Eightynine of the duplicate samples could not be used in the averaging. See Table 14. The county percentage of samples whose concentration is greater than 4 picocuries per liter is shown in Table 14. Description of Statistics by Selected Parameters Data for parameters as required for the national database may be found in Table 13. Many buildings are built on flood plains and a large number have sumps in basements.
Sumps are especially prevalent in cities built near rivers.
It has been noted in previous survey reports by the Department, that basements with sumps generally have higher radon concentrations. The radon concentration can usually be lowered by covering the sump. The Department found it surprising that the average mobile home radon concentration was almost as high as the concentration in conventional homes. The reasons for mobile homes having such high concentrations of radon are unknown at this time. Older homes generally have crawl spaces for small houses and basements for larger houses.