The question most often asked by homebuilders is: Can one determine whether radon-resistant construction techniques should be applied to a given site?
A simple test that could identify problem sites would be very helpful. At present, there are no simple, reliable methods for performing this. In the absence of a simple site screening test, guidance can be sought in the growing body of information developed at regional, state, and local levels. Many researchers, public agencies, and private homeowners are making soil, bedrock, and indoor radon measurements. From these data, a picture of the extent of the problem is emerging. Although it is not yet possible to be certain about a given site, some idea of where the problem areas are has been developed. At a recent meeting of several leading mitigation contractors, the general consensus was to install radon-resistant techniques rather than spend extra time and money performing the number of preconstruction tests it would take to confidently evaluate the site. However, a group of testing contractors may decide just the opposite. Although no definitive methods for predicting possible indoor radon concentrations based on preconstriction soil measurements exist, it is clear that a building being erected on a site that is known to contain high concentrations of radon should have radon-resistant construction techniques applied.16 Another concern when evaluating the site potential for supplying radon to the soon-to-be-constructed home is the permeability of the soil. A highly permeable soil allows easy movement of soil gases; therefore, radon can move a greater distance from the source to the building than in a tighter, less permeable soil. This can also allow soil gases that contain lower concentrations of radon to enter the home in greater quantities, which can produce elevated indoor concentrations. The Swedish Authorities suggest that a building site with soil radon concentrations greater than 1350pCi/L or with a highly permeable soil should use radon-resistant construction techniques.17
U.S. EPA does not recommend the avoidance of building sites that are suspected to contain strong radon; it does, however, strongly recommend that the homes built on those sites be designed and built with radon-resistant construction techniques.9
Water from wells has been found to be a major source of radon in some homes in the United States. Radon will outgas from the rocks into the groundwater. When the water is exposed to the atmosphere, some of the radon is released.
Builders should be aware that wells can be a potential problem. The only way to ensure that a well is not a potential radon source is to have the water tested after the well is drilled. It is not adequate to make a decision based on tests made in wells in the same area or even on adjoining building sites. A recent research project disclosed two homes with water radon concentrations of over 400,000 pCi/L, while the well used at a house between the two had waterborne radon concentrations of less than 1000 pCi/L.18 It should be understood that, when considering waterborne radon, the concentrations that concern us are much higher than when we are considering radon in the air. As a rule of thumb, between 8000 and 10,000 pCi/L of radon in the water will contribute 1 pCi/L of radon to the air.
If radon is present in water, the current state of technology offers two possible solutions. Water that is aerated will release the radon it carries. Several manufacturers have systems designed to aerate the water and vent the redone outdoors. An alternative system filters the water through granular activated carbon, which removes the radon from the water. There are several manufacturers of granular activated carbon water filters. It should be noted here that at high radon levels (>5000 pCi/L) the buildup of radon decay products in the charcoal can produce a significant level of gamma radiation. Although this can be alleviated by proper shielding, disposal of the charcoal filter media can be a problem.
A site suspected to contain a waterborne source of radon should not be avoided solely on the basis of the existence of radon. Methods can be utilized to alleviate any problem that may arise from waterborne radon.
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