| Radon in Well Water, Mitigation Radon gas from the surrounding soil can dissolve in groundwater. If the groundwater is drawn directly into a house from an individual well (or perhaps from a small community well), the dissolved radon can escape into the air, contributing to airborne radon levels. Houses receiving water from a municipal water treatment plant will not have this potential problem, because any radon in the water supply will have been released during treatment and handling before the water reaches the house. As a rule of thumb, 10,000 pCi/L of radon in well water will contribute roughly 1 pCi/L of airborne radon to the house air on the average, although localized airborne levels can be much higher. If water concentrations are sufficiently high (above perhaps 40,000 pCi/L), some effort to address the water source of radon would be advisable, in addition to efforts addressing the soil gas source. One option for addressing the radon in water is to ventilate the house near the point of usage whenever water is used. A second option-- more practical as a long-term solution--is to treat the well water before it is used in the house. One approach for treating the water is to install a granular activated carbon (GAC) treatment unit on the water line entering the house from the well, following the pressure tank. These GAC units have been used in residential applications for removing water contaminants other than radon (for example, organics). A number of GAC units have been installed over the past 6 years specifically for radon removal. If the unit is properly sized and contains a brand of carbon specifically selected for radon removal, radon removals of over 99% have sometimes been obtained. The reported performance of those carbon units that have been in operation for several years suggests that the units can operate with no degradation in radon reduction performance for at least several years, with minimal maintenance. One major consideration with GAC units is that they must be properly shielded (or else located remote from the house), in order to protect the occupants from gamma radiation resulting from radon and radon decay products accumulated on the carbon bed. Another consideration is that, depending upon State regulations, the spent carbon might in some cases have to be disposed of as a low- level radioactive waste. An additional concern that will not be discussed here is the possible bacterial growth that has been reported to occur in the carbon bed. Aeration of the well water is another treatment option, to release and vent the dissolved radon before the water is used in the house. Several aerator designs have been tested for residential use, and reductions above 90% have been reported with some of them. Aerators will avoid the need for gamma shielding that carbon units have, and will avoid concerns regarding the disposal of waste carbon. However, aeration units are more expensive to install and operate than are GAC units, and the radon removal capabilities of the aerators that are currently being marketed are generally lower than the 99 + % that has sometimes been reported for GAC. Although home aeration units are commercially available, experience with aerators for residential use is limited to date. In addition, aerators will be more complex than GAC units, generally requiring at least one additional water pump (to boost the low-radon water from the aerator back up to the pressure needed to move it through the house plumbing) and a fan or air compressor (to provide the stripping air). |