Based on homesite surveys in approximately 1500 homes Virginia and Maryland homes tested for indoor radon for one year in the lowest level of the homes (alpha-track monitors), it can be concluded that higher concentrations of indoor radon can be correlated with geology (i.e., with overall soil radioactivity, areas of greater topographic relief, areas where sand predominates over clay), with intervals or seasons with greater rainfall, and with home design factors (i.e., indoor radon is higher in homes with concrete block walls and in homes with electrical heating and cooling systems). In this study, in some areas over 20% of the homes have indoor radon in excess of 4 pCi/L, the level at which the US-EPA says that the home should not be purchased without the installation of radon-reduction equipment. In homes with water wells used for potable water, the average waterbone radon is about 10 times the US-EPA suggested maximum of 300 pCi/L.