Residential Homes with Extremely High Indoor Radon Concentrations in Southern Lehigh County, Pennsylvania.

A housing development of 87 new homes on approximately 300 acres of former farm land was found to have 19 homes with basement radon-222 ( 222 Rn) concentrations greater than 37,000 Bq m -3 , with the highest recorded result to date being 648,000 +/- 1,031 Bq m -3 , based upon the diffusion barrier charcoal canister result. The US Environmental Protection Agency (EPA) Action Level for 222 Rn is 148 Bq m -3 . This single-family housing development is in the southeast corner of Lehigh County, Pennsylvania, about 58 km northwest of Philadelphia, in a geologic unit known as the Epler Formation. Radon testing in homes in this development began in the fall of 2014 and is now complete. Initial testing consisted of charcoal canisters mailed to homeowners. Subsequent testing in newly built homes consisted of testing prior to occupancy. This testing was quite extensive, with continuous radon monitors, passive radon monitors, and grab sampling for radon gas and progeny in the basement and on the first floor of each home as well as gamma surveys in the basement, on the first and second floors, and outside of each home. All but one of the new houses in this development had passive radon resistant features installed during the construction phase. In all cases, fans were added to the passive systems to make them active systems, which were needed to control these extremely high radon levels. Additional radon mitigation work such as adding additional suction points was also needed in several homes to reduce levels to below EPA guidelines. The unique geology and high 226 Ra soil concentrations in this specific area are the causes of these extremely high radon levels. Radon measurement data both inside these homes and in the outdoor ambient air, as well as 238 U and 222 Ra rock and soil concentrations, are presented.