Follow-up alpha-track monitoring in 40 eastern Pennsylvania houses with indoor radon-reduction systems (Winter 1987-1988). Final report, December 1987-May 1988

This report gives results of follow-up alpha-track detector (ATD) measurements. The systems involved some form of active soil ventilation, although three involved heat-recovery ventilators and two included carbon filters for removing radon from well water. The reduction in indoor radon concentration achieved in each house was described in an earlier report. The purpose of the ATD measurements was to determine how well the radon-reduction performance of the systems was being maintained. The ATD measurements were scheduled to assess system performance when cold weather would be giving the systems a significant challenge. These 1987-88 ATD results are compared with post-mitigation ATD measurements during the previous winter (1986-87), and with ATD measurements made prior to the installation of the radon reduction systems. Of the 34 houses where radon mitigation was in operation during the entire measurement period, the radon levels measured in 1988 compared well with those measured in 1987 in all but one house, indicating no significant degradation in system performance: in House 10, levels had increased 50-70% from 1987 with no apparent reason