THE IMPORTANCE OF SEASON IN THE TESTING OF RADON USING SHORT-TERM TESTS IN RESIDENTIAL STRUCTURES, PORTLAND, OREGON

Radon has been identified by the U.S. EPA as the second leading cause of lung cancer. Radon gas exists naturally at low levels. When the gas becomes concentrated in living spaces, a health hazard arises. The most recent radon risk assessment for Portland, Oregon was performed in 2013. For the first time the 2013 analysis included long-term and short-term (3-7 day) tests. Access to this new short-term radon data allowed for analysis based on season. Season was defined for the climate of Portland, Oregon as tests ending: winter (October 1-March 31), summer (June 1-August 31), and swing (March 1-April 31 and September 1-30). A total of 14,873 indoor residential structure readings were analyzed, defining 66 zip codes with one or more seasonal radon potentials. Both overall and within season zip code radon data were examined for maximum radon reading, average radon reading, and percent greater than 4 pCi/l, which combine to determine the radon potential. Statistical t-tests were also performed to determine significance. Based on the analysis of all seasonal short-term radon testing, winter tests result in statistically significantly higher readings than tests in summer or swing months. No significant difference was found in tests between summer and swing months. Winter short-term radon potential most closely parallels overall short-term radon potential for individual zip codes (89% agreement). Short-term tests are not good indicators of long-term test results (<66% agreement). If a short-term test is necessary, a winter season test is suitable. These data support current EPA guidelines regarding radon testing.