e., city council,
board of supervisors, district board, etc.). These written, administrative
rules can be as comprehensive as a formally adopted ordinance or resolution,
and offer some advantages. Proponents of this approach point out that administrative
thresholds are easier to adopt and amend and are less subject to conflicting
political pressures than thresholds which are adopted by the governing body.
In addition, they contend that administrative adoption avoids potential
difficulties and misunderstandings arising from attempting to explain the
technically and legally complex CEQA process. It may be cheaper as well.
Nonetheless, OPR recommends that whenever possible the governing body adopt
thresholds by either resolution or ordinance after a public hearing. We
believe formal adoption is preferable because: (1) the thresholds will
carry the full authority of the city or county, (2) the adoption process
is a fully public undertaking, and (3) decision makers will have made a
commitment to the thresholds by participating in their preparation and adoption.
Thresholds may be either qualitative or quantitative. Some effects, such
as traffic or noise, lend themselves to numerical standards. Others, such
as aesthetics or wildlife habitat are difficult to quantify and must rely
upon qualitative descriptions. In either case, thresholds should be based
on legal standards, studies, surveys, reports, or other data which can identify
that point at which a given environmental effect becomes significant. Thresholds
are intended to be analytic tools to assist in significance determinations,
not rigid standards. They should not result in de facto policy making. Along
this same vein, thresholds must reflect CEQA's fair argument standard, as
discussed under the Limitations section of this paper.
The significance of an activity may vary with its setting. For instance,
a subdivision which would create 10 new lots may not be significant in an
urban area, but may be significant in an undeveloped rural area. In such
instances, the Lead Agency could adopt more than one threshold of significance
for a given effect or include flexible standards which recognize differences
Developing thresholds is not simple. The first step should be to identify
those effects for which thresholds are to be drafted. These might be chosen
from the agency's initial study work sheet or, they may be based upon the
significant effects identified in Appendix G of the Guidelines.
The next step should be to gather and evaluate existing information relative
to the chosen effects. Review past Master Environmental Assessments (MEAs),
EIRs, Negative Declarations, and related environmental studies-at what point
or under what circumstances was a given effect deemed significant? Are
there effective criteria by which to measure significance?
The agency should also rely upon its general plan as a source of environmental
standards. For instance, policies for the conservation of agricultural land
may yield a threshold based on soil type, project size, and water availability.
The noise element may provide noise exposure standards. The circulation
element may establish level of service (LOS) standards for roads, sewers,
and other services. Whenever possible, thresholds should be based on or
otherwise reflect the community's adopted planning policies and regulations.
The general plan and associated community plans, and specific plans can
provide a long-term context for issues relating to land use, resources,
and open space. By establishing thresholds, a jurisdiction is effectively
recognizing the environmental ethics that are consistent with accepted local
A note of caution regarding the use of general plan policies: remember
that a threshold represents that point at which a project's potential environmental
effects are considered significant. The focus of the threshold is on actual
limits to significant environmental impacts. When general plan policies
or standards do not actually limit the potential impacts of a project to
a particular level they are not effective measures of significance. Accordingly,
at least two courts have held that "conformity with a general plan
does not insulate a project from EIR review where it can be fairly argued
that the project will generate significant environmental effects" (Oro
Fino Gold Mining Corp. v. County of El Dorado (1990) 225 Cal.App.3d
872), citing City of Antioch v. City Council (1986) 187 Cal.App.3d
1325). In Oro Fino Gold Mining, the project proponent unsuccessfully
argued that no significant impact existed because the proposed exploratory
mine would not exceed the noise standards of the county general plan. The
court dismissed this argument, marking that the county did not enforce those
standards. Similarly, when examining a major road and sewer project, the
City of Antioch court held that "general plan conformity alone
does not effectively 'mitigate' significant effects of a project."
The Lead Agency should also survey other agencies for adopted standards
which might lend themselves to thresholds. For example, the South Coast
Air Quality Management District's CEQA Air Quality Handbook promulgates
quantitative pollutant emissions thresholds. A county Congestion Management
Agency will have LOS standards for regionally significant roads. Neighboring
cities and counties may have enacted pertinent thresholds of significance.
Air, water, and toxic standards established by the Environmental Protection
Agency and state and local agencies should also be reviewed. The Lead Agency
should contact these other agencies to discuss incorporation of their thresholds
into its own. Thresholds can and should be based on existing environmental
laws and regulations whenever possible to reduce duplicative environmental
reviews and take advantage of regulatory agency expertise.
Previously prepared studies and research are additional sources of thresholds,
provided that they offer clear standards for assessing significance. These
might include, but are not limited to, wetlands delineations, archaeological
surveys, historic resources surveys or registers, capital improvement plans,
and water district capacity studies.
Most agencies allow for some flexibility in the application of thresholds
to individual projects. This is generally a good idea. It allows, for example,
agencies to presume a certain project will have a significant effect if
a threshold is exceeded, but allows case-by-case deviation from the threshold
when unusual circumstances warrant.
When enacting a resolution or ordinance establishing thresholds, the agency's
legislative body should hold at least one public hearing before taking action.
Because the thresholds relate to development projects, OPR recommends including
the planning commission in the process of drafting thresholds. Through its
public hearings, the commission can fine tune the work of staff as well
as offer a forum for the concerns of its members and the public.
A jurisdiction may choose to offer more opportunities for public involvement.
The City of Mountain View, for example, relied an informal committee of
citizens, planners, environmentalists, and representatives of regional agencies
to cooperatively draft its thresholds. This effort provided these interests
a stake in the city's thresholds, ensured that the thresholds did not conflict
with the requirements of regional agencies, and, importantly, reflected
community values. The process had the further advantage of educating decision
makers about the environmental review process.
If the jurisdiction decides to adopt its thresholds administratively, e.g.,
by an agency rather than the governing body, OPR suggests: (1) adopting
a single set of thresholds for use by all agencies and departments within
the jurisdiction; (2) undertaking the same broad review of sources recommended
above; and (3) providing the public with opportunities to assist in drafting
or at least review and comment on the proposed thresholds prior to adopting
Thresholds can offer the same basic advantages whether they are adopted
legislatively or administratively. Jurisdictions will weigh their own political
and administrative situation before deciding which style of adoption would
work best for them.
A fully-fledged threshold should contain, in some form, the following elements:
The threshold may also contain a menu of standardized mitigation measures.
These should be flexible enough to be tailored to individual projects. Standardized
measures offer project proponents the opportunity to design their projects
so that environmental effects are minimized from an early stage. Standardized
measures can also assure the agency and the public that potential effects
will be mitigated on a consistent basis and that the threshold represents
the boundary between significance and insignificance.
- A brief definition of the potential effect.
- Reasons for its significance.
- Threshold criteria for significance.
- Geographic scope of the criteria, if applicable.
- References to the facts or data upon which the criteria are based.
The description of a threshold may be long or short depending upon its subject.
In a jurisdiction with diverse locales, there may be more than one or even
a sliding scale of thresholds for a single effect. For example, Ventura
County has adopted two thresholds for surface water quality impacts based
on project location within specified groundwater basins. Santa Barbara County
uses a weighted point system to determine whether a given project will have
a significant impact on agricultural lands.
OPR does not suggest that an agency establish a threshold for every conceivable
environmental effect. This may be neither practical nor desireable. There
may be certain effects, such as aesthetic impacts, which for one reason
or another are not easily described. There is no advantage to adopting a
threshold which does not clarify or otherwise improve the process of determining
Once adopted, thresholds should be reviewed periodically and revised as
necessary to incorporate changes as conditions and regulations change.
Ten Tips for Thresholds
Return to top
Thresholds can help determine the significance of environmental effects,
but are not necessarily conclusive. A lead agency's significance determination
can be challenged if opponents of the determination produce substantial
evidence supporting a fair argument that a significant effect does exist.
Even more troublesome, what happens when the thresholds adopted by the Lead
Agency are less stringent than those adopted by another agency for the same
effect? Can project opponents (other than a Responsible Agency, which is
limited by Section 21167.3) reference the stricter thresholds as evidence
of a significant environmental effect?
The original determination whether to prepare either a Negative Declaration
or an EIR is subject to the "fair argument" test (Laurel Heights
Improvement Assoc. v. U.C. Regents (1993) 47 Cal.3d 376). In other words,
when a fair argument can be raised on the basis of substantial evidence
in the record that the project may have a significant adverse environmental
impact -- even if evidence also exists to the contrary -- then an EIR is
required. If another agency's more stringent thresholds are based upon substantial
evidence of environmental effects, then the fair argument test would seem
to require preparation of an EIR even though the project does not exceed
the Lead Agency's threshold (this would not apply to subsequent activities
under a program EIR or the decision to prepare a subsequent/supplemental
EIR). Although there is no absolute means of avoiding this problem, the
agency preparing the thresholds may minimize it by consulting with other
agencies during the drafting process and working out inconsistencies before
Furthermore, significance thresholds may not obviate the need to provide
information to support the determinations made in the initial study. Simply
filling out an initial study checklist without citing supporting information
is insufficient to show the absence of significant effects (Sundstrom
v. County of Mendocino (1988) 202 Cal.App.3d 296). Proper thresholds
give the checklist reviewer sufficient background to make reasonable determinations
on the basis of facts and should be referenced in the initial study. An
initial study is not intended to provide the full-blown analysis that would
be contained in a complete EIR (Leonoff v. Monterey County Board of Supervisors
(1990) 222 Cal.App.3d 1337) and, by inference, neither is the discussion
Return to top
EXCERPTS FROM THE PUBLIC RESOURCES CODE
21082. All public agencies shall adopt by ordinance, resolution,
rule, or regulation, objectives, criteria, and procedures for the evaluation
of projects and the preparation of environmental impact reports and negative
declarations pursuant to this division. A school district, or any other
district, whose boundaries are coterminous with a city, county, or city
and county, may utilize the objectives, criteria, and procedures of the
city, county, or city and county, as may be applicable, in which case, the
school district or other district need not adopt objectives, criteria, and
procedures of its own. The objectives, criteria, and procedures shall be
consistent with the provisions of this division and with the Guidelines
adopted by the Secretary of the Resources Agency pursuant to Section 21083.
Such objectives, criteria, and procedures shall be adopted by each public
agency no later than 60 days after the Secretary of the Resources Agency
has adopted guidelines pursuant to Section 21083.
EXCERPTS FROM THE CEQA GUIDELINES
15355. "Cumulative impacts" refers to two or more individual
effects which, when considered together, are considerable or which compound
or increase other environmental impacts.
(a) The individual effects may be changes resulting from a single project
or a number of separate projects.
(b) The cumulative impact from several projects is the change in the environment
which results from the incremental impact of the project when added to other
closely related past, present, and reasonably foreseeable probable future
projects. Cumulative impacts can result from individually minor but collectively
significant projects taking place over a period of time.
15382. "Significant effect on the environment" means a
substantial, or potentially substantial, adverse change in any of the physical
conditions within the area affected by the project including land , air,
water, minerals, flora, fauna, ambient noise, and objects of historic or
aesthetic significance. An economic or social change by itself shall not
be considered a significant effect on the environment. A social or economic
change related to a physical change may be considered in determining whether
the physical change is significant.
Return to top