The concept of a risk perception shadow (RPS) has been suggested to describe the locally affected population that perceives itself to be at risk from a proposed project. Such projects generally involve potentially dangerous substances or activities. The RPS concept first derived from the social assessment of the proposed superconducting super collider in Michigan. The current paper describes the mapping and analysis of an RPS produced by a proposal to site a low-level radioactive waste storage facility in Michigan. A unique sampling technique defined the boundary of the generally concentric RPS. Risk perception mapping (RPM) is suggested as a rapid and inexpensive method for defining locally affected populations for social impact studies.