THIRTY YEARS OF RADON SUSCEPTIBILITY MAPS IN PORTLAND, OREGON: A GREAT SUCCESS (Invited Presentation)

For the past 30 years my research team has been monitoring household radon in homes and tying in into local geology in Portland, Oregon. Our first study had data from 1000 homes and today we have over 20,000 data points. We get test data from the radon testing kit companies and local radon mitigating companies. We divide the data into three groups: Long term tests (alpha track detectors), short term tests (activated charcoal), and CRM’s from testing companies. Originally, we used only the long term test data, but we have found that there is also a correlation between all three. First, we divided the test data into zip codes to keep the homeowners anonymous. Then, we determined three radon numbers: the highest value, the average value, and the percentage of homes with values > 4 pCi/l. We assigned high (3), moderate (2) and low values (1) for each category. Then, we added those values up and assigned a High, Moderate, or Low susceptibility evaluation for the zip code. Our last evaluation showed zip code evaluations of 19 High, 41 Moderate and 14 Low. That means that 81% of the zip codes fall into the High and Moderate Susceptibility categories. We found that the highest zip code values were on coarse-grained Missoula Flood deposits (contain granitic sediments), were near faults or were on old landslides. In an area where the bedrock is mainly basalt, having such a high percentage of High and Moderate areas was not expected!