Radon levels in Minnesota - by zip code.

This map shows indoor radon concentration contours. County boundaries for Minnesota and Iowa are superimposed. The contours result from an analysis of approximately 33,000 Landauer-brand alpha track detectors (ATDs) obtained from the Minnesota Health Department, the American Lung Association of Minnesota, and Landauer Tech Ops Inc.. A contour map was developed from these data using a kriging algorithm with grid points separated by approximately 10 km.

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. The data is relatively sparse in Iowa.The areas bordering Iowa and Minnesota have few measurements included in this analysis. Hence the concentrations in these areas is not well known.

To test the utility of the contour 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 contour values correlate well with the average independant measurements in the 51 Minnesota towns. A deviation of the slope of the regression line (0.62 + 0.06) from unity may reflect the smoothing effects of the contouring algorithm on the contours, especially for the two towns with very high average radon (> 400 Bq m-3; 11 pCi/L). It may also reflect a difference in sampling protocol between the two data sets.

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.