The site meets Federal standards for residual radioactivity. Those standards are published in the Code of Federal Regulations, Title 10, Part 20 (10 CFR 20).
The regulations require that a person living or working on the site will receive no more than 25 millirem of radiation per year in excess of normal background. The regulations further require PGE to clean the site so that the level of residual radiation is "as low as reasonably achievable" (the "ALARA" standard).
A millirem is a unit of radiation. For reference, an average person in the U.S. receives between 200 and 300 millirem per year from a combination of cosmic radiation, natural background and medical or industrial sources.
PGE showed that the site meets the standard. Between 2001 and 2005, they measured the entire plant site for residual contamination in a process called a "final survey." Regulators from the U.S. Nuclear Regulatory Commission (NRC) and from the Oregon Department of Energy (ODOE) inspected and reviewed the final survey and the NRC has also done some confirmatory surveys. Before PGE can release the site for unrestricted use, the final survey must get approval from the NRC and the Oregon Energy Facility Siting Council. The Council aproved the site's unrestricted release in April 2005.