Aerial Radiological Survey for King and Pierce Counties

The state Department of Health (the department) contracted with the U.S. Department of Energy, a federal partner, to do an aerial radiological survey to determine the normal levels of radiation around Puget Sound. The department received a federal grant to do the aerial survey. The contractor completed the survey on July 22, 2011.

The contractor used a Bell 412 helicopter with special radiation detection and measuring gear attached to the fuselage. The helicopter flew parallel flight lines about 600 feet apart and 300 feet off the ground at 70 knots, ground speed. This pattern gave 100 percent coverage for the survey areas.

The contractor separated the survey into two areas: King and Pierce counties. Two dozen flights covered about 345 square miles in King County from Puget Sound to Redmond and SeaTac Airport to the intersection of I-5 and 104th. In Pierce County, five flights covered 60 square miles from Commencement Bay to South 56th Street and Union Avenue to South 1st Avenue. The helicopter covered 405 square miles in total.

The contractor used software programs during the data collection and analysis that correct for variables, then calculated radiation exposure rates at ground level, man-made radiation (from industrial and medical sources, for example), and radiation contamination on the ground. The contractor also used a strict set of quality control measures to sort out things that might cause inconsistent or irregular readings. There were pre-flight, in-flight, and post-flight calibration checks to verify that everything was working properly.

The results show very low levels of radiation at the ground level, and most of the man-made sources were where the department expected to find them. The man-made sources are at levels that do not pose a health risk. The department did find some unexpected sources in locations we didn't expect to find man-made radiation activity. We did check out those locations and found those locations are legal, legitimate, licensed sources below regulatory levels and pose no health risk.

The flyovers provided a baseline of the current radiation levels for the Seattle and Tacoma areas, which is well below levels of health concern. If there was some type of disaster, the department will use this information to compare it to see if radiation levels change.

We're providing the summary report and the technical report online so people can see the results for themselves.

The Summary Report offers an abbreviated version of technical data, with fewer details and data from survey techniques and data analysis. It includes the data, but does not go into detail on survey methods or data analysis. It shows maps of the survey areas, photos, and descriptions of the equipment used, with color coded illustrations and explanations of the survey data.

The technical report includes the information in the summary report and offers more detail on survey methods, quality assurance, equipment used, and data analysis. It describes the mathematical formula and procedures used to calculate the results.

No radiation levels found during the survey caused any concern about the health of area residents. Some radiation sources and readings were unexpected; our Radiation Protection staff investigated and found that all were legal sources of radiation, below regulatory requirements, and would not cause any health effects.

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