Characterizing the Occurrence, Sources, and Variability of Radon in Pacific Northwest Homes

Abstract

A compilation of data from earlier studies of 172 homes in the Pacific Northwest indicated that approximately 65 percent of the 46 homes tested in the Spokane River Valley/Rathdrum Prairie region of eastern Washington/northern Idaho had heating season indoor radon (222Rn) concentrations above the U. S. EPA guideline of 148 Bq m-3 (4 pCi L-1). A subset of 35 homes was selected for additional study. The primary source of indoor radon in the Spokane River Valley/Rathdrum Prairie was pressure-driven flow of soil gas containing moderate radon concentrations (geometric mean concentration of 16,000 Bq m-3) from the highly permeable soils (geometric mean permeability of 5 x 10(-11) m2) surrounding the house substructures. Estimated soil gas entry rates ranged from 0.4 to 39 m3h-1 and 1 percent to 21 percent of total building air infiltration. Radon from other sources, including domestic water supplies and building materials was negligible. In high radon homes, winter indoor levels averaged 13 times higher than summer concentrations, while in low radon homes winter levels averaged only 2.5 times higher. Short-term variations in indoor radon were observed to be dependent upon indoor-outdoor temperature differences, wind speed, and operation of forced-air furnace fans. Forced-air furnace operation, along with leaky return ducts and plenums, and openings between the substructure and upper floors enhanced mixing of radon-laden substructure air throughout the rest of the building.

Soil-gas entry into an experimental basement: model measurement comparisons and seasonal effects

“…Figure Captions Only probes with complete data sets are included (7,8,5, and 4 probes in the high-, mid-, low-, and sub-slab-levels, respectively). Vertical bars indicate the standard error in the mean values.…”

Wind-induced ground-surface pressures around a single-family house

“…The 50th and 95th percentile wind speeds over a period of 25 years in Spokane, Washington, are 3.6 and 8.3 m S·I, respectively (NOAA [30]). We chose Spokane for this illustration because radon entry and mitigation have been investigated in several houses in the area (Turk et al [10]). For a 3.6 m S-l wind the corresponding mean ground-surface pressures range from about 3.1 to 7.8 Pa; at 8.3 m S-1 the range is about 17 to 41 Pa.…”

“…However, the wind-induced ground-surface pressure field has largely been ignored in models of contaminant entry into houses (Gadgil [9]). Several authors have presented empirical evidence indicating that this pressure field may be significant when determining radon entry rates (Turk et al [10], Nazaroff et al [11]). A related paper (Riley et al [12]) investigates the effects of wind on radon entry and indoor radon concentrations.…”

The effect of steady winds on radon-222 entry from soil into houses

“…(Spokane, WA) from the study by Turk, et al (1990). Streamlines of soil gas flow in the soil block and in the gravel layer.…”