OPINION

PANELLI, J. —

I. INTRODUCTION

After the passage of almost five years, we are again called upon to evaluate the efforts of the Regents of the University of California (Regents) to comply with the mandates of the California Environmental Quality Act (CEQA) (Pub. Resources Code, § 21000 et seq.) in connection with the proposed relocation within the City of San Francisco of the biomedical research facilities of the School of Pharmacy at the University of California, San Francisco (UCSF). (See Laurel Heights Improvement Assn. v. Regents of University of California (1988) 47 Cal.3d 376 [ 253 Cal.Rptr. 426, 764 P.2d 278] [hereafter Laurel Heights I].) We undertake review of this dispute between the Regents and the Laurel Heights Improvement Association of San Francisco, Inc. (Association), a second time in order to address the question of what constitutes "significant new information" in a final environmental impact report (EIR) so as to require its recirculation for public comment before certification pursuant to Public Resources Code section 21092.1 We also consider the standard of review to be applied to the decision whether to recirculate.

We conclude that recirculation is only required when the information added to the EIR changes the EIR in a way that deprives the public of a meaningful opportunity to comment upon a substantial adverse environmental effect of the project or a feasible project alternative or mitigation measure that would clearly reduce such an effect and that the project's proponents have declined to implement. We further conclude that a decision not to recirculate an EIR must be supported by substantial evidence. Finally, we conclude that substantial evidence supports the Regents' decision in this case not to recirculate the final EIR; therefore, the judgment of the Court of Appeal is reversed.

II. BACKGROUND

A. A Project Mired in Controversy

The early history of the dispute between the Regents and the Association is set forth in detail in Laurel Heights I, supra, 47 Cal.3d at pages 388-390. A brief reprise of these facts as well as what has occurred since that case was decided is essential to understanding this continuing controversy.

"The UCSF Parnassus campus in San Francisco is the site of the University's Schools of Medicine, Nursing, Pharmacy, and Dentistry. In 1982, the University of California (University) prepared a long range development plan for UCSF, which indicated there were serious space constraints at the Parnassus campus and concluded there was a need to develop off-campus locations for academic and support activities.

"To alleviate these space constraints, in February 1985 the Regents . . . purchased the Presidio Corporate Center, formerly known as the Fireman's Fund Insurance Building, located in the Laurel Heights neighborhood of San Francisco, approximately two miles northeast of the Parnassus campus. The Laurel Heights neighborhood is a mixture of residential and commercial development. The facility purchased by the Regents is a 10-acre site containing a 354,000 square-foot building (exclusive of parking area) and a 13,000 square-foot annex." ( Laurel Heights I, supra, 47 Cal.3d at p. 388.) The Regents decided to relocate the School of Pharmacy biomedical research units to the Laurel Heights facilities.

After the relocation decision was made, UCSF began the CEQA review process. A draft EIR was prepared and circulated. During the period for public review and comment on the EIR, it became evident that the proposed relocation was the subject of intense controversy. Neighborhood opinion coalesced around the question of whether "scientific research using toxic chemicals, carcinogens, and radioactive materials is too high-risk to be conducted in a residential neighborhood. [After a public comment period,] the Regents held a public meeting to respond to comments received during the review period. UCSF proposed measures to mitigate the identified environmental effects and prepared a final EIR, concluding that the environmental effects had been `reduced to a level of insignificance.' The Regents certified the final EIR." ( Laurel Heights I, supra, 47 Cal.3d at p. 389.)

The Association challenged the final 1986 EIR on grounds it failed to comply with CEQA. The trial court upheld the Regents' certification. In 1987, the Court of Appeal reversed on three primary grounds: insufficient description of the project, inadequate discussion of feasible alternatives to the project, and a lack of showing that significant environmental effects would be mitigated. ( Laurel Heights I, supra, 47 Cal.3d at pp. 389-390.)

We granted review. In December of 1988, we affirmed the decision of the Court of Appeal on the first two grounds, but reversed on the third. After discussing the mitigation measures in the final 1986 EIR at some length, we held that there was substantial evidence in the record to support the Regents' finding that any significant adverse effects of the project would be mitigated. ( Laurel Heights I, supra, 47 Cal.3d at pp. 407-422.) Because of deficiencies in the project description and the discussion of alternatives, however, we directed the Regents to prepare and certify an adequate EIR. We stated that, with respect to mitigation measures, the new EIR was required to discuss only those mitigation measures necessary for new or more significant adverse environmental effects not discussed in the final 1986 EIR. ( Id. at p. 422.) We also specified that the Regents were not to expand or add additional operations at the Laurel Heights facilities until a "proper" EIR was certified. ( Id. at p. 428.)

In the wake of our decision, the Regents produced a completely new and more thorough draft EIR. After the draft EIR was published in October 1989, UCSF solicited public comment over a sixty-day period, sponsored two informational meetings, held a public hearing over three successive evenings, evaluated the comments, and prepared detailed responses to the comments.

UCSF received voluminous written comments on the draft EIR. According to the Regents and undisputed by the Association, the Association alone submitted letters containing over 50 pages of comments on over 150 separate topics or issues and included in its written comments 2 boxes of unindexed documents containing nearly 5,000 pages of exhibits.

In April 1990, the final EIR was published. The final EIR consists of six volumes containing more than two thousand pages analyzing the environmental consequences of the proposed relocation. The final EIR contains information that was not present in the draft EIR. According to the Association, the new information includes three new noise studies, two new studies relating to potential toxic discharges, a clarification that one loading dock, rather than three, will be used for shipping and receiving, the recognition that "night lighting glare" could result from the use of the laboratories in the evening and early morning, and an expanded analysis of the alternative of expansion at the Parnassus campus. The final EIR was not recirculated for public comment, although the Association and others requested orally and in writing that it be recirculated. On May 18, 1990, the Regents certified the final EIR, adopted findings required in connection with the certification, as well as a mitigation monitoring program, and approved the Laurel Heights project.

The Association filed a writ of mandate challenging the validity of the final EIR on numerous grounds and requesting vacation of the Regents' certification. The trial court denied the petition. The Association appealed.

Finding it necessary to reach only one of the Association's numerous contentions, the Court of Appeal reversed. It held that the final EIR contained "significant new information," which, under section 21092.1, required that the final EIR be recirculated for additional public comment prior to certification.

We granted review to consider the issue addressed by the Court of Appeal.

B. The CEQA Review Process

The dispute over the proper interpretation of section 21092.1 cannot be resolved without an understanding of both the purposes and framework of the CEQA review process. (1) We have repeatedly recognized that the EIR is the "heart of CEQA." ( Citizens of Goleta Valley v. Board of Supervisors (1990) 52 Cal.3d 553, 564 [ 276 Cal.Rptr. 410, 801 P.2d 1161] [hereafter Goleta Valley II]; Laurel Heights I, supra, 47 Cal. 3d at p. 392; see also Guidelines, § 15003, subd. (a).) "Its purpose is to inform the public and its responsible officials of the environmental consequences of their decisions before they are made. Thus, the EIR `protects not only the environment but also informed self-government.' ( Laurel Heights [ I], supra, 47 Cal.3d at p. 392.)" ( Goleta Valley II, supra, 52 Cal.3d at p. 564.) To this end, public participation is an "essential part of the CEQA process." (Guidelines, § 15201; see also Concerned Citizens of Costa Mesa, Inc. v. 32nd Dist. Agricultural Assn. (1986) 42 Cal.3d 929, 936 [ 231 Cal.Rptr. 748, 727 P.2d 1029].)

With certain limited exceptions, a public agency must prepare an EIR whenever substantial evidence supports a fair argument that a proposed project "may have a significant effect on the environment." (§§ 21100, 21151, 21080, 21082.2 [fair argument standard]; Guidelines, §§ 15002, subd. (f)(1), (2), 15063; No Oil, Inc. v. City of Los Angeles (1974) 13 Cal.3d 68, 75 [ 118 Cal.Rptr. 34, 529 P.2d 66] [fair argument standard of review].) "`Significant effect on the environment' means a substantial, or potentially substantial, adverse change in the environment. (§ 21068; see also Guidelines, § 15382.)

When an EIR is required, the lead agency initially prepares a draft EIR. Once the draft EIR is completed, a comment period is provided for the public and interested agencies. (§§ 21091, 21092.2, 21104, 21153; Guidelines, §§ 15085, 15086, 15087.) Public hearings to discuss the draft EIR are encouraged, but not required. (Guidelines, § 15087, subd. (g).) The comment period is generally no shorter than 30 days and no longer than 90 days. (§ 21091, subd. (a); Guidelines, § 15087, subd. (c).)

In the course of preparing a final EIR, the lead agency must evaluate and respond to comments relating to significant environmental issues. (§ 21092.5, subd. (a); Guidelines, §§ 15088, 15132, subds. (b-d).) In particular, the lead agency must explain in detail its reasons for rejecting suggestions and proceeding with the project despite its environmental effects. (Guidelines, § 15088, subd. (b).) "There must be good faith, reasoned analysis in response [to the comments received]. Conclusory statements unsupported by factual information will not suffice." ( Ibid.) Thus, it is plain that the final EIR will almost always contain information not included in the draft EIR.

The final substantive step in the EIR review process is certification of the final EIR. The lead agency is required to certify that the final EIR has been completed in compliance with CEQA, and that it reviewed and considered the information in the final EIR prior to approving the project. (Guidelines, § 15090.) CEQA also requires that, before approving a project, the lead agency "find either that the project's significant environmental effects identified in the [final] EIR have been avoided or mitigated or that the unmitigated effects are outweighed by the project's benefits. (§§ 21002, 21002.1 and 21081; Guidelines, §§ 15091-15093.)" ( Laurel Heights I, supra, 47 Cal.3d at p. 391.)

If the lead agency adds "significant new information" to the EIR subsequent to the close of the public comment period but prior to certification of the final EIR, CEQA requires that the lead agency provide a new public comment period. (§ 21092.1)

The statutory scheme also provides for an additional public comment period after the certification of a final EIR if: (1) "substantial changes in the project" are made; (2) "substantial changes" occur regarding the circumstances under which the project is being undertaken; or (3) "new information, which was not known and could not have been known," when the EIR was certified, becomes available. (§ 21166; see also Guidelines, §§ 15162, 15163.) The Guidelines in turn generally define "new information" as information which shows that the project will have new or more severe "significant effects" on the environment not disclosed in the prior EIR (Guidelines, § 15162, subd. (a).) A "significant effect" is further defined in the Guidelines as a "substantial, or potentially substantial, adverse change." (Guidelines, § 15382.)

With this statutory framework in mind, we address the issues before us.

III. DISCUSSION

A. When Does Section 21092.1 Require Recirculation?

The key to whether the Regents were required to recirculate the final EIR in this case is the meaning of the statutory phrase "significant new information." Neither statutes nor the Guidelines define this phrase. The Regents argue that the Legislature did not intend to require recirculation of a final EIR prior to certification except on the grounds found in the previously enacted standards for preparation of subsequent and supplemental EIR's after certification which were set forth in section 21166 and the guidelines implementing that statute. According to the Regents, "significant new information" therefore must mean new information that shows that the project will have new or more severe adverse effects on the environment not previously disclosed in the EIR. On the other hand, the Association argues that the phrase "significant new information" is derived directly from Sutter Sensible Planning, Inc. v. Board of Supervisors (1981) 122 Cal.App.3d 813 [ 176 Cal.Rptr. 342] (hereafter Sutter). The Association further contends that the statutory language imposes a duty to recirculate whenever any new, arguably significant information or data, is added to the final EIR, regardless of whether the information reveals environmental bad news. Various amici curiae have advanced other interpretations of the phrase. For reasons explained below, our interpretation of the statutory language is generally in accord with the Regents' position.

As we have often noted, our role in interpreting or construing a statute is to ascertain and effectuate the legislative intent. (E.g., City of San Jose v. Superior Court (1993) 5 Cal.4th 47, 54 [ 19 Cal.Rptr.2d 73, 850 P.2d 621].) When appropriate, we look to legislative history as an extrinsic aid in order to assist us in our task. ( Ibid.)

The statutory language in question was enacted in 1984 as part of a larger measure amending CEQA. (Assem. Bill No. 2583 (1983-1984 Reg. Sess.) § 7, enacted as Stats. 1984, ch. 1514, § 7, p. 5340.) The bill was the result of a study for improving CEQA that was conducted by the Committee on the Environment of the State Bar of California at the request of the Assembly Committee on Natural Resources. The State Bar committee's December 1983 report suggested, among other measures, that the Legislature specify the circumstances under which a public agency is required to recirculate an environmental impact report. (The Cal. Environmental Quality Act: Recommendations for Legis. and Admin. Change, A Rep. to the Assem. on Natural Resources by the Com. on the Environment of the State Bar of Cal. (Dec. 1983) at p. 26 [hereafter State Bar Report].) To clarify this issue, the State Bar committee recommended that the Legislature codify Sutter, supra, 122 Cal.App.3d 813. (State Bar Rep., supra, at p. 28.) The committee stated that Sutter correctly summarized the law and enunciated standards that are usable in determining whether an EIR should be recirculated. ( Ibid.)

In Sutter, a county board of supervisors prepared an EIR for a tomato paste processing plant. At a public hearing the final EIR was criticized for several deficiencies and two board members expressed the opinion that the final EIR was "`inadequate'" and "could not survive judicial review." ( Sutter, supra, 122 Cal.App. 3d at p. 821.) As a result, the board directed its staff to rewrite the final EIR. The revised final EIR "fundamentally" reorganized the previous information and provided a substantial amount of new information, including additional details about the potential effects of the plant on the environment and substituting some new data for information which had been repudiated by its purported author.

The Sutter court observed that neither the statute nor the Guidelines addressed the question of what procedures should be followed when new information is added to an EIR between the close of the public comment period and certification. The Sutter court looked for guidance to the state law governing the requirements for subsequent and supplemental EIR's as found in section 21166 and its implementing regulations, and to federal cases applying the National Environmental Protection Act (NEPA), which provides that supplements to environmental impact statements (the federal equivalent of EIR's) must be circulated. ( Sutter, supra, 122 Cal.App.3d at pp. 821-823.)

Reasoning by analogy, the Sutter court determined that recirculation for public comment would be an appropriate procedure to follow in the situation where "significant new information" is added to an EIR after the close of the public comment period, but prior to certification. ( Sutter, supra, 122 Cal.App.3d at pp. 818, 822-823.) The Sutter court further explained that recirculation should not be required where the new information added to the EIR "merely clarifies or amplifies [citations] or makes insignificant modifications in [citation] an adequate EIR. . . ." ( Id. at pp. 822-823.) On the other hand, where "`substantial changes' in the EIR are made, recirculation is required. [Citation.]" ( Id. at p. 823.)

By adopting this standard, the Sutter court explicitly rejected the proposition that the addition of any new information triggers recirculation. A contrary conclusion indeed would have been at odds with the statutory scheme, which did not (and does not) generally require that a final EIR be recirculated even though that document by definition contains information not found in the draft EIR in the form of public comments and responses thereto.

In determining when recirculation prior to certification should be required, the Sutter court used CEQA terms with specific meanings. As previously mentioned, the Sutter court looked for guidance to section 21166 and its implementing guidelines. Section 21166 governs the analogous situation of preparation of a subsequent or supplemental EIR after a final EIR is certified. The terms "significant," "new information," and "substantial change" are all found in section 21166 or its implementing guidelines. For these reasons, we believe it is appropriate to look to these sources for guidance in interpreting section 21092.1

The reasons that public comment in the CEQA review process is initially solicited also help guide us in our interpretation of section 21092.1 The primary reason for soliciting comments from interested parties is to allow the lead agency to identify, at the earliest possible time, the potential significant adverse effects of the project and alternatives and mitigation measures that would substantially reduce these effects. (§ 21003.1, subds. (a) (b).)

(2) With these sources of guidance in mind, we conclude that the addition of new information to an EIR after the close of the public comment period is not "significant" unless the EIR is changed in a way that deprives the public of a meaningful opportunity to comment upon a substantial adverse environmental effect of the project or a feasible way to mitigate or avoid such an effect (including a feasible project alternative) that the project's proponents have declined to implement. (Cf. Cal. Pub. Resources Agency, Dig. of Assem. Bill No. 2583 (1983-1984 Reg. Sess.) at p. 7 [stating that Sutter and the bill recognize "the importance of notifying the public of changes to an environmental document which deals with significant new information on significant effects which has not been previously reviewed by the public"].) (3a) As recognized by the Sutter court, recirculation is not required where the new information added to the EIR "merely clarifies or amplifies [citations] or makes insignificant modifications in [citation] an adequate EIR." ( Sutter, supra, 122 Cal.App.3d at pp. 822-823.) On the other hand, recirculation is required, for example, when the new information added to an EIR discloses: (1) a new substantial environmental impact resulting from the project or from a new mitigation measure proposed to be implemented (cf. Guidelines, § 15162, subd. (a)(1), (3)(B)(1)); (2) a substantial increase in the severity of an environmental impact unless mitigation measures are adopted that reduce the impact to a level of insignificance (cf. Guidelines, § 15162, subd. (a)(3)(B)(2)); (3) a feasible project alternative or mitigation measure that clearly would lessen the environmental impacts of the project, but which the project's proponents decline to adopt (cf. Guidelines, § 15162, subd. (a)(3)(B)(3), (4)); or (4) that the draft EIR was so fundamentally and basically inadequate and conclusory in nature that public comment on the draft was in effect meaningless ( Mountain Lion Coalition v. Fish Game Com. (1989) 214 Cal.App.3d 1043 [ 263 Cal.Rptr. 104]).

With the addition of the fourth category of "triggering information" to the list, we recognize that "significance" for purposes of section 21092.1 cannot be defined exclusively in terms of the grounds for recirculation found in section 21166, from which the first three categories are drawn. The different circumstances governed by these statutes mandate this conclusion.

(4) In the case of a certified EIR, which is a prerequisite for application of section 21166, section 21167.2 mandates that the EIR be conclusively presumed valid unless a lawsuit has been timely brought to contest the validity of the EIR. This presumption acts to preclude reopening of the CEQA process even if the initial EIR is discovered to have been fundamentally inaccurate and misleading in the description of a significant effect or the severity of its consequences. After certification, the interests of finality are favored over the policy of encouraging public comment.

(3b) By way of contrast, section 21092.1 was intended to encourage meaningful public comment. (See State Bar Rep., supra, at p. 28.) Therefore, new information that demonstrates that an EIR commented upon by the public was so fundamentally and basically inadequate or conclusory in nature that public comment was in effect meaningless triggers recirculation under section 21092.1 (See, e.g., Mountain Lion Coalition v. Fish Game Com., supra, 214 Cal.App.3d 1043.)

Contrary to the arguments of the Association, the holding of Sutter is consistent with the views we express here. Although the Sutter opinion does not clearly explain the extent of the changes made between the draft EIR and the final EIR at issue in that case, it is apparent that the court and the agency viewed the draft EIR as fundamentally and basically inadequate in many respects. ( Sutter, supra, 122 Cal.App.3d at pp. 821, 823.)

Furthermore, our understanding of the term "significant new information" is reflected explicitly or implicitly in other holdings of our lower courts. For example, in Marin Mun. Water Dist. v. KG Land California Corp. (1991) 235 Cal.App.3d 1652, 1667 [ 1 Cal.Rptr.2d 767], recirculation was not required when the final EIR contained a revised estimate that the subject water moratorium could last 10 years or more. The draft EIR disclosed that the duration of the proposed moratorium was indefinite and had considered the impacts of a moratorium of at least five to six years in duration. The new information merely served to clarify an environmental effect that was adequately discussed in the draft EIR.

In Sierra Club v. Gilroy City Council (1990) 222 Cal.App.3d 30 [ 271 Cal.Rptr. 393], the presence on the project site of the potentially endangered California tiger salamander was discovered after the close of the public comment period for the draft EIR. In response to public comment, however, the lead agency delayed approval of the project and commissioned a study. A "preliminary" final EIR was prepared relying upon the study and was made available for public and agency comment before the project was certified. The new information, the presence of the tiger salamander, demonstrated that the draft EIR had not addressed a potentially substantial adverse environmental effect. Therefore, revision and recirculation were required and were voluntarily undertaken by the agency.

Similarly, a "woefully inadequate" draft EIR was found to have deprived the public of its opportunity to comment upon the resumption of sport hunting of mountain lions. ( Mountain Lion Coalition v. Fish Game Com., supra, 214 Cal.App.3d at pp. 1050-1051.) In defiance of a previously issued writ, the agency failed to address in other than conclusory fashion many areas relating to the cumulative impacts of the proposed hunting.

Discovery that a project encroached upon wetlands, when the text of the draft EIR indicated that the wetlands area would remain undeveloped, was a substantial change in circumstances requiring revision and recirculation of the EIR. The failure to do so "deprived the public, who relied upon the EIR's representations, of meaningful participation regarding the issue of wetlands degradation," a significant adverse effect. ( Mira Monte Homeowners Assn. v. County of Ventura (1985) 165 Cal.App.3d 357, 365 [ 212 Cal.Rptr. 127].)

Finally, the opportunity for additional public comment was also required where an uncirculated EIR disclosed for the first time that, for mitigation purposes, a street would be extended through a ridge line resulting in a previously unidentified adverse visual impact. ( Stevens v. City of Glendale (1981) 125 Cal.App.3d 986, 998-999 [ 178 Cal.Rptr. 367].)

(5) By codifying the "significant new information" language of Sutter, supra, 122 Cal.App.3d 813, the Legislature apparently intended to reaffirm the goal of meaningful public participation in the CEQA review process. (State Bar Rep., supra, at p. 28.) It is also clear, however, that by doing so the Legislature did not intend to promote endless rounds of revision and recirculation of EIR's. Recirculation was intended to be an exception, rather than the general rule. Significantly, at the time section 21092.1 was enacted, the Legislature had been and was continuing to streamline the CEQA review process. Recognizing the legislative trend, we previously have cautioned: "[R]ules regulating the protection of the environment must not be subverted into an instrument for the oppression and delay of social, economic, or recreational development and advancement." ( Goleta Valley II, supra, 52 Cal.3d at p. 576.) In our interpretation of section 21092.1, we have given consideration to both the legislative goals of furthering public participation in the CEQA process and of not unduly prolonging the process so that the process deters development and advancement.

B. What Standard of Review Applies to the Decision Whether to Recirculate?

It remains to be considered whether the trial court erred in not requiring recirculation. In reviewing an agency's determination, finding or decision under CEQA, a court must determine whether the agency prejudicially abused its discretion. (§ 21168.5.) "Abuse of discretion is established if the agency has not proceeded in a manner required by law or if the determination or decision is not supported by substantial evidence." ( Ibid., italics added.) The Guidelines further define "substantial evidence" as "enough relevant information and reasonable inferences from this information that a fair argument can be made to support a conclusion, even though other conclusions might also be reached." (Guidelines, § 15384, subd. (a).) (6a) The Regents contend that the substantial evidence standard of review is mandated in this case by these authorities. By contrast, the Association advances several independent arguments, two of which are premised directly upon the language of section 21168.5, for applying a more stringent standard of review. We agree with the Regents that the appropriate standard is the substantial evidence standard.

To counter our determination, the Association contends that, if a procedural violation of CEQA is shown, the substantial evidence prong of the statutory standard of review does not come into play. While the Association's contention may have merit in the abstract, it does not apply to the facts of the present case. (7) The Association first argues that the Regents failed to proceed as required by law, because they did not set forth express findings denying the Association's request that the final EIR be recirculated. We are not persuaded by the Association's claim. CEQA does not require an express order or finding on the subject of whether to recirculate a final EIR. (Cf. No Oil, Inc. v. City of Los Angeles, supra, 13 Cal.3d at p. 81, fn. 12 [finding requirement of written negative declaration implicit in certain statutory and regulatory language].)

Furthermore, we are not faced in this case with an administrative record that is silent on the question of whether the recirculation request was considered by the decision maker. (Cf. City of San Jose v. Great Oaks Water Co. (1987) 192 Cal.App.3d 1005, 1017 [ 237 Cal.Rptr. 845] [agency did not consider whether change in source of water supply for development triggered the need for a subsequent EIR, a supplemental EIR or an addendum to the original EIR].) The Regents were aware of the requests by the Association and others to recirculate the final EIR. The final EIR contained a response to the request for recirculation. The response stated that, since the final EIR "[did] not include significant new information about environmental impacts and did not require a fundamental reorganization of the [draft EIR], there [was] no need to recirculate the [f]inal EIR for an additional public review period." The Regents certified the final EIR. By doing so, the Regents necessarily concluded that the final EIR did not contain significant new information requiring additional public comment. While express findings are preferable for the reason that they make the task of the reviewing court easier, there is no need in this case to remand for the Regents to clarify or expressly state their findings.

The Association also contends that the Regents committed a separate procedural violation of CEQA by failing to recirculate the final EIR. Such an argument begs the question. The Association's position ignores the statutory mandate that only the addition of significant new information triggers recirculation. (§ 21092.1) Barring unusual circumstances not present here, the agency necessarily must decide whether the information meets this statutory requirement. A procedural violation cannot be found in this case unless the Regents' decision regarding the significance of the new information fails to pass muster under the applicable standard of review.

(8) The Association next argues that, if the substantial evidence prong of the standard of review is applicable, then in deciding whether to recirculate the final EIR under section 21092.1, the "fair argument" test used to review the decision, pursuant to section 21151, to prepare a negative declaration, rather than an EIR, should apply. However, section 21151 commands that an EIR must be prepared whenever a project " may have a significant effect on the environment." (Italics added.) In No Oil, Inc. v. City of Los Angeles, supra, 13 Cal.3d at pages 68, 75, 83-85, we interpreted section 21151 to require preparation of an EIR whenever it can be fairly argued on the basis of substantial evidence that the project may have significant environmental impact. (See also Friends of "B" Street v. City of Hayward (1980) 106 Cal.App.3d 988, 1002 [ 165 Cal.Rptr. 514] [applying "fair argument" test to affirm judgment invalidating decision not to prepare an EIR].) Our decision, however, expressly acknowledged that judicial review of agency decisions under CEQA is governed by sections 21168 (administrative mandamus) and 21168.5 (traditional mandamus) and, of course, did not purport to alter the standard of review set forth in those statutes. Rather, the "fair argument" test was derived from an interpretation of the language of, and policies underlying, section 21151 itself. For this reason, the "fair argument" test has been applied only to the decision whether to prepare an original EIR or a negative declaration. (E.g., Benton v. Board of Supervisors (1991) 226 Cal.App.3d 1467, 1481-1483 [ 277 Cal.Rptr. 481] [rejecting use of test to review decision of whether second negative declaration proper for modified project]; Bowman v. City of Petaluma (1986) 185 Cal.App.3d 1065, 1071-1072 [ 230 Cal.Rptr. 413] [rejecting use of test to review decision under section 21166].) The Association has advanced no persuasive authority or reasons for taking this test out of the context of the statutory language of section 21151 and applying it to an agency's decision under section 21092.1 (6b) We conclude that the substantial evidence standard set forth in section 21168.5 governs the Regents' decision not to recirculate the EIR in this case. As we observed in Laurel Heights I, "[i]n applying the substantial evidence standard, `the reviewing court must resolve reasonable doubts in favor of the administrative finding and decision.'" (47 Cal.3d at p. 393, quoting Topanga Assn. for a Scenic Community v. County of Los Angeles (1974) 11 Cal.3d 506, 514 [ 113 Cal.Rptr. 836, 522 P.2d 12].) It is this standard of review that we apply to the Regents' determination that the new information in the final EIR was not "significant" pursuant to section 21092.1

C. Does Substantial Evidence Support the Regents' Decision Not to Recirculate the Final EIR?

1. Mechanical Noise Studies

21092.1 Laurel Heights I, supra, (9)

Regardless of what conclusions may be appropriately drawn from these studies, we find that substantial evidence supports the Regents' decision that the additional data do not constitute "significant new information." These studies merely serve to amplify, at the public's request, the information found in the draft EIR. The basis of the conclusion in both the draft and final EIR's that mechanical noise effects would be insignificant is the representation that any effects will be mitigated to insignificance by appropriate choices of equipment and installation measures. The new studies do not alter this analysis in any way. Substantial evidence thus supports the Regents' conclusion that additional public comment is not required. (Cf. Holy Cross Wilderness Fund v. Madigan (10th Cir. 1992) 960 F.2d 1515, 1526-1527 [new report questioning ability to mitigate environmental impact on wetlands did not require supplemental environmental impact statement under NEPA when project permit was expressly conditioned upon no loss of wetlands].)

2. Cumulative Toxic Air Emissions Studies

In considering the cumulative effect of project toxic emissions together with emissions attributable to other anticipated projects in the Laurel Heights area, the draft EIR states that "there are no accepted methodologies or standards by which to quantitatively measure the cumulative toxic emission impacts of all potential sources of toxic air emissions in the Laurel Heights vicinity. . . ." The draft EIR, therefore, concludes that "the potential cumulative impacts of toxic air emissions are too speculative for evaluation." Such a conclusion is specifically authorized by Guidelines section 15145, which states: "If, after thorough investigation, a lead agency finds that a particular impact is too speculative for evaluation, the agency should note its conclusion and terminate discussion of the impact."

The final EIR adopts the same conclusion. Nevertheless, in response to public comments, and "in an effort to provide as much information as possible," the final EIR discusses the health risks from background toxic air contaminant levels and presents two possible approaches to assessing impacts of cumulative toxic air emissions, based upon an experimental study. The study concludes that the "maximum estimated cumulative cancer risk increase would be below the project significance standard," and that "no non-carcinogenic health effects are expected to occur." The final EIR concludes that "due to incomplete data and the lack of accepted means of conducting cumulative toxic air contaminant health risk analysis, for purposes of this EIR the cumulative impact of toxic air emissions is unknown as stated in the DEIR [draft EIR]." The Regents, however, treated the unknown impact for purposes of their required findings "as if it were an unavoidable significant adverse impact" and found that "if the impacts were significant, specific economic, social or other considerations make infeasible project alternatives in the FEIR [final EIR]."

(10) Substantial evidence again supports the Regents' conclusion that the experimental study does not constitute "significant new information." First, no new adverse environmental impact was shown by the study. To the extent the study can be credited, it reveals comforting news.

Moreover, the studies are experimental; both the draft EIR and final EIR acknowledge that the conclusions are not based upon accepted scientific methodology. The information was merely provided at the request of the public in the interest of amplifying or clarifying the discussion of cumulative toxic air emissions contained in the draft EIR. The minimal value of the experimental study is fully disclosed in the final EIR.

Finally, the Regents did not rely upon the study in deciding whether to approve the project; rather, they conservatively adopted a worst case approach to this unknown impact. Therefore, public comment on this study would not further the purposes of CEQA.

3. Description of Use of Loading Docks

The draft EIR considers the environmental impacts of an increased number of truck trips to the project and deems the impacts to be insignificant, primarily based on the assessment that most of the trucks would be small trucks and that they would arrive at and depart from the project at fairly even intervals throughout the day. The draft EIR also describes the three existing loading docks at the project and the modifications planned for the Laurel Street dock. In describing these loading docks the draft EIR states: "The University does require trucks over three tons to use the entrance at the intersection of California and Walnut Streets. Trucks weighing less than three tons are required to use the entrance near the intersection of Laurel Street and Euclid Avenue. Commercial trucks over three tons are not allowed on Laurel Street." Thus, it is apparent from the draft EIR that the majority of the trucks will use the Laurel/Euclid entrance.

The final EIR clarifies the uses for each of the loading docks described in the draft EIR as follows: "With project implementation, large trucks (over three tons) would continue to use the California/Walnut entrance to the site, while smaller trucks (less than three tons) would enter from Laurel near Euclid. The loading area noted on pages 118 and 133 of the DEIR, off Presidio Avenue, is currently used, and would continue to be used, only for early morning garbage pick ups. The existing receiving area on the Building's north side just east of the main entrance would no longer be used for deliveries. Under the project, all delivery trucks would be directed to the expanded loading dock on the west [Laurel Street] side of the Building." Thus, the final EIR states that almost all of the truck traffic will be directed to use the expanded Laurel Street loading area.

(11) The Association contends that the change in the description of the use of the loading docks is substantial and requires additional public comment. We conclude that substantial evidence supports the Regents' decision not to seek additional public comment regarding the use of the loading docks.

Contrary to the Association's arguments, we are not confronted with a case where the physical description or scope of the project has changed. (Cf. Concerned Citizens of Costa Mesa, Inc. v. 32nd Dist. Agricultural Assn., supra, 42 Cal.3d 929 [orientation of amphitheater changed after adoption of final EIR]; City of San Jose v. Great Oaks Water Company, supra, 192 Cal.App.3d at pp. 1015, 1017 [drilling of three new wells added to the project after adoption of final EIR].) Rather, in this case, the discussion of the use of the loading docks merely clarifies the existing description of the environmental impacts of the estimated increase in truck traffic by specifically stating that almost all of the trucks will use the expanded Laurel Street loading area. The expansion of this loading area and mitigation measures to reduce environmental effects from the expansion are fully described in the draft EIR. Moreover, the conclusions regarding the significance of the impacts of this traffic unsurprisingly were not affected. The number of estimated trips for various-sized trucks and the entrances used by the trucks are the same in both the draft and final EIR's. Substantial evidence supports the conclusion that the additional information in the final EIR simply clarifies the original discussion of the effects of increased truck traffic at the project. The clarification does not reveal a new or more severe adverse environmental impact. Recirculation was not required.

4. Discussion of Night-lighting Glare

The draft EIR does not discuss the potential visual effects of the use of project lights after dark. In response to public comments regarding the hours the lights were expected to be used in the building, the final EIR adds a discussion of the subject. The final EIR concludes that lighting of the project would "add only incrementally to existing night lighting in the project vicinity and is not considered significant." Nevertheless, the final EIR also adopts a mitigation measure to reduce any effects of night lighting even further: design and position interior and exterior light fixtures to minimize light intrusion upon adjacent land uses.

(12) The Association contends that this newly recognized impact is "potentially significant" and that public comment on mitigation measures should be obtained. We conclude, however, that addition of the discussion of night-lighting glare is an insignificant modification to the EIR that does not disclose a new adverse environmental impact.

Under the circumstances of this case, we do not fault the draft EIR for failing to discuss the potential effect of glare from night lighting at the project. The area in which the project is located is urbanized. A substantial number of street lights surround the project and the adjacent shopping area. Headlights from traffic also diminish the darkness. Moreover, the project building has always been an office building. It is not uncommon for office buildings to be lit in whole or in part after regular business hours. Thus, the Regents could reasonably conclude that any extension in the hours of use of the building would have a de minimis effect on the environment. Based upon the entire record, we conclude that substantial evidence supports a determination that the effect of night lighting would be insignificant. (Guidelines, § 15002, subd. (g) [definition of "effect"].) An insignificant modification to an EIR does not require recirculation for additional public comment.

Although the Association claims that the public should be provided the opportunity to comment upon mitigation measures for the potential glare, mitigation measures are not required where the environmental effect is insignificant. Moreover, it is clear in this case that the mitigation measure adopted by the Regents will not cause additional adverse environmental effects. Further, the Regents did not decline to adopt any suggested mitigation measures. None of the purposes of CEQA will be served by solicitation of further public comment on this subject; only needless delay will result. The decision makers and the public were both adequately informed by the final EIR about the consequences of the project with respect to night-lighting glare.

5. Expanded Discussion of Parnassus Alternative

The draft EIR devotes over 100 pages to discussion of alternatives to the project. The draft EIR discusses in detail six different uses for the Laurel Heights site and five other locations, some owned by the university and some not, for the research facilities proposed to be located at Laurel Heights. In addition, the draft EIR briefly discusses other alternatives that were considered, but were not addressed in detail, because they were found to be "infeasible, remote or speculative."

Among the alternatives considered, but not addressed in detail, was expansion of the Parnassus Heights campus to accommodate the new research facilities. The draft EIR explains the space deficit at the Parnassus Heights campus and the limitations adopted in the 1976 long-range development plan, at the urging of the state Legislature, on additional development of that campus, which is the most densely developed of all University of California facilities. The draft EIR further explains that, because the necessary space at the Parnassus Heights campus can only be created by demolition of existing buildings fully in use or by violating the limits adopted in the long-range development plan, the alternative of expansion at this site is infeasible.

In response to a single public comment claiming that the alternative of locating the research programs at the Parnassus Heights campus had not been adequately explored in the draft EIR, the final EIR contains a 12-page discussion expanding upon the possible environmental consequences of the alternative. The final EIR concludes that the alternative is infeasible for the reasons stated in the draft EIR. The final EIR also concludes that in no respect is the Parnassus Heights alternative environmentally superior to the proposed project. (13a) The Association nevertheless contends that the expanded discussion of this alternative constitutes "significant new information" triggering recirculation of the EIR. We, however, agree with the Regents that recirculation was not required.

(14) An EIR need not consider every conceivable alternative to a project. ( Laurel Heights I, supra, 47 Cal.3d at pp. 406-407.) Rather, consideration of a reasonable range of feasible alternatives is required to foster informed decisionmaking and public participation. (13b) The draft EIR accomplished this goal by considering a wide variety of alternatives ranging from several different uses for the Laurel Heights site to different locations for the research laboratories. The draft EIR also contains succinct statements of the reasons that other alternatives, such as expansion of the Parnassus Heights campus, were deemed not to warrant further discussion. ( Id. at pp. 404-405.)

Furthermore, the reasons given for the rejection of the Parnassus Heights alternative do not constitute an abuse of discretion and are supported by the record. Since the 1976 long-range development plan embodied a decision that expansion at the Parnassus Heights campus was not desirable and that additional space should be developed in other locations, the Regents did not abuse their discretion by relying upon the policies stated in the long-range development plan to assist them in assessing the feasibility of this alternative. (Cf. Goleta Valley II, supra, 52 Cal.3d at pp. 570-573 [county's reliance on its local coastal program in assessing feasibility of alternative sites for EIR permissible].) An alternative is "feasible" and therefore worthy of consideration only if it is "capable of being accomplished in a successful manner within a reasonable period of time, taking into account, economic, environmental, social, and technological factors." (§ 21061.1; see also Guidelines, § 15364.) Substantial evidence supports the conclusion that the Parnassus Heights alternative does not meet this requirement.

The expanded discussion in the final EIR does not change the determination that the expansion of the Parnassus Heights campus is infeasible. Rather it merely amplifies the reasons why the alternative is infeasible and ultimately less desirable. Recirculation is only required when a discussion of a new feasible project alternative, which will not be implemented, is added to the EIR.

IV. DISPOSITION

Lucas, C.J., Mosk, J., Kennard, J., Arabian, J., and Baxter, J., concurred.