This map shows the results of approximately 20,000 Landauer-brand alpha track detector (ATD) measurements in and near the Twin Cities (Minneapolis and St. Paul) metropolitan area. The data were obtained from the Minnesota Health Department, the American Lung Association of Minnesota, and Landauer Tech Ops Inc. Most of these measurements were made by individual homeowners for an interval of 30 days or more during the years 1987 to 1992. These data were scanned to eliminate obvious cases where the measurements were short-term, soil or water measurements, duplicates, or laboratory blanks or spikes. The data were then aggregated by Zipcode and only zipcodes with two or more results were retained. A contour map was developed from these data using a Kriging algorithm with grid points separated by approximately 10 km. These contours are called the ZIPCON values. To test the utility of the Zipcon values to predict annual average radon concentrations in living spaces, we compared them to our independent measurements during the past 10 years of more than 400 homes in 51 small and medium sized towns throughout Minnesota. In each home, the lowest two levels were measured with ATDs (Steck 1989) for one year. The average of the two ATDs is used to estimate the average concentration in the house. The ZIPCON values are pretty good predictors (r2=0.7) for these long-term radon concentrations.
This map was provided by Dr. Dan Steck and his students from “The Minnesota Radon Project.” They are located in the Physics Department at St. John’s University in Collegeville, Minnesota.