Figure 13-1 illustrates the major topics discussed in this unit. These topics include sub-slab depressurization system, sub membrane depressurization and methods use to tighten the building foundation. Methods used to evaluate the radon potential of a site will also be discussed.

SITE EVALUATION

Home builders often ask, "Can soil measurements made before the house is built indicate if radon-resistant techniques are necessary?" If a builder is interested in accurately predicting what the indoor radon concentration will be in a home after it is built, the answer is, "No", because:

• Houses vary greatly in their ability to resist radon entry.
• Bedrock and soils interact in complex ways with dynamic house conditions.
• Environmental factors make accurate predictions virtually impossible.

There are too many combinations of factors that affect indoor radon concentrations for simple correlations to exist.

Figure 13-1. Radon-Resistant New Construction Topics Source: MURC Used with permission.

If the builder's interest is in determining the potential for elevated indoor radon in a home built on a particular site, the answer is "maybe". Soil radon, radium and permeability measurements can be made: however, interpretation of the results can still be difficult or misleading. Clearly, a soil that contains high levels of radon, and is very permeable to airflow, has a potential for causing elevated indoor radon, and use of radon-resistant construction techniques should be considered. However, a soil with low radon content and low permeability does not necessarily indicate a low potential for elevated indoor radon concentrations. A soil-gas radon level reveals what the radon concentration was at the time of the measurement. However, radon concentrations can fluctuate over time, sometimes by several orders of magnitude. Although soil permeability is often more consistent at a given depth on a site, once the foundation hole is excavated, the permeability of the soil will be changed.

Researches have been trying to develop a method for determining the relationships between site measurements and indoor radon concentrations for specific areas and regions (Ref.7). Substantial progress has been made in identifying areas where a potential for elevated radon concentrations exists. However, many measurements are required to assess a particular site adequately. The decision that the builder faces is whether or not it is more cost effective to make the building radon-resistant to begin with, or to put the money into site evaluation and possible avoid the need for radon-resistant construction techniques.

Qualified methods of determining the potential for radon in a building by testing the site before construction have not been developed.

Copyright 2000, Great Lakes Center for Occupational & Environmental Safety & Health, School of Public Health, University of Illinois at Chicago