UPDATED RADON HAZARD MAPS FOR PORTLAND, OREGON

Most of Oregon has been mapped as having low radon potential because basalt is the dominant bedrock. Overall, elevated levels of indoor radon are found in 4% of Oregon homes compared to 8% of homes nationally. Yet, there are some areas in Portland, Oregon with high levels of indoor radon. Using data collected by the Oregon Health Division's Radiation Protection Services Section, we found Portland to have elevated radon values (>4pCi/l) in 16% of the homes. A radon potential map has been produced for 43 zip code regions of Portland based on the rank sums of maximum radon values, average indoor radon values, and percentage of homes with radon values > 4pCi/l. Seven zip codes have high, 21 moderate and 15 low radon potential. The maps were constructed by taking the indoor radon values from 4751 homes, categorizing the data in terms of radon values, and plotting the points geographically by zip codes. Trends became obvious when geologic maps were compared to the areas of radon potential. Most of the high potential sites lie on highly permeable Missoula Flood sediments in north Portland which have a granitic provenance.