A project that has been determined to conform with the Secretary of the Interior’s Standards for the Treatment of Historic Properties can generally be considered to be a project that will not cause a significant impact (14 CCR Section 15126.4(b)(1)). In fact, in most cases if a project meets the Secretary of Interior’s Standards for the Treatment of Historic Properties it can be considered categorically exempt from CEQA (14 CCR Section 15331).

Mitigation of significant impacts must lessen or eliminate the physical impact that the project will have on the historical resource. This is often accomplished through redesign of a project to eliminate objectionable or damaging aspects of the project (e.g., retaining rather than removing a character-defining feature, reducing the size or massing of a proposed addition, or relocating a structure outside the boundaries of an archeological site).

Relocation of an historical resource may constitute an adverse impact to the resource. However, in situations where relocation is the only feasible alternative to demolition, relocation may mitigate below a level of significance provided that the new location is compatible with the original character and use of the historical resource and the resource retains its eligibility for listing on the California Register (14 CCR Section 4852(d)(1)).

In most cases the use of drawings, photographs, and/or displays does not mitigate the physical impact on the environment caused by demolition or destruction of an historical resource (14 CCR Section 15126.4(b)). However, CEQA requires that all feasible mitigation be undertaken even if it does not mitigate below a level of significance. In this context, recordation serves a legitimate archival purpose. The level of documentation required as a mitigation should be proportionate with the level of significance of the resource.

Avoidance and preservation in place are the preferable forms of mitigation for archeological sites. When avoidance is infeasible, a data recovery plan should be prepared which adequately provides for recovering scientifically consequential information from the site. Studies and reports resulting from excavations must be deposited with the California Historical Resources Regional Information Center. Merely recovering artifacts and storing them does not mitigate impacts below a level of significance.