An adequate assessment of site geologic and geotechnical conditions is one of the most important aspects of a dam safety evaluation. Evaluation of the safety of either a new or an existing dam requires, among other things, that its foundation has been adequately examined, explored, and investigated so
that it is as fully understood as possible. Foundation explorations should be directed towards obtaining only such information as may be important to an evaluation of the dam. The exploration program should identify the factors that critically affect the safe performance of the dam, and not develop
extraneous information. The following sections of this chapter briefly identify the principal methods commonly employed in foundation investigations, and are intended to suggest approaches and scopes of investigations which, when properly implemented, should comply with FERC requirements and expectations. It is emphasized that, because of the almost infinite variety of geologic conditions from site to site, it would be unreasonable and impractical to attempt to set forth in these Guidelines specific investigation programs.
While this chapter is principally directed toward dams and dam sites, the types of investigations and studies discussed are also applicable to other water retention structures and appurtenant structures of hydropower projects.