Evaluation of Radon Mitigation Systems in 14 Houses Over a Two-year Period

Abstract

Fourteen single-family detached houses in Spokane, Washington, and Coeur D'Alene, Idaho, were monitored for two years after high concentrations of indoor radon had been mitigated. Each house was monitored quarterly using mailed alpha-track radon detectors deployed in each zone of the structure. To assess performance of mitigation systems during the second heating season after mitigation, radon concentrations in seven houses were monitored continuously for several weeks, mitigation systems in all houses were inspected, and selected other measurements were taken. In addition, occupants were also interviewed regarding their maintenance, operation, and subjective evaluation of the radon mitigation systems. Quarterly alpha-track measurements showed that radon levels had increased in most of the homes during many follow-up measurement periods when compared with concentrations measured immediately after mitigation. Mitigation-system performance was adversely affected by (1) accumulated outdoor debris blocking the outlets of subsurface pressurization pipes; (2) fans being turned off (e.g., because of excessive noise or vibration); (3) air-to-air heat exchanger, basement pressurization, and subsurface ventilation fans being turned off and fan speeds reduced; and (4) crawl-space vents being closed or sealed.

Indoor Radon and Its Decay Products: Concentrations, Causes, and Control Strategies

“…Experience with the systems installed in Spokane indicates the need for some degree of care in avoiding degradation of performance or defeat of the systems (Prill et al 1989), observations that also come out of the work of Nitschke et al (1988).…”

“…This experience is too recent to yield reliable information on the long-term efficacy of remedial measures, a necessary feature of an effective control program. Studies conducted a few years after installation indicate that a monitoring and maintenance program is necessary to ensure that mitigation measures continue to function effectively (Prill et al 1989;Nitschke et al 1988). Moreover, building practices vary widely across the country, so that the experience gained in one region may not be directly transferrable to another.…”

“…In general, it was subslab ventilation (especially used in a pressurization mode) that effected the most substantial reductions in indoor concentrations. This work has included follow-up studies of previously installed remedial systems (Prill et al 1989).…”

Summary of residential environmental issues and program consistency

“…identical homes, researchers found that weatherization resulted in a 25% to 30% increase in radon levels, which was consistent with the percentage decrease in air infiltration (Nagda, Koontz, and Rector 1985, p. 10-2). Turk and others suggest that this study may have limited applicability to other house types and geographic regions (Turk et al 1988, p. 1).…”

New Methods of Energy Efficient Radon Mitigation

“…The long-term reliability of ASD and ASP systems is another area of concern. Failed fans and fans turned off by home owners because of noise or energy use have been recorded in follow-up studies of ASD and ASP systems conducted only a few years after system installation (e.g., Prill et al 1990, Gadsby and Harrje 1990, Scott 1990.…”