Preferred sites represent those locations that have been identified and subsequently survived a Phase I screening against a set of general locational, design, and environmental requirements, which provide the basic ingredients for functionality. Ordinarily, the candidate sites are identified on a broad basis, using small-scale topographic maps (less than 1:250,000 scale), remote images such as aerial photographs, and aerial reconnaissance; geologic factors are partly downgraded, due to the lack of specific details provided during this second phase of feasibility investigations (Chapter 18, Fig. 1).
Preferred sites, representing Phase II of a project, are those considered worthwhile on the general basis of location and topography, design requirements, environmental impact potential, seismic and groundwater characteristics. By their nature, Phase II efforts are geologically intensive. During Phase II investigations, reconnaissance-level mapping and subsurface exploration, sampling, and testing of the materials can provide enormous returns when planned and conducted by mature and field-experienced applied geologists.
The concept of the alternative site-selection process emerged in the 1930s, as a result of developments in the internal combustion engine, which served as a power plant to drive mass-produced heavy construction equipment. Thus, early, large-scale heavy construction projects, such as dams, canals, and tunnels, were possible. With this capacity, national governments and cities alike became owners of transportation and water supply projects that could have, by nature of their function, several choices for location.
Heavy construction was widespread during the 1930s, with projects like dams of the Tennessee Valley Authority, and Boulder (Hoover), Coulee, and Shasta dams, and dozens of military bases and installations for World War II.
