1.1 ,This guide is intended to assist in the development of conceptual site models to be used for the following: (1) integration of technical information from various sources, (2) support the selection of sample locations for establishing background concentrations of substances, (3) identify data needs and guide data collection activities, and (4) evaluate the risk to human health and the environment posed by a contaminated site. This guide generally describes the major components of conceptual site models, provides an outline for developing models, and presents an example of the parts of a model. This guide does not provide a detailed description of a site-specific conceptual site model because conditions at contaminated sites can vary greatly from one site to another.