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Seattle Parks and Recreation completes voluntary radiological survey at Magnuson Park

A health and safety radiological survey completed by a consultant to Seattle Parks and Recreation and released on Monday, March 7 reveals no harmful levels at surveyed sites within Warren G. Magnuson Park.

The survey results are posted here.

The survey also confirmed that radiological materials used by the U.S. Navy to refurbish aircraft instrument dials between the late 1930s and early 1960s at the former military base did not migrate into areas now used for recreation and housing.

Seattle Parks and Recreation conducted the survey voluntarily after park staff discovered the existence of instrument repair shops in two hangars located in the north end of the historic district. One of these shops included a “radium room.” Further investigation revealed that primarily civilian workers during the 1940’s through early 1950’s repainted Navy airplane instrument dials in the “radium room” with paint containing radium, which caused the instrument dials to glow in the dark.

Under the Base Realignment and Closure Act (BRAC), the U.S. Navy took responsibility for the cleanup of the low-level radium at both the former instrument shop locations where dial repainting took place. Clean-up was completed in May 2015 in close consultation with Seattle Parks and Recreation, the Washington State Department of Health (DOH), and the Washington State Department of Ecology (Ecology). For more information about the cleanup project, visit the DOH website at

In addition to this cleanup, to ensure the safety of residents and visitors, Seattle Parks and Recreation hired a consultant to survey the park for possible additional contamination. The focus of the work was to: 1) conduct an historical review of site documents to understand if there were any additional locations where work with radiological materials could have taken place; 2) collect soil and take readings at locations where people live and recreate, particularly children.

The consultant’s historical investigation showed that there were no other locations within Magnuson Park or the historic district where work with radiological materials could have taken place. For current residential and recreational areas, the survey collected soils data specific to use:

  1. Solid Ground low-income housing
  2. Junior League of Seattle Children’s Playground
  3. Community garden
  4. Children’s garden
  5. Amphitheater
  6. Dog off-leash area

Consultant Thomas L. Gray and Associates (TGA) was primarily looking for remnants of Radium-226, as it was the product used to paint airplane instrument dials in the “radium room.” At five of the six locations investigated, the concentration of man-made radionuclides was zero.

At the dog off-leash area, the contractor discovered extremely low levels of Radium-226, and the possible presence of Cesium-137. TGA reports that an individual would have to spend 6 hours a day/365 days a year for 30 consecutive years to receive about 2 millirems (mrem) a year of the radium. For comparison, the National Council on Radiation Protection and Measurements reports that the average U.S. resident receives about 620 mrem a year from average daily life.

The contractor writes in its report, “…Ra-226 is a naturally occurring radionuclide present in all soils and the measured concentration in the dog off-leash area [is] completely consistent with world-wide…averages.”

In response to the unexpected possible presence of Cesium-137, the contractor re-tested and re-sampled the dog off-leash area. Initial results were below the laboratory’s detectable activity level. The second sample revealed no presence of Cesium-137, which meant that the first readings were a false positive.

Cesium-137 is used in small amounts to calibrate radiation-detection equipment, and in radiation therapy in medicine, as well as other uses.

This investigative survey was conducted solely by Seattle Parks and Recreation, and the results will be shared with the State Department of Health and the State Department of Ecology.

The Navy began turning over portions of the former Naval Station Puget Sound in 1975. Today, Magnuson Park is a revamped 350-acre park with wetlands, ballfields, beaches, play areas and much more. Several low-income housing buildings are located is the southern end of the historic district and adjacent to the park.