The Environmental Protection Agency has set a threshold of 4 pico curies per liter as the safe level of radon in the home. Credible sources have reported that no levels higher than 1 pico curie have been found in the Puget Sound Basin.  For this reason, it is not customary to test for radon in this area. 

See the EPA zone map at: /Apps/PageManager/CEIFrame.aspx?URL=www.epa.gov/radon/zonemap/washington.htm&secure=false