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

Abstract

The article has not been subjected to CARB review and does not necessarily reflect their views. Additional funding from NIEHS Superfund Program under Grant 5 P42 ES04699-05 is gratefully acknowledged.Previous studies have reported a large and persistent discrepancy between field measurements and model predictions of pressure-driven entry of soil gas into housesthe phenomenon that causes high concentrations of radon indoors. The discrepancy is often attributed to poor understanding of inherently complex field sites. This paper compares measurements of soil-gas entry made at a fullscale test basement located in natural solid with predictions of a three-dimensional finite difference model. The results corroborate the earlier findings, with the model underpredicting the soil-gas entry rate by a factor of 7. The effect of seasonal changes in soil conditions on soil-gas entry is also examined. Despite large seasonal changes in near-surface soil moisture content and air permeability, there is no observable effect on soil-gas entry, apparently because critical soil conditions near the soil-gas entry location in the structure floor remain relatively constant.

Factors Affecting Indoor Air Concentrations of Volatile Organic Compounds at a Site of Subsurface Gasoline Contamination

“…Because measurements of the building depressurization under ambient conditions were not made, the effective entry rate under ambient conditions (shown as a hatched region in Figure 7) is estimated from the one week average of indoor SF6 concentrations, assuming a range of depressurizations between 1 and 4 Pa. The dependence of the soil-gas entry rate on building depressurization is approximately linear (see thick solid line in Figure 7), in agreement with a model for advective soil-gas entry limited by the soil permeability to air rather (26), although the available data can not discriminate against small deviations from linearity.…”

Radon entry into basements: Approach, experimental structures, and instrumentation of the small structures research project

“…However, the non-uniform soil permeability, in particular the generally higher permeability of the undisturbed soil relative the permeability of the backfill, is a possible explanation for the increased pressure coupling further from the structure walls. Garbesi et al (1992) discuss the pressure field data in more detail and show that the measured pressure field and the associated soil gas entry rates deviate substantially from quantitative predictions made with a numerical model.…”

“…Examples of the experimental data are presented and discussed. In a companion paper, Garbesi et al (1992) describe the results of the initial experimental investigation of steadystate soil gas transport driven by a steady pressure difference, compare the experimental results to predictions of a steady-state numerical model, and discuss possible explanations for the substantial discrepancy between measured data and predictions.…”

The Use of Indoor Air Measurements To Evaluate Intrusion of Subsurface VOC Vapors into Buildings

“…Several radon studies also suggest that radon intrusion by advection is typically a more significant process than is diffusion. [7][8][9][10] The most significant factors affecting the near-field compartment would therefore tend to be building underpressurization, the permeability of the building envelope and nearby soil, and depth to contamination.…”