Considerations when Preparing an EIR


An EIR shall be written in plain language and use appropriate graphics so that decision-makers and the public can rapidly understand the documents. This is intended to improve the clarity of the EIR.

Page Limits

The text of a draft EIR should normally be no longer than 150 pages and for proposals of unusual scope or complexity should be no longer than 300 pages. The recommended page limits encourage agencies to reduce unneeded bulk in an EIR and to help the documents disclose the key environmental issues to the decision-makers and the public. Further, the page limits match the page limits under the federal system. Adopting the same limits as used in the federal system improves compatibility of the two systems.

Interdisciplinary Approach

An EIR shall be prepared using an interdisciplinary approach, which will ensure the integrated use of the natural, and social sciences, and the consideration of qualitative as well as quantitative factors. The interdisciplinary analysis shall be conducted by competent individuals, but no single discipline shall be designated or required to undertake this evaluation. This is necessary to show that an EIR may use many disciplines in order to find the interrelationships among the various factors in the environmental effects. The requirement for an interdisciplinary is also part of the National Environmental Policy Act (NEPA). Accordingly, this requirement comes from the legislative history of CEQA. This section also makes the essential point that an EIR must consider qualitative factors as well as quantitative, economic, and technical factors.


The EIR shall focus on the significant effects on the environment. The significant effects should be discussed with emphasis in proportion to their severity and probability of occurrence. Effects dismissed in an initial study as clearly insignificant and unlikely to occur need not be discussed further in the EIR unless the lead agency subsequently receives information inconsistent with the finding in the initial study. A copy of the initial study may be attached to the EIR to provide the basis for limiting the impacts discussed.


Drafting an EIR or preparing a ND necessarily involves some degree of forecasting. While foreseeing the unforeseeable is not possible, an agency must use its best efforts to find out and disclose all that it reasonably can.


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.

This pertains to the difficulty in forecasting where a thorough investigation is unable to resolve an issue and the answer remains purely speculative. This is necessary to relieve the lead agency from a requirement to engage in idle speculation. Once an agency finds that a particular effect is too speculative for evaluation, discussion of that effect should be terminated.

Degree of Specificity

The degree of specificity required in an EIR will correspond to the degree of specificity involved in the underlying activity that is described in the EIR.

As with the range of alternatives, the level of analysis provided in an EIR is subject to the rule of reason. The level of specificity for a given EIR depends upon the type of project. The analysis must be specific enough to permit informed decision making and public participation. The need for thorough discussion and analysis is not to be construed unreasonably, however, to serve as an easy way of defeating projects. What is required is the production of information sufficient to understand the environmental impacts of the proposed project and to permit a reasonable choice of alternatives as far as environmental aspects are concerned.

Technical Detail

The information contained in an EIR shall include summarized technical data, maps, plot plans, diagrams, and similar relevant information sufficient to permit full assessment of significant environmental impacts by reviewing agencies and members of the public. Placement of highly technical and specialized analysis and data in the body of an EIR should be avoided through inclusion of supporting information and analyses as appendices to the main body of the EIR. Appendices to the EIR may be prepared in volumes separate from the basic EIR document, but shall be readily available for public examination and shall be submitted to all clearinghouses, which assist in public review.


Preparation of an EIR is dependent upon information from many sources, including engineering project reports and many scientific documents relating to environmental features. These documents should be cited but not included in the EIR. The EIR shall cite all documents used in its preparation including, where possible, the page and section number of any technical reports that were used as the basis for any statements in the EIR.

Citations are required for accountability and to allow statements to be verifiable. This section is necessary to keep the size of an EIR down to manageable levels and at the same time maintain the accuracy of the information in the document.

Use of Registered Professionals in Preparing an EIR

A number of statutes provide that certain professional services can be provided to the public only by individuals who have been registered by a registration board established under California law. Such statutory restrictions apply to a number of professions including but not limited to engineering, land surveying, forestry, geology, and geophysics.

In its intended usage, an EIR is not a technical document that can be prepared only by a registered professional. The EIR serves as a public disclosure document explaining the effects of the proposed project on the environment, alternatives to the project, and ways to minimize adverse effects and to increase beneficial effects. As a result of information in the EIR, the lead agency should establish requirements or conditions on project design, construction, or operation in order to protect or enhance the environment. State statutes may provide that only registered professionals can prepare technical studies which will be used in or which will control the detailed design, construction, or operation of the proposed project and which will be prepared in support of an EIR.

Incorporation by Reference

An EIR or ND may incorporate by reference all or a portion of another document that is a matter of public record or is generally available to the public. Where all or part of another document is incorporated by reference, the incorporated language shall be considered part of the text of the EIR or ND.

Where part of another document is incorporated by reference, such other document shall be made available to the public for inspection at a public place or public building. The EIR or ND shall state where the incorporated documents will be available for inspection. At a minimum, the incorporated document shall be made available to the public in an office of the lead agency in the county where the project would be carried out or in one or more public buildings such as county offices or public libraries if the lead agency does not have an office in the county.

Where an EIR or ND uses incorporation by reference, the incorporated part of the referenced document shall be briefly summarized where possible or briefly described if the data or information cannot be summarized. The relationship between the incorporated part of the referenced document and the EIR shall be described. Where an agency incorporates information from an EIR that has previously been reviewed through the state review system, the state State Clearinghouse Number of the incorporated document should be included in the EIR.

Standards for Adequacy of an EIR

An EIR should be prepared with a sufficient degree of analysis to provide decision-makers with information that enables them to make a decision, which intelligently takes account of environmental consequences. 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. Disagreement among experts does not make an EIR inadequate, but the EIR should summarize the main points of disagreement among the experts. The courts have looked not for perfection but for adequacy, completeness, and a good faith effort at full disclosure.


“Tiering” refers to using the analysis of general matters contained in a broader EIR with a later EIR or ND on narrower projects; incorporating by reference the general discussions from the broader EIR; and concentrating the later EIR solely on the issues specific to the later project.

Tiering does not excuse the lead agency from adequately analyzing reasonably foreseeable significant environmental effects of the project and does not justify deferring such analysis to a later tier EIR or ND. However, the level of detail contained in a first tier EIR need not be greater than that of the program, plan, policy, or ordinance being analyzed. A later EIR shall be required when the initial study or other analysis finds that the later project may cause significant effects on the environment that were not adequately addressed in the prior EIR.

Where a lead agency determines that a cumulative effect has been adequately addressed in the prior EIR, that effect is not treated as significant for purposes of the later EIR or negative declaration, and need not be discussed in detail. When assessing whether there is a new significant cumulative effect, the lead agency shall consider whether the incremental effects of the project would be considerable when viewed in the context of past, present, and probable future projects. At this point, the question is not whether there is a significant cumulative impact, but whether the effects of the project are cumulatively considerable.

The Use of an EIR from an Earlier Project

The lead agency may employ a single EIR to describe more than one project, if such projects are essentially the same in terms of environmental impact. Further, the lead agency may use an earlier EIR prepared in connection with an earlier project to apply to a later project, if the circumstances of the projects are essentially the same.

When a lead agency proposes to use an EIR from an earlier project as the EIR for a separate, later project, the lead agency shall use the following procedures:

  • The lead agency shall review the proposed project with an initial study, using incorporation by reference if necessary, to determine whether the EIR would adequately describe:
    • The general environmental setting of the project,
    • The significant environmental impacts of the project, and
    • Alternatives and mitigation measures related to each significant effect.

If the lead agency believes that a previous EIR would meet the requirements, it shall provide public review as provided in Section 15087 stating that it plans to use the previously prepared EIR as the draft EIR for this project. The notice shall include as a minimum:

  • An identification of the project with a brief description;
  • A statement that the agency plans to use a certain EIR prepared for a previous project as the EIR for this project;
  • A listing of places where copies of the EIR may be examined; and
  • A statement that the key issues involving the EIR are whether the EIR should be used for this project and whether there are any additional, reasonable alternatives or mitigation measures that should be considered as ways of avoiding or reducing the significant effects of the project.

An EIR prepared for an earlier project may also be used as part of an initial study to document a finding that a later project will not have a significant effect. In this situation, a negative declaration will be prepared. An EIR prepared for an earlier project shall not be used as the EIR for a later project, if any of the conditions described in Section 15162 would require preparation of a subsequent or supplemental EIR.

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