If impact to a National or State Register eligible site cannot be avoided through project redesign, then other measures will be needed to mitigate the adverse impact to the site.

What is mitigation?

Mitigation is a process that lessens the impacts on a site or historic structure. If preservation of an archaeological site in an undisturbed state is not possible or if the site will no longer be accessible for research due to project development, then the site's data can be retrieved prior to the start of the project. Data Recovery is a form of mitigation that includes intensive field investigations on the site before its destruction. Recovered data are then analyzed by professional archaeologists and other specialists according to the research goals of the project. For standing historic buildings that have been determined to be eligible for the Registers, a professional architectural historian and photographer will document the structure, both inside and outside, prior to its demolition. Mitigation may take the form of site enhancement, such as the restoration and/or stabilization of a part of the site that will not be destroyed. Data Recovery is the most intense form of archaeological and documentary research that occurs on a site that will be destroyed. Because of this, public outreach programs and sharing of the results with professional and avocational colleagues are important parts of Phase III mitigation. These data recovery and outreach steps must first be outlined in a Data Recovery Plan which is reviewed and authorized by the lead agency and the state reviewers before the plan is executed in the field.

What is involved with a Data Recovery Plan?

A Data Recovery Plan (or mitigation plan) is a research design that outlines the documentary research, field objectives, and analysis plans for the site. The plan should include the following items:
 

• a summary of the site, as determined from the Phase I and II investigations;
• a discussion of the categories of data present on the site that contributed to the determination of significance (e.g., specific artifact categories, features, structural remains, specialized remains such as faunal, etc.);
• a presentation of background information from the literature that outlines the research topics that will be addressed for the project;
• a discussion of the field techniques and sampling design needed to recover the types of information that are significant for the site;
• an analysis plan that details the specific techniques (e.g., C-14 or other dating methods, botanical identification, lithic and/or micro-wear analysis, geomorphological assessment, etc.) that will gather the data needed to address the research objectives;
• procedures for handling human remains if they are found;
• plans for public outreach during and/or after excavation;
• plans for dissemination of important results to lay and professional audiences; and,
• plans for the curation of artifacts and documents associated with the project.

The data recovery plan must be approved by the lead agency and the OPR&HP (Standards, Section 4.2). This review can take as long as 30 days, sometimes longer if extensive revision is needed.